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+In combination with oxygen in carbon dioxide, carbon is found in the Earth's atmosphere (approximately 900 gigatonnes of carbon — each ppm corresponds to 2.13 Gt) and dissolved in all water bodies (approximately 36,000 gigatonnes of carbon). Carbon in the biosphere has been estimated at 550 gigatonnes but with a large uncertainty, due mostly to a huge uncertainty in the amount of terrestrial deep subsurface bacteria. Hydrocarbons (such as coal, petroleum, and natural gas) contain carbon as well. Coal "reserves" (not "resources") amount to around 900 gigatonnes with perhaps 18,000 Gt of resources. Oil reserves are around 150 gigatonnes. Proven sources of natural gas are about  (containing about 105 gigatonnes of carbon), but studies estimate another  of "unconventional" deposits such as shale gas, representing about 540 gigatonnes of carbon.
+
+Carbon is also found in methane hydrates in polar regions and under the seas. Various estimates put this carbon between 500, 2500, or 3,000 Gt.
+
+According to one source, in the period from 1751 to 2008 about 347 gigatonnes of carbon were released as carbon dioxide to the atmosphere from burning of fossil fuels. Another source puts the amount added to the atmosphere for the period since 1750 at 879 Gt, and the total going to the atmosphere, sea, and land (such as peat bogs) at almost 2,000 Gt.
+
+Carbon is a constituent (about 12% by mass) of the very large masses of carbonate rock (limestone, dolomite, marble, and others). Coal is very rich in carbon (anthracite contains 92–98%) and is the largest commercial source of mineral carbon, accounting for 4,000 gigatonnes or 80% of fossil fuel.
+
+As for individual carbon allotropes, graphite is found in large quantities in the United States (mostly in New York and Texas), Russia, Mexico, Greenland, and India. Natural diamonds occur in the rock kimberlite, found in ancient volcanic "necks", or "pipes". Most diamond deposits are in Africa, notably in South Africa, Namibia, Botswana, the Republic of the Congo, and Sierra Leone. Diamond deposits have also been found in Arkansas, Canada, the Russian Arctic, Brazil, and in Northern and Western Australia. Diamonds are now also being recovered from the ocean floor off the Cape of Good Hope. Diamonds are found naturally, but about 30% of all industrial diamonds used in the U.S. are now manufactured.
+
+Carbon-14 is formed in upper layers of the troposphere and the stratosphere at altitudes of 9–15 km by a reaction that is precipitated by cosmic rays. Thermal neutrons are produced that collide with the nuclei of nitrogen-14, forming carbon-14 and a proton. As such,  of atmospheric carbon dioxide contains carbon-14.
+
+Carbon-rich asteroids are relatively preponderant in the outer parts of the asteroid belt in the Solar System. These asteroids have not yet been directly sampled by scientists. The asteroids can be used in hypothetical space-based carbon mining, which may be possible in the future, but is currently technologically impossible.
+
+Isotopes
+
+Isotopes of carbon are atomic nuclei that contain six protons plus a number of neutrons (varying from 2 to 16). Carbon has two stable, naturally occurring isotopes. The isotope carbon-12 (C) forms 98.93% of the carbon on Earth, while carbon-13 (C) forms the remaining 1.07%. The concentration of C is further increased in biological materials because biochemical reactions discriminate against C. In 1961, the International Union of Pure and Applied Chemistry (IUPAC) adopted the isotope carbon-12 as the basis for atomic weights. Identification of carbon in nuclear magnetic resonance (NMR) experiments is done with the isotope C.
+
+Carbon-14 (C) is a naturally occurring radioisotope, created in the upper atmosphere (lower stratosphere and upper troposphere) by interaction of nitrogen with cosmic rays. It is found in trace amounts on Earth of 1 part per trillion (0.0000000001%) or more, mostly confined to the atmosphere and superficial deposits, particularly of peat and other organic materials. This isotope decays by 0.158 MeV β emission. Because of its relatively short half-life of 5730 years, C is virtually absent in ancient rocks. The amount of C in the atmosphere and in living organisms is almost constant, but decreases predictably in their bodies after death. This principle is used in radiocarbon dating, invented in 1949, which has been used extensively to determine the age of carbonaceous materials with ages up to about 40,000 years.
+
+There are 15 known isotopes of carbon and the shortest-lived of these is C which decays through proton emission and alpha decay and has a half-life of 1.98739 × 10 s. The exotic C exhibits a nuclear halo, which means its radius is appreciably larger than would be expected if the nucleus were a sphere of constant density.
+
+Formation in stars
+
+Formation of the carbon atomic nucleus occurs within a giant or supergiant star through the triple-alpha process. This requires a nearly simultaneous collision of three alpha particles (helium nuclei), as the products of further nuclear fusion reactions of helium with hydrogen or another helium nucleus produce lithium-5 and beryllium-8 respectively, both of which are highly unstable and decay almost instantly back into smaller nuclei. The triple-alpha process happens in conditions of temperatures over 100 megakelvins and helium concentration that the rapid expansion and cooling of the early universe prohibited, and therefore no significant carbon was created during the Big Bang.
+
+According to current physical cosmology theory, carbon is formed in the interiors of stars on the horizontal branch. When massive stars die as supernova, the carbon is scattered into space as dust. This dust becomes component material for the formation of the next-generation star systems with accreted planets. The Solar System is one such star system with an abundance of carbon, enabling the existence of life as we know it. It is the opinion of most scholars that all the carbon in the Solar System and the Milky Way comes from dying stars.
+
+The CNO cycle is an additional hydrogen fusion mechanism that powers stars, wherein carbon operates as a catalyst.
+
+Rotational transitions of various isotopic forms of carbon monoxide (for example, CO, CO, and CO) are detectable in the submillimeter wavelength range, and are used in the study of newly forming stars in molecular clouds.
+
+Carbon cycle
+
+Under terrestrial conditions, conversion of one element to another is very rare. Therefore, the amount of carbon on Earth is effectively constant. Thus, processes that use carbon must obtain it from somewhere and dispose of it somewhere else. The paths of carbon in the environment form the carbon cycle. For example, photosynthetic plants draw carbon dioxide from the atmosphere (or seawater) and build it into biomass, as in the Calvin cycle, a process of carbon fixation. Some of this biomass is eaten by animals, while some carbon is exhaled by animals as carbon dioxide. The carbon cycle is considerably more complicated than this short loop; for example, some carbon dioxide is dissolved in the oceans; if bacteria do not consume it, dead plant or animal matter may become petroleum or coal, which releases carbon when burned.
+
+Compounds
+
+Organic compounds
+
+Carbon can form very long chains of interconnecting carbon–carbon bonds, a property that is called catenation. Carbon-carbon bonds are strong and stable. Through catenation, carbon forms a countless number of compounds. A tally of unique compounds shows that more contain carbon than do not. A similar claim can be made for hydrogen because most organic compounds contain hydrogen chemically bonded to carbon or another common element like oxygen or nitrogen.
+
+The simplest form of an organic molecule is the hydrocarbon—a large family of organic molecules that are composed of hydrogen atoms bonded to a chain of carbon atoms. A hydrocarbon backbone can be substituted by other atoms, known as heteroatoms. Common heteroatoms that appear in organic compounds include oxygen, nitrogen, sulfur, phosphorus, and the nonradioactive halogens, as well as the metals lithium and magnesium. Organic compounds containing bonds to metal are known as organometallic compounds (see below). Certain groupings of atoms, often including heteroatoms, recur in large numbers of organic compounds. These collections, known as functional groups, confer common reactivity patterns and allow for the systematic study and categorization of organic compounds. Chain length, shape and functional groups all affect the properties of organic molecules.
+
+In most stable compounds of carbon (and nearly all stable organic compounds), carbon obeys the octet rule and is tetravalent, meaning that a carbon atom forms a total of four covalent bonds (which may include double and triple bonds). Exceptions include a small number of stabilized carbocations (three bonds, positive charge), radicals (three bonds, neutral), carbanions (three bonds, negative charge) and carbenes (two bonds, neutral), although these species are much more likely to be encountered as unstable, reactive intermediates.
+
+Carbon occurs in all known organic life and is the basis of organic chemistry. When united with hydrogen, it forms various hydrocarbons that are important to industry as refrigerants, lubricants, solvents, as chemical feedstock for the manufacture of plastics and petrochemicals, and as fossil fuels.
+
+When combined with oxygen and hydrogen, carbon can form many groups of important biological compounds including sugars, lignans, chitins, alcohols, fats, aromatic esters, carotenoids and terpenes. With nitrogen it forms alkaloids, and with the addition of sulfur also it forms antibiotics, amino acids, and rubber products. With the addition of phosphorus to these other elements, it forms DNA and RNA, the chemical-code carriers of life, and adenosine triphosphate (ATP), the most important energy-transfer molecule in all living cells.  Norman Horowitz, head of the Mariner and Viking missions to Mars (1965-1976), considered that the unique characteristics of carbon made it unlikely that any other element could replace carbon, even on another planet, to generate the biochemistry necessary for life.
+
+Inorganic compounds
+Commonly carbon-containing compounds which are associated with minerals or which do not contain bonds to the other carbon atoms, halogens, or hydrogen, are treated separately from classical organic compounds; the definition is not rigid, and the classification of some compounds can vary from author to author (see reference articles above). Among these are the simple oxides of carbon. The most prominent oxide is carbon dioxide (). This was once the principal constituent of the paleoatmosphere, but is a minor component of the Earth's atmosphere today. Dissolved in water, it forms carbonic acid (), but as most compounds with multiple single-bonded oxygens on a single carbon it is unstable. Through this intermediate, though, resonance-stabilized carbonate ions are produced. Some important minerals are carbonates, notably calcite. Carbon disulfide () is similar. Nevertheless, due to its physical properties and its association with organic synthesis, carbon disulfide is sometimes classified as an organic solvent.
+
+The other common oxide is carbon monoxide (CO). It is formed by incomplete combustion, and is a colorless, odorless gas. The molecules each contain a triple bond and are fairly polar, resulting in a tendency to bind permanently to hemoglobin molecules, displacing oxygen, which has a lower binding affinity. Cyanide (CN), has a similar structure, but behaves much like a halide ion (pseudohalogen). For example, it can form the nitride cyanogen molecule ((CN)), similar to diatomic halides. Likewise, the heavier analog of cyanide, cyaphide (CP), is also considered inorganic, though most simple derivatives are highly unstable. Other uncommon oxides are carbon suboxide (), the unstable dicarbon monoxide (CO), carbon trioxide (CO), cyclopentanepentone (CO), cyclohexanehexone (CO), and mellitic anhydride (CO). However, mellitic anhydride is the triple acyl anhydride of mellitic acid; moreover, it contains a benzene ring. Thus, many chemists consider it to be organic.
+
+With reactive metals, such as tungsten, carbon forms either carbides (C) or acetylides () to form alloys with high melting points. These anions are also associated with methane and acetylene, both very weak acids. With an electronegativity of 2.5, carbon prefers to form covalent bonds. A few carbides are covalent lattices, like carborundum (SiC), which resembles diamond. Nevertheless, even the most polar and salt-like of carbides are not completely ionic compounds.
+
+Organometallic compounds
+
+Organometallic compounds by definition contain at least one carbon-metal covalent bond. A wide range of such compounds exist; major classes include simple alkyl-metal compounds (for example, tetraethyllead), η-alkene compounds (for example, Zeise's salt), and η-allyl compounds (for example, allylpalladium chloride dimer); metallocenes containing cyclopentadienyl ligands (for example, ferrocene); and transition metal carbene complexes. Many metal carbonyls and metal cyanides exist (for example, tetracarbonylnickel and potassium ferricyanide); some workers consider metal carbonyl and cyanide complexes without other carbon ligands to be purely inorganic, and not organometallic. However, most organometallic chemists consider metal complexes with any carbon ligand, even 'inorganic carbon' (e.g., carbonyls, cyanides, and certain types of carbides and acetylides) to be organometallic in nature. Metal complexes containing organic ligands without a carbon-metal covalent bond (e.g., metal carboxylates) are termed metalorganic compounds.
+
+While carbon is understood to strongly prefer formation of four covalent bonds, other exotic bonding schemes are also known. Carboranes are highly stable dodecahedral derivatives of the [B12H12]2- unit, with one BH replaced with a CH+. Thus, the carbon is bonded to five boron atoms and one hydrogen atom. The cation [(PhPAu)C] contains an octahedral carbon bound to six phosphine-gold fragments. This phenomenon has been attributed to the aurophilicity of the gold ligands, which provide additional stabilization of an otherwise labile species. In nature, the iron-molybdenum cofactor (FeMoco) responsible for microbial nitrogen fixation likewise has an octahedral carbon center (formally a carbide, C(-IV)) bonded to six iron atoms. In 2016, it was confirmed that, in line with earlier theoretical predictions, the hexamethylbenzene dication contains a carbon atom with six bonds. More specifically, the dication could be described structurally by the formulation [MeC(η5-C5Me5)]2+, making it an "organic metallocene" in which a MeC3+ fragment is bonded to a η5-C5Me5− fragment through all five of the carbons of the ring.
+
+It is important to note that in the cases above, each of the bonds to carbon contain less than two formal electron pairs. Thus, the formal electron count of these species does not exceed an octet. This makes them hypercoordinate but not hypervalent. Even in cases of alleged 10-C-5 species (that is, a carbon with five ligands and a formal electron count of ten), as reported by Akiba and co-workers, electronic structure calculations conclude that the electron population around carbon is still less than eight, as is true for other compounds featuring four-electron three-center bonding.
+
+History and etymology
+
+The English name carbon comes from the Latin carbo for coal and charcoal, whence also comes the French charbon, meaning charcoal. In German, Dutch and Danish, the names for carbon are Kohlenstoff, koolstof, and kulstof respectively, all literally meaning coal-substance.
+
+Carbon was discovered in prehistory and was known in the forms of soot and charcoal to the earliest human civilizations. Diamonds were known probably as early as 2500 BCE in China, while carbon in the form of charcoal was made around Roman times by the same chemistry as it is today, by heating wood in a pyramid covered with clay to exclude air.
+
+ In 1722, René Antoine Ferchault de Réaumur demonstrated that iron was transformed into steel through the absorption of some substance, now known to be carbon. In 1772, Antoine Lavoisier showed that diamonds are a form of carbon; when he burned samples of charcoal and diamond and found that neither produced any water and that both released the same amount of carbon dioxide per gram. In 1779, Carl Wilhelm Scheele showed that graphite, which had been thought of as a form of lead, was instead identical with charcoal but with a small admixture of iron, and that it gave "aerial acid" (his name for carbon dioxide) when oxidized with nitric acid. In 1786, the French scientists Claude Louis Berthollet, Gaspard Monge and C. A. Vandermonde confirmed that graphite was mostly carbon by oxidizing it in oxygen in much the same way Lavoisier had done with diamond. Some iron again was left, which the French scientists thought was necessary to the graphite structure. In their publication they proposed the name carbone (Latin carbonum) for the element in graphite which was given off as a gas upon burning graphite. Antoine Lavoisier then listed carbon as an element in his 1789 textbook.
+
+A new allotrope of carbon, fullerene, that was discovered in 1985 includes nanostructured forms such as buckyballs and nanotubes. Their discoverers – Robert Curl, Harold Kroto, and Richard Smalley – received the Nobel Prize in Chemistry in 1996. The resulting renewed interest in new forms led to the discovery of further exotic allotropes, including glassy carbon, and the realization that "amorphous carbon" is not strictly amorphous.
+
+Production
+
+Graphite
+
+Commercially viable natural deposits of graphite occur in many parts of the world, but the most important sources economically are in China, India, Brazil, and North Korea. Graphite deposits are of metamorphic origin, found in association with quartz, mica, and feldspars in schists, gneisses, and metamorphosed sandstones and limestone as lenses or veins, sometimes of a metre or more in thickness. Deposits of graphite in Borrowdale, Cumberland, England were at first of sufficient size and purity that, until the 19th century, pencils were made by sawing blocks of natural graphite into strips before encasing the strips in wood. Today, smaller deposits of graphite are obtained by crushing the parent rock and floating the lighter graphite out on water.
+
+There are three types of natural graphite—amorphous, flake or crystalline flake, and vein or lump. Amorphous graphite is the lowest quality and most abundant. Contrary to science, in industry "amorphous" refers to very small crystal size rather than complete lack of crystal structure. Amorphous is used for lower value graphite products and is the lowest priced graphite. Large amorphous graphite deposits are found in China, Europe, Mexico and the United States. Flake graphite is less common and of higher quality than amorphous; it occurs as separate plates that crystallized in metamorphic rock. Flake graphite can be four times the price of amorphous. Good quality flakes can be processed into expandable graphite for many uses, such as flame retardants. The foremost deposits are found in Austria, Brazil, Canada, China, Germany and Madagascar. Vein or lump graphite is the rarest, most valuable, and highest quality type of natural graphite. It occurs in veins along intrusive contacts in solid lumps, and it is only commercially mined in Sri Lanka.
+
+According to the USGS, world production of natural graphite was 1.1 million tonnes in 2010, to which China contributed 800,000 t, India 130,000 t, Brazil 76,000 t, North Korea 30,000 t and Canada 25,000 t. No natural graphite was reported mined in the United States, but 118,000 t of synthetic graphite with an estimated value of $998 million was produced in 2009.
+
+Diamond
+
+The diamond supply chain is controlled by a limited number of powerful businesses, and is also highly concentrated in a small number of locations around the world (see figure).
+
+Only a very small fraction of the diamond ore consists of actual diamonds. The ore is crushed, during which care has to be taken in order to prevent larger diamonds from being destroyed in this process and subsequently the particles are sorted by density. Today, diamonds are located in the diamond-rich density fraction with the help of X-ray fluorescence, after which the final sorting steps are done by hand. Before the use of X-rays became commonplace, the separation was done with grease belts; diamonds have a stronger tendency to stick to grease than the other minerals in the ore.
+
+Historically diamonds were known to be found only in alluvial deposits in southern India. India led the world in diamond production from the time of their discovery in approximately the 9th century BC to the mid-18th century AD, but the commercial potential of these sources had been exhausted by the late 18th century and at that time India was eclipsed by Brazil where the first non-Indian diamonds were found in 1725.
+
+Diamond production of primary deposits (kimberlites and lamproites) only started in the 1870s after the discovery of the diamond fields in South Africa. Production has increased over time and an accumulated total of over 4.5 billion carats have been mined since that date. Most commercially viable diamond deposits were in Russia, Botswana, Australia and the Democratic Republic of Congo. By 2005, Russia produced almost one-fifth of the global diamond output (mostly in Yakutia territory; for example, Mir pipe and Udachnaya pipe) but the Argyle mine in Australia became the single largest source, producing 14 million carats in 2018. New finds, the Canadian mines at Diavik and Ekati, are expected to become even more valuable owing to their production of gem quality stones.
+
+In the United States, diamonds have been found in Arkansas, Colorado, and Montana. In 2004, a startling discovery of a microscopic diamond in the United States led to the January 2008 bulk-sampling of kimberlite pipes in a remote part of Montana.
+
+Applications
+
+Carbon is essential to all known living systems, and without it life as we know it could not exist (see alternative biochemistry). The major economic use of carbon other than food and wood is in the form of hydrocarbons, most notably the fossil fuel methane gas and crude oil (petroleum). Crude oil is distilled in refineries by the petrochemical industry to produce gasoline, kerosene, and other products. Cellulose is a natural, carbon-containing polymer produced by plants in the form of wood, cotton, linen, and hemp. Cellulose is used primarily for maintaining structure in plants. Commercially valuable carbon polymers of animal origin include wool, cashmere, and silk. Plastics are made from synthetic carbon polymers, often with oxygen and nitrogen atoms included at regular intervals in the main polymer chain. The raw materials for many of these synthetic substances come from crude oil.
+
+The uses of carbon and its compounds are extremely varied. It can form alloys with iron, of which the most common is carbon steel. Graphite is combined with clays to form the 'lead' used in pencils used for writing and drawing. It is also used as a lubricant and a pigment, as a molding material in glass manufacture, in electrodes for dry batteries and in electroplating and electroforming, in brushes for electric motors, and as a neutron moderator in nuclear reactors.
+
+Charcoal is used as a drawing material in artwork, barbecue grilling, iron smelting, and in many other applications. Wood, coal and oil are used as fuel for production of energy and heating. Gem quality diamond is used in jewelry, and industrial diamonds are used in drilling, cutting and polishing tools for machining metals and stone. Plastics are made from fossil hydrocarbons, and carbon fiber, made by pyrolysis of synthetic polyester fibers is used to reinforce plastics to form advanced, lightweight composite materials.
+
+Carbon fiber is made by pyrolysis of extruded and stretched filaments of polyacrylonitrile (PAN) and other organic substances. The crystallographic structure and mechanical properties of the fiber depend on the type of starting material, and on the subsequent processing. Carbon fibers made from PAN have structure resembling narrow filaments of graphite, but thermal processing may re-order the structure into a continuous rolled sheet. The result is fibers with higher specific tensile strength than steel.
+
+Carbon black is used as the black pigment in printing ink, artist's oil paint, and water colours, carbon paper, automotive finishes, India ink and laser printer toner. Carbon black is also used as a filler in rubber products such as tyres and in plastic compounds. Activated charcoal is used as an absorbent and adsorbent in filter material in applications as diverse as gas masks, water purification, and kitchen extractor hoods, and in medicine to absorb toxins, poisons, or gases from the digestive system. Carbon is used in chemical reduction at high temperatures. Coke is used to reduce iron ore into iron (smelting). Case hardening of steel is achieved by heating finished steel components in carbon powder. Carbides of silicon, tungsten, boron, and titanium are among the hardest known materials, and are used as abrasives in cutting and grinding tools. Carbon compounds make up most of the materials used in clothing, such as natural and synthetic textiles and leather, and almost all of the interior surfaces in the built environment other than glass, stone, drywall and metal.
+
+Diamonds
+The diamond industry falls into two categories: one dealing with gem-grade diamonds and the other, with industrial-grade diamonds. While a large trade in both types of diamonds exists, the two markets function dramatically differently.
+
+Unlike precious metals such as gold or platinum, gem diamonds do not trade as a commodity: there is a substantial mark-up in the sale of diamonds, and there is not a very active market for resale of diamonds.
+
+Industrial diamonds are valued mostly for their hardness and heat conductivity, with the gemological qualities of clarity and color being mostly irrelevant. About 80% of mined diamonds (equal to about 100 million carats or 20 tonnes annually) are unsuitable for use as gemstones and relegated for industrial use (known as bort). Synthetic diamonds, invented in the 1950s, found almost immediate industrial applications; 3 billion carats (600 tonnes) of synthetic diamond is produced annually.
+
+The dominant industrial use of diamond is in cutting, drilling, grinding, and polishing. Most of these applications do not require large diamonds; in fact, most diamonds of gem-quality except for their small size can be used industrially. Diamonds are embedded in drill tips or saw blades, or ground into a powder for use in grinding and polishing applications. Specialized applications include use in laboratories as containment for high-pressure experiments (see diamond anvil cell), high-performance bearings, and limited use in specialized windows. With the continuing advances in the production of synthetic diamonds, new applications are becoming feasible. Garnering much excitement is the possible use of diamond as a semiconductor suitable for microchips, and because of its exceptional heat conductance property, as a heat sink in electronics.
+
+Precautions
+
+Pure carbon has extremely low toxicity to humans and can be handled safely in the form of graphite or charcoal. It is resistant to dissolution or chemical attack, even in the acidic contents of the digestive tract. Consequently, once it enters into the body's tissues it is likely to remain there indefinitely. Carbon black was probably one of the first pigments to be used for tattooing, and Ötzi the Iceman was found to have carbon tattoos that survived during his life and for 5200 years after his death. Inhalation of coal dust or soot (carbon black) in large quantities can be dangerous, irritating lung tissues and causing the congestive lung disease, coalworker's pneumoconiosis. Diamond dust used as an abrasive can be harmful if ingested or inhaled. Microparticles of carbon are produced in diesel engine exhaust fumes, and may accumulate in the lungs. In these examples, the harm may result from contaminants (e.g., organic chemicals, heavy metals) rather than from the carbon itself.
+
+Carbon generally has low toxicity to life on Earth; but carbon nanoparticles are deadly to Drosophila.
+
+Carbon may burn vigorously and brightly in the presence of air at high temperatures. Large accumulations of coal, which have remained inert for hundreds of millions of years in the absence of oxygen, may spontaneously combust when exposed to air in coal mine waste tips, ship cargo holds and coal bunkers, and storage dumps.
+
+In nuclear applications where graphite is used as a neutron moderator, accumulation of Wigner energy followed by a sudden, spontaneous release may occur. Annealing to at least 250 °C can release the energy safely, although in the Windscale fire the procedure went wrong, causing other reactor materials to combust.
+
+The great variety of carbon compounds include such lethal poisons as tetrodotoxin, the lectin ricin from seeds of the castor oil plant Ricinus communis, cyanide (CN), and carbon monoxide; and such essentials to life as glucose and protein.
+
+See also
+
+ Carbon chauvinism
+ Carbon detonation
+ Carbon footprint
+ Carbon star
+ Carbon planet
+ Gas carbon
+ Low-carbon economy
+ Timeline of carbon nanotubes
+
+References
+
+Bibliography
+
+External links
+ 
+ Carbon at The Periodic Table of Videos (University of Nottingham)
+ Carbon on Britannica
+ Extensive Carbon page at asu.edu (archived 18 June 2010)
+ Electrochemical uses of carbon (archived 9 November 2001)
+ Carbon—Super Stuff. Animation with sound and interactive 3D-models. (archived 9 November 2012)
+
+ 
+Allotropes of carbon
+Chemical elements with hexagonal planar structure
+Chemical elements
+Native element minerals
+Polyatomic nonmetals
+Reactive nonmetals
+Reducing agents
+Computer data storage is a technology consisting of computer components and recording media that are used to retain digital data. It is a core function and fundamental component of computers.
+
+The central processing unit (CPU) of a computer is what manipulates data by performing computations. In practice, almost all computers use a storage hierarchy, which puts fast but expensive and small storage options close to the CPU and slower but less expensive and larger options further away. Generally, the fast technologies are referred to as "memory", while slower persistent technologies are referred to as "storage".
+
+Even the first computer designs, Charles Babbage's Analytical Engine and Percy Ludgate's Analytical Machine, clearly distinguished between processing and memory (Babbage stored numbers as rotations of gears, while Ludgate stored numbers as displacements of rods in shuttles). This distinction was extended in the Von Neumann architecture, where the CPU consists of two main parts: The control unit and the arithmetic logic unit (ALU). The former controls the flow of data between the CPU and memory, while the latter performs arithmetic and logical operations on data.
+
+Functionality 
+Without a significant amount of memory, a computer would merely be able to perform fixed operations and immediately output the result. It would have to be reconfigured to change its behavior. This is acceptable for devices such as desk calculators, digital signal processors, and other specialized devices. Von Neumann machines differ in having a memory in which they store their operating instructions and data. Such computers are more versatile in that they do not need to have their hardware reconfigured for each new program, but can simply be reprogrammed with new in-memory instructions; they also tend to be simpler to design, in that a relatively simple processor may keep state between successive computations to build up complex procedural results. Most modern computers are von Neumann machines.
+
+Data organization and representation 
+A modern digital computer represents data using the binary numeral system. Text, numbers, pictures, audio, and nearly any other form of information can be converted into a string of bits, or binary digits, each of which has a value of 0 or 1. The most common unit of storage is the byte, equal to 8 bits. A piece of information can be handled by any computer or device whose storage space is large enough to accommodate the binary representation of the piece of information, or simply data. For example, the complete works of Shakespeare, about 1250 pages in print, can be stored in about five megabytes (40 million bits) with one byte per character.
+
+Data are encoded by assigning a bit pattern to each character, digit, or multimedia object. Many standards exist for encoding (e.g. character encodings like ASCII, image encodings like JPEG, and video encodings like MPEG-4).
+
+By adding bits to each encoded unit, redundancy allows the computer to detect errors in coded data and correct them based on mathematical algorithms. Errors generally occur in low probabilities due to random bit value flipping, or "physical bit fatigue", loss of the physical bit in the storage of its ability to maintain a distinguishable value (0 or 1), or due to errors in inter or intra-computer communication. A random bit flip (e.g. due to random radiation) is typically corrected upon detection. A bit or a group of malfunctioning physical bits (the specific defective bit is not always known; group definition depends on the specific storage device) is typically automatically fenced out, taken out of use by the device, and replaced with another functioning equivalent group in the device, where the corrected bit values are restored (if possible). The cyclic redundancy check (CRC) method is typically used in communications and storage for error detection. A detected error is then retried.
+
+Data compression methods allow in many cases (such as a database) to represent a string of bits by a shorter bit string ("compress") and reconstruct the original string ("decompress") when needed. This utilizes substantially less storage (tens of percent) for many types of data at the cost of more computation (compress and decompress when needed). Analysis of the trade-off between storage cost saving and costs of related computations and possible delays in data availability is done before deciding whether to keep certain data compressed or not.
+
+For security reasons, certain types of data (e.g. credit card information) may be kept encrypted in storage to prevent the possibility of unauthorized information reconstruction from chunks of storage snapshots.
+
+Hierarchy of storage 
+
+Generally, the lower a storage is in the hierarchy, the lesser its bandwidth and the greater its access latency is from the CPU. This traditional division of storage to primary, secondary, tertiary, and off-line storage is also guided by cost per bit.
+
+In contemporary usage, memory is usually semiconductor storage read-write random-access memory, typically DRAM (dynamic RAM) or other forms of fast but temporary storage. Storage consists of storage devices and their media not directly accessible by the CPU (secondary or tertiary storage), typically hard disk drives, optical disc drives, and other devices slower than RAM but non-volatile (retaining contents when powered down).
+
+Historically, memory has, depending on technology, been called central memory, core memory, core storage, drum, main memory, real storage, or internal memory. Meanwhile, slower persistent storage devices have been referred to as secondary storage, external memory, or auxiliary/peripheral storage.
+
+Primary storage 
+
+Primary storage (also known as main memory, internal memory, or prime memory), often referred to simply as memory, is the only one directly accessible to the CPU. The CPU continuously reads instructions stored there and executes them as required. Any data actively operated on is also stored there in a uniform manner.
+
+Historically, early computers used delay lines, Williams tubes, or rotating magnetic drums as primary storage. By 1954, those unreliable methods were mostly replaced by magnetic-core memory. Core memory remained dominant until the 1970s, when advances in integrated circuit technology allowed semiconductor memory to become economically competitive.
+
+This led to modern random-access memory (RAM). It is small-sized, light, but quite expensive at the same time. The particular types of RAM used for primary storage are volatile, meaning that they lose the information when not powered. Besides storing opened programs, it serves as disk cache and write buffer to improve both reading and writing performance. Operating systems borrow RAM capacity for caching so long as it's not needed by running software. Spare memory can be utilized as RAM drive for temporary high-speed data storage.
+
+As shown in the diagram, traditionally there are two more sub-layers of the primary storage, besides main large-capacity RAM:
+ Processor registers are located inside the processor. Each register typically holds a word of data (often 32 or 64 bits). CPU instructions instruct the arithmetic logic unit to perform various calculations or other operations on this data (or with the help of it). Registers are the fastest of all forms of computer data storage. 
+ Processor cache is an intermediate stage between ultra-fast registers and much slower main memory. It was introduced solely to improve the performance of computers. Most actively used information in the main memory is just duplicated in the cache memory, which is faster, but of much lesser capacity. On the other hand, main memory is much slower, but has a much greater storage capacity than processor registers. Multi-level hierarchical cache setup is also commonly used—primary cache being smallest, fastest and located inside the processor; secondary cache being somewhat larger and slower. 
+
+Main memory is directly or indirectly connected to the central processing unit via a memory bus. It is actually two buses (not on the diagram): an address bus and a data bus. The CPU firstly sends a number through an address bus, a number called memory address, that indicates the desired location of data. Then it reads or writes the data in the memory cells using the data bus. Additionally, a memory management unit (MMU) is a small device between CPU and RAM recalculating the actual memory address, for example to provide an abstraction of virtual memory or other tasks.
+
+As the RAM types used for primary storage are volatile (uninitialized at start up), a computer containing only such storage would not have a source to read instructions from, in order to start the computer. Hence, non-volatile primary storage containing a small startup program (BIOS) is used to bootstrap the computer, that is, to read a larger program from non-volatile secondary storage to RAM and start to execute it. A non-volatile technology used for this purpose is called ROM, for read-only memory (the terminology may be somewhat confusing as most ROM types are also capable of random access).
+
+Many types of "ROM" are not literally read only, as updates to them are possible; however it is slow and memory must be erased in large portions before it can be re-written. Some embedded systems run programs directly from ROM (or similar), because such programs are rarely changed. Standard computers do not store non-rudimentary programs in ROM, and rather, use large capacities of secondary storage, which is non-volatile as well, and not as costly.
+
+Recently, primary storage and secondary storage in some uses refer to what was historically called, respectively, secondary storage and tertiary storage.
+
+Secondary storage 
+
+Secondary storage (also known as external memory or auxiliary storage) differs from primary storage in that it is not directly accessible by the CPU. The computer usually uses its input/output channels to access secondary storage and transfer the desired data to primary storage. Secondary storage is non-volatile (retaining data when its power is shut off). Modern computer systems typically have two orders of magnitude more secondary storage than primary storage because secondary storage is less expensive.
+
+In modern computers, hard disk drives (HDDs) or solid-state drives (SSDs) are usually used as secondary storage. The access time per byte for HDDs or SSDs is typically measured in milliseconds (thousandths of a second), while the access time per byte for primary storage is measured in nanoseconds (billionths of a second). Thus, secondary storage is significantly slower than primary storage. Rotating optical storage devices, such as CD and DVD drives, have even longer access times. Other examples of secondary storage technologies include USB flash drives, floppy disks, magnetic tape, paper tape, punched cards, and RAM disks.
+
+Once the disk read/write head on HDDs reaches the proper placement and the data, subsequent data on the track are very fast to access. To reduce the seek time and rotational latency, data are transferred to and from disks in large contiguous blocks. Sequential or block access on disks is orders of magnitude faster than random access, and many sophisticated paradigms have been developed to design efficient algorithms based on sequential and block access. Another way to reduce the I/O bottleneck is to use multiple disks in parallel to increase the bandwidth between primary and secondary memory.
+
+Secondary storage is often formatted according to a file system format, which provides the abstraction necessary to organize data into files and directories, while also providing metadata describing the owner of a certain file, the access time, the access permissions, and other information.
+
+Most computer operating systems use the concept of virtual memory, allowing the utilization of more primary storage capacity than is physically available in the system. As the primary memory fills up, the system moves the least-used chunks (pages) to a swap file or page file on secondary storage, retrieving them later when needed. If a lot of pages are moved to slower secondary storage, the system performance is degraded.
+
+Tertiary storage 
+
+Tertiary storage or tertiary memory is a level below secondary storage. Typically, it involves a robotic mechanism which will mount (insert) and dismount removable mass storage media into a storage device according to the system's demands; such data are often copied to secondary storage before use. It is primarily used for archiving rarely accessed information since it is much slower than secondary storage (e.g. 5–60 seconds vs. 1–10 milliseconds). This is primarily useful for extraordinarily large data stores, accessed without human operators. Typical examples include tape libraries and optical jukeboxes.
+
+When a computer needs to read information from the tertiary storage, it will first consult a catalog database to determine which tape or disc contains the information. Next, the computer will instruct a robotic arm to fetch the medium and place it in a drive. When the computer has finished reading the information, the robotic arm will return the medium to its place in the library.
+
+Tertiary storage is also known as nearline storage because it is "near to online". The formal distinction between online, nearline, and offline storage is:
+
+ Online storage is immediately available for I/O.
+ Nearline storage is not immediately available, but can be made online quickly without human intervention.
+ Offline storage is not immediately available, and requires some human intervention to become online.
+
+For example, always-on spinning hard disk drives are online storage, while spinning drives that spin down automatically, such as in massive arrays of idle disks (MAID), are nearline storage. Removable media such as tape cartridges that can be automatically loaded, as in tape libraries, are nearline storage, while tape cartridges that must be manually loaded are offline storage.
+
+Off-line storage 
+
+Off-line storage is computer data storage on a medium or a device that is not under the control of a processing unit. The medium is recorded, usually in a secondary or tertiary storage device, and then physically removed or disconnected. It must be inserted or connected by a human operator before a computer can access it again. Unlike tertiary storage, it cannot be accessed without human interaction.
+
+Off-line storage is used to transfer information since the detached medium can easily be physically transported. Additionally, it is useful for cases of disaster, where, for example, a fire destroys the original data, a medium in a remote location will be unaffected, enabling disaster recovery. Off-line storage increases general information security since it is physically inaccessible from a computer, and data confidentiality or integrity cannot be affected by computer-based attack techniques. Also, if the information stored for archival purposes is rarely accessed, off-line storage is less expensive than tertiary storage.
+
+In modern personal computers, most secondary and tertiary storage media are also used for off-line storage. Optical discs and flash memory devices are the most popular, and to a much lesser extent removable hard disk drives; older examples include floppy disks and Zip disks. In enterprise uses, magnetic tape cartridges are predominant; older examples include open-reel magnetic tape and punched cards.
+
+Characteristics of storage 
+
+Storage technologies at all levels of the storage hierarchy can be differentiated by evaluating certain core characteristics as well as measuring characteristics specific to a particular implementation. These core characteristics are volatility, mutability, accessibility, and addressability. For any particular implementation of any storage technology, the characteristics worth measuring are capacity and performance.
+
+Volatility 
+Non-volatile memory retains the stored information even if not constantly supplied with electric power. It is suitable for long-term storage of information. Volatile memory requires constant power to maintain the stored information. The fastest memory technologies are volatile ones, although that is not a universal rule. Since the primary storage is required to be very fast, it predominantly uses volatile memory.
+
+Dynamic random-access memory is a form of volatile memory that also requires the stored information to be periodically reread and rewritten, or refreshed, otherwise it would vanish. Static random-access memory is a form of volatile memory similar to DRAM with the exception that it never needs to be refreshed as long as power is applied; it loses its content when the power supply is lost.
+
+An uninterruptible power supply (UPS) can be used to give a computer a brief window of time to move information from primary volatile storage into non-volatile storage before the batteries are exhausted. Some systems, for example EMC Symmetrix, have integrated batteries that maintain volatile storage for several minutes.
+
+Mutability 
+ Read/write storage or mutable storage  Allows information to be overwritten at any time. A computer without some amount of read/write storage for primary storage purposes would be useless for many tasks. Modern computers typically use read/write storage also for secondary storage.
+ Slow write, fast read storage  Read/write storage which allows information to be overwritten multiple times, but with the write operation being much slower than the read operation. Examples include CD-RW and SSD.
+ Write once storage  Write once read many (WORM) allows the information to be written only once at some point after manufacture. Examples include semiconductor programmable read-only memory and CD-R.
+ Read only storage  Retains the information stored at the time of manufacture. Examples include mask ROM ICs and CD-ROM.
+
+Accessibility 
+ Random access Any location in storage can be accessed at any moment in approximately the same amount of time. Such characteristic is well suited for primary and secondary storage. Most semiconductor memories, flash memories and hard disk drives provide random access, though both semiconductor and flash memories have minimal latency when compared to hard disk drives, as no mechanical parts need to be moved.
+ Sequential access The accessing of pieces of information will be in a serial order, one after the other; therefore the time to access a particular piece of information depends upon which piece of information was last accessed. Such characteristic is typical of off-line storage.
+
+Addressability 
+ Location-addressable  Each individually accessible unit of information in storage is selected with its numerical memory address. In modern computers, location-addressable storage usually limits to primary storage, accessed internally by computer programs, since location-addressability is very efficient, but burdensome for humans.
+ File addressable Information is divided into files of variable length, and a particular file is selected with human-readable directory and file names. The underlying device is still location-addressable, but the operating system of a computer provides the file system abstraction to make the operation more understandable. In modern computers, secondary, tertiary and off-line storage use file systems.
+ Content-addressable Each individually accessible unit of information is selected based on the basis of (part of) the contents stored there. Content-addressable storage can be implemented using software (computer program) or hardware (computer device), with hardware being faster but more expensive option. Hardware content addressable memory is often used in a computer's CPU cache.
+
+Capacity 
+ Raw capacity The total amount of stored information that a storage device or medium can hold. It is expressed as a quantity of bits or bytes (e.g. 10.4 megabytes).
+ Memory storage density The compactness of stored information. It is the storage capacity of a medium divided with a unit of length, area or volume (e.g. 1.2 megabytes per square inch).
+
+Performance 
+ Latency The time it takes to access a particular location in storage. The relevant unit of measurement is typically nanosecond for primary storage, millisecond for secondary storage, and second for tertiary storage. It may make sense to separate read latency and write latency (especially for non-volatile memory) and in case of sequential access storage, minimum, maximum and average latency.
+ Throughput The rate at which information can be read from or written to the storage. In computer data storage, throughput is usually expressed in terms of megabytes per second (MB/s), though bit rate may also be used. As with latency, read rate and write rate may need to be differentiated. Also accessing media sequentially, as opposed to randomly, typically yields maximum throughput.
+ Granularity The size of the largest "chunk" of data that can be efficiently accessed as a single unit, e.g. without introducing additional latency.
+Reliability The probability of spontaneous bit value change under various conditions, or overall failure rate.
+Utilities such as hdparm and sar can be used to measure IO performance in Linux.
+
+Energy use 
+ Storage devices that reduce fan usage automatically shut-down during inactivity, and low power hard drives can reduce energy consumption by 90 percent.
+ 2.5-inch hard disk drives often consume less power than larger ones. Low capacity solid-state drives have no moving parts and consume less power than hard disks. Also, memory may use more power than hard disks. Large caches, which are used to avoid hitting the memory wall, may also consume a large amount of power.
+
+Security 
+Full disk encryption, volume and virtual disk encryption, andor file/folder encryption is readily available for most storage devices.
+
+Hardware memory encryption is available in Intel Architecture, supporting Total Memory Encryption (TME) and page granular memory encryption with multiple keys (MKTME). and in SPARC M7 generation since October 2015.
+
+Vulnerability and reliability 
+
+Distinct types of data storage have different points of failure and various methods of predictive failure analysis.
+
+Vulnerabilities that can instantly lead to total loss are head crashing on mechanical hard drives and failure of electronic components on flash storage.
+
+Error detection 
+
+Impending failure on hard disk drives is estimable using S.M.A.R.T. diagnostic data that includes the hours of operation and the count of spin-ups, though its reliability is disputed.
+
+Flash storage may experience downspiking transfer rates as a result of accumulating errors, which the flash memory controller attempts to correct.
+
+The health of optical media can be determined by measuring correctable minor errors, of which high counts signify deteriorating and/or low-quality media. Too many consecutive minor errors can lead to data corruption. Not all vendors and models of optical drives support error scanning.
+
+Storage media 
+, the most commonly used data storage media are semiconductor, magnetic, and optical, while paper still sees some limited usage. Some other fundamental storage technologies, such as all-flash arrays (AFAs) are proposed for development.
+
+Semiconductor 
+
+Semiconductor memory uses semiconductor-based integrated circuit (IC) chips to store information. Data are typically stored in metal–oxide–semiconductor (MOS) memory cells. A semiconductor memory chip may contain millions of memory cells, consisting of tiny MOS field-effect transistors (MOSFETs) and/or MOS capacitors. Both volatile and non-volatile forms of semiconductor memory exist, the former using standard MOSFETs and the latter using floating-gate MOSFETs.
+
+In modern computers, primary storage almost exclusively consists of dynamic volatile semiconductor random-access memory (RAM), particularly dynamic random-access memory (DRAM). Since the turn of the century, a type of non-volatile floating-gate semiconductor memory known as flash memory has steadily gained share as off-line storage for home computers. Non-volatile semiconductor memory is also used for secondary storage in various advanced electronic devices and specialized computers that are designed for them.
+
+As early as 2006, notebook and desktop computer manufacturers started using flash-based solid-state drives (SSDs) as default configuration options for the secondary storage either in addition to or instead of the more traditional HDD.
+
+Magnetic 
+
+Magnetic storage uses different patterns of magnetization on a magnetically coated surface to store information. Magnetic storage is non-volatile. The information is accessed using one or more read/write heads which may contain one or more recording transducers. A read/write head only covers a part of the surface so that the head or medium or both must be moved relative to another in order to access data. In modern computers, magnetic storage will take these forms:
+
+ Magnetic disk;
+ Floppy disk, used for off-line storage;
+ Hard disk drive, used for secondary storage.
+ Magnetic tape, used for tertiary and off-line storage;
+ Carousel memory (magnetic rolls).
+
+In early computers, magnetic storage was also used as:
+
+ Primary storage in a form of magnetic memory, or core memory, core rope memory, thin-film memory and/or twistor memory;
+ Tertiary (e.g. NCR CRAM) or off line storage in the form of magnetic cards;
+ Magnetic tape was then often used for secondary storage.
+
+Magnetic storage does not have a definite limit of rewriting cycles like flash storage and re-writeable optical media, as altering magnetic fields causes no physical wear. Rather, their life span is limited by mechanical parts.
+
+Optical 
+
+Optical storage, the typical optical disc, stores information in deformities on the surface of a circular disc and reads this information by illuminating the surface with a laser diode and observing the reflection. Optical disc storage is non-volatile. The deformities may be permanent (read only media), formed once (write once media) or reversible (recordable or read/write media). The following forms are in common use :
+
+ CD, CD-ROM, DVD, BD-ROM: Read only storage, used for mass distribution of digital information (music, video, computer programs);
+ CD-R, DVD-R, DVD+R, BD-R: Write once storage, used for tertiary and off-line storage;
+ CD-RW, DVD-RW, DVD+RW, DVD-RAM, BD-RE: Slow write, fast read storage, used for tertiary and off-line storage;
+ Ultra Density Optical or UDO is similar in capacity to BD-R or BD-RE and is slow write, fast read storage used for tertiary and off-line storage.
+
+Magneto-optical disc storage is optical disc storage where the magnetic state on a ferromagnetic surface stores information. The information is read optically and written by combining magnetic and optical methods. Magneto-optical disc storage is non-volatile, sequential access, slow write, fast read storage used for tertiary and off-line storage.
+
+3D optical data storage has also been proposed.
+
+Light induced magnetization melting in magnetic photoconductors has also been proposed for high-speed low-energy consumption magneto-optical storage.
+
+Paper 
+
+Paper data storage, typically in the form of paper tape or punched cards, has long been used to store information for automatic processing, particularly before general-purpose computers existed. Information was recorded by punching holes into the paper or cardboard medium and was read mechanically (or later optically) to determine whether a particular location on the medium was solid or contained a hole. Barcodes make it possible for objects that are sold or transported to have some computer-readable information securely attached.
+
+Relatively small amounts of digital data (compared to other digital data storage) may be backed up on paper as a matrix barcode for very long-term storage, as the longevity of paper typically exceeds even magnetic data storage.
+
+Other storage media or substrates 
+ Vacuum-tube memory A Williams tube used a cathode-ray tube, and a Selectron tube used a large vacuum tube to store information. These primary storage devices were short-lived in the market, since the Williams tube was unreliable, and the Selectron tube was expensive.
+
+ Electro-acoustic memory Delay-line memory used sound waves in a substance such as mercury to store information. Delay-line memory was dynamic volatile, cycle sequential read/write storage, and was used for primary storage.
+
+ Optical tape is a medium for optical storage, generally consisting of a long and narrow strip of plastic, onto which patterns can be written and from which the patterns can be read back. It shares some technologies with cinema film stock and optical discs, but is compatible with neither. The motivation behind developing this technology was the possibility of far greater storage capacities than either magnetic tape or optical discs.
+
+ Phase-change memory uses different mechanical phases of phase-change material to store information in an X–Y addressable matrix and reads the information by observing the varying electrical resistance of the material. Phase-change memory would be non-volatile, random-access read/write storage, and might be used for primary, secondary and off-line storage. Most rewritable and many write-once optical disks already use phase-change material to store information.
+
+ Holographic data storage stores information optically inside crystals or photopolymers. Holographic storage can utilize the whole volume of the storage medium, unlike optical disc storage, which is limited to a small number of surface layers. Holographic storage would be non-volatile, sequential-access, and either write-once or read/write storage. It might be used for secondary and off-line storage. See Holographic Versatile Disc (HVD).
+
+ Molecular memory stores information in polymer that can store electric charge. Molecular memory might be especially suited for primary storage. The theoretical storage capacity of molecular memory is 10 terabits per square inch (16 Gbit/mm2).
+
+ Magnetic photoconductors store magnetic information, which can be modified by low-light illumination.
+
+ DNA stores information in DNA nucleotides. It was first done in 2012, when researchers achieved a ratio of 1.28 petabytes per gram of DNA. In March 2017 scientists reported that a new algorithm called a DNA fountain achieved 85% of the theoretical limit, at 215 petabytes per gram of DNA.
+
+Related technologies
+
+Redundancy 
+
+While a group of bits malfunction may be resolved by error detection and correction mechanisms (see above), storage device malfunction requires different solutions. The following solutions are commonly used and valid for most storage devices:
+
+ Device mirroring (replication) – A common solution to the problem is constantly maintaining an identical copy of device content on another device (typically of the same type). The downside is that this doubles the storage, and both devices (copies) need to be updated simultaneously with some overhead and possibly some delays. The upside is the possible concurrent reading of the same data group by two independent processes, which increases performance. When one of the replicated devices is detected to be defective, the other copy is still operational and is being utilized to generate a new copy on another device (usually available operational in a pool of stand-by devices for this purpose).
+ Redundant array of independent disks (RAID) – This method generalizes the device mirroring above by allowing one device in a group of devices to fail and be replaced with the content restored (Device mirroring is RAID with n=2). RAID groups of n=5 or n=6 are common. n>2 saves storage, when compared with n=2, at the cost of more processing during both regular operation (with often reduced performance) and defective device replacement.
+
+Device mirroring and typical RAID are designed to handle a single device failure in the RAID group of devices. However, if a second failure occurs before the RAID group is completely repaired from the first failure, then data can be lost. The probability of a single failure is typically small. Thus the probability of two failures in the same RAID group in time proximity is much smaller (approximately the probability squared, i.e., multiplied by itself). If a database cannot tolerate even such a smaller probability of data loss, then the RAID group itself is replicated (mirrored). In many cases such mirroring is done geographically remotely, in a different storage array, to handle recovery from disasters (see disaster recovery above).
+
+Network connectivity 
+A secondary or tertiary storage may connect to a computer utilizing computer networks. This concept does not pertain to the primary storage, which is shared between multiple processors to a lesser degree.
+
+ Direct-attached storage (DAS) is a traditional mass storage, that does not use any network. This is still a most popular approach. This retronym was coined recently, together with NAS and SAN.
+ Network-attached storage (NAS) is mass storage attached to a computer which another computer can access at file level over a local area network, a private wide area network, or in the case of online file storage, over the Internet. NAS is commonly associated with the NFS and CIFS/SMB protocols.
+ Storage area network (SAN) is a specialized network, that provides other computers with storage capacity. The crucial difference between NAS and SAN, is that NAS presents and manages file systems to client computers, while SAN provides access at block-addressing (raw) level, leaving it to attaching systems to manage data or file systems within the provided capacity. SAN is commonly associated with Fibre Channel networks.
+
+Robotic storage 
+Large quantities of individual magnetic tapes, and optical or magneto-optical discs may be stored in robotic tertiary storage devices. In tape storage field they are known as tape libraries, and in optical storage field optical jukeboxes, or optical disk libraries per analogy. The smallest forms of either technology containing just one drive device are referred to as autoloaders or autochangers.
+
+Robotic-access storage devices may have a number of slots, each holding individual media, and usually one or more picking robots that traverse the slots and load media to built-in drives. The arrangement of the slots and picking devices affects performance. Important characteristics of such storage are possible expansion options: adding slots, modules, drives, robots. Tape libraries may have from 10 to more than 100,000 slots, and provide terabytes or petabytes of near-line information. Optical jukeboxes are somewhat smaller solutions, up to 1,000 slots.
+
+Robotic storage is used for backups, and for high-capacity archives in imaging, medical, and video industries. Hierarchical storage management is a most known archiving strategy of automatically migrating long-unused files from fast hard disk storage to libraries or jukeboxes. If the files are needed, they are retrieved back to disk.
+
+See also
+
+Primary storage topics 
+ Aperture (computer memory)
+ Dynamic random-access memory (DRAM)
+ Memory latency
+ Mass storage
+ Memory cell (disambiguation) 
+ Memory management
+ Memory leak
+ Virtual memory
+ Memory protection
+ Page address register
+ Stable storage
+ Static random-access memory (SRAM)
+
+Secondary, tertiary and off-line storage topics 
+ Cloud storage
+ Hybrid cloud storage
+ Data deduplication
+ Data proliferation
+ Data storage tag used for capturing research data
+ Disk utility
+ File system
+ List of file formats
+ Global filesystem
+ Flash memory
+ Geoplexing
+ Information repository
+ Noise-predictive maximum-likelihood detection
+ Object(-based) storage
+ Removable media
+ Solid-state drive
+ Spindle
+ Virtual tape library
+ Wait state
+ Write buffer
+ Write protection
+
+Data storage conferences 
+ Storage Networking World
+ Storage World Conference
+
+Notes
+
+References
+
+Further reading 
+ 
+ Memory & storage, Computer history museum
+
+ 
+Computer architecture
+Conditional (if then) may refer to:
+
+Causal conditional, if X then Y, where X is a cause of Y
+Conditional probability, the probability of an event A given that another event B has occurred
+Conditional proof, in logic: a proof that asserts a conditional, and proves that the antecedent leads to the consequent
+Strict conditional, in philosophy, logic, and mathematics
+Material conditional, in propositional calculus, or logical calculus in mathematics
+Relevance conditional, in relevance logic
+Conditional (computer programming), a statement or expression in computer programming languages
+A conditional expression in computer programming languages such as ?:
+Conditions in a contract
+
+Grammar and linguistics
+Conditional mood (or conditional tense), a verb form in many languages
+Conditional sentence, a sentence type used to refer to hypothetical situations and their consequences
+Indicative conditional, a conditional sentence expressing "if A then B" in a natural language
+Counterfactual conditional, a conditional sentence indicating what would be the case if its antecedent were true
+
+Other 
+ "Conditional" (Laura Mvula song)
+ Conditional jockey, an apprentice jockey in British or Irish National Hunt racing
+ Conditional short-circuit current
+ Conditional Value-at-Risk
+
+See also
+Condition (disambiguation)
+Conditional statement (disambiguation)
+A cone is a basic geometrical shape.
+
+Cone may also refer to:
+
+Mathematics
+Cone (category theory)
+Cone (formal languages)
+Cone (graph theory), a graph in which one vertex is adjacent to all others
+Cone (linear algebra), a subset of vector space
+Mapping cone (homological algebra)
+Cone (topology)
+Conic bundle, a concept in algebraic geometry
+Conical surface, generated by a moving line with one fixed point
+Projective cone, the union of all lines that intersect a projective subspace and an arbitrary subset of some other disjoint subspace
+
+Computing
+Cone tracing, a derivative of the ray-tracing algorithm that replaces rays, which have no thickness, with cones
+Second-order cone programming, a library of routines that implements a predictor corrector variant of the semidefinite programming algorithm
+
+Astronomy
+Cone Nebula (also known as NGC 2264), an H II region in the constellation of Monoceros
+Ionization cone, cones of material extending out from spiral galaxies
+
+Engineering and physical science
+Antenna blind cone, the volume of space that cannot be scanned by an antenna
+Carbon nanocones, conical structures which are made predominantly from carbon and which have at least one dimension of the order one micrometer or smaller
+Cone algorithm identifies surface particles quickly and accurately for three-dimensional clusters composed of discrete particles
+Cone beam reconstruction, a method of X-ray scanning in microtomography
+Cone calorimeter, a modern device used to study the fire behavior of small samples of various materials in condensed phase
+Cone clutch serves the same purpose as a disk or plate clutch
+Cone of depression occurs in an aquifer when groundwater is pumped from a well
+Cone penetration test (CPT), an in situ testing method used to determine the geotechnical engineering properties of soils
+Cone Penetrometer apparatus, an alternative method to the Casagrande Device in measuring the Liquid Limit of a soil sample
+Conical intersection of two potential energy surfaces of the same spatial and spin symmetries
+Conical measure, a type of graduated laboratory glassware with a conical cup and a notch on the top to facilitate pouring of liquids
+Conical mill (or conical screen mill), a machine used to reduce the size of material in a uniform manner
+Conical pendulum, a weight (or bob) fixed on the end of a string (or rod) suspended from a pivot
+Conical scanning, a system used in early radar units to improve their accuracy
+Helical cone beam computed tomography, a type of three-dimensional computed tomography
+Hertzian cone, the cone of force that propagates through a brittle, amorphous or cryptocrystalline solid material from a point of impact
+Nose cone, used to refer to the forwardmost section of a rocket, guided missile or aircraft
+Pyrometric cone, pyrometric devices that are used to gauge time and temperature during the firing of ceramic materials
+Roller cone bit, a drill bit used for drilling through rock, for example when drilling for oil and gas
+Skid cone, a hollow steel or plastic cone placed over the sawn end of a log
+Speaker cone, the cone inside a loudspeaker that moves to generate sound
+Spinning cone columns are used in a form of steam distillation to gently extract volatile chemicals from liquid foodstuffs
+
+Biology and medicine
+Cone cell, in anatomy, a type of light-sensitive cell found along with rods in the retina of the eye
+Cone dystrophy, an inherited ocular disorder characterized by the loss of cone cells
+Cone snail, a carnivorous mollusc of the family Conidae
+Cone-billed tanager (Conothraupis mesoleuca), a species of bird in the family Thraupidae
+Conifer cone, a seed-bearing organ on conifer plants
+Growth cone, a dynamic, actin-supported extension of a developing axon seeking its synaptic target
+Witch-hazel cone gall aphid (Hormaphis hamamelidis), a minuscule insect, a member of the aphid superfamily
+Coning, a brain herniation in which the cerebellar tonsils move downwards through the foramen magnum
+
+Geography
+Cinder cone, a steep conical hill of volcanic fragments around and downwind from a volcanic vent
+Cone (hill), a hill in the shape of a cone which may or may not be volcanic in origin
+Dirt cone, a feature of a glacier or snow patch, in which dirt forms a coating insulating the ice below
+Parasitic cone (or satellite cone), a geographical feature found around a volcano
+Shatter cone, rare geological feature in the bedrock beneath meteorite impact craters or underground nuclear explosions
+Volcanic cone, among the simplest volcanic formations in the world
+Lambert conformal conic projection (LCC), a conic map projection, which is often used for aeronautical charts
+
+Places
+Cone (Phrygia), a town and bishopric of ancient Phrygia
+Cone, Michigan, an unincorporated community in Michigan
+Cone, Texas, an unincorporated community in Crosby County, Texas, United States
+Cone Islet, a small granite island in south-eastern Australia
+Conical Range, a small mountain range in southwestern British Columbia, Canada, between Seymour Inlet and Belize Inlet
+
+People
+
+Bonnie Ethel Cone (1907–2003), American educator and founder of the University of North Carolina at Charlotte
+Carin Cone (born 1940), American swimmer, Olympic medalist, world record holder, and gold medal winner from the Pan American Games
+Chadrick Cone (born 1983), American football wide receiver for the Georgia Force in the Arena Football League
+Cindy Parlow Cone (born 1978), American soccer player and coach
+Cone sisters, Claribel Cone (1864–1929), and Etta Cone (1870–1949), collectors and socialites
+David Cone (born 1963), former Major League Baseball pitcher
+Edward T. Cone (1917–2004), American music theorist and composer
+Fairfax M. Cone (1903–1977), director of the American Association of Advertising Agencies
+Fred Cone (baseball) (1848–1909), pioneer professional baseball player
+Fred Cone (American football) (born 1926), former professional American football running back
+Fred P. Cone (1871–1948), twenty-seventh governor of Florida (Frederick Preston)
+Jason McCaslin (born 1980), nicknamed Cone, bassist for the Canadian band Sum 41
+James Hal Cone (born 1938), advocate of Black liberation theology
+John Cone (born 1974), American professional wrestling referee
+John J. Cone, the fourth Supreme Knight of the Knights of Columbus from 1898 to 1899
+Mac Cone (born 1952), Canadian show jumper
+Martin Cone (1882–1963), 6th president of St. Ambrose College from 1930 to 1937
+Marvin Cone (1891–1965), American painter
+Reuben Cone (1788–1851), pioneer and landowner in Atlanta, Georgia
+Robert W. Cone (1957-2016), major general in the United States Army, and Special Assistant to the Commanding General of TRADOC
+Sara Cone Bryant (1873–?), author of various children's book in the early 20th century
+Spencer Cone Jones (1836–1915), President of the Maryland State Senate, Mayor of Rockville, Maryland
+Spencer Houghton Cone (1785–1855), American Baptist minister and president of the American and Foreign Bible Society
+Tim Cone (born 1957), American basketball coach
+
+Other uses
+Conical Asian hat, a simple style of straw hat originating in East and Southeast Asia
+Ice cream cone, an edible container in which ice cream is served, shaped like an inverted cone open at its top
+Snow cone, a dessert usually made of crushed or shaved ice, flavored with sweet, usually fruit-flavored, brightly colored syrup
+Traffic cone, a brightly colored cone-shaped plastic object commonly used as a temporary traffic barrier or warning sign
+USS Cone (DD-866), a Gearing-class destroyer of the United States Navy
+Elizabethan collar or e-collar, a device to keep an animal from licking or biting itself
+To locate an aircraft using a searchlight
+Cone Mills Corporation, a textile manufacturer
+
+See also 
+
+Kone (disambiguation)
+Colne (disambiguation) (pronounced cone)
+Kegel (disambiguation) (German/Dutch translation of cone)
+In a chemical reaction, chemical equilibrium is the state in which both the reactants and products are present in concentrations which have no further tendency to change with time, so that there is no observable change in the properties of the system. This state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but they are equal. Thus, there are no net changes in the concentrations of the reactants and products. Such a state is known as dynamic equilibrium.
+
+Historical introduction 
+
+The concept of chemical equilibrium was developed in 1803, after Berthollet found that some chemical reactions are reversible. For any reaction mixture to exist at equilibrium, the rates of the forward and backward (reverse) reactions must be equal. In the following chemical equation, arrows point both ways to indicate equilibrium. A and B are reactant chemical species, S and T are product species, and α, β, σ, and τ are the stoichiometric coefficients of the respective reactants and products:
+α A + β B  σ S + τ T
+
+The equilibrium concentration position of a reaction is said to lie "far to the right" if, at equilibrium, nearly all the reactants are consumed. Conversely the equilibrium position is said to be "far to the left" if hardly any product is formed from the reactants.
+
+Guldberg and Waage (1865), building on Berthollet's ideas, proposed the law of mass action:
+
+where A, B, S and T are active masses and k+ and k− are rate constants. Since at equilibrium forward and backward rates are equal:
+
+and the ratio of the rate constants is also a constant, now known as an equilibrium constant.
+
+By convention, the products form the numerator.
+However, the law of mass action is valid only for concerted one-step reactions that proceed through a single transition state and is not valid in general because rate equations do not, in general, follow the stoichiometry of the reaction as Guldberg and Waage had proposed (see, for example, nucleophilic aliphatic substitution by SN1 or reaction of hydrogen and bromine to form hydrogen bromide). Equality of forward and backward reaction rates, however, is a necessary condition for chemical equilibrium, though it is not sufficient to explain why equilibrium occurs.
+
+Despite the limitations of this derivation, the equilibrium constant for a reaction is indeed a constant, independent of the activities of the various species involved, though it does depend on temperature as observed by the van 't Hoff equation. Adding a catalyst will affect both the forward reaction and the reverse reaction in the same way and will not have an effect on the equilibrium constant. The catalyst will speed up both reactions thereby increasing the speed at which equilibrium is reached.
+
+Although the macroscopic equilibrium concentrations are constant in time, reactions do occur at the molecular level. For example, in the case of acetic acid dissolved in water and forming acetate and hydronium ions,
+
+a proton may hop from one molecule of acetic acid onto a water molecule and then onto an acetate anion to form another molecule of acetic acid and leaving the number of acetic acid molecules unchanged. This is an example of dynamic equilibrium. Equilibria, like the rest of thermodynamics, are statistical phenomena, averages of microscopic behavior.
+
+Le Châtelier's principle (1884) predicts the behavior of an equilibrium system when changes to its reaction conditions occur. If a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to partially reverse the change. For example, adding more S (to the chemical reaction above) from the outside will cause an excess of products, and the system will try to counteract this by increasing the reverse reaction and pushing the equilibrium point backward (though the equilibrium constant will stay the same).
+
+If mineral acid is added to the acetic acid mixture, increasing the concentration of hydronium ion, the amount of dissociation must decrease as the reaction is driven to the left in accordance with this principle. This can also be deduced from the equilibrium constant expression for the reaction:
+
+If {H3O+} increases {CH3CO2H} must increase and  must decrease. The H2O is left out, as it is the solvent and its concentration remains high and nearly constant.
+
+A quantitative version is given by the reaction quotient.
+
+J. W. Gibbs suggested in 1873 that equilibrium is attained when the Gibbs free energy of the system is at its minimum value (assuming the reaction is carried out at a constant temperature and pressure). What this means is that the derivative of the Gibbs energy with respect to reaction coordinate (a measure of the extent of reaction that has occurred, ranging from zero for all reactants to a maximum for all products) vanishes (because dG = 0), signaling a stationary point. This derivative is called the reaction Gibbs energy (or energy change) and corresponds to the difference between the chemical potentials of reactants and products at the composition of the reaction mixture. This criterion is both necessary and sufficient. If a mixture is not at equilibrium, the liberation of the excess Gibbs energy (or Helmholtz energy at constant volume reactions) is the "driving force" for the composition of the mixture to change until equilibrium is reached. The equilibrium constant can be related to the standard Gibbs free energy change for the reaction by the equation
+
+where R is the universal gas constant and T the temperature.
+
+When the reactants are dissolved in a medium of high ionic strength the quotient of activity coefficients may be taken to be constant. In that case the concentration quotient, Kc,
+
+where [A] is the concentration of A, etc., is independent of the analytical concentration of the reactants. For this reason, equilibrium constants for solutions are usually determined in media of high ionic strength. Kc varies with ionic strength, temperature and pressure (or volume). Likewise Kp for gases depends on partial pressure. These constants are easier to measure and encountered in high-school chemistry courses.
+
+Thermodynamics
+
+At constant temperature and pressure, one must consider the Gibbs free energy, G, while at constant temperature and volume, one must consider the Helmholtz free energy, A, for the reaction; and at constant internal energy and volume, one must consider the entropy, S, for the reaction.
+
+The constant volume case is important in geochemistry and atmospheric chemistry where pressure variations are significant. Note that, if reactants and products were in standard state (completely pure), then there would be no reversibility and no equilibrium. Indeed, they would necessarily occupy disjoint volumes of space. The mixing of the products and reactants contributes a large entropy increase (known as entropy of mixing) to states containing equal mixture of products and reactants and gives rise to a distinctive minimum in the Gibbs energy as a function of the extent of reaction. The standard Gibbs energy change, together with the Gibbs energy of mixing, determine the equilibrium state.
+
+In this article only the constant pressure case is considered. The relation between the Gibbs free energy and the equilibrium constant can be found by considering chemical potentials.
+
+At constant temperature and pressure in the absence of an applied voltage, the Gibbs free energy, G, for the reaction depends only on the extent of reaction: ξ (Greek letter xi), and can only decrease according to the second law of thermodynamics. It means that the derivative of G with respect to ξ must be negative if the reaction happens; at the equilibrium this derivative is equal to zero.
+:equilibrium
+
+In order to meet the thermodynamic condition for equilibrium, the Gibbs energy must be stationary, meaning that the derivative of G with respect to the extent of reaction, ξ, must be zero. It can be shown that in this case, the sum of chemical potentials times the stoichiometric coefficients of the products is equal to the sum of those corresponding to the reactants. Therefore, the sum of the Gibbs energies of the reactants must be the equal to the sum of the Gibbs energies of the products.
+
+where μ is in this case a partial molar Gibbs energy, a chemical potential. The chemical potential of a reagent A is a function of the activity, {A} of that reagent.
+
+(where μ is the standard chemical potential).
+
+The definition of the Gibbs energy equation interacts with the fundamental thermodynamic relation to produce
+
+.
+
+Inserting dNi = νi dξ into the above equation gives a stoichiometric coefficient () and a differential that denotes the reaction occurring to an infinitesimal extent (dξ). At constant pressure and temperature the above equations can be written as
+
+  
+
+which is the "Gibbs free energy change for the reaction. This results in:
+
+.
+
+By substituting the chemical potentials:
+
+,
+
+the relationship becomes:
+
+:
+which is the standard Gibbs energy change for the reaction' that can be calculated using thermodynamical tables.
+The reaction quotient is defined as:
+
+Therefore,
+
+At equilibrium:
+
+leading to:
+
+and
+
+Obtaining the value of the standard Gibbs energy change, allows the calculation of the equilibrium constant.
+
+Addition of reactants or products
+For a reactional system at equilibrium: Qr = Keq; ξ = ξeq.
+If the activities of constituents are modified, the value of the reaction quotient changes and becomes different from the equilibrium constant: Qr ≠ Keq  and  then 
+If activity of a reagent i increases  the reaction quotient decreases. Then  and  The reaction will shift to the right (i.e. in the forward direction, and thus more products will form).
+If activity of a product j increases, then  and  The reaction will shift to the left (i.e. in the reverse direction, and thus less products will form).
+
+Note that activities and equilibrium constants are dimensionless numbers.
+
+Treatment of activity
+
+The expression for the equilibrium constant can be rewritten as the product of a concentration quotient, Kc and an activity coefficient quotient, Γ.
+
+[A] is the concentration of reagent A, etc. It is possible in principle to obtain values of the activity coefficients, γ. For solutions, equations such as the Debye–Hückel equation or extensions such as Davies equation Specific ion interaction theory or Pitzer equations may be used.Software (below) However this is not always possible. It is common practice to assume that Γ is a constant, and to use the concentration quotient in place of the thermodynamic equilibrium constant. It is also general practice to use the term equilibrium constant instead of the more accurate concentration quotient. This practice will be followed here.
+
+For reactions in the gas phase partial pressure is used in place of concentration and fugacity coefficient in place of activity coefficient. In the real world, for example, when making ammonia in industry, fugacity coefficients must be taken into account. Fugacity, f, is the product of partial pressure and fugacity coefficient. The chemical potential of a species in the real gas phase is given by
+
+so the general expression defining an equilibrium constant is valid for both solution and gas phases.
+
+Concentration quotients
+
+In aqueous solution, equilibrium constants are usually determined in the presence of an "inert" electrolyte such as sodium nitrate, NaNO3, or potassium perchlorate, KClO4. The ionic strength of a solution is given by
+
+where ci and zi stand for the concentration and ionic charge of ion type i, and the sum is taken over all the N types of charged species in solution. When the concentration of dissolved salt is much higher than the analytical concentrations of the reagents, the ions originating from the dissolved salt determine the ionic strength, and the ionic strength is effectively constant. Since activity coefficients depend on ionic strength, the activity coefficients of the species are effectively independent of concentration. Thus, the assumption that Γ is constant is justified. The concentration quotient is a simple multiple of the equilibrium constant.
+
+However, Kc will vary with ionic strength. If it is measured at a series of different ionic strengths, the value can be extrapolated to zero ionic strength. The concentration quotient obtained in this manner is known, paradoxically, as a thermodynamic equilibrium constant.
+
+Before using a published value of an equilibrium constant in conditions of ionic strength different from the conditions used in its determination, the value should be adjustedSoftware (below).
+
+Metastable mixtures
+
+A mixture may appear to have no tendency to change, though it is not at equilibrium. For example, a mixture of SO2 and O2 is metastable as there is a kinetic barrier to formation of the product, SO3.
+2 SO2 + O2  2 SO3
+
+The barrier can be overcome when a catalyst is also present in the mixture as in the contact process, but the catalyst does not affect the equilibrium concentrations.
+
+Likewise, the formation of bicarbonate from carbon dioxide and water is very slow under normal conditions
+
+but almost instantaneous in the presence of the catalytic enzyme carbonic anhydrase.
+
+Pure substances
+
+When pure substances (liquids or solids) are involved in equilibria their activities do not appear in the equilibrium constant because their numerical values are considered one.
+
+Applying the general formula for an equilibrium constant to the specific case of a dilute solution of acetic acid in water one obtains
+CH3CO2H + H2O  CH3CO2− + H3O+
+
+For all but very concentrated solutions, the water can be considered a "pure" liquid, and therefore it has an activity of one. The equilibrium constant expression is therefore usually written as
+.
+
+A particular case is the self-ionization of water
+
+2 H2O  H3O+ + OH−
+
+Because water is the solvent, and has an activity of one, the self-ionization constant of water is defined as
+
+It is perfectly legitimate to write [H+] for the hydronium ion concentration, since the state of solvation of the proton is constant (in dilute solutions) and so does not affect the equilibrium concentrations. Kw varies with variation in ionic strength and/or temperature.
+
+The concentrations of H+ and OH− are not independent quantities. Most commonly [OH−] is replaced by Kw[H+]−1 in equilibrium constant expressions which would otherwise include hydroxide ion.
+
+Solids also do not appear in the equilibrium constant expression, if they are considered to be pure and thus their activities taken to be one. An example is the Boudouard reaction:
+
+2 CO  CO2 + C
+
+for which the equation (without solid carbon) is written as:
+
+Multiple equilibria
+
+Consider the case of a dibasic acid H2A. When dissolved in water, the mixture will contain H2A, HA− and A2−. This equilibrium can be split into two steps in each of which one proton is liberated.K1 and K2 are examples of stepwise equilibrium constants. The overall equilibrium constant, βD, is product of the stepwise constants.
+{H2A} <=> {A^{2-}} + {2H+}:
+Note that these constants are dissociation constants because the products on the right hand side of the equilibrium expression are dissociation products. In many systems, it is preferable to use association constants.β1 and β2 are examples of association constants. Clearly  and ;  and 
+For multiple equilibrium systems, also see: theory of Response reactions.
+
+Effect of temperature
+
+The effect of changing temperature on an equilibrium constant is given by the van 't Hoff equation
+
+Thus, for exothermic reactions (ΔH is negative), K decreases with an increase in temperature, but, for endothermic reactions, (ΔH is positive) K increases with an increase temperature. An alternative formulation is
+
+At first sight this appears to offer a means of obtaining the standard molar enthalpy of the reaction by studying the variation of K with temperature. In practice, however, the method is unreliable because error propagation almost always gives very large errors on the values calculated in this way.
+
+Effect of electric and magnetic fields
+The effect of electric field on equilibrium has been studied by Manfred Eigen among others.
+
+Types of equilibrium
+
+Equilibrium can be broadly classified as heterogeneous and homogeneous equilibrium. Homogeneous equilibrium consists of reactants and products belonging in the same phase whereas heterogeneous equilibrium comes into play for reactants and products in different phases.   
+ In the gas phase: rocket engines
+ The industrial synthesis such as ammonia in the Haber–Bosch process (depicted right) takes place through a succession of equilibrium steps including adsorption processes
+ Atmospheric chemistry
+ Seawater and other natural waters: chemical oceanography
+ Distribution between two phases
+ log D distribution coefficient: important for pharmaceuticals where lipophilicity is a significant property of a drug
+ Liquid–liquid extraction, Ion exchange, Chromatography
+ Solubility product
+ Uptake and release of oxygen by hemoglobin in blood
+ Acid–base equilibria: acid dissociation constant, hydrolysis, buffer solutions, indicators, acid–base homeostasis
+ Metal–ligand complexation: sequestering agents, chelation therapy, MRI contrast reagents, Schlenk equilibrium
+ Adduct formation: host–guest chemistry, supramolecular chemistry, molecular recognition, dinitrogen tetroxide
+ In certain oscillating reactions, the approach to equilibrium is not asymptotically but in the form of a damped oscillation .
+ The related Nernst equation in electrochemistry gives the difference in electrode potential as a function of redox concentrations.
+ When molecules on each side of the equilibrium are able to further react irreversibly in secondary reactions, the final product ratio is determined according to the Curtin–Hammett principle.
+
+In these applications, terms such as stability constant, formation constant, binding constant, affinity constant, association constant and dissociation constant are used. In biochemistry, it is common to give units for binding constants, which serve to define the concentration units used when the constant's value was determined.
+
+Composition of a mixture
+
+When the only equilibrium is that of the formation of a 1:1 adduct as the composition of a mixture, there are many ways that the composition of a mixture can be calculated. For example, see ICE table for a traditional method of calculating the pH of a solution of a weak acid.
+
+There are three approaches to the general calculation of the composition of a mixture at equilibrium.
+
+The most basic approach is to manipulate the various equilibrium constants until the desired concentrations are expressed in terms of measured equilibrium constants (equivalent to measuring chemical potentials) and initial conditions.
+Minimize the Gibbs energy of the system.
+ Satisfy the equation of mass balance. The equations of mass balance are simply statements that demonstrate that the total concentration of each reactant must be constant by the law of conservation of mass.
+
+Mass-balance equations
+
+In general, the calculations are rather complicated or complex. For instance, in the case of a dibasic acid, H2A dissolved in water the two reactants can be specified as the conjugate base, A2−, and the proton, H+. The following equations of mass-balance could apply equally well to a base such as 1,2-diaminoethane, in which case the base itself is designated as the reactant A:
+
+with TA the total concentration of species A. Note that it is customary to omit the ionic charges when writing and using these equations.
+
+When the equilibrium constants are known and the total concentrations are specified there are two equations in two unknown "free concentrations" [A] and [H]. This follows from the fact that [HA] = β1[A][H], [H2A] = β2[A][H]2 and [OH] = Kw[H]−1
+
+so the concentrations of the "complexes" are calculated from the free concentrations and the equilibrium constants.
+General expressions applicable to all systems with two reagents, A and B would be
+
+It is easy to see how this can be extended to three or more reagents.
+
+Polybasic acids
+
+The composition of solutions containing reactants A and H is easy to calculate as a function of p[H]. When [H] is known, the free concentration [A] is calculated from the mass-balance equation in A.
+
+The diagram alongside, shows an example of the hydrolysis of the aluminium Lewis acid Al3+(aq) shows the species concentrations for a 5 × 10−6 M solution of an aluminium salt as a function of pH. Each concentration is shown as a percentage of the total aluminium.
+
+Solution and precipitation
+
+The diagram above illustrates the point that a precipitate that is not one of the main species in the solution equilibrium may be formed. At pH just below 5.5 the main species present in a 5 μM solution of Al3+ are aluminium hydroxides Al(OH)2+,  and , but on raising the pH Al(OH)3 precipitates from the solution. This occurs because Al(OH)3 has a very large lattice energy. As the pH rises more and more Al(OH)3 comes out of solution. This is an example of Le Châtelier's principle in action: Increasing the concentration of the hydroxide ion causes more aluminium hydroxide to precipitate, which removes hydroxide from the solution. When the hydroxide concentration becomes sufficiently high the soluble aluminate, , is formed.
+
+Another common instance where precipitation occurs is when a metal cation interacts with an anionic ligand to form an electrically neutral complex. If the complex is hydrophobic, it will precipitate out of water. This occurs with the nickel ion Ni2+ and dimethylglyoxime, (dmgH2): in this case the lattice energy of the solid is not particularly large, but it greatly exceeds the energy of solvation of the molecule Ni(dmgH)2.
+
+Minimization of Gibbs energy
+
+At equilibrium, at a specified temperature and pressure, and with no external forces, the Gibbs free energy G is at a minimum:
+
+where μj is the chemical potential of molecular species j, and Nj is the amount of molecular species j. It may be expressed in terms of thermodynamic activity as:
+
+where  is the chemical potential in the standard state, R is the gas constant T is the absolute temperature, and Aj is the activity.
+
+For a closed system, no particles may enter or leave, although they may combine in various ways. The total number of atoms of each element will remain constant. This means that the minimization above must be subjected to the constraints:
+
+where aij is the number of atoms of element i in molecule j and b is the total number of atoms of element i, which is a constant, since the system is closed. If there are a total of k types of atoms in the system, then there will be k such equations. If ions are involved, an additional row is added to the aij matrix specifying the respective charge on each molecule which will sum to zero.
+
+This is a standard problem in optimisation, known as constrained minimisation. The most common method of solving it is using the method of Lagrange multipliers (although other methods may be used).
+
+Define:
+
+where the λi are the Lagrange multipliers, one for each element. This allows each of the Nj and λj to be treated independently, and it can be shown using the tools of multivariate calculus that the equilibrium condition is given by
+
+(For proof see Lagrange multipliers.) This is a set of (m + k) equations in (m + k) unknowns (the Nj and the λi) and may, therefore, be solved for the equilibrium concentrations Nj as long as the chemical activities are known as functions of the concentrations at the given temperature and pressure. (In the ideal case, activities are proportional to concentrations.) (See Thermodynamic databases for pure substances.) Note that the second equation is just the initial constraints for minimization.
+
+This method of calculating equilibrium chemical concentrations is useful for systems with a large number of different molecules. The use of k atomic element conservation equations for the mass constraint is straightforward, and replaces the use of the stoichiometric coefficient equations. The results are consistent with those specified by chemical equations. For example, if equilibrium is specified by a single chemical equation:,
+
+where νj is the stoichiometric coefficient for the j th molecule (negative for reactants, positive for products) and Rj is the symbol for the j th molecule, a properly balanced equation will obey:
+
+Multiplying the first equilibrium condition by νj and using the above equation yields:
+
+As above, defining ΔG
+
+where Kc'' is the equilibrium constant, and ΔG will be zero at equilibrium.
+
+Analogous procedures exist for the minimization of other thermodynamic potentials.
+
+See also
+
+ Acidosis
+ Alkalosis
+ Arterial blood gas
+ Benesi–Hildebrand method
+ Determination of equilibrium constants
+ Equilibrium constant
+ Henderson–Hasselbalch equation
+ Michaelis–Menten kinetics
+ pCO2
+ pH
+ pKa
+ Redox equilibria
+ Steady state (chemistry)
+ Thermodynamic databases for pure substances
+ Non-random two-liquid model (NRTL model) - Phase equilibrium calculations
+ UNIQUAC model - Phase equilibrium calculations
+
+References
+
+Further reading
+
+ Mainly concerned with gas-phase equilibria.
+
+External links
+
+Analytical chemistry
+Physical chemistry
+In mathematics, a combination is a selection of items from a set that has distinct members, such that the order of selection does not matter (unlike permutations). For example, given three fruits, say an apple, an orange and a pear, there are three combinations of two that can be drawn from this set: an apple and a pear; an apple and an orange; or a pear and an orange. More formally, a k-combination of a set S is a subset of k distinct elements of S. So, two combinations are identical if and only if each combination has the same members. (The arrangement of the members in each set does not matter.) If the set has n elements, the number of k-combinations, denoted by  or , is equal to the binomial coefficient
+
+which can be written using factorials as  whenever , and which is zero when . This formula can be derived from the fact that each k-combination of a set S of n members has  permutations so  or . The set of all k-combinations of a set S is often denoted by .
+
+A combination is a combination of n things taken k at a time without repetition. To refer to combinations in which repetition is allowed, the terms k-combination with repetition, k-multiset, or k-selection, are often used. If, in the above example, it were possible to have two of any one kind of fruit there would be 3 more 2-selections: one with two apples, one with two oranges, and one with two pears.
+
+Although the set of three fruits was small enough to write a complete list of combinations, this becomes impractical as the size of the set increases. For example, a poker hand can be described as a 5-combination (k = 5) of cards from a 52 card deck (n = 52). The 5 cards of the hand are all distinct, and the order of cards in the hand does not matter. There are 2,598,960 such combinations, and the chance of drawing any one hand at random is 1 / 2,598,960.
+
+Number of k-combinations 
+
+The number of k-combinations from a given set S of n elements is often denoted in elementary combinatorics texts by , or by a variation such as ,  , ,  or even  (the last form is standard in French, Romanian, Russian, Chinese and Polish texts).  The same number however occurs in many other mathematical contexts, where it is denoted by  (often read as "n choose k"); notably it occurs as a coefficient in the binomial formula, hence its name binomial coefficient. One can define  for all natural numbers k at once by the relation
+
+from which it is clear that
+
+and further,
+
+for k > n.
+
+To see that these coefficients count k-combinations from S, one can first consider a collection of n distinct variables Xs labeled by the elements s of S, and expand the product over all elements of S:
+
+it has 2n distinct terms corresponding to all the subsets of S, each subset giving the product of the corresponding variables Xs. Now setting all of the Xs equal to the unlabeled variable X, so that the product becomes , the term for each k-combination from S becomes Xk, so that the coefficient of that power in the result equals the number of such k-combinations.
+
+Binomial coefficients can be computed explicitly in various ways. To get all of them for the expansions up to , one can use (in addition to the basic cases already given) the recursion relation
+
+for 0 < k < n, which follows from =; this leads to the construction of Pascal's triangle.
+
+For determining an individual binomial coefficient, it is more practical to use the formula
+
+The numerator gives the number of k-permutations of n, i.e., of sequences of k distinct elements of S, while the denominator gives the number of such k-permutations that give the same k-combination when the order is ignored.
+
+When k exceeds n/2, the above formula contains factors common to the numerator and the denominator, and canceling them out gives the relation
+
+for 0 ≤ k ≤ n. This expresses a symmetry that is evident from the binomial formula, and can also be understood in terms of k-combinations by taking the complement of such a combination, which is an -combination.
+
+Finally there is a formula which exhibits this symmetry directly, and has the merit of being easy to remember:
+
+where n! denotes the factorial of n. It is obtained from the previous formula by multiplying denominator and numerator by !, so it is certainly computationally less efficient than that formula.
+
+The last formula can be understood directly, by considering the n! permutations of all the elements of S. Each such permutation gives a k-combination by selecting its first k elements. There are many duplicate selections: any combined permutation of the first k elements among each other, and of the final (n − k) elements among each other produces the same combination; this explains the division in the formula.
+
+From the above formulas follow relations between adjacent numbers in Pascal's triangle in all three directions:
+
+Together with the basic cases , these allow successive computation of respectively all numbers of combinations from the same set (a row in Pascal's triangle), of k-combinations of sets of growing sizes, and of combinations with a complement of fixed size .
+
+Example of counting combinations 
+As a specific example, one can compute the number of five-card hands possible from a standard fifty-two card deck as:
+
+Alternatively one may use the formula in terms of factorials and cancel the factors in the numerator against parts of the factors in the denominator, after which only multiplication of the remaining factors is required:
+
+Another alternative computation, equivalent to the first, is based on writing
+
+which gives
+
+When evaluated in the following order, , this can be computed using only integer arithmetic. The reason is that when each division occurs, the intermediate result that is produced is itself a binomial coefficient, so no remainders ever occur.
+
+Using the symmetric formula in terms of factorials without performing simplifications gives a rather extensive calculation:
+
+Enumerating k-combinations 
+
+One can enumerate all k-combinations of a given set S of n elements in some fixed order, which establishes a bijection from an interval of  integers with the set of those k-combinations. Assuming S is itself ordered, for instance S = { 1, 2, ..., n }, there are two natural possibilities for ordering its k-combinations: by comparing their smallest elements first (as in the illustrations above) or by comparing their largest elements first. The latter option has the advantage that adding a new largest element to S will not change the initial part of the enumeration, but just add the new k-combinations of the larger set after the previous ones. Repeating this process, the enumeration can be extended indefinitely with k-combinations of ever larger sets. If moreover the intervals of the integers are taken to start at 0, then the k-combination at a given place i in the enumeration can be computed easily from i, and the bijection so obtained is known as the combinatorial number system. It is also known as "rank"/"ranking" and "unranking" in computational mathematics.
+
+There are many ways to enumerate k combinations. One way is to visit all the binary numbers less than 2n. Choose those numbers having k nonzero bits, although this is very inefficient even for small n (e.g. n = 20 would require visiting about one million numbers while the maximum number of allowed k combinations is about 186 thousand for k = 10). The positions of these 1 bits in such a number is a specific k-combination of the set { 1, ..., n }. Another simple, faster way is to track k index numbers of the elements selected, starting with {0 .. k−1} (zero-based) or {1 .. k} (one-based) as the first allowed k-combination and then repeatedly moving to the next allowed k-combination by incrementing the last index number if it is lower than n-1 (zero-based) or n (one-based) or the last index number x that is less than the index number following it minus one if such an index exists and resetting the index numbers after x to {x+1, x+2, ...}.
+
+Number of combinations with repetition 
+
+A k-combination with repetitions, or k-multicombination, or multisubset of size k from a set S of size n is given by a set of k not necessarily distinct elements of S, where order is not taken into account: two sequences define the same multiset if one can be obtained from the other by permuting the terms. In other words, it is a sample of k elements from a set of n elements allowing for duplicates (i.e., with replacement) but disregarding different orderings (e.g. {2,1,2} = {1,2,2}). Associate an index to each element of S and think of the elements of S as types of objects, then we can let  denote the number of elements of type i in a multisubset. The number of multisubsets of size k is then the number of nonnegative integer (so allowing zero) solutions of the Diophantine equation:
+
+If S has n elements, the number of such k-multisubsets is denoted by
+
+a notation that is analogous to the binomial coefficient which counts k-subsets. This expression, n multichoose k, can also be given in terms of binomial coefficients:
+
+This relationship can be easily proved using a representation known as stars and bars. 
+
+A solution of the above Diophantine equation can be represented by  stars, a separator (a bar), then  more stars, another separator, and so on. The total number of stars in this representation is k and the number of bars is n - 1 (since a separation into n parts needs n-1 separators). Thus, a string of k + n - 1 (or n + k - 1) symbols (stars and bars) corresponds to a solution if there are k stars in the string. Any solution can be represented by choosing k out of  positions to place stars and filling the remaining positions with bars. For example, the solution  of the equation  (n = 4 and k = 10) can be represented by
+
+The number of such strings is the number of ways to place 10 stars in 13 positions,  which is the number of 10-multisubsets of a set with 4 elements.
+
+As with binomial coefficients, there are several relationships between these multichoose expressions. For example, for ,
+
+This identity follows from interchanging the stars and bars in the above representation.
+
+Example of counting multisubsets 
+For example, if you have four types of donuts (n = 4) on a menu to choose from and you want three donuts (k = 3), the number of ways to choose the donuts with repetition can be calculated as
+
+This result can be verified by listing all the 3-multisubsets of the set S = {1,2,3,4}. This is displayed in the following table. The second column lists the donuts you actually chose, the third column shows the nonnegative integer solutions  of the equation  and the last column gives the stars and bars representation of the solutions.
+
+Number of k-combinations for all k 
+
+The number of k-combinations for all k is the number of subsets of a set of n elements. There are several ways to see that this number is 2n. In terms of combinations, , which is the sum of the nth row (counting from 0) of the binomial coefficients in Pascal's triangle. These combinations (subsets) are enumerated by the 1 digits of the set of base 2 numbers counting from 0 to 2n − 1, where each digit position is an item from the set of n.
+
+Given 3 cards numbered 1 to 3, there are 8 distinct combinations (subsets), including the empty set:
+
+Representing these subsets (in the same order) as base 2 numerals:
+
+0 – 000
+1 – 001
+2 – 010
+3 – 011
+4 – 100
+5 – 101
+6 – 110
+7 – 111
+
+Probability: sampling a random combination 
+
+There are various algorithms to pick out a random combination from a given set or list. Rejection sampling is extremely slow for large sample sizes. One way to select a k-combination efficiently from a population of size n is to iterate across each element of the population, and at each step pick that element with a dynamically changing probability of  (see Reservoir sampling). Another is to pick a random non-negative integer less than  and convert it into a combination using the combinatorial number system.
+
+Number of ways to put objects into bins 
+
+A combination can also be thought of as a selection of two sets of items: those that go into the chosen bin and those that go into the unchosen bin. This can be generalized to any number of bins with the constraint that every item must go to exactly one bin. The number of ways to put objects into bins is given by the multinomial coefficient
+
+where n is the number of items, m is the number of bins, and  is the number of items that go into bin i.
+
+One way to see why this equation holds is to first number the objects arbitrarily from 1 to n and put the objects with numbers  into the first bin in order, the objects with numbers  into the second bin in order, and so on. There are  distinct numberings, but many of them are equivalent, because only the set of items in a bin matters, not their order in it. Every combined permutation of each bins' contents produces an equivalent way of putting items into bins. As a result, every equivalence class consists of  distinct numberings, and the number of equivalence classes is .
+
+The binomial coefficient is the special case where k items go into the chosen bin and the remaining  items go into the unchosen bin:
+
+See also
+
+ Binomial coefficient
+ Combinatorics
+ Block design
+ Kneser graph
+ List of permutation topics
+ Multiset
+ Pascal's triangle
+ Permutation
+ Probability
+ Subset
+
+Notes
+
+References
+ 
+ 
+ Erwin Kreyszig, Advanced Engineering Mathematics, John Wiley & Sons, INC, 1999.
+
+External links
+ Topcoder tutorial on combinatorics  
+ C code to generate all combinations of n elements chosen as k
+ Many Common types of permutation and combination math problems, with detailed solutions
+ The Unknown Formula For combinations when choices can be repeated and order does not matter
+ Combinations with repetitions (by: Akshatha AG and Smitha B)
+ The dice roll with a given sum problem An application of the combinations with repetition to rolling multiple dice
+
+Combinatorics
+Software is a set of computer programs and associated documentation and data. This is in contrast to hardware, from which the system is built and which actually performs the work.
+
+At the lowest programming level, executable code consists of machine language instructions supported by an individual processor—typically a central processing unit (CPU) or a graphics processing unit (GPU). Machine language consists of groups of binary values signifying processor instructions that change the state of the computer from its preceding state. For example, an instruction may change the value stored in a particular storage location in the computer—an effect that is not directly observable to the user. An instruction may also invoke one of many input or output operations, for example, displaying some text on a computer screen, causing state changes that should be visible to the user. The processor executes the instructions in the order they are provided, unless it is instructed to "jump" to a different instruction or is interrupted by the operating system. , most personal computers, smartphone devices, and servers have processors with multiple execution units, or multiple processors performing computation together, so computing has become a much more concurrent activity than in the past.
+
+The majority of software is written in high-level programming languages. They are easier and more efficient for programmers because they are closer to natural languages than machine languages. High-level languages are translated into machine language using a compiler, an interpreter, or a combination of the two. Software may also be written in a low-level assembly language that has a strong correspondence to the computer's machine language instructions and is translated into machine language using an assembler.
+
+History
+
+An algorithm for what would have been the first piece of software was written by Ada Lovelace in the 19th century, for the planned Analytical Engine. She created proofs to show how the engine would calculate Bernoulli numbers. Because of the proofs and the algorithm, she is considered the first computer programmer.
+
+The first theory about software, prior to the creation of computers as we know them today, was proposed by Alan Turing in his 1936 essay, On Computable Numbers, with an Application to the Entscheidungsproblem (decision problem). This eventually led to the creation of the academic fields of computer science and software engineering; both fields study software and its creation. Computer science is the theoretical study of computer and software (Turing's essay is an example of computer science), whereas software engineering is the application of engineering principles to development of software.
+
+In 2000, Fred Shapiro, a librarian at the Yale Law School, published a letter revealing that John Wilder Tukey's 1958 paper "The Teaching of Concrete Mathematics" contained the earliest known usage of the term "software" found in a search of JSTOR's electronic archives, predating the Oxford English Dictionary's citation by two years. This led many to credit Tukey with coining the term, particularly in obituaries published that same year, although Tukey never claimed credit for any such coinage. In 1995, Paul Niquette claimed he had originally coined the term in October 1953, although he could not find any documents supporting his claim. The earliest known publication of the term "software" in an engineering context was in August 1953 by Richard R. Carhart, in a Rand Corporation Research Memorandum.
+
+Types
+
+On virtually all computer platforms, software can be grouped into a few broad categories.
+
+Purpose, or domain of use
+Based on the goal, computer software can be divided into:
+ Application software uses the computer system to perform special functions beyond the basic operation of the computer itself. There are many different types of application software because the range of tasks that can be performed with a modern computer is so large—see list of software.
+ System software manages hardware behaviour, as to provide basic functionalities that are required by users, or for other software to run properly, if at all. System software is also designed for providing a platform for running application software, and it includes the following:
+ Operating systems are essential collections of software that manage resources and provide common services for other software that runs "on top" of them. Supervisory programs, boot loaders, shells and window systems are core parts of operating systems. In practice, an operating system comes bundled with additional software (including application software) so that a user can potentially do some work with a computer that only has one operating system.
+ Device drivers operate or control a particular type of device that is attached to a computer. Each device needs at least one corresponding device driver; because a computer typically has at minimum at least one input device and at least one output device, a computer typically needs more than one device driver.
+ Utilities are computer programs designed to assist users in the maintenance and care of their computers.
+ Malicious software, or malware, is software that is developed to harm or disrupt computers. Malware is closely associated with computer-related crimes, though some malicious programs may have been designed as practical jokes.
+
+Nature or domain of execution
+ Desktop applications such as web browsers and Microsoft Office and LibreOffice and WordPerfect, as well as smartphone and tablet applications (called "apps").
+ JavaScript scripts are pieces of software traditionally embedded in web pages that are run directly inside the web browser when a web page is loaded without the need for a web browser plugin. Software written in other programming languages can also be run within the web browser if the software is either translated into JavaScript, or if a web browser plugin that supports that language is installed; the most common example of the latter is ActionScript scripts, which are supported by the Adobe Flash plugin.
+ Server software, including:
+ Web applications, which usually run on the web server and output dynamically generated web pages to web browsers, using e.g. PHP, Java, ASP.NET, or even JavaScript that runs on the server. In modern times these commonly include some JavaScript to be run in the web browser as well, in which case they typically run partly on the server, partly in the web browser.
+ Plugins and extensions are software that extends or modifies the functionality of another piece of software, and require that software be used in order to function.
+ Embedded software resides as firmware within embedded systems, devices dedicated to a single use or a few uses such as cars and televisions (although some embedded devices such as wireless chipsets can themselves be part of an ordinary, non-embedded computer system such as a PC or smartphone). In the embedded system context there is sometimes no clear distinction between the system software and the application software. However, some embedded systems run embedded operating systems, and these systems do retain the distinction between system software and application software (although typically there will only be one, fixed application which is always run).
+ Microcode is a special, relatively obscure type of embedded software which tells the processor itself how to execute machine code, so it is actually a lower level than machine code. It is typically proprietary to the processor manufacturer, and any necessary correctional microcode software updates are supplied by them to users (which is much cheaper than shipping replacement processor hardware). Thus an ordinary programmer would not expect to ever have to deal with it.
+
+Programming tools
+
+Programming tools are also software in the form of programs or applications that developers use to create, debug, maintain, or otherwise support software.
+
+Software is written in one or more programming languages; there are many programming languages in existence, and each has at least one implementation, each of which consists of its own set of programming tools. These tools may be relatively self-contained programs such as compilers, debuggers, interpreters, linkers, and text editors, that can be combined to accomplish a task; or they may form an integrated development environment (IDE), which combines much or all of the functionality of such self-contained tools. IDEs may do this by either invoking the relevant individual tools or by re-implementing their functionality in a new way. An IDE can make it easier to do specific tasks, such as searching in files in a particular project. Many programming language implementations provide the option of using both individual tools or an IDE.
+
+Topics
+
+Architecture
+
+People who use modern general purpose computers (as opposed to embedded systems, analog computers and supercomputers) usually see three layers of software performing a variety of tasks: platform, application, and user software.
+ Platform software: The platform includes the firmware, device drivers, an operating system, and typically a graphical user interface which, in total, allow a user to interact with the computer and its peripherals (associated equipment). Platform software often comes bundled with the computer. On a PC one will usually have the ability to change the platform software.
+ Application software: Application software is what most people think of when they think of software. Typical examples include office suites and video games. Application software is often purchased separately from computer hardware. Sometimes applications are bundled with the computer, but that does not change the fact that they run as independent applications. Applications are usually independent programs from the operating system, though they are often tailored for specific platforms. Most users think of compilers, databases, and other "system software" as applications.
+ User-written software: End-user development tailors systems to meet users' specific needs. User software includes spreadsheet templates and word processor templates. Even email filters are a kind of user software. Users create this software themselves and often overlook how important it is. Depending on how competently the user-written software has been integrated into default application packages, many users may not be aware of the distinction between the original packages, and what has been added by co-workers.
+
+Execution
+
+Computer software has to be "loaded" into the computer's storage (such as the hard drive or memory). Once the software has loaded, the computer is able to execute the software. This involves passing instructions from the application software, through the system software, to the hardware which ultimately receives the instruction as machine code. Each instruction causes the computer to carry out an operation—moving data, carrying out a computation, or altering the control flow of instructions.
+
+Data movement is typically from one place in memory to another. Sometimes it involves moving data between memory and registers which enable high-speed data access in the CPU. Moving data, especially large amounts of it, can be costly; this is sometimes avoided by using "pointers" to data instead. Computations include simple operations such as incrementing the value of a variable data element. More complex computations may involve many operations and data elements together.
+
+Quality and reliability
+
+Software quality is very important, especially for commercial and system software. If software is faulty, it can delete a person's work, crash the computer and do other unexpected things. Faults and errors are called "bugs" which are often discovered during alpha and beta testing. Software is often also a victim to what is known as software aging, the progressive performance degradation resulting from a combination of unseen bugs.
+
+Many bugs are discovered and fixed through software testing. However, software testing rarely—if ever—eliminates every bug; some programmers say that "every program has at least one more bug" (Lubarsky's Law). In the waterfall method of software development, separate testing teams are typically employed, but in newer approaches, collectively termed agile software development, developers often do all their own testing, and demonstrate the software to users/clients regularly to obtain feedback. Software can be tested through unit testing, regression testing and other methods, which are done manually, or most commonly, automatically, since the amount of code to be tested can be large. Programs containing command software enable hardware engineering and system operations to function much easier together.
+
+License
+
+The software's license gives the user the right to use the software in the licensed environment, and in the case of free software licenses, also grants other rights such as the right to make copies.
+
+Proprietary software can be divided into two types:
+ freeware, which includes the category of "free trial" software or "freemium" software (in the past, the term shareware was often used for free trial/freemium software). As the name suggests, freeware can be used for free, although in the case of free trials or freemium software, this is sometimes only true for a limited period of time or with limited functionality.
+ software available for a fee, which can only be legally used on purchase of a license.
+
+Open-source software comes with a free software license, granting the recipient the rights to modify and redistribute the software.
+
+Patents
+
+Software patents, like other types of patents, are theoretically supposed to give an inventor an exclusive, time-limited license for a detailed idea (e.g. an algorithm) on how to implement a piece of software, or a component of a piece of software. Ideas for useful things that software could do, and user requirements, are not supposed to be patentable, and concrete implementations (i.e. the actual software packages implementing the patent) are not supposed to be patentable either—the latter are already covered by copyright, generally automatically. So software patents are supposed to cover the middle area, between requirements and concrete implementation. In some countries, a requirement for the claimed invention to have an effect on the physical world may also be part of the requirements for a software patent to be held valid—although since all useful software has effects on the physical world, this requirement may be open to debate. Meanwhile, American copyright law was applied to various aspects of the writing of the software code.
+
+Software patents are controversial in the software industry with many people holding different views about them. One of the sources of controversy is that the aforementioned split between initial ideas and patent does not seem to be honored in practice by patent lawyers—for example the patent for aspect-oriented programming (AOP), which purported to claim rights over any programming tool implementing the idea of AOP, howsoever implemented. Another source of controversy is the effect on innovation, with many distinguished experts and companies arguing that software is such a fast-moving field that software patents merely create vast additional litigation costs and risks, and actually retard innovation. In the case of debates about software patents outside the United States, the argument has been made that large American corporations and patent lawyers are likely to be the primary beneficiaries of allowing or continue to allow software patents.
+
+Design and implementation
+
+Design and implementation of software vary depending on the complexity of the software. For instance, the design and creation of Microsoft Word took much more time than designing and developing Microsoft Notepad because the former has much more basic functionality.
+
+Software is usually developed in integrated development environments (IDE) like Eclipse, IntelliJ and Microsoft Visual Studio that can simplify the process and compile the software. As noted in a different section, software is usually created on top of existing software and the application programming interface (API) that the underlying software provides like GTK+, JavaBeans or Swing. Libraries (APIs) can be categorized by their purpose. For instance, the Spring Framework is used for implementing enterprise applications, the Windows Forms library is used for designing graphical user interface (GUI) applications like Microsoft Word, and Windows Communication Foundation is used for designing web services. When a program is designed, it relies upon the API. For instance, a Microsoft Windows desktop application might call API functions in the .NET Windows Forms library like Form1.Close() and Form1.Show() to close or open the application. Without these APIs, the programmer needs to write these functionalities entirely themselves. Companies like Oracle and Microsoft provide their own APIs so that many applications are written using their software libraries that usually have numerous APIs in them.
+
+Data structures such as hash tables, arrays, and binary trees, and algorithms such as quicksort, can be useful for creating software.
+
+Computer software has special economic characteristics that make its design, creation, and distribution different from most other economic goods.
+
+A person who creates software is called a programmer, software engineer or software developer, terms that all have a similar meaning. More informal terms for programmer also exist such as "coder" and "hacker"although use of the latter word may cause confusion, because it is more often used to mean someone who illegally breaks into computer systems.
+
+See also
+ Computer program
+ Independent software vendor
+ Open-source software
+ Outline of software
+ Software asset management
+ Software release life cycle
+
+References
+
+Sources
+
+External links
+ Software at Encyclopædia Britannica
+Computer programming or coding is the composition of sequences of instructions, called programs, that computers can follow to perform tasks. It involves designing and implementing algorithms, step-by-step specifications of procedures, by writing code in one or more programming languages. Programmers typically use high-level programming languages that are more easily intelligible to humans than machine code, which is directly executed by the central processing unit. Proficient programming usually requires expertise in several different subjects, including knowledge of the application domain, details of programming languages and generic code libraries, specialized algorithms, and formal logic.
+
+Auxiliary tasks accompanying and related to programming include analyzing requirements, testing, debugging (investigating and fixing problems), implementation of build systems, and management of derived artifacts, such as programs' machine code. While these are sometimes considered programming, often the term software development is used for this larger overall process – with the terms programming, implementation, and coding reserved for the writing and editing of code per se. Sometimes software development is known as software engineering, especially when it employs formal methods or follows an engineering design process.
+
+History
+
+Programmable devices have existed for centuries. As early as the 9th century, a programmable music sequencer was invented by the Persian Banu Musa brothers, who described an automated mechanical flute player in the Book of Ingenious Devices. In 1206, the Arab engineer Al-Jazari invented a programmable drum machine where a musical mechanical automaton could be made to play different rhythms and drum patterns, via pegs and cams. In 1801, the Jacquard loom could produce entirely different weaves by changing the "program" – a series of pasteboard cards with holes punched in them.
+
+Code-breaking algorithms have also existed for centuries. In the 9th century, the Arab mathematician Al-Kindi described a cryptographic algorithm for deciphering encrypted code, in A Manuscript on Deciphering Cryptographic Messages. He gave the first description of cryptanalysis by frequency analysis, the earliest code-breaking algorithm.
+
+The first computer program is generally dated to 1843, when mathematician Ada Lovelace published an algorithm to calculate a sequence of Bernoulli numbers, intended to be carried out by Charles Babbage's Analytical Engine. However, Charles Babbage had already written his first program for the Analytical Engine in 1837.
+
+In the 1880s, Herman Hollerith invented the concept of storing data in machine-readable form. Later a control panel (plug board) added to his 1906 Type I Tabulator allowed it to be programmed for different jobs, and by the late 1940s, unit record equipment such as the IBM 602 and IBM 604, were programmed by control panels in a similar way, as were the first electronic computers. However, with the concept of the stored-program computer introduced in 1949, both programs and data were stored and manipulated in the same way in computer memory.
+
+Machine language
+Machine code was the language of early programs, written in the instruction set of the particular machine, often in binary notation. Assembly languages were soon developed that let the programmer specify instruction in a text format (e.g., ADD X, TOTAL), with abbreviations for each operation code and meaningful names for specifying addresses. However, because an assembly language is little more than a different notation for a machine language,  two machines with different instruction sets also have different assembly languages.
+
+Compiler languages
+
+High-level languages made the process of developing a program simpler and more understandable, and less bound to the underlying hardware. 
+The first compiler related tool, the A-0 System, was developed in 1952 by Grace Hopper, who also coined the term 'compiler'. FORTRAN, the first widely used high-level language to have a functional implementation, came out in 1957, and many other languages were soon developed—in particular, COBOL aimed at commercial data processing, and Lisp for computer research.
+
+These compiled languages allow the programmer to write programs in terms that are syntactically richer, and more capable of abstracting the code, making it easy to target varying machine instruction sets via compilation declarations and heuristics. Compilers harnessed the power of computers to make programming easier by allowing programmers to specify calculations by entering a formula using infix notation.
+
+Source code entry
+
+Programs were mostly entered using punched cards or paper tape. By the late 1960s, data storage devices and computer terminals became inexpensive enough that programs could be created by typing directly into the computers. Text editors were also developed that allowed changes and corrections to be made much more easily than with punched cards.
+
+Modern programming
+
+Quality requirements
+
+Whatever the approach to development may be, the final program must satisfy some fundamental properties. The following properties are among the most important:
+
+Reliability: how often the results of a program are correct. This depends on conceptual correctness of algorithms and minimization of programming mistakes, such as mistakes in resource management (e.g., buffer overflows and race conditions) and logic errors (such as division by zero or off-by-one errors).
+Robustness: how well a program anticipates problems due to errors (not bugs). This includes situations such as incorrect, inappropriate or corrupt data, unavailability of needed resources such as memory, operating system services, and network connections, user error, and unexpected power outages.
+Usability: the ergonomics of a program: the ease with which a person can use the program for its intended purpose or in some cases even unanticipated purposes. Such issues can make or break its success even regardless of other issues. This involves a wide range of textual, graphical, and sometimes hardware elements that improve the clarity, intuitiveness, cohesiveness and completeness of a program's user interface.
+Portability: the range of computer hardware and operating system platforms on which the source code of a program can be compiled/interpreted and run. This depends on differences in the programming facilities provided by the different platforms, including hardware and operating system resources, expected behavior of the hardware and operating system, and availability of platform-specific compilers (and sometimes libraries) for the language of the source code.
+Maintainability: the ease with which a program can be modified by its present or future developers in order to make improvements or to customize, fix bugs and security holes, or adapt it to new environments. Good practices during initial development make the difference in this regard. This quality may not be directly apparent to the end user but it can significantly affect the fate of a program over the long term.
+Efficiency/performance: Measure of system resources a program consumes (processor time, memory space, slow devices such as disks, network bandwidth and to some extent even user interaction): the less, the better. This also includes careful management of resources, for example cleaning up temporary files and eliminating memory leaks. This is often discussed under the shadow of a chosen programming language. Although the language certainly affects performance, even slower languages, such as Python, can execute programs instantly from a human perspective. Speed, resource usage, and performance are important for programs that bottleneck the system, but efficient use of programmer time is also important and is related to cost: more hardware may be cheaper.
+
+Readability of source code
+In computer programming, readability refers to the ease with which a human reader can comprehend the purpose, control flow, and operation of source code. It affects the aspects of quality above, including portability, usability and most importantly maintainability.
+
+Readability is important because programmers spend the majority of their time reading, trying to understand, reusing and modifying existing source code, rather than writing new source code. Unreadable code often leads to bugs, inefficiencies, and duplicated code. A study found that a few simple readability transformations made code shorter and drastically reduced the time to understand it.
+
+Following a consistent programming style often helps readability. However, readability is more than just programming style. Many factors, having little or nothing to do with the ability of the computer to efficiently compile and execute the code, contribute to readability. Some of these factors include:
+Different indent styles (whitespace)
+Comments
+Decomposition
+Naming conventions for objects (such as variables, classes, functions, procedures, etc.)
+
+The presentation aspects of this (such as indents, line breaks, color highlighting, and so on) are often handled by the source code editor, but the content aspects reflect the programmer's talent and skills.
+
+Various visual programming languages have also been developed with the intent to resolve readability concerns by adopting non-traditional approaches to code structure and display. Integrated development environments (IDEs) aim to integrate all such help. Techniques like Code refactoring can enhance readability.
+
+Algorithmic complexity
+The academic field and the engineering practice of computer programming are both largely concerned with discovering and implementing the most efficient algorithms for a given class of problems. For this purpose, algorithms are classified into orders using so-called Big O notation, which expresses resource use, such as execution time or memory consumption, in terms of the size of an input. Expert programmers are familiar with a variety of well-established algorithms and their respective complexities and use this knowledge to choose algorithms that are best suited to the circumstances.
+
+Methodologies
+The first step in most formal software development processes is requirements analysis, followed by testing to determine value modeling, implementation, and failure elimination (debugging). There exist a lot of different approaches for each of those tasks. One approach popular for requirements analysis is Use Case analysis. Many programmers use forms of Agile software development where the various stages of formal software development are more integrated together into short cycles that take a few weeks rather than years. There are many approaches to the Software development process.
+
+Popular modeling techniques include Object-Oriented Analysis and Design (OOAD) and Model-Driven Architecture (MDA). The Unified Modeling Language (UML) is a notation used for both the OOAD and MDA.
+
+A similar technique used for database design is Entity-Relationship Modeling (ER Modeling).
+
+Implementation techniques include imperative languages (object-oriented or procedural), functional languages, and logic languages.
+
+Measuring language usage
+It is very difficult to determine what are the most popular modern programming languages. Methods of measuring programming language popularity include: counting the number of job advertisements that mention the language, the number of books sold and courses teaching the language (this overestimates the importance of newer languages), and estimates of the number of existing lines of code written in the language (this underestimates the number of users of business languages such as COBOL).
+
+Some languages are very popular for particular kinds of applications, while some languages are regularly used to write many different kinds of applications. For example, COBOL is still strong in corporate data centers often on large mainframe computers, Fortran in engineering applications, scripting languages in Web development, and C in embedded software. Many applications use a mix of several languages in their construction and use.  New languages are generally designed around the syntax of a prior language with new functionality added, (for example C++ adds object-orientation to C, and Java adds memory management and bytecode to C++, but as a result, loses efficiency and the ability for low-level manipulation).
+
+Debugging
+
+Debugging is a very important task in the software development process since having defects in a program can have significant consequences for its users. Some languages are more prone to some kinds of faults because their specification does not require compilers to perform as much checking as other languages. Use of a static code analysis tool can help detect some possible problems. Normally the first step in debugging is to attempt to reproduce the problem. This can be a non-trivial task, for example as with parallel processes or some unusual software bugs. Also, specific user environment and usage history can make it difficult to reproduce the problem.
+
+After the bug is reproduced, the input of the program may need to be simplified to make it easier to debug. For example, when a bug in a compiler can make it crash when parsing some large source file, a simplification of the test case that results in only few lines from the original source file can be sufficient to reproduce the same crash. Trial-and-error/divide-and-conquer is needed: the programmer will try to remove some parts of the original test case and check if the problem still exists. When debugging the problem in a GUI, the programmer can try to skip some user interaction from the original problem description and check if remaining actions are sufficient for bugs to appear. Scripting and breakpointing is also part of this process.
+
+Debugging is often done with IDEs. Standalone debuggers like GDB are also used, and these often provide less of a visual environment, usually using a command line. Some text editors such as Emacs allow GDB to be invoked through them, to provide a visual environment.
+
+Programming languages
+
+Different programming languages support different styles of programming (called programming paradigms). The choice of language used is subject to many considerations, such as company policy, suitability to task, availability of third-party packages, or individual preference. Ideally, the programming language best suited for the task at hand will be selected. Trade-offs from this ideal involve finding enough programmers who know the language to build a team, the availability of compilers for that language, and the efficiency with which programs written in a given language execute. Languages form an approximate spectrum from "low-level" to "high-level"; "low-level" languages are typically more machine-oriented and faster to execute, whereas "high-level" languages are more abstract and easier to use but execute less quickly. It is usually easier to code in "high-level" languages than in "low-level" ones.
+Programming languages are essential for software development. They are the building blocks for all software, from the simplest applications to the most sophisticated ones.
+
+Allen Downey, in his book How To Think Like A Computer Scientist, writes:
+
+The details look different in different languages, but a few basic instructions appear in just about every language:
+Input: Gather data from the keyboard, a file, or some other device.
+Output: Display data on the screen or send data to a file or other device.
+Arithmetic: Perform basic arithmetical operations like addition and multiplication.
+Conditional Execution: Check for certain conditions and execute the appropriate sequence of statements.
+Repetition: Perform some action repeatedly, usually with some variation.
+
+Many computer languages provide a mechanism to call functions provided by shared libraries. Provided the functions in a library follow the appropriate run-time conventions (e.g., method of passing arguments), then these functions may be written in any other language.
+
+Programmers
+
+Computer programmers are those who write computer software. Their jobs usually involve:
+
+Prototyping
+Coding
+Debugging
+Documentation
+Integration
+Maintenance
+Requirements analysis
+Software architecture
+Software testing
+Specification
+Although programming has been presented in the media as a somewhat mathematical subject, some research shows that good programmers have strong skills in natural human languages, and that learning to code is similar to learning a foreign language.
+
+See also
+
+ACCU
+Association for Computing Machinery
+Computer networking
+Hello world program
+Institution of Analysts and Programmers
+National Coding Week
+Object hierarchy
+Programming best practices
+System programming
+Computer programming in the punched card era
+The Art of Computer Programming
+Women in computing
+Timeline of women in computing
+
+References
+
+Sources
+
+Further reading
+ A.K. Hartmann, Practical Guide to Computer Simulations, Singapore: World Scientific (2009)
+ A. Hunt, D. Thomas, and W. Cunningham, The Pragmatic Programmer. From Journeyman to Master, Amsterdam: Addison-Wesley Longman (1999)
+ Brian W. Kernighan, The Practice of Programming, Pearson (1999)
+ Weinberg, Gerald M., The Psychology of Computer Programming, New York: Van Nostrand Reinhold (1971)
+ Edsger W. Dijkstra, A Discipline of Programming, Prentice-Hall (1976)
+ O.-J. Dahl, E.W.Dijkstra, C.A.R. Hoare, Structured Programming, Academic Press (1972)
+ David Gries, The Science of Programming, Springer-Verlag (1981)
+
+External links
+
+ 
+
+ 
+Programming
+On the Consolation of Philosophy (), often titled as The Consolation of Philosophy or simply the Consolation, is a philosophical work by the Roman philosopher Boethius. Written in 523 while he was imprisoned and awaiting execution by the Ostrogothic King Theodoric, it is often described as the last great Western work of the Classical Period. Boethius' Consolation heavily influenced the philosophy of late antiquity, as well as Medieval and early Renaissance Christianity.
+
+Description
+On the Consolation of Philosophy was written in AD 523 during a one-year imprisonment Boethius served while awaiting trial—and eventual execution—for the alleged crime of treason under the Ostrogothic King Theodoric the Great. Boethius was at the very heights of power in Rome, holding the prestigious office of magister officiorum, and was brought down by treachery. This experience inspired the text, which reflects on how evil can exist in a world governed by God (the problem of theodicy), and how happiness is still attainable amidst fickle fortune, while also considering the nature of happiness and God. In 1891, the academic Hugh Fraser Stewart described the work as "by far the most interesting example of prison literature the world has ever seen."
+
+Boethius writes the book as a conversation between himself and a female personification of philosophy, referred to as "Lady Philosophy". Philosophy consoles Boethius by discussing the transitory nature of wealth, fame, and power ("no man can ever truly be secure until he has been forsaken by Fortune"), and the ultimate superiority of things of the mind, which she calls the "one true good". She contends that happiness comes from within, and that virtue is all that one truly has because it is not imperiled by the vicissitudes of fortune.
+
+Boethius engages with the nature of predestination and free will, the problem of evil and the "problem of desert", human nature, virtue, and justice. He speaks about the nature of free will and determinism when he asks if God knows and sees all, or does man have free will. On human nature, Boethius says that humans are essentially good, and only when they give in to "wickedness" do they "sink to the level of being an animal." On justice, he says criminals are not to be abused, but rather treated with sympathy and respect, using the analogy of doctor and patient to illustrate the ideal relationship between prosecutor and criminal.
+
+Outline
+On the Consolation of Philosophy is laid out as follows:
+Book I: Boethius laments his imprisonment before he is visited by Philosophy, personified as a woman.
+Book II: Philosophy illustrates the capricious nature of Fate by discussing the "wheel of Fortune"; she further argues that true happiness lies in the pursuit of wisdom.
+Book III: Building on the ideas laid out in the previous book, Philosophy explains how wisdom has a divine source; she also demonstrates how many earthly goods (e.g., wealth, beauty) are fleeting at best.
+Book IV: Philosophy and Boethius discuss the nature of good and evil, with Philosophy offering several explanations for why evil exists and why the wicked can never attain true happiness.
+Book V: Boethius asks Philosophy about the role Chance plays in the order of everything. Philosophy argues that Chance is guided by Providence. Boethius then asks Philosophy about the compatibility of an omniscient God and free will.
+
+Interpretation
+In the Consolation, Boethius answered religious questions without reference to Christianity, relying solely on natural philosophy and the Classical Greek tradition. He believed in the correspondence between faith and reason. The truths found in Christianity would be no different from the truths found in philosophy. In the words of Henry Chadwick, "If the Consolation contains nothing distinctively Christian, it is also relevant that it contains nothing specifically pagan either...[it] is a work written by a Platonist who is also a Christian."
+
+Boethius repeats the Macrobius model of the Earth in the center of a spherical cosmos.
+
+The philosophical message of the book fits well with the religious piety of the Middle Ages. Boethius encouraged readers not to pursue worldly goods such as money and power, but to seek internalized virtues. Evil had a purpose, to provide a lesson to help change for good; while suffering from evil was seen as virtuous. Because God ruled the universe through Love, prayer to God and the application of Love would lead to true happiness. The Middle Ages, with their vivid sense of an overruling fate, found in Boethius an interpretation of life closely akin to the spirit of Christianity. The Consolation stands, by its note of fatalism and its affinities with the Christian doctrine of humility, midway between the pagan philosophy of Seneca the Younger and the later Christian philosophy of consolation represented by Thomas à Kempis.
+
+The book is heavily influenced by Plato and his dialogues (as was Boethius himself). Its popularity can in part be explained by its Neoplatonic and Christian ethical messages, although current scholarly research is still far from clear exactly why and how the work became so vastly popular in the Middle Ages.
+
+Influence
+
+From the Carolingian epoch to the end of the Middle Ages and beyond, The Consolation of Philosophy was one of the most popular and influential philosophical works, read by statesmen, poets, historians, philosophers, and theologians. It is through Boethius that much of the thought of the Classical period was made available to the Western Medieval world. It has often been said Boethius was the "last of the Romans and the first of the Scholastics".
+
+Translations into the vernacular were done by famous notables, including King Alfred (Old English), Jean de Meun (Old French), Geoffrey Chaucer (Middle English), Queen Elizabeth I (Early Modern English) and Notker Labeo (Old High German). Boethius's Consolation of Philosophy was translated into Italian by Alberto della Piagentina (1332), Anselmo Tanso (Milan, 1520), Lodovico Domenichi (Florence, 1550), Benedetto Varchi (Florence, 1551), Cosimo Bartoli (Florence, 1551) and Tommaso Tamburini (Palermo, 1657).
+
+Found within the Consolation are themes that have echoed throughout the Western canon: the female figure of wisdom that informs Dante, the ascent through the layered universe that is shared with Milton, the reconciliation of opposing forces that find their way into Chaucer in The Knight's Tale, and the Wheel of Fortune so popular throughout the Middle Ages.
+
+Citations from it occur frequently in Dante's Divina Commedia. Of Boethius, Dante remarked: "The blessed soul who exposes the deceptive world to anyone who gives ear to him."
+
+Boethian influence can be found nearly everywhere in Geoffrey Chaucer's poetry, e.g. in Troilus and Criseyde, The Knight's Tale, The Clerk's Tale, The Franklin's Tale, The Parson's Tale and The Tale of Melibee, in the character of Lady Nature in The Parliament of Fowls and some of the shorter poems, such as Truth, The Former Age and Lak of Stedfastnesse. Chaucer translated the work in his Boece.
+
+The Italian composer Luigi Dallapiccola used some of the text in his choral work Canti di prigionia (1938). The Australian composer Peter Sculthorpe quoted parts of it in his opera or music theatre work Rites of Passage (1972–73), which was commissioned for the opening of the Sydney Opera House but was not ready in time.
+
+Tom Shippey in The Road to Middle-earth says how "Boethian" much of the treatment of evil is in Tolkien's The Lord of the Rings. Shippey says that Tolkien knew well the translation of Boethius that was made by King Alfred and he quotes some "Boethian" remarks from Frodo, Treebeard, and Elrond.
+
+Boethius and Consolatio Philosophiae are cited frequently by the main character Ignatius J. Reilly in the Pulitzer Prize-winning A Confederacy of Dunces (1980).
+
+It is a prosimetrical text, meaning that it is written in alternating sections of prose and metered verse. In the course of the text, Boethius displays a virtuosic command of the forms of Latin poetry. It is classified as a Menippean satire, a fusion of allegorical tale, platonic dialogue, and lyrical poetry.
+
+Edward Gibbon described the work as "a golden volume not unworthy of the leisure of Plato or Tully."
+
+In the 20th century, there were close to four hundred manuscripts still surviving, a testament to its popularity.
+
+Of the work, C. S. Lewis wrote: "To acquire a taste for it is almost to become naturalised in the Middle Ages."
+
+Reconstruction of lost songs
+Hundreds of Latin songs were recorded in neumes from the ninth century through to the thirteenth century, including settings of the poetic passages from Boethius's The Consolation of Philosophy. The music of this song repertory had long been considered irretrievably lost because the notational signs indicated only melodic outlines, relying on now-lapsed oral traditions to fill in the missing details. However, research conducted by Sam Barrett at the University of Cambridge, extended in collaboration with medieval music ensemble Sequentia, has shown that principles of musical setting for this period can be identified, providing crucial information to enable modern realisations. Sequentia performed the world premiere of the reconstructed songs from Boethius's The Consolation of Philosophy at Pembroke College, Cambridge, in April 2016, bringing to life music not heard in over 1,000 years; a number of the songs were subsequently recorded on the CD Boethius: Songs of Consolation. Metra from 11th-Century Canterbury (Glossa, 2018). The detective story behind the recovery of these lost songs is told in a documentary film, and a website launched by the University of Cambridge in 2018 provides further details of the reconstruction process, bringing together manuscripts, reconstructions, and video resources.
+
+See also
+Allegory in the Middle Ages
+Consolatio
+Girdle book
+Metres of Boethius
+Prosimetrum
+Stoicism
+The Wheel of Fortune
+
+References
+
+Sources 
+ 
+ Boethius, The Consolation of Philosophy.
+ Trans. Joel C. Relihan, (Hackett Publishing), 2001. 
+ Trans. P. G. Walsh, (Oxford World's Classics), 2001. 
+ Trans. Richard H. Green, (Library of the Liberal Arts), 1962. 
+ Trans. Victor Watts, (Penguin Classics), 2000. 
+ Cochrane, Charles Norris., Christianity and Classical Culture, 1940, .
+ Henry Chadwick, Boethius: The Consolations of Music, Logic, Theology and Philosophy, 1990, 
+ .
+ .
+ Relihan, Joel C., Ancient Menippean Satire, 1993, 
+ Relihan, Joel C., The Prisoner's Philosophy: Life and Death in Boethius's Consolation,  2007, .
+ Sanderson Beck, The Consolation of Boethius an analysis and commentary. 1996.
+ The Cambridge History of English and American Literature, Volume I Ch.6.5: De Consolatione Philosophiae, 1907–1921.
+
+External links
+
+ 
+ Consolatio Philosophiae from Project Gutenberg, HTML conversion, originally translated by H. R. James, London 1897.
+ Consolatio Philosophiae in the original Latin with English comments at the University of Georgetown
+ First Performance in 1000 years: lost songs from the Middle Ages are brought back to life
+ Medieval translations into Old English by Alfred the Great, Old High German by Notker Labeo, Middle (originally Old) French by Jean de Meun, and Middle English by Geoffrey Chaucer
+
+ The Consolation of Philosophy, many translations and commentaries from Internet Archive
+ The Consolation of Philosophy, Translated by: W.V. Cooper : J.M. Dent and Company London 1902 The Temple Classics, edited by Israel Golancz M.A. Online reading and multiple ebook formats at Ex-classics.
+
+524
+6th-century Latin books
+Dialogues
+Prose texts in Latin
+Medieval philosophical literature
+Prison writings
+Theodicy
+Visionary literature
+Crouching Tiger, Hidden Dragon is a 2000 Mandarin-language wuxia martial arts adventure film directed by Ang Lee and written for the screen by Wang Hui-ling, James Schamus, and Tsai Kuo-jung. The film stars Chow Yun-fat, Michelle Yeoh, Zhang Ziyi, and Chang Chen. It is based on the Chinese novel of the same name serialized between 1941 and 1942 by Wang Dulu, the fourth part of his Crane Iron pentalogy.
+
+A multinational venture, the film was made on a US$17 million budget, and was produced by Edko Films and Zoom Hunt Productions in collaboration with China Film Co-productions Corporation and Asian Union Film & Entertainment for Columbia Pictures Film Production Asia in association with Good Machine International. The film premiered at the Cannes Film Festival on 18 May 2000, and was theatrically released in the United States on 8 December. With dialogue in Standard Chinese, subtitled for various markets, Crouching Tiger, Hidden Dragon became a surprise international success, grossing $213.5 million worldwide. It grossed US$128 million in the United States, becoming the highest-grossing foreign-language film produced overseas in American history. The film was the first foreign-language film to break the $100 million mark in the United States.
+
+The film received universal acclaim from critics, praised for its story, direction, cinematography, and martial arts sequences. Crouching Tiger, Hidden Dragon won over 40 awards and was nominated for 10 Academy Awards in 2001, including Best Picture, and won Best Foreign Language Film, Best Art Direction, Best Original Score, and Best Cinematography, receiving the most nominations ever for a non-English-language film at the time, until 2018's Roma tied this record. The film also won four BAFTAs and two Golden Globe Awards, each of them for Best Foreign Film. For retrospective years, Crouching Tiger is often cited as one of the finest wuxia films ever made and has been widely regarded one of the greatest films in the 21st century.
+
+Plot 
+In Qing dynasty China, Li Mu Bai is a renowned Wudang swordsman, and his friend Yu Shu Lien, a female warrior, heads a private security company. Shu Lien and Mu Bai have long had feelings for each other, but because Shu Lien had been engaged to Mu Bai's close friend, Meng Sizhao before his death, Shu Lien and Mu Bai feel bound by loyalty to Meng Sizhao and have not revealed their feelings to each other. Mu Bai, choosing to retire from the life of a swordsman, asks Shu Lien to give his fabled 400-year-old sword "Green Destiny" to their benefactor Sir Te in Beijing. Long ago, Mu Bai's teacher was killed by Jade Fox, a woman who sought to learn Wudang secrets. While at Sir Te's place, Shu Lien meets Yu Jiaolong, or Jen, who is the daughter of the rich and powerful Governor Yu and is about to get married.
+
+One evening, a masked thief sneaks into Sir Te's estate and steals the Green Destiny. Sir Te's servant Master Bo and Shu Lien trace the theft to Governor Yu's compound, where Jade Fox had been posing as Jen's governess for many years. Soon after, Mu Bai arrives in Beijing and discusses the theft with Shu Lien. Master Bo makes the acquaintance of Inspector Tsai, a police investigator from the provinces, and his daughter May, who have come to Beijing in pursuit of Fox. Fox challenges the pair and Master Bo to a showdown that night.  Following a protracted battle, the group is on the verge of defeat when Mu Bai arrives and outmaneuvers Fox. She reveals that she killed Mu Bai's teacher because he would sleep with her, but refuse to take a woman as a disciple, and she felt it poetic justice for him to die at a woman's hand. Just as Mu Bai is about to kill her, the masked thief reappears and helps Fox. Fox kills Tsai before fleeing with the thief (who is revealed to be Jen). After seeing Jen fight Mu Bai, Fox realizes Jen had been secretly studying the Wudang manual. Fox is illiterate and could only follow the diagrams, whereas Jen's ability to read the manual allowed her to surpass her teacher in martial arts.
+
+At night, a bandit named Lo breaks into Jen's bedroom and asks her to leave with him. In the past, when Governor Yu and his family were traveling in the western deserts of Xinjiang, Lo and his bandits raided Jen's caravan and Lo stole her comb. She pursued him to his desert cave to retrieve her comb. However, the pair soon fell in love. Lo eventually convinced Jen to return to her family, though not before telling her a legend of a man who jumped off a mountain to make his wishes come true. Because the man's heart was pure, his wish was granted and he was unharmed, but flew away never to be seen again. Lo has come now to Beijing to persuade Jen not to go through with her arranged marriage. However, Jen refuses to leave with him. Later, Lo interrupts Jen's wedding procession, begging her to leave with him. Shu Lien and Mu Bai convince Lo to wait for Jen at Mount Wudang, where he will be safe from Jen's family, who are furious with him. Jen runs away from her husband on their wedding night before the marriage can be consummated. Disguised in men's clothing, she is accosted at an inn by a large group of warriors; armed with the Green Destiny and her own superior combat skills, she emerges victorious.
+
+Jen visits Shu Lien, who tells her that Lo is waiting for her at Mount Wudang. After an angry exchange, the two women engage in a duel. Shu Lien is the superior fighter, but Jen wields the Green Destiny and is able to destroy each weapon that Shu Lien wields, until Shu Lien finally manages to defeat Jen with a broken sword. When Shu Lien shows mercy, Jen wounds Shu Lien in the arm. Mu Bai arrives and pursues Jen into a bamboo forest, where he offers to take her as his student. Jen agrees if he can take Green Destiny from her in three moves. Mu Bai is able to take the sword in only one move, but Jen reneges on her promise, and Mu Bai throws the sword over a waterfall. Jen dives after the sword and is rescued by Fox. Fox puts Jen into a drugged sleep and places her in a cavern, where Mu Bai and Shu Lien discover her. Fox suddenly attacks them with poisoned needles. Mu Bai mortally wounds Fox, only to realize that one of the needles has hit him in the neck. Before dying, Fox confesses that her goal had been to kill Jen because Jen had hidden the secrets of Wudang's fighting techniques from her.
+
+Contrite, Jen leaves to prepare an antidote for the poisoned dart. With his last breath, Mu Bai finally confesses his love for Shu Lien. He dies in her arms as Jen returns. Shu Lien forgives Jen, telling her to go to Lo and always be true to herself. The Green Destiny is returned to Sir Te. Jen goes to Mount Wudang and spends the night with Lo. The next morning, Lo finds Jen standing on a bridge overlooking the edge of the mountain. In an echo of the legend that they spoke about in the desert, she asks him to make a wish. Lo wishes for them to be together again, back in the desert. Jen leaps from the bridge, falling into the mists below.
+
+Cast
+
+Credits from British Film Institute:
+
+ Chow Yun-fat as Li Mu Bai (, )
+ Michelle Yeoh as Yu Shu Lien (, )
+ Zhang Ziyi as Jen Yu (, )
+ Chang Chen as Lo "Dark Cloud" Xiao Hou (, )
+ Lang Sihung as Sir Te (, )
+ Cheng Pei-pei as Jade Fox (, )
+ Li Fazeng as Governor Yu (, )
+ Wang Deming as Inspector Tsai (, )
+ Li Li as Tsai May (, )
+ Hai Yan as Madam Yu (, )
+ Gao Xi'an as Bo (, )
+ Huang Suying as Aunt Wu (, )
+ Zhang Jinting as De Lu (, )
+ Du Zhenxi as Uncle Jiao (, )
+ Li Kai as Gou Jun Pei (, )
+ Feng Jianhua as Shining Phoenix Mountain Gou (, )
+ Ma Zhongxuan as Iron Arm Mi (, )
+ Li Bao-Cheng as Flying Machete Chang (, )
+ Yang Yongde as Monk Jing (, )
+
+Themes and interpretations
+
+Title
+The title "Crouching Tiger, Hidden Dragon" is a literal translation of the Chinese idiom "臥虎藏龍" which describes a place or situation that is full of unnoticed masters. It is from a poem of the ancient Chinese poet Yu Xin (513–581) that reads "暗石疑藏虎，盤根似臥龍", which means "behind the rock in the dark probably hides a tiger, and the coiling giant root resembles a crouching dragon". The title also has several other layers of meaning. On one level, the Chinese characters in the title connect to the narrative that the last character in Xiaohu and Jiaolong's names mean "tiger" and "dragon", respectively. On another level, the Chinese idiomatic phrase is an expression referring to the undercurrents of emotion, passion, and secret desire that lie beneath the surface of polite society and civil behavior, which alludes to the film's storyline.
+
+Gender roles 
+The success of the Disney animated feature Mulan (1998) popularized the image of the Chinese woman warrior in the west. The storyline of Crouching Tiger, Hidden Dragon is mostly driven by the three female characters. In particular, Jen is driven by her desire to be free from the gender role imposed on her, while Shu Lien, herself oppressed by the gender role, tries to lead Jen back into the role deemed appropriate for her. Some prominent martial arts disciplines are traditionally held to have been originated by women, e.g., Wing Chun. The film's title refers to masters one does not notice, which necessarily includes mostly women, and therefore suggests the advantage of a female bodyguard.
+
+Poison
+Poison is also a significant theme in the film. The Chinese word "毒" (dú) means not only physical poison but also cruelty and sinfulness. In the world of martial arts, the use of poison is considered an act of one who is too cowardly and dishonorable to fight; and indeed, the only character who explicitly fits these characteristics is Jade Fox. The poison is a weapon of her bitterness and quest for vengeance: she poisons the master of Wudang, attempts to poison Jen, and succeeds in killing Mu Bai using a poisoned needle. In further play on this theme by the director, Jade Fox, as she dies, refers to the poison from a young child, "the deceit of an eight-year-old girl", referring to what she considers her own spiritual poisoning by her young apprentice Jen. Li Mu Bai himself warns that, without guidance, Jen could become a "poison dragon".
+
+China of the imagination
+The story is set during the Qing dynasty (1644–1912), but it does not specify an exact time. Lee sought to present a "China of the imagination" rather than an accurate vision of Chinese history. At the same time, Lee also wanted to make a film that Western audiences would want to see. Thus, the film is shot for a balance between Eastern and Western aesthetics. There are some scenes showing uncommon artistry for the typical martial arts film such as an airborne battle among wispy bamboo plants.
+
+Production
+The film was adapted from the novel Crouching Tiger, Hidden Dragon by Wang Dulu, serialized between 1941 and 1942 in Qingdao Xinmin News. The novel is the fourth in a sequence of five. In the contract reached between Columbia Pictures and Ang Lee and Hsu Li-kong, they agreed to invest US$6 million in filming, but the stipulated recovery amount must be more than six times before the two parties will start to pay dividends.
+
+Casting
+Shu Qi was Ang Lee's first choice for the role of Jen, but she turned it down.
+
+Filming
+
+Although its Academy Award for Best Foreign Language Film was presented to Taiwan, Crouching Tiger, Hidden Dragon was in fact an international co-production between companies in four regions: the Chinese company China Film Co-production Corporation, the American companies Columbia Pictures Film Production Asia, Sony Pictures Classics, and Good Machine, the Hong Kong company Edko Films, and the Taiwanese Zoom Hunt Productions, as well as the unspecified United China Vision and Asia Union Film & Entertainment, created solely for this film.
+
+The film was made in Beijing, with location shooting in Urumchi, Western Provinces, Taklamakan Plateau, 
+Shanghai and Anji of China. The first phase of shooting was in the Gobi Desert where it consistently rained. Director Ang Lee noted, "I didn't take one break in eight months, not even for half a day. I was miserable—I just didn't have the extra energy to be happy. Near the end, I could hardly breathe. I thought I was about to have a stroke." The stunt work was mostly performed by the actors themselves and Ang Lee stated in an interview that computers were used "only to remove the safety wires that held the actors" aloft. "Most of the time you can see their faces," he added. "That's really them in the trees."
+
+Another compounding issue was the difference between accents of the four lead actors: Chow Yun-fat is from Hong Kong and speaks Cantonese natively; Michelle Yeoh is from Malaysia and grew up speaking English and Malay, so she learned the Standard Chinese lines phonetically; Chang Chen is from Taiwan and he speaks Standard Chinese in a Taiwanese accent. Only Zhang Ziyi spoke with a native Mandarin accent that Ang Lee wanted. Chow Yun Fat said, on "the first day [of shooting], I had to do 28 takes just because of the language. That's never happened before in my life."
+
+The film specifically targeted Western audiences rather than the domestic audiences who were already used to Wuxia films. As a result, high-quality English subtitles were needed. Ang Lee, who was educated in the West, personally edited the subtitles to ensure they were satisfactory for Western audiences.
+
+Soundtrack
+
+The score was composed by Dun TAN in 1999. It was played for the movie by the Shanghai Symphony Orchestra, the Shanghai National Orchestra and the Shanghai Percussion Ensemble. It features solo passages for cello played by Yo-Yo Ma. The "last track" ("A Love Before Time") features Coco Lee, who later sang it at the Academy Awards. The composer Chen Yuanlin also collaborated in the project. The music for the entire film was produced in two weeks. Tan the next year (2000) adapted his filmscore as a cello concerto called simply "Crouching Tiger."
+
+Release
+
+Marketing
+The film was adapted into a video game and a series of comics, and it led to the original novel being adapted into a 34-episode Taiwanese television series. The latter was released in 2004 as New Crouching Tiger, Hidden Dragon for Northern American release.
+
+Home media
+The film was released on VHS and DVD on 5 June 2001 by Columbia TriStar Home Entertainment. It was also released on UMD on 26 June 2005. In the United Kingdom, it was watched by  viewers on television in 2004, making it the year's most-watched foreign-language film on television.
+
+Restoration 
+The film was re-released in a 4K restoration by Sony Pictures Classics in 2023.
+
+Reception
+
+Box office
+The film premiered in cinemas on 8 December 2000, in limited release within the United States. During its opening weekend, the film opened in 15th place, grossing $663,205 in business, showing at 16 locations. On 12 January 2001, Crouching Tiger, Hidden Dragon premiered in cinemas in wide release throughout the U.S., grossing $8,647,295 in business, ranking in sixth place. The film Save the Last Dance came in first place during that weekend, grossing $23,444,930. The film's revenue dropped by almost 30% in its second week of release, earning $6,080,357. For that particular weekend, the film fell to eighth place, screening in 837 theaters. Save the Last Dance remained unchanged in first place, grossing $15,366,047 in box-office revenue. During its final week in release, Crouching Tiger, Hidden Dragon opened in a distant 50th place with $37,233 in revenue. The film went on to top out domestically at $128,078,872 in total ticket sales through a 31-week theatrical run. Internationally, the film took in an additional $85,446,864 in box-office business for a combined worldwide total of $213,525,736. For 2000 as a whole, the film cumulatively ranked at a worldwide box-office performance position of 19.
+
+Critical response
+
+Crouching Tiger, Hidden Dragon was widely acclaimed in the Western world, receiving numerous awards. On Rotten Tomatoes, the film holds an approval rating of 98% based on 168 reviews, with an average rating of 8.6/10. The site's critical consensus states: "The movie that catapulted Ang Lee into the ranks of upper echelon Hollywood filmmakers, Crouching Tiger, Hidden Dragon features a deft mix of amazing martial arts battles, beautiful scenery, and tasteful drama." Metacritic reported the film had an average score of 94 out of 100, based on 32 reviews, indicating "universal acclaim".
+
+Some Chinese-speaking viewers were bothered by the accents of the leading actors. Neither Chow (a native Cantonese speaker) nor Yeoh (who was born and raised in Malaysia) spoke Mandarin Chinese as a mother tongue. All four main actors spoke Standard Chinese with vastly different accents: Chow speaks with a Cantonese accent, Yeoh with a Malaysian accent, Chang Chen with a Taiwanese accent, and Zhang Ziyi with a Beijing accent. Yeoh responded to this complaint in a 28 December 2000, interview with Cinescape. She argued, "My character lived outside of Beijing, and so I didn't have to do the Beijing accent." When the interviewer, Craig Reid, remarked, "My mother-in-law has this strange Sichuan-Mandarin accent that's hard for me to understand," Yeoh responded: "Yes, provinces all have their very own strong accents. When we first started the movie, Cheng Pei Pei was going to have her accent, and Chang Zhen was going to have his accent, and this person would have that accent. And in the end nobody could understand what they were saying. Forget about us, even the crew from Beijing thought this was all weird."
+
+The film led to a boost in popularity of Chinese wuxia films in the western world, where they were previously little known, and led to films such as Hero and House of Flying Daggers, both directed by Zhang Yimou, being marketed towards Western audiences. The film also provided the breakthrough role for Zhang Ziyi's career, who noted:
+
+Film Journal noted that Crouching Tiger, Hidden Dragon "pulled off the rare trifecta of critical acclaim, boffo box-office and gestalt shift", in reference to its ground-breaking success for a subtitled film in the American market.
+
+Accolades
+Gathering widespread critical acclaim at the Toronto and New York film festivals, the film also became a favorite when Academy Awards nominations were announced in 2001. The film was screened out of competition at the 2000 Cannes Film Festival. The film received ten Academy Award nominations, which was the highest ever for a non-English language film, up until it was tied by Roma (2018).
+
+The film is ranked at number 497 on Empire's 2008 list of the 500 greatest movies of all time. and at number 66 in the magazine's 100 Best Films of World Cinema, published in 2010.
+In 2010, the Independent Film & Television Alliance selected the film as one of the 30 Most Significant Independent Films of the last 30 years.
+In 2016, it was voted the 35th-best film of the 21st century as picked by 177 film critics from around the world in a poll conducted by BBC.
+The film was included in BBC's 2018 list of The 100 greatest foreign language films ranked by 209 critics from 43 countries around the world. In 2019, The Guardian ranked the film 51st in its 100 best films of the 21st century list.
+
+Sequel
+A sequel to the film, Crouching Tiger, Hidden Dragon: Sword of Destiny, was released in 2016. It was directed by Yuen Wo-ping, who was the action choreographer for the first film. It is a co-production between Pegasus Media, China Film Group Corporation, and the Weinstein Company. Unlike the original film, the sequel was filmed in English for international release and dubbed into Chinese for Chinese releases.
+
+Sword of Destiny is based on Iron Knight, Silver Vase, the next (and last) novel in the Crane–Iron Pentalogy. It features a mostly new cast, headed by Donnie Yen. Michelle Yeoh reprised her role from the original. Zhang Ziyi was also approached to appear in Sword of Destiny but refused, stating that she would only appear in a sequel if Ang Lee were directing it.
+
+In the West, the sequel was for the most part not shown in theaters, instead being distributed direct-to-video by the streaming service Netflix.
+
+Posterity 
+The theme of Janet Jackson's song "China Love" was related to the film by MTV News, in which Jackson sings of the daughter of an emperor in love with a warrior, unable to sustain relations when forced to marry into royalty.
+
+The names of the pterosaur genus Kryptodrakon and the ceratopsian genus Yinlong (both meaning "hidden dragon" in Greek and Chinese respectively) allude to the film.
+
+The character of Lo, or "Dark Cloud" the desert bandit, influenced the development of the protagonist of the Prince of Persia series of video games.
+
+In the video game Def Jam Fight for NY: The Takeover there are two hybrid fighting styles that pay homage to this movie. Which have the following combinations: Crouching tiger (Martial Arts + Streetfighting + Submissions) and Hidden Dragon (Martial Arts + Streetfighting + Kickboxing).
+
+See also
+Anji County
+Clear waters and green mountains
+
+References
+
+Further reading
+ 
+  – Collection of articles
+
+External links
+
+ 
+ 
+ 
+ 
+ 
+
+2000 films
+2000 fantasy films
+2000 martial arts films
+2000s adventure films
+American martial arts films
+Martial arts fantasy films
+BAFTA winners (films)
+Best Film HKFA
+Best Foreign Language Film Academy Award winners
+Best Foreign Language Film BAFTA Award winners
+Best Foreign Language Film Golden Globe winners
+Chinese martial arts films
+Films based on Chinese novels
+Films directed by Ang Lee
+Films scored by Tan Dun
+Films set in 18th-century Qing dynasty
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+Films set in the 1770s
+Films that won the Best Original Score Academy Award
+Films whose art director won the Best Art Direction Academy Award
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+Charlemagne ( ) or Charles the Great (, Frankish: Karl; 2 April 747 – 28 January 814), a member of the Carolingian dynasty, was King of the Franks from 768, King of the Lombards from 774, and was crowned as the Emperor of the Romans by Pope Leo III in 800. Charlemagne succeeded in uniting the majority of western and central Europe and was the first recognized emperor to rule from western Europe after the fall of the Western Roman Empire approximately three centuries earlier. The expanded Frankish state that Charlemagne founded was the Carolingian Empire, which is considered the first phase in the history of the Holy Roman Empire. He was canonized by Antipope Paschal III—an act later treated as invalid—and he is now regarded by some as beatified (which is a step on the path to sainthood) in the Catholic Church.
+
+Charlemagne was the eldest son of Pepin the Short and Bertrada of Laon. He was born before their canonical marriage. He became king of the Franks in 768 following his father's death, and was initially co-ruler with his brother Carloman I until the latter's death in 771. As sole ruler, he continued his father's policy towards the protection of the papacy and became its sole defender, removing the Lombards from power in northern Italy and leading an incursion into Muslim Spain. He also campaigned against the Saxons to his east, Christianizing them (upon penalty of death). These mass executions led to events such as the Massacre of Verden. He reached the height of his power in 800 when he was crowned Emperor of the Romans by Pope Leo III on Christmas Day at Old St. Peter's Basilica in Rome.
+
+Charlemagne has been called the "Father of Europe" (Pater Europae), as he united most of Western Europe for the first time since the classical era of the Roman Empire, as well as uniting parts of Europe that had never been under Frankish or Roman rule. His reign spurred the Carolingian Renaissance, a period of energetic cultural and intellectual activity within the Western Church. The Eastern Orthodox Church viewed Charlemagne less favourably, due to his support of the filioque and the Pope's preference of him as emperor over the Byzantine Empire's first female monarch, Irene of Athens. These and other disputes led to the eventual split of Rome and Constantinople in the Great Schism of 1054.
+
+Charlemagne died in 814 after contracting an infectious lung disease. He was laid to rest in the Aachen Cathedral, in his imperial capital city of Aachen. He married at least four times, and three of his legitimate sons lived to adulthood. Only the youngest of them, Louis the Pious, survived to succeed him. Charlemagne is a direct ancestor of many of Europe's royal houses, including the Capetian dynasty, the Ottonian dynasty, the House of Luxembourg, the House of Ivrea and the House of Habsburg.
+
+Names and nicknames 
+The name Charlemagne ( ), by which the emperor is normally known in English, comes from the French Charles-le-magne, meaning "Charles the Great". In modern German, Karl der Große has the same meaning. His given name in his native Frankish dialect was Karl ("Charles", Latin: Carolus; Old High German: Karlus; Gallo-Romance: Karlo). He was named after his grandfather, Charles Martel, a choice which intentionally marked him as Martel's true heir.
+
+The nickname magnus (great) may have been associated with him already in his lifetime, but this is not certain. The contemporary Latin Royal Frankish Annals routinely call him Carolus magnus rex, "Charles the great king". As a nickname, it is only certainly attested in the works of the Poeta Saxo around 900 and it only became standard in all the lands of his former empire around 1000.
+
+Charles' achievements gave a new meaning to his name. In many languages of Europe, the very word for "king" derives from his name; e.g., , , , , , , , , , , . This development parallels that of the name of the Caesars in the original Roman Empire, which became kaiser and tsar (or czar), among others.
+
+Political background
+
+By the 6th century, the western Germanic tribe of the Franks had been Christianised, due in considerable measure to the Catholic conversion of Clovis I. Francia, ruled by the Merovingians, was the most powerful of the kingdoms that succeeded the Western Roman Empire. Following the Battle of Tertry, the Merovingians declined into powerlessness, for which they have been dubbed the rois fainéants ("do-nothing kings"). Almost all government powers were exercised by their chief officer, the mayor of the palace.
+
+In 687, Pepin of Herstal, mayor of the palace of Austrasia, ended the strife between various kings and their mayors with his victory at Tertry. He became the sole governor of the entire Frankish kingdom. Pepin was the grandson of two important figures of the Austrasian Kingdom: Saint Arnulf of Metz and Pepin of Landen. Pepin of Herstal was eventually succeeded by his son Charles, later known as Charles Martel (Charles the Hammer).
+
+After 737, Charles governed the Franks in lieu of a king and declined to call himself king. Charles was succeeded in 741 by his sons Carloman and Pepin the Short, the father of Charlemagne. In 743, the brothers placed Childeric III on the throne to curb separatism in the periphery. He was the last Merovingian king. Carloman resigned office in 746, preferring to enter the church as a monk. Pepin brought the question of the kingship before Pope Zachary, asking whether it was logical for a king to have no royal power. The pope handed down his decision in 749, decreeing that it was better for Pepin to be called king, as he had the powers of high office as Mayor, so as not to confuse the hierarchy. He, therefore, ordered him to become the true king.
+
+In 750, Pepin was elected by an assembly of the Franks, anointed by the archbishop, and then raised to the office of king. The Pope branded Childeric III as "the false king" and ordered him into a monastery. The Merovingian dynasty was thereby replaced by the Carolingian dynasty, named after Charles Martel. In 753, Pope Stephen II fled from Italy to Francia, appealing to Pepin for assistance for the rights of St. Peter. He was supported in this appeal by Carloman, Charles' brother. In return, the pope could provide only legitimacy. He did this by again anointing and confirming Pepin, this time adding his young sons Carolus (Charlemagne) and Carloman to the royal patrimony. They thereby became heirs to the realm that already covered most of western Europe. In 754, Pepin accepted the Pope's invitation to visit Italy on behalf of St. Peter's rights, dealing successfully with the Lombards.
+
+Under the Carolingians, the Frankish kingdom spread to encompass an area including most of Western Europe; the later east–west division of the kingdom formed the basis for modern France and Germany. Orman portrays the Treaty of Verdun (843) between the warring grandsons of Charlemagne as the foundation event of an independent France under its first king Charles the Bald; an independent Germany under its first king Louis the German; and an independent intermediate state stretching from the Low Countries along the borderlands to south of Rome under Lothair I, who retained the title of emperor and the capitals Aachen and Rome without the jurisdiction. The middle kingdom had broken up by 890 and partly absorbed into the Western kingdom (later France) and the Eastern kingdom (Germany) and the rest developing into smaller "buffer" states that exist between France and Germany to this day, namely Benelux and Switzerland.
+
+Rise to power
+
+Early life 
+
+The most likely date of Charlemagne's birth is reconstructed from several sources. The date of 742—calculated from Einhard's date of death of January 814 at age 72—predates the marriage of his parents in 744. The year given in the Annales Petaviani, 747, would be more likely, except that it contradicts Einhard and a few other sources in making Charlemagne sixty-seven years old at his death. The month and day of 2 April are based on a calendar from Lorsch Abbey. Charlemagne claimed descent from the Roman emperor, Constantine I.
+
+In 747, Easter fell on 2 April, a coincidence that likely would have been remarked upon by chroniclers. If Easter was being used as the beginning of the calendar year, then 2 April 747 could have been, by modern reckoning, April 748 (not on Easter). The date favoured by the preponderance of evidence is 2 April 742, based on Charlemagne's age at the time of his death. This date supports the concept that Charlemagne was technically an illegitimate child, although that is not mentioned by Einhard in either since he was born out of wedlock; Pepin and Bertrada were bound by a private contract or Friedelehe at the time of his birth, but did not marry until 744.
+
+Charlemagne's exact birthplace is unknown, although historians have suggested Aachen in modern-day Germany, and Liège (Herstal) in present-day Belgium as possible locations. Aachen and Liège are close to the region whence the Merovingian and Carolingian families originated. Other cities have been suggested, including Düren, Gauting, Mürlenbach, Quierzy, and Prüm. No definitive evidence resolves the question.
+
+Ancestry 
+Charlemagne was the eldest child of Pepin the Short (714 – 24 September 768, reigned from 751) and his wife Bertrada of Laon (720 – 12 July 783), daughter of Caribert of Laon. Many historians consider Charlemagne (Charles) to have been illegitimate, although some state that this is arguable, because Pepin did not marry Bertrada until 744, which was after Charles' birth; this status did not exclude him from the succession.
+
+Records name only Carloman, Gisela, and three short-lived children named Pepin, Chrothais and Adelais as his younger siblings.
+
+Ambiguous high office
+
+The most powerful officers of the Frankish people, the Mayor of the Palace (Maior Domus) and one or more kings (rex, reges), were appointed by the election of the people. Elections were not periodic, but were held as required to elect officers ad quos summa imperii pertinebat, "to whom the highest matters of state pertained". Evidently, interim decisions could be made by the Pope, which ultimately needed to be ratified using an assembly of the people that met annually.
+
+Before he was elected king in 751, Pepin was initially a mayor, a high office he held "as though hereditary" (velut hereditario fungebatur). Einhard explains that "the honour" was usually "given by the people" to the distinguished, but Pepin the Great and his brother Carloman the Wise received it as though hereditary, as had their father, Charles Martel. There was, however, a certain ambiguity about quasi-inheritance. The office was treated as joint property: one Mayorship held by two brothers jointly. Each, however, had his own geographic jurisdiction. When Carloman decided to resign, becoming ultimately a Benedictine at Monte Cassino, the question of the disposition of his quasi-share was settled by the pope. He converted the mayorship into a kingship and awarded the joint property to Pepin, who gained the right to pass it on by inheritance.
+
+This decision was not accepted by all family members. Carloman had consented to the temporary tenancy of his own share, which he intended to pass on to his son, Drogo, when the inheritance should be settled at someone's death. By the Pope's decision, in which Pepin had a hand, Drogo was to be disqualified as an heir in favour of his cousin Charles. He took up arms in opposition to the decision and was joined by Grifo, a half-brother of Pepin and Carloman, who had been given a share by Charles Martel, but was stripped of it and held under loose arrest by his half-brothers after an attempt to seize their shares by military action. Grifo perished in combat in the Battle of Saint-Jean-de-Maurienne while Drogo was hunted down and taken into custody.
+
+According to the Life, Pepin died in Paris on 24 September 768, whereupon the kingship passed jointly to his sons, "with divine assent" (divino nutu).  The Franks "in general assembly" (generali conventu) gave them both the rank of a king (reges) but "partitioned the whole body of the kingdom equally" (totum regni corpus ex aequo partirentur). The annals tell a slightly different version, with the king dying at St-Denis, near Paris. The two "lords" (domni) were "elevated to kingship" (elevati sunt in regnum), Charles on 9 October in Noyon, Carloman on an unspecified date in Soissons. If born in 742, Charles was 26 years old, but he had been campaigning at his father's right hand for several years, which may help to account for his military skill. Carloman was 17.
+
+The language, in either case, suggests that there were not two inheritances, which would have created distinct kings ruling over distinct kingdoms, but a single joint inheritance and a joint kingship tenanted by two equal kings, Charles and his brother Carloman. As before, distinct jurisdictions were awarded. Charles received Pepin's original share as Mayor: the outer parts of the kingdom bordering on the sea, namely Neustria, western Aquitaine, and the northern parts of Austrasia; while Carloman was awarded his uncle's former share, the inner parts: southern Austrasia, Septimania, eastern Aquitaine, Burgundy, Provence, and Swabia, lands bordering Italy. The question of whether these jurisdictions were joint shares reverting to the other brother if one brother died or were inherited property passed on to the descendants of the brother who died was never definitely settled. It came up repeatedly over the succeeding decades until the grandsons of Charlemagne created distinct sovereign kingdoms.
+
+Aquitainian rebellion
+
+Formation of a new Aquitaine
+
+In southern Gaul, Aquitaine had been Romanised and people spoke a Romance language. Similarly, Hispania had been populated by peoples who spoke various languages, including Celtic, but these had now been mostly replaced by Romance languages. Between Aquitaine and Hispania were the Euskaldunak, Latinised to Vascones, or Basques, whose country, Vasconia, extended, according to the distributions of place names attributable to the Basques, mainly in the western Pyrenees but also as far south as the upper river Ebro in Spain and as far north as the river Garonne in France. The French name Gascony derives from Vasconia. The Romans were never able to subjugate the whole of Vasconia. The border with Aquitaine was at Toulouse.
+
+In about 660, the Duchy of Vasconia united with the Duchy of Aquitaine to form a single realm under Felix of Aquitaine, ruling from Toulouse. This was a joint kingship with a Basque Duke, Lupus I. Lupus is the Latin translation of Basque Otsoa, "wolf". At Felix's death in 670 the joint property of the kingship reverted entirely to Lupus. As the Basques had no law of joint inheritance but relied on primogeniture, Lupus in effect founded a hereditary dynasty of Basque rulers of an expanded Aquitaine.
+
+Acquisition of Aquitaine by the Carolingians
+
+The Latin chronicles of the end of Visigothic Hispania omit many details, such as identification of characters, filling in the gaps and reconciliation of numerous contradictions. Muslim sources, however, present a more coherent view, such as in the Ta'rikh iftitah al-Andalus ("History of the Conquest of al-Andalus") by Ibn al-Qūṭiyya ("the son of the Gothic woman", referring to the granddaughter of Wittiza, the last Visigothic king of a united Hispania, who married a Moor). Ibn al-Qūṭiyya, who had another, much longer name, must have been relying to some degree on family oral tradition.
+
+According to Ibn al-Qūṭiyya Wittiza, the last Visigothic king of a united Hispania, died before his three sons, Almund, Romulo, and Ardabast reached maturity. Their mother was queen regent at Toledo, but Roderic, army chief of staff, staged a rebellion, capturing Córdoba. He chose to impose a joint rule over distinct jurisdictions on the true heirs. Evidence of a division of some sort can be found in the distribution of coins imprinted with the name of each king and in the king lists. Wittiza was succeeded by Roderic, who reigned for seven and a half years, followed by Achila (Aquila), who reigned three and a half years. If the reigns of both terminated with the incursion of the Saracens, then Roderic appears to have reigned a few years before the majority of Achila. The latter's kingdom was securely placed to the northeast, while Roderic seems to have taken the rest, notably modern Portugal.
+
+The Saracens crossed the mountains to claim Ardo's Septimania, only to encounter the Basque dynasty of Aquitaine, always the allies of the Goths. Odo the Great of Aquitaine was at first victorious at the Battle of Toulouse in 721. Saracen troops gradually massed in Septimania and, in 732, an army under Emir Abdul Rahman Al Ghafiqi advanced into Vasconia, and Odo was defeated at the Battle of the River Garonne. They took Bordeaux and were advancing towards Tours when Odo, powerless to stop them, appealed to his arch-enemy, Charles Martel, mayor of the Franks. In one of the first of the lightning marches for which the Carolingian kings became famous, Charles and his army appeared in the path of the Saracens between Tours and Poitiers, and in the Battle of Tours decisively defeated and killed al-Ghafiqi. The Moors returned twice more, each time suffering defeat at Charles' hands—at the River Berre near Narbonne in 737 and in the Dauphiné in 740. Odo's price for salvation from the Saracens was incorporation into the Frankish kingdom, a decision that was repugnant to him and also to his heirs.
+
+Loss and recovery of Aquitaine
+After the death of his father, Hunald I allied himself with free Lombardy. However, Odo had ambiguously left the kingdom jointly to his two sons, Hunald and Hatto. The latter, loyal to Francia, now went to war with his brother over full possession. Victorious, Hunald blinded and imprisoned his brother, only to be so stricken by conscience that he resigned and entered the church as a monk to do penance. The story is told in Annales Mettenses priores. His son Waifer took an early inheritance, becoming duke of Aquitaine and ratifying the alliance with Lombardy. Waifer, deciding to honour it, repeated his father's decision, which he justified by arguing that any agreements with Charles Martel became invalid on Martel's death. Since Aquitaine was now Pepin's inheritance because of the earlier assistance given by Charles Martel, according to some, the latter and his son, the young Charles, hunted down Waifer, who could only conduct a guerrilla war, and executed him.
+
+Among the contingents of the Frankish army were Bavarians under Tassilo III, Duke of Bavaria, an Agilofing, the hereditary Bavarian ducal family. Grifo had installed himself as Duke of Bavaria, but Pepin replaced him with a member of the ducal family yet a child, Tassilo, whose protector he had become after the death of his father. The loyalty of the Agilolfings was perpetually in question, but Pepin exacted numerous oaths of loyalty from Tassilo. However, the latter had married Liutperga, a daughter of Desiderius, king of Lombardy. At a critical point in the campaign, Tassilo left the field with all his Bavarians. Out of reach of Pepin, he repudiated all loyalty to Francia. Pepin had no chance to respond as he grew ill and died within a few weeks after Waifer's execution.
+
+The first event of the brothers' reign was the uprising of the Aquitainians and Gascons in 769, in that territory split between the two kings. One year earlier, Pepin had finally defeated Waifer, Duke of Aquitaine, after waging a destructive, ten-year war against Aquitaine. Now, Hunald II led the Aquitainians as far north as Angoulême. Charles met Carloman, but Carloman refused to participate and returned to Burgundy. Charles went to war, leading an army to Bordeaux, where he built a fortified camp on the mound at Fronsac. Hunald was forced to flee to the court of Duke Lupus II of Gascony. Lupus, fearing Charles, turned Hunald over in exchange for peace, and Hunald was put in a monastery. Gascon lords also surrendered, and Aquitaine and Gascony were finally fully subdued by the Franks.
+
+Marriage to Desiderata
+The brothers maintained lukewarm relations with the assistance of their mother Bertrada, but in 770 Charles signed a treaty with Duke Tassilo III of Bavaria and married a Lombard Princess (commonly known today as Desiderata), the daughter of King Desiderius, to surround Carloman with his own allies. Though Pope Stephen III first opposed the marriage with the Lombard princess, he found little to fear from a Frankish-Lombard alliance.
+
+Less than a year after his marriage, Charlemagne repudiated Desiderata and married a 13-year-old Swabian named Hildegard. The repudiated Desiderata returned to her father's court at Pavia. Her father's wrath was now aroused, and he would have gladly allied with Carloman to defeat Charles. Before any open hostilities could be declared, however, Carloman died on 5 December 771, apparently of natural causes. Carloman's widow Gerberga fled to Desiderius' court with her sons for protection.
+
+Wives, concubines, and children 
+
+Charlemagne had eighteen children with seven of his ten known wives or concubines. Nonetheless, he had only four legitimate grandsons, the four sons of his fourth son, Louis. In addition, he had a grandson (Bernard of Italy, the only son of his third son, Pepin of Italy), who was illegitimate but included in the line of inheritance. Among his descendants are several royal dynasties, including the Habsburg, and Capetian dynasties. By consequence, most if not all established European noble families ever since can genealogically trace some of their background to Charlemagne.
+
+Children
+
+During the first peace of any substantial length (780–782), Charles began to appoint his sons to positions of authority. In 781, during a visit to Rome, he made his two youngest sons kings, crowned by the Pope. The elder of these two, Carloman, was made the king of Italy, taking the Iron Crown that his father had first worn in 774, and in the same ceremony was renamed "Pepin" (not to be confused with Charlemagne's eldest, possibly illegitimate son, Pepin the Hunchback). The younger of the two, Louis, became King of Aquitaine. Charlemagne ordered Pepin and Louis to be raised in the customs of their kingdoms, and he gave their regents some control of their subkingdoms, but kept the real power, though he intended his sons to inherit their realms. He did not tolerate insubordination in his sons: in 792, he banished Pepin the Hunchback to Prüm Abbey because the young man had joined a rebellion against him.
+
+Charles was determined to have his children educated, including his daughters, as his parents had instilled the importance of learning in him at an early age. His children were also taught skills in accord with their aristocratic status, which included training in riding and weaponry for his sons, and embroidery, spinning and weaving for his daughters.
+
+The sons fought many wars on behalf of their father. Charles was mostly preoccupied with the Bretons, whose border he shared and who insurrected on at least two occasions and were easily put down. He also fought the Saxons on multiple occasions. In 805 and 806, he was sent into the Böhmerwald (modern Bohemia) to deal with the Slavs living there (Bohemian tribes, ancestors of the modern Czechs). He subjected them to Frankish authority and devastated the valley of the Elbe, forcing tribute from them. Pippin had to hold the Avar and Beneventan borders and fought the Slavs to his north. He was uniquely poised to fight the Byzantine Empire when that conflict arose after Charlemagne's imperial coronation and a Venetian rebellion. Finally, Louis was in charge of the Spanish March and fought the Duke of Benevento in southern Italy on at least one occasion. He took Barcelona in a great siege in 801.
+
+Charlemagne kept his daughters at home with him and refused to allow them to contract sacramental marriages (though he originally condoned an engagement between his eldest daughter Rotrude and Constantine VI of Byzantium, this engagement was annulled when Rotrude was 11). Charlemagne's opposition to his daughters' marriages may possibly have intended to prevent the creation of cadet branches of the family to challenge the main line, as had been the case with Tassilo of Bavaria. However, he tolerated their extramarital relationships, even rewarding their common-law husbands and treasuring the illegitimate grandchildren they produced for him. He also refused to believe stories of their wild behaviour. After his death the surviving daughters were banished from the court by their brother, the pious Louis, to take up residence in the convents they had been bequeathed by their father. At least one of them, Bertha, had a recognised relationship, if not a marriage, with Angilbert, a member of Charlemagne's court circle.
+
+Italian campaigns
+
+Conquest of the Lombard kingdom
+
+At his succession in 772, Pope Adrian I demanded the return of certain cities in the former exarchate of Ravenna in accordance with a promise at the succession of Desiderius. Instead, Desiderius took over certain papal cities and invaded the Pentapolis, heading for Rome. Adrian sent ambassadors to Charlemagne in autumn requesting he enforce the policies of his father, Pepin. Desiderius sent his own ambassadors denying the pope's charges. The ambassadors met at Thionville, and Charlemagne upheld the pope's side. Charlemagne demanded what the pope had requested, but Desiderius swore never to comply. Charlemagne and his uncle Bernard crossed the Alps in 773 and chased the Lombards back to Pavia, which they then besieged. Charlemagne temporarily left the siege to deal with Adelchis, son of Desiderius, who was raising an army at Verona. The young prince was chased to the Adriatic littoral and fled to Constantinople to plead for assistance from Constantine V, who was waging war with Bulgaria.
+
+The siege lasted until the spring of 774 when Charlemagne visited the pope in Rome. There he confirmed his father's grants of land, with some later chronicles falsely claiming that he also expanded them, granting Tuscany, Emilia, Venice and Corsica. The pope granted him the title patrician. He then returned to Pavia, where the Lombards were on the verge of surrendering. In return for their lives, the Lombards surrendered and opened the gates in early summer. Desiderius was sent to the abbey of Corbie, and his son Adelchis died in Constantinople, a patrician. Charles, unusually, had himself crowned with the Iron Crown and made the magnates of Lombardy pay homage to him at Pavia. Only Duke Arechis II of Benevento refused to submit and proclaimed independence. Charlemagne was then master of Italy as king of the Lombards. He left Italy with a garrison in Pavia and a few Frankish counts in place the same year.
+
+Instability continued in Italy. In 776, Dukes Hrodgaud of Friuli and Hildeprand of Spoleto rebelled. Charlemagne rushed back from Saxony and defeated the Duke of Friuli in battle; the Duke was slain. The Duke of Spoleto signed a treaty. Their co-conspirator, Arechis, was not subdued, and Adelchis, their candidate in Byzantium, never left that city. Northern Italy was now faithfully his.
+
+Southern Italy
+In 787, Charlemagne directed his attention towards the Duchy of Benevento, where Arechis II was reigning independently with the self-given title of Princeps. Charlemagne's siege of Salerno forced Arechis into submission, and in return for peace, Arechis recognized Charlemagne's suzerainty and handed his son Grimoald III over as a hostage. After Arechis' death in 787, Grimoald was allowed to return to Benevento. In 788, the principality was invaded by Byzantine troops led by Adelchis, but his attempts were thwarted by Grimoald. The Franks assisted in the repulsion of Adelchis, but, in turn, attacked Benevento's territories several times, obtaining small gains, notably the annexation of Chieti to the duchy of Spoleto. Later, Grimoald tried to throw off Frankish suzerainty, but Charles' sons, Pepin of Italy and Charles the Younger, forced him to submit in 792.
+
+Carolingian expansion to the south
+
+Vasconia and the Pyrenees
+The destructive war led by Pepin in Aquitaine, although brought to a satisfactory conclusion for the Franks, proved the Frankish power structure south of the Loire was feeble and unreliable. After the defeat and death of Waifer in 768, while Aquitaine submitted again to the Carolingian dynasty, a new rebellion broke out in 769 led by Hunald II, a possible son of Waifer. He took refuge with the ally Duke Lupus II of Gascony, but probably out of fear of Charlemagne's reprisal, Lupus handed him over to the new King of the Franks to whom he pledged loyalty, which seemed to confirm the peace in the Basque area south of the Garonne. In the campaign of 769, Charlemagne seems to have followed a policy of "overwhelming force" and avoided a major pitched battle
+
+Wary of new Basque uprisings, Charlemagne seems to have tried to contain Duke Lupus's power by appointing Seguin as the Count of Bordeaux (778) and other counts of Frankish background in bordering areas (Toulouse, County of Fézensac). The Basque Duke, in turn, seems to have contributed decisively or schemed the Battle of Roncevaux Pass (referred to as "Basque treachery"). The defeat of Charlemagne's army in Roncevaux (778) confirmed his determination to rule directly by establishing the Kingdom of Aquitaine (ruled by Louis the Pious) based on a power base of Frankish officials, distributing lands among colonisers and allocating lands to the Church, which he took as an ally. A Christianisation programme was put in place across the high Pyrenees (778).
+
+The new political arrangement for Vasconia did not sit well with local lords. As of 788 Adalric was fighting and capturing Chorson, Carolingian Count of Toulouse. He was eventually released, but Charlemagne, enraged at the compromise, decided to depose him and appointed his trustee William of Gellone. William, in turn, fought the Basques and defeated them after banishing Adalric (790).
+
+From 781 (Pallars, Ribagorça) to 806 (Pamplona under Frankish influence), taking the County of Toulouse for a power base, Charlemagne asserted Frankish authority over the Pyrenees by subduing the south-western marches of Toulouse (790) and establishing vassal counties on the southern Pyrenees that were to make up the Marca Hispanica. As of 794, a Frankish vassal, the Basque lord Belasko (al-Galashki, 'the Gaul') ruled Álava, but Pamplona remained under Cordovan and local control up to 806. Belasko and the counties in the Marca Hispánica provided the necessary base to attack the Andalusians (an expedition led by William Count of Toulouse and Louis the Pious to capture Barcelona in 801). Events in the Duchy of Vasconia (rebellion in Pamplona, count overthrown in Aragon, Duke Seguin of Bordeaux deposed, uprising of the Basque lords, etc.) were to prove it ephemeral upon Charlemagne's death.
+
+Roncesvalles campaign
+
+According to the Muslim historian Ibn al-Athir, the Diet of Paderborn had received the representatives of the Muslim rulers of Zaragoza, Girona, Barcelona and Huesca. Their masters had been cornered in the Iberian peninsula by Abd ar-Rahman I, the Umayyad emir of Cordova. These "Saracen" (Moorish and Muwallad) rulers offered their homage to the king of the Franks in return for military support. Seeing an opportunity to extend Christendom and his own power, and believing the Saxons to be a fully conquered nation, Charlemagne agreed to go to Spain.
+
+In 778, he led the Neustrian army across the Western Pyrenees, while the Austrasians, Lombards, and Burgundians passed over the Eastern Pyrenees. The armies met at Saragossa and Charlemagne received the homage of the Muslim rulers, Sulayman al-Arabi and Kasmin ibn Yusuf, but the city did not fall for him. Indeed, Charlemagne faced the toughest battle of his career. The Muslims forced him to retreat, so he decided to go home, as he could not trust the Basques, whom he had subdued by conquering Pamplona. He turned to leave Iberia, but as his army was crossing back through the Pass of Roncesvalles, one of the most famous events of his reign occurred: the Basques attacked and destroyed his rearguard and baggage train. The Battle of Roncevaux Pass, though less a battle than a skirmish, left many famous dead, including the seneschal Eggihard, the count of the palace Anselm, and the warden of the Breton March, Roland, inspiring the subsequent creation of The Song of Roland (La Chanson de Roland), regarded as the first major work in the French language.
+
+Contact with Muslims
+
+The conquest of Italy brought Charlemagne in contact with Muslims who, at the time, controlled the Mediterranean. Charlemagne's eldest son, Pepin the Hunchback, was much occupied with Muslims in Italy. Charlemagne conquered Corsica and Sardinia at an unknown date and in 799 the Balearic Islands. The islands were often attacked by Muslim pirates, but the counts of Genoa and Tuscany (Boniface) controlled them with large fleets until the end of Charlemagne's reign. Charlemagne even had contact with the caliphal court in Baghdad. In 797 (or possibly 801), the caliph of Baghdad, Harun al-Rashid, presented Charlemagne with an Asian elephant named Abul-Abbas and a clock.
+
+Wars with the Moors
+
+In Hispania, the struggle against Islam continued unabated throughout the latter half of his reign. Louis was in charge of the Spanish border. In 785, his men captured Girona permanently and extended Frankish control into the Catalan littoral for the duration of Charlemagne's reign (the area remained nominally Frankish until the Treaty of Corbeil in 1258). The Muslim chiefs in the northeast of Islamic Spain were constantly rebelling against Cordovan authority, and they often turned to the Franks for help. The Frankish border was slowly extended until 795, when Girona, Cardona, Ausona and Urgell were united into the new Spanish March, within the old duchy of Septimania.
+
+In 797, Barcelona, the greatest city of the region, fell to the Franks when Zeid, its governor, rebelled against Cordova and, failing, handed it to them. The Umayyad authority recaptured it in 799. However, Louis of Aquitaine marched the entire army of his kingdom over the Pyrenees and besieged it for two years, wintering there from 800 to 801, when it capitulated. The Franks continued to press forward against the emir. They probably took Tarragona and forced the submission of Tortosa in 809. The last conquest brought them to the mouth of the Ebro and gave them raiding access to Valencia, prompting the Emir al-Hakam I to recognise their conquests in 813.
+
+Eastern campaigns
+
+Saxon Wars
+
+Charlemagne was engaged in almost constant warfare throughout his reign, often at the head of his elite scara bodyguard squadrons. In the Saxon Wars, spanning thirty years and eighteen battles, he conquered Saxonia and proceeded to convert it to Christianity.
+
+The Germanic Saxons were divided into four subgroups in four regions. Nearest to Austrasia was Westphalia and farthest away was Eastphalia. Between them was Engria and north of these three, at the base of the Jutland peninsula, was Nordalbingia.
+
+In his first campaign, in 773, Charlemagne forced the Engrians to submit and cut down an Irminsul pillar near Paderborn. The campaign was cut short by his first expedition to Italy. He returned in 775, marching through Westphalia and conquering the Saxon fort at Sigiburg. He then crossed Engria, where he defeated the Saxons again. Finally, in Eastphalia, he defeated a Saxon force, and its leader  converted to Christianity. Charlemagne returned through Westphalia, leaving encampments at Sigiburg and Eresburg, which had been important Saxon bastions. He then controlled Saxony with the exception of Nordalbingia, but Saxon resistance had not ended.
+
+Following his subjugation of the Dukes of Friuli and Spoleto, Charlemagne returned rapidly to Saxony in 776, where a rebellion had destroyed his fortress at Eresburg. The Saxons were once again defeated, but their main leader, Widukind, escaped to Denmark, his wife's home. Charlemagne built a new camp at Karlstadt. In 777, he called a national diet at Paderborn to integrate Saxony fully into the Frankish kingdom. Many Saxons were baptised as Christians.
+
+In the summer of 779, he again invaded Saxony and reconquered Eastphalia, Engria and Westphalia. At a diet near Lippe, he divided the land into missionary districts and himself assisted in several mass baptisms (780). He then returned to Italy and, for the first time, the Saxons did not immediately revolt. Saxony was peaceful from 780 to 782.
+
+He returned to Saxony in 782 and instituted a code of law and appointed counts, both Saxon and Frank. The laws were draconian on religious issues; for example, the Capitulatio de partibus Saxoniae prescribed death to Saxon pagans who refused to convert to Christianity. This led to renewed conflict. That year, in autumn, Widukind returned and led a new revolt. In response, at Verden in Lower Saxony, Charlemagne is recorded as having ordered the execution of 4,500 Saxon prisoners by beheading, known as the Massacre of Verden ("Verdener Blutgericht"). The killings triggered three years of renewed bloody warfare. During this war, the East Frisians between the Lauwers and the Weser joined the Saxons in revolt and were finally subdued. The war ended with Widukind accepting baptism. The Frisians afterwards asked for missionaries to be sent to them and a bishop of their own nation, Ludger, was sent. Charlemagne also promulgated a law code, the Lex Frisonum, as he did for most subject peoples.
+
+Thereafter, the Saxons maintained the peace for seven years, but in 792 Westphalia again rebelled. The Eastphalians and Nordalbingians joined them in 793, but the insurrection was unpopular and was put down by 794. An Engrian rebellion followed in 796, but the presence of Charlemagne, Christian Saxons and Slavs quickly crushed it. The last insurrection occurred in 804, more than thirty years after Charlemagne's first campaign against them, but also failed. According to Einhard:
+
+Submission of Bavaria
+
+By 774, Charlemagne had invaded the Kingdom of Lombardy, and he later annexed the Lombardian territories and assumed its crown, placing the Papal States under Frankish protection. The Duchy of Spoleto south of Rome was acquired in 774, while in the central western parts of Europe, the Duchy of Bavaria was absorbed and the Bavarian policy continued of establishing tributary marches, (borders protected in return for tribute or taxes) among the Slavic Sorbs and Czechs. The remaining power confronting the Franks in the east were the Avars. However, Charlemagne acquired other Slavic areas, including Bohemia, Moravia, Austria and Croatia.
+
+In 789, Charlemagne turned to Bavaria. He claimed that Tassilo III, Duke of Bavaria was an unfit ruler, due to his oath-breaking. The charges were exaggerated, but Tassilo was deposed anyway and put in the monastery of Jumièges. In 794, Tassilo was made to renounce any claim to Bavaria for himself and his family (the Agilolfings) at the synod of Frankfurt; he formally handed over to the king all of the rights he had held. Bavaria was subdivided into Frankish counties, as had been done with Saxony.
+
+Avar campaigns
+
+In 788, the Avars, an Asian nomadic group that had settled down in what is today Hungary (Einhard called them Huns), invaded Friuli and Bavaria. Charlemagne was preoccupied with other matters until 790 when he marched down the Danube and ravaged Avar territory to the Győr. A Lombard army under Pippin then marched into the Drava valley and ravaged Pannonia. The campaigns ended when the Saxons revolted again in 792.
+
+For the next two years, Charlemagne was occupied, along with the Slavs, against the Saxons. Pippin and Duke Eric of Friuli continued, however, to assault the Avars' ring-shaped strongholds. The great Ring of the Avars, their capital fortress, was taken twice. The booty was sent to Charlemagne at his capital, Aachen, and redistributed to his followers and to foreign rulers, including King Offa of Mercia. Soon the Avar tuduns had lost the will to fight and travelled to Aachen to become vassals to Charlemagne and to become Christians. Charlemagne accepted their surrender and sent one native chief, baptised Abraham, back to Avaria with the ancient title of khagan. Abraham kept his people in line, but in 800, the Bulgarians under Khan Krum attacked the remains of the Avar state.
+
+In 803, Charlemagne sent a Bavarian army into Pannonia, defeating and bringing an end to the Avar confederation.
+
+In November of the same year, Charlemagne went to Regensburg where the Avar leaders acknowledged him as their ruler. In 805, the Avar khagan, who had already been baptised, went to Aachen to ask permission to settle with his people south-eastward from Vienna. The Transdanubian territories became integral parts of the Frankish realm, which was abolished by the Magyars in 899–900.
+
+Northeast Slav expeditions
+In 789, in recognition of his new pagan neighbours, the Slavs, Charlemagne marched an Austrasian-Saxon army across the Elbe into Obotrite territory. The Slavs ultimately submitted, led by their leader Witzin. Charlemagne then accepted the surrender of the Veleti under Dragovit and demanded many hostages. He also demanded permission to send missionaries into this pagan region unmolested. The army marched to the Baltic before turning around and marching to the Rhine, winning much booty with no harassment. The tributary Slavs became loyal allies. In 795, when the Saxons broke the peace, the Abotrites and Veleti rebelled with their new ruler against the Saxons. Witzin died in battle and Charlemagne avenged him by harrying the Eastphalians on the Elbe. Thrasuco, his successor, led his men to conquest over the Nordalbingians and handed their leaders over to Charlemagne, who honoured him. The Abotrites remained loyal until Charles' death and fought later against the Danes.
+
+Southeast Slav expeditions
+When Charlemagne incorporated much of Central Europe, he brought the Frankish state face to face with the Avars and Slavs in the southeast. The most southeast Frankish neighbours were Croats, who settled in Lower Pannonia and Duchy of Croatia. While fighting the Avars, the Franks had called for their support. During the 790s, he won a major victory over them in 796. Duke Vojnomir of Lower Pannonia aided Charlemagne, and the Franks made themselves overlords over the Croats of northern Dalmatia, Slavonia and Pannonia.
+
+The Frankish commander Eric of Friuli wanted to extend his dominion by conquering the Littoral Croat Duchy. During that time, Dalmatian Croatia was ruled by Duke Višeslav of Croatia. In the Battle of Trsat, the forces of Eric fled their positions and were routed by the forces of Višeslav. Eric was among those killed which was a great blow for the Carolingian Empire.
+
+Charlemagne also directed his attention to the Slavs to the west of the Avar khaganate: the Carantanians and Carniolans. These people were subdued by the Lombards and Bavarii and made tributaries, but were never fully incorporated into the Frankish state.
+
+Imperium
+
+Coronation
+
+In 799, Pope Leo III had been assaulted by some of the Romans, who tried to pull out his eyes and tear out his tongue. Leo escaped and fled to Charlemagne at Paderborn. Charlemagne, advised by scholar Alcuin, travelled to Rome, in November 800 and held a synod. On 23 December, Leo swore an oath of innocence to Charlemagne. His position having thereby been weakened, the Pope sought to restore his status. Two days later, at Mass, on Christmas Day (25 December), when Charlemagne knelt at the altar to pray, the Pope crowned him Imperator Romanorum ("Emperor of the Romans") in Saint Peter's Basilica. In so doing, the Pope rejected the legitimacy of Empress Irene of Constantinople:
+
+Charlemagne's coronation as Emperor, though intended to represent the continuation of the unbroken line of Emperors from Augustus to Constantine VI, had the effect of setting up two separate (and often opposing) Empires and two separate claims to imperial authority. It led to war in 802, and for centuries to come, the Emperors of both West and East would make competing claims of sovereignty over the whole.
+
+Einhard says that Charlemagne was ignorant of the Pope's intent and did not want any such coronation:
+
+A number of modern scholars, however, suggest that Charlemagne was indeed aware of the coronation; certainly, he cannot have missed the bejewelled crown waiting on the altar when he came to pray—something even contemporary sources support.
+
+Debate 
+
+Historians have debated for centuries whether Charlemagne was aware before the coronation of the Pope's intention to crown him Emperor (Charlemagne declared that he would not have entered Saint Peter's had he known, according to chapter twenty-eight of Einhard's Vita Karoli Magni), but that debate obscured the more significant question of why the Pope granted the title and why Charlemagne accepted it.
+
+Collins points out "[t]hat the motivation behind the acceptance of the imperial title was a romantic and antiquarian interest in reviving the Roman Empire is highly unlikely." For one thing, such romance would not have appealed either to Franks or Roman Catholics at the turn of the ninth century, both of whom viewed the Classical heritage of the Roman Empire with distrust. The Franks took pride in having "fought against and thrown from their shoulders the heavy yoke of the Romans" and "from the knowledge gained in baptism, clothed in gold and precious stones the bodies of the holy martyrs whom the Romans had killed by fire, by the sword and by wild animals", as Pepin III described it in a law of 763 or 764.
+
+Furthermore, the new title—carrying with it the risk that the new emperor would "make drastic changes to the traditional styles and procedures of government" or "concentrate his attentions on Italy or on Mediterranean concerns more generally"—risked alienating the Frankish leadership.
+
+For both the Pope and Charlemagne, the Roman Empire remained a significant power in European politics at this time. The Byzantine Empire, based in Constantinople, continued to hold a substantial portion of Italy, with borders not far south of Rome. Charles' sitting in judgment of the Pope could be seen as usurping the prerogatives of the Emperor in Constantinople:
+
+For the Pope, then, there was "no living Emperor at that time" though Henri Pirenne disputes this saying that the coronation "was not in any sense explained by the fact that at this moment a woman was reigning in Constantinople". Nonetheless, the Pope took the extraordinary step of creating one. The papacy had since 727 been in conflict with Irene's predecessors in Constantinople over a number of issues, chiefly the continued Byzantine adherence to the doctrine of iconoclasm, the destruction of Christian images; while from 750, the secular power of the Byzantine Empire in central Italy had been nullified.
+
+By bestowing the Imperial crown upon Charlemagne, the Pope arrogated to himself "the right to appoint ... the Emperor of the Romans, ... establishing the imperial crown as his own personal gift but simultaneously granting himself implicit superiority over the Emperor whom he had created." And "because the Byzantines had proved so unsatisfactory from every point of view—political, military and doctrinal—he would select a westerner: the one man who by his wisdom and statesmanship and the vastness of his dominions ... stood out head and shoulders above his contemporaries."
+
+With Charlemagne's coronation, therefore, "the Roman Empire remained, so far as either of them [Charlemagne and Leo] were concerned, one and indivisible, with Charles as its Emperor", though there can have been "little doubt that the coronation, with all that it implied, would be furiously contested in Constantinople".
+
+Alcuin writes hopefully in his letters of an Imperium Christianum ("Christian Empire"), wherein, "just as the inhabitants of the [Roman Empire] had been united by a common Roman citizenship", presumably this new empire would be united by a common Christian faith. This is the view of Pirenne when he says "Charles was the Emperor of the ecclesia as the Pope conceived it, of the Roman Church, regarded as the universal Church". The Imperium Christianum was further supported at a number of synods all across Europe by Paulinus of Aquileia.
+
+What is known, from the Byzantine chronicler Theophanes, is that Charlemagne's reaction to his coronation was to take the initial steps towards securing the Constantinopolitan throne by sending envoys of marriage to Irene, and that Irene reacted somewhat favourably to them.
+
+Distinctions between the universalist and localist conceptions of the empire remain controversial among historians. According to the former, the empire was a universal monarchy, a "commonwealth of the whole world, whose sublime unity transcended every minor distinction"; and the emperor "was entitled to the obedience of Christendom". According to the latter, the emperor had no ambition for universal dominion; his realm was limited in the same way as that of every other ruler, and when he made more far-reaching claims his object was normally to ward off the attacks either of the Pope or of the Byzantine emperor. According to this view, also, the origin of the empire is to be explained by specific local circumstances rather than by overarching theories.
+
+According to Ohnsorge, for a long time, it had been the custom of Byzantium to designate the German princes as spiritual "sons" of the Romans. What might have been acceptable in the fifth century had become provoking and insulting to the Franks in the eighth century. Charles came to believe that the Roman emperor, who claimed to head the world hierarchy of states, was, in reality, no greater than Charles himself, a king as other kings, since beginning in 629 he had entitled himself "Basileus" (translated literally as "king"). Ohnsorge finds it significant that the chief wax seal of Charles, which bore only the inscription: "Christe, protege Carolum regem Francorum" [Christ, protect Charles, king of the Franks], was used from 772 to 813, even during the imperial period and was not replaced by a special imperial seal; indicating that Charles felt himself to be just the king of the Franks. Finally, Ohnsorge points out that in the spring of 813 at Aachen, Charles crowned his only surviving son, Louis, as the emperor without recourse to Rome with only the acclamation of his Franks. The form in which this acclamation was offered was Frankish-Christian rather than Roman. This implies both independence from Rome and a Frankish (non-Roman) understanding of empire.
+
+Mayr-Harting argues that the Imperial title was Charlemagne's face-saving offer to incorporate the recently conquered Saxons. Since the Saxons did not have an institution of kingship for their own ethnicity, claiming the right to rule them as King of the Saxons was not possible. Hence, it is argued, Charlemagne used the supra-ethnic Imperial title to incorporate the Saxons, which helped to cement the diverse peoples under his rule.
+
+Imperial title
+Charlemagne used these circumstances to claim that he was the "renewer of the Roman Empire", which had declined under the Byzantines. In his official charters, Charles preferred the style Karolus serenissimus Augustus a Deo coronatus magnus pacificus imperator Romanum gubernans imperium ("Charles, most serene Augustus crowned by God, the great, peaceful emperor ruling the Roman empire") to the more direct Imperator Romanorum ("Emperor of the Romans").
+
+The title of Emperor remained in the Carolingian family for years to come, but divisions of territory and in-fighting over supremacy of the Frankish state weakened its significance. The papacy itself never forgot the title nor abandoned the right to bestow it. When the family of Charles ceased to produce worthy heirs, the Pope gladly crowned whichever Italian magnate could best protect him from his local enemies. The empire would remain in continuous existence for over a millennium, as the Holy Roman Empire, a true imperial successor to Charles.
+
+Imperial diplomacy
+
+The iconoclasm of the Byzantine Isaurian Dynasty was endorsed by the Franks. The Second Council of Nicaea reintroduced the veneration of icons under Empress Irene. The council was not recognised by Charlemagne since no Frankish emissaries had been invited, even though Charlemagne ruled more than three provinces of the classical Roman empire and was considered equal in rank to the Byzantine emperor. And while the Pope supported the reintroduction of the iconic veneration, he politically digressed from Byzantium. He certainly desired to increase the influence of the papacy, to honour his saviour Charlemagne, and to solve the constitutional issues then most troubling to European jurists in an era when Rome was not in the hands of an emperor. Thus, Charlemagne's assumption of the imperial title was not a usurpation in the eyes of the Franks or Italians. It was, however, seen as such in Byzantium, where it was protested by Irene and her successor Nikephoros I—neither of whom had any great effect in enforcing their protests.
+
+The East Romans, however, still held several territories in Italy: Venice (what was left of the Exarchate of Ravenna), Reggio (in Calabria), Otranto (in Apulia), and Naples (the Ducatus Neapolitanus). These regions remained outside of Frankish hands until 804, when the Venetians, torn by infighting, transferred their allegiance to the Iron Crown of Pippin, Charles' son. The Pax Nicephori ended. Nicephorus ravaged the coasts with a fleet, initiating the only instance of war between the Byzantines and the Franks. The conflict lasted until 810 when the pro-Byzantine party in Venice gave their city back to the Byzantine Emperor, and the two emperors of Europe made peace: Charlemagne received the Istrian peninsula and in 812 the emperor Michael I Rangabe recognised his status as Emperor, although not necessarily as "Emperor of the Romans".
+
+Danish attacks
+After the conquest of Nordalbingia, the Frankish frontier was brought into contact with Scandinavia. The pagan Danes, "a race almost unknown to his ancestors, but destined to be only too well known to his sons" as Charles Oman described them, inhabiting the Jutland peninsula, had heard many stories from Widukind and his allies who had taken refuge with them about the dangers of the Franks and the fury which their Christian king could direct against pagan neighbours.
+
+In 808, the king of the Danes, Godfred, expanded the vast Danevirke across the isthmus of Schleswig. This defence, last employed in the Danish-Prussian War of 1864, was at its beginning a  long earthenwork rampart. The Danevirke protected Danish land and gave Godfred the opportunity to harass Frisia and Flanders with pirate raids. He also subdued the Frank-allied Veleti and fought the Abotrites.
+
+Godfred invaded Frisia, joked of visiting Aachen, but was murdered before he could do any more, either by a Frankish assassin or by one of his own men. Godfred was succeeded by his nephew Hemming, who concluded the Treaty of Heiligen with Charlemagne in late 811.
+
+Death
+
+In 813, Charlemagne called Louis the Pious, king of Aquitaine, his only surviving legitimate son, to his court. There Charlemagne crowned his son as co-emperor and sent him back to Aquitaine. He then spent the autumn hunting before returning to Aachen on 1 November. In January, he fell ill with pleurisy. In deep depression (mostly because many of his plans were not yet realised), he took to his bed on 21 January and as Einhard tells it:
+
+He was buried that same day, in Aachen Cathedral. The earliest surviving planctus, the Planctus de obitu Karoli, was composed by a monk of Bobbio, which he had patronised. A later story, told by Otho of Lomello, Count of the Palace at Aachen in the time of Emperor Otto III, would claim that he and Otto had discovered Charlemagne's tomb: Charlemagne, they claimed, was seated upon a throne, wearing a crown and holding a sceptre, his flesh almost entirely incorrupt. In 1165, Emperor Frederick I re-opened the tomb again and placed the emperor in a sarcophagus beneath the floor of the cathedral. In 1215 Emperor Frederick II re-interred him in a casket made of gold and silver known as the Karlsschrein.
+
+Charlemagne's death emotionally affected many of his subjects, particularly those of the literary clique who had surrounded him at Aachen. An anonymous monk of Bobbio lamented:
+
+Louis succeeded him as Charles had intended. He left a testament allocating his assets in 811 that was not updated prior to his death. He left most of his wealth to the Church, to be used for charity. His empire lasted only another generation in its entirety; its division, according to custom, between Louis's own sons after their father's death laid the foundation for the modern states of Germany and France.
+
+Administration
+
+Organisation
+The Carolingian king exercised the bannum, the right to rule and command. Under the Franks, it was a royal prerogative but could be delegated. He had supreme jurisdiction in judicial matters, made legislation, led the army, and protected both the Church and the poor. His administration was an attempt to organise the kingdom, church and nobility around him. As an administrator, Charlemagne stands out for his many reforms: monetary, governmental, military, cultural and ecclesiastical. He is the main protagonist of the "Carolingian Renaissance".
+
+Military
+Charlemagne's success rested primarily on novel siege technologies and excellent logistics rather than the long-claimed "cavalry revolution" led by Charles Martel in 730s. However, the stirrup, which made the "shock cavalry" lance charge possible, was not introduced to the Frankish kingdom until the late eighth century.
+
+Horses were used extensively by the Frankish military because they provided a quick, long-distance method of transporting troops, which was critical to building and maintaining the large empire.
+
+Economic and monetary reforms
+
+Charlemagne had an important role in determining Europe's immediate economic future. Pursuing his father's reforms, Charlemagne abolished the monetary system based on the gold . Instead, he and the Anglo-Saxon King Offa of Mercia took up Pippin's system for pragmatic reasons, notably a shortage of the metal.
+
+The gold shortage was a direct consequence of the conclusion of peace with Byzantium, which resulted in ceding Venice and Sicily to the East and losing their trade routes to Africa. The resulting standardisation economically harmonised and unified the complex array of currencies that had been in use at the commencement of his reign, thus simplifying trade and commerce.
+
+Charlemagne established a new standard, the  (from the Latin , the modern pound), which was based upon a pound of silver—a unit of both money and weight—worth 20 sous (from the Latin  [which was primarily an accounting device and never actually minted], the modern shilling) or 240  (from the Latin , the modern penny). During this period, the  and the  were counting units; only the  was a coin of the realm.
+
+Charlemagne instituted principles for accounting practice by means of the Capitulare de villis of 802, which laid down strict rules for the way in which incomes and expenses were to be recorded.
+
+Charlemagne applied this system to much of the European continent, and Offa's standard was voluntarily adopted by much of England. After Charlemagne's death, continental coinage degraded, and most of Europe resorted to using the continued high-quality English coin until about 1100.
+
+Jews in Charlemagne's realm
+Early in Charlemagne's rule he tacitly allowed Jews to monopolise money lending. He invited Italian Jews to immigrate, as royal clients independent of the feudal landowners, and form trading communities in the agricultural regions of Provence and the Rhineland. Their trading activities augmented the otherwise almost exclusively agricultural economies of these regions. His personal physician was Jewish, and he employed a Jew named Isaac as his personal representative to the Muslim caliphate of Baghdad.
+
+Education reforms
+
+Part of Charlemagne's success as a warrior, an administrator and ruler can be traced to his admiration for learning and education. His reign is often referred to as the Carolingian Renaissance because of the flowering of scholarship, literature, art and architecture that characterise it. Charlemagne came into contact with the culture and learning of other countries (especially Moorish Spain, Anglo-Saxon England, and Lombard Italy) due to his vast conquests. He greatly increased the provision of monastic schools and scriptoria (centres for book-copying) in Francia.
+
+Charlemagne was a lover of books, sometimes having them read to him during meals. He was thought to enjoy the works of Augustine of Hippo. His court played a key role in producing books that taught elementary Latin and different aspects of the church. It also played a part in creating a royal library that contained in-depth works on language and Christian faith.
+
+Charlemagne encouraged clerics to translate Christian creeds and prayers into their respective vernaculars as well to teach grammar and music. Due to the increased interest of intellectual pursuits and the urging of their king, the monks accomplished so much copying that almost every manuscript from that time was preserved. At the same time, at the urging of their king, scholars were producing more secular books on many subjects, including history, poetry, art, music, law, theology, etc. Due to the increased number of titles, private libraries flourished. These were mainly supported by aristocrats and churchmen who could afford to sustain them. At Charlemagne's court, a library was founded and a number of copies of books were produced, to be distributed by Charlemagne. Book production was completed slowly by hand and took place mainly in large monastic libraries. Books were so in demand during Charlemagne's time that these libraries lent out some books, but only if that borrower offered valuable collateral in return.
+
+Most of the surviving works of classical Latin were copied and preserved by Carolingian scholars. Indeed, the earliest manuscripts available for many ancient texts are Carolingian. It is almost certain that a text which survived to the Carolingian age survives still.
+
+The pan-European nature of Charlemagne's influence is indicated by the origins of many of the men who worked for him: Alcuin, an Anglo-Saxon from York; Theodulf, a Visigoth, probably from Septimania; Paul the Deacon, Lombard; Italians Peter of Pisa and Paulinus of Aquileia; and Franks Angilbert, Angilram, Einhard and Waldo of Reichenau.
+
+Charlemagne promoted the liberal arts at court, ordering that his children and grandchildren be well-educated, and even studying himself (in a time when even leaders who promoted education did not take time to learn themselves) under the tutelage of Peter of Pisa, from whom he learned grammar; Alcuin, with whom he studied rhetoric, dialectic (logic), and astronomy (he was particularly interested in the movements of the stars); and Einhard, who tutored him in arithmetic.
+
+His great scholarly failure, as Einhard relates, was his inability to write: when in his old age he attempted to learn—practising the formation of letters in his bed during his free time on books and wax tablets he hid under his pillow—"his effort came too late in life and achieved little success", and his ability to read—which Einhard is silent about, and which no contemporary source supports—has also been called into question.
+
+In 800, Charlemagne enlarged the hostel at the Muristan in Jerusalem and added a library to it. He certainly had not been personally in Jerusalem.
+
+Church reforms
+
+Charlemagne expanded the reform Church's programme unlike his father, Pippin, and uncle, Carloman. The deepening of the spiritual life was later to be seen as central to public policy and royal governance. His reform focused on strengthening the church's power structure, improving clergy's skill and moral quality, standardising liturgical practices, improvements on the basic tenets of the faith and the rooting out of paganism. His authority extended over church and state. He could discipline clerics, control ecclesiastical property and define orthodox doctrine. Despite the harsh legislation and sudden change, he had developed support from clergy who approved his desire to deepen the piety and morals of his subjects.
+
+In 809–810, Charlemagne called a church council in Aachen, which confirmed the unanimous belief in the West that the Holy Spirit proceeds from the Father and the Son (ex Patre Filioque) and sanctioned inclusion in the Nicene Creed of the phrase Filioque (and the Son). For this Charlemagne sought the approval of Pope Leo III. The Pope, while affirming the doctrine and approving its use in teaching, opposed its inclusion in the text of the Creed as adopted in the 381 First Council of Constantinople. This spoke of the procession of the Holy Spirit from the Father, without adding phrases such as "and the Son", "through the Son", or "alone". Stressing his opposition, the Pope had the original text inscribed in Greek and Latin on two heavy shields that were displayed in Saint Peter's Basilica.
+
+Writing reforms
+
+During Charles' reign, the Roman half uncial script and its cursive version, which had given rise to various continental minuscule scripts, were combined with features from the insular scripts in use in Irish and English monasteries. Carolingian minuscule was created partly under the patronage of Charlemagne. Alcuin, who ran the palace school and scriptorium at Aachen, was probably a chief influence.
+
+The revolutionary character of the Carolingian reform, however, can be overemphasised; efforts at taming Merovingian and Germanic influence had been underway before Alcuin arrived at Aachen. The new minuscule was disseminated first from Aachen and later from the influential scriptorium at Tours, where Alcuin retired as an abbot.
+
+Political reforms
+Charlemagne engaged in many reforms of Frankish governance while continuing many traditional practices, such as the division of the kingdom among sons.
+
+Divisio regnorum
+In 806, Charlemagne first made provision for the traditional division of the empire on his death. For Charles the Younger he designated Austrasia and Neustria, Saxony, Burgundy and Thuringia. To Pippin, he gave Italy, Bavaria, and Swabia. Louis received Aquitaine, the Spanish March and Provence. The imperial title was not mentioned, which led to the suggestion that, at that particular time, Charlemagne regarded the title as an honorary achievement that held no hereditary significance.
+
+Pepin died in 810 and Charles in 811. Charlemagne then reconsidered the matter, and in 813, crowned his youngest son, Louis, co-emperor and co-King of the Franks, granting him a half-share of the empire and the rest upon Charlemagne's own death. The only part of the Empire that Louis was not promised was Italy, which Charlemagne specifically bestowed upon Pippin's illegitimate son Bernard.
+
+Appearance
+
+Manner
+
+Einhard tells in his twenty-fourth chapter: Charlemagne threw grand banquets and feasts for special occasions such as religious holidays and four of his weddings. When he was not working, he loved Christian books, horseback riding, swimming, bathing in natural hot springs with his friends and family, and hunting. Franks were well known for horsemanship and hunting skills. Charles was a light sleeper and would stay in his bed chambers for entire days at a time due to restless nights. During these days, he would not get out of bed when a quarrel occurred in his kingdom, instead summoning all members of the situation into his bedroom to be given orders. Einhard tells again in the twenty-fourth chapter: "In summer after the midday meal, he would eat some fruit, drain a single cup, put off his clothes and shoes, just as he did for the night, and rest for two or three hours. He was in the habit of awaking and rising from bed four or five times during the night."
+
+Language
+
+Charlemagne probably spoke a Rhenish Franconian dialect.
+
+He also spoke Latin and had at least some understanding of Greek, according to Einhard (Grecam vero melius intellegere quam pronuntiare poterat, "he could understand Greek better than he could speak it").
+
+The largely fictional account of Charlemagne's Iberian campaigns by Pseudo-Turpin, written some three centuries after his death, gave rise to the legend that the king also spoke Arabic.
+
+Physical appearance
+
+Charlemagne's personal appearance is known from a good description by Einhard after his death in the biography Vita Karoli Magni. Einhard states:
+
+The physical portrait provided by Einhard is confirmed by contemporary depictions such as coins and his  bronze statuette kept in the Louvre. In 1861, Charlemagne's tomb was opened by scientists who reconstructed his skeleton and estimated it to be measured . A 2010 estimate of his height from an X-ray and CT scan of his tibia was . This puts him in the 99th percentile of height for his period, given that average male height of his time was . The width of the bone suggested he was gracile in body build.
+
+Dress
+
+Charlemagne wore the traditional costume of the Frankish people, described by Einhard thus:
+
+He wore a blue cloak and always carried a sword typically of a golden or silver hilt. He wore intricately jeweled swords to banquets or ambassadorial receptions. Nevertheless:
+
+On great feast days, he wore embroidery and jewels on his clothing and shoes. He had a golden buckle for his cloak on such occasions and would appear with his great diadem, but he despised such apparel according to Einhard, and usually dressed like the common people.
+
+Homes 
+Charlemagne had residences across his kingdom, including numerous private estates that were governed in accordance with the Capitulare de villis. A 9th-century document detailing the inventory of an estate at Asnapium listed amounts of livestock, plants and vegetables and kitchenware including cauldrons, drinking cups, brass kettles and firewood. The manor contained seventeen houses built inside the courtyard for nobles and family members and was separated from its supporting villas.
+
+Beatification 
+
+Charlemagne was revered as a saint in the Holy Roman Empire and some other locations after the twelfth century. The Apostolic See did not recognise his invalid canonisation by Antipope Paschal III, done to gain the favour of Frederick Barbarossa in 1165. The Apostolic See annulled all of Paschal's ordinances at the Third Lateran Council in 1179. He is not enumerated among the 28 saints named "Charles" in the Roman Martyrology. His beatification has been acknowledged as cultus confirmed and is celebrated on 28 January.
+
+Cultural impact
+
+Middle Ages 
+The author of the Visio Karoli Magni written around 865 uses facts gathered apparently from Einhard and his own observations on the decline of Charlemagne's family after the dissensions war (840–43) as the basis for a visionary tale of Charles' meeting with a prophetic spectre in a dream.
+
+Charlemagne was a model knight as one of the Nine Worthies who enjoyed an important legacy in European culture. One of the great medieval literary cycles, the Charlemagne cycle or the Matter of France, centres on his deeds—the Emperor with the Flowing Beard of Roland fame—and his historical commander of the border with Brittany, Roland, and the 12 paladins. These are analogous to, and inspired the myth of, the Knights of the Round Table of King Arthur's court. Their tales constitute the first chansons de geste.
+
+In the 12th century, Geoffrey of Monmouth based his stories of Arthur largely on stories of Charlemagne. During the Hundred Years' War in the 14th century, there was considerable cultural conflict in England, where the Norman rulers were aware of their French roots and identified with Charlemagne, Anglo-Saxon natives felt more affinity for Arthur, whose own legends were relatively primitive. Therefore, storytellers in England adapted legends of Charlemagne and his 12 Peers to the Arthurian tales.
+
+In the Divine Comedy, the spirit of Charlemagne appears to Dante in the Heaven of Mars, among the other "warriors of the faith".
+
+19th century 
+
+Charlemagne's capitularies were quoted by Pope Benedict XIV in his apostolic constitution 'Providas' against freemasonry: "For in no way are we able to understand how they can be faithful to us, who have shown themselves unfaithful to God and disobedient to their Priests".
+
+Charlemagne appears in Adelchi, the second tragedy by Italian writer Alessandro Manzoni, first published in 1822.
+
+In 1867, an equestrian statue of Charlemagne was made by Louis Jehotte and was inaugurated in 1868 on the Boulevard d'Avroy in Liège. In the niches of the neo-roman pedestal are six statues of Charlemagne's ancestors (Sainte Begge, Pépin de Herstal, Charles Martel, Bertrude, Pépin de Landen and Pépin le Bref).
+
+The North Wall Frieze in the courtroom of the Supreme Court of the United States depicts Charlemagne as a legal reformer.
+
+20th century 
+The city of Aachen has, since 1949, awarded an international prize (called the Karlspreis der Stadt Aachen) in honour of Charlemagne. It is awarded annually to "personages of merit who have promoted the idea of Western unity by their political, economic and literary endeavours." Winners of the prize include Richard von Coudenhove-Kalergi, the founder of the pan-European movement, Alcide De Gasperi, and Winston Churchill.
+
+In its national anthem, "El Gran Carlemany", the microstate of Andorra credits Charlemagne with its independence.
+
+In 1964, young French singer France Gall released the hit song "Sacré Charlemagne" in which the lyrics blame the great king for imposing the burden of compulsory education on French children.
+
+Charlemagne is quoted by Henry Jones, Sr. in Indiana Jones and the Last Crusade. After using his umbrella to induce a flock of seagulls to smash through the glass cockpit of a pursuing German fighter plane, Henry Jones remarks, "I suddenly remembered my Charlemagne: 'Let my armies be the rocks and the trees and the birds in the sky. Despite the quote's popularity since the movie, there is no evidence that Charlemagne actually said this.
+
+21st century
+A 2010 episode of QI discussed the mathematics completed by Mark Humphrys that calculated that all modern Europeans are highly likely to share Charlemagne as a common ancestor (see most recent common ancestor).
+
+The Economist featured a weekly column entitled "Charlemagne", focusing generally on European affairs and, more usually and specifically, on the European Union and its politics.
+
+Actor and singer Christopher Lee's symphonic metal concept album Charlemagne: By the Sword and the Cross and its heavy metal follow-up Charlemagne: The Omens of Death feature the events of Charlemagne's life.
+
+In April 2014, on the occasion of the 1200th anniversary of Charlemagne's death, public art Mein Karl by Ottmar Hörl at Katschhof place was installed between city hall and the Aachen cathedral, displaying 500 Charlemagne statues.
+
+Charlemagne features as a playable character in the 2014 Charlemagne expansion for the grand strategy video game Crusader Kings 2.
+
+Charlemagne is a playable character in the Mobile/PC Game Rise of Kingdoms.
+
+In the 2018 video game Fate/Extella Link, Charlemagne appears as a Heroic Spirit separated into two Saint Graphs: the adventurous hero Charlemagne, who embodies the fantasy aspect as leader of the Twelve Paladins, and the villain Karl de Große, who embodies the historical aspect as Holy Roman Emperor.
+
+In July 2022, Charlemagne featured as a character in an episode of The Family Histories Podcast, and it references his role as an ancestor of all modern Europeans. He is portrayed here in later life, and is speaking Latin, which is translated by a device. He is returned to 9th Century Aquitaine by the end of the episode after a DNA sample has been extracted.
+
+Notes
+
+References
+
+Citations
+
+Bibliography
+
+ Charlemagne, from Encyclopædia Britannica, full-article, latest edition.
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+  Comprises the Annales regni Francorum and The History of the Sons of Louis the Pious
+
+External links
+
+ The Making of Charlemagne's Europe (freely available database of prosopographical and socio-economic data from legal documents dating to Charlemagne's reign, produced by King's College London)
+ 
+ 
+ The Sword of Charlemagne (myArmoury.com article)
+ 
+ Charter given by Charlemagne for St. Emmeram's Abbey showing the Emperor's seal, 22.2.794 . Taken from the collections of the Lichtbildarchiv älterer Originalurkunden at Marburg University
+ 
+ 
+ An interactive map of Charlemagne's travels
+ 
+ 
+
+ 
+740s births
+814 deaths
+8th-century dukes of Bavaria
+8th-century Frankish kings
+8th-century Lombard monarchs
+9th-century dukes of Bavaria
+9th-century Holy Roman Emperors
+9th-century kings of Italy
+Beatifications by Pope Benedict XIV
+Captains General of the Church
+Carolingian dynasty
+Chansons de geste
+Characters in Orlando Innamorato and Orlando Furioso
+Characters in The Song of Roland
+Christian royal saints
+Deaths from respiratory disease
+Founding monarchs
+Frankish warriors
+French bibliophiles
+French Christians
+German bibliophiles
+German Christians
+Matter of France
+Medieval Low Countries
+Medieval Roman consuls
+While Hypertext Markup Language (HTML) has been in use since 1991, HTML 4.0 from December 1997 was the first standardized version where international characters were given reasonably complete treatment. When an HTML document includes special characters outside the range of seven-bit ASCII, two goals are worth considering: the information's integrity, and universal browser display.
+
+Specifying the document's character encoding
+There are two general ways to specify which character encoding is used in the document.
+
+First, the web server can include the character encoding or "charset" in the Hypertext Transfer Protocol (HTTP) Content-Type header, which would typically look like this:
+Content-Type: text/html; charset=utf-8
+This method gives the HTTP server a convenient way to alter document's encoding according to content negotiation; certain HTTP server software can do it, for example Apache with the module mod_charset_lite.
+
+Second, a declaration can be included within the document itself.
+
+For HTML it is possible to include this information inside the head element near the top of the document:
+
+<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
+
+HTML5 also allows the following syntax to mean exactly the same:
+
+<meta charset="utf-8">
+
+XHTML documents have a third option: to express the character encoding via XML declaration, as follows:
+<?xml version="1.0" encoding="utf-8"?>
+
+With this second approach, because the character encoding cannot be known until the declaration is parsed, there is a problem knowing which character encoding is used in the document up to and including the declaration itself. If the character encoding is an ASCII extension then the content up to and including the declaration itself should be pure ASCII and this will work correctly. For character encodings that are not ASCII extensions (i.e. not a superset of ASCII), such as UTF-16BE and UTF-16LE, a processor of HTML, such as a web browser, should be able to parse the declaration in some cases through the use of heuristics.
+
+Encoding detection algorithm 
+As of HTML5 the recommended charset is UTF-8. An "encoding sniffing algorithm" is defined in the specification to determine the character encoding of the document based on multiple sources of input, including:
+ Explicit user instruction
+ An explicit meta tag within the first 1024 bytes of the document
+ A byte order mark (BOM) within the first three bytes of the document
+ The HTTP Content-Type or other transport layer information
+ Analysis of the document bytes looking for specific sequences or ranges of byte values, and other tentative detection mechanisms.
+
+Characters outside of the printable ASCII range (32 to 126) usually appear incorrectly. This presents few problems for English-speaking users, but other languages regularly—in some cases, always—require characters outside that range. In Chinese, Japanese, and Korean (CJK) language environments where there are several different multi-byte encodings in use, auto-detection is also often employed. Finally, browsers usually permit the user to override incorrect charset label manually as well.
+
+It is increasingly common for multilingual websites and websites in non-Western languages to use UTF-8, which allows use of the same encoding for all languages. UTF-16 or UTF-32, which can be used for all languages as well, are less widely used because they can be harder to handle in programming languages that assume a byte-oriented ASCII superset encoding, and they are less efficient for text with a high frequency of ASCII characters, which is usually the case for HTML documents.
+
+Successful viewing of a page is not necessarily an indication that its encoding is specified correctly. If the page's creator and reader are both assuming some platform-specific character encoding, and the server does not send any identifying information, then the reader will nonetheless see the page as the creator intended, but other readers on different platforms or with different native languages will not see the page as intended.
+
+Permitted encodings
+The WHATWG Encoding Standard, referenced by recent HTML standards (the current WHATWG HTML Living Standard, as well as the formerly competing W3C HTML 5.0 and 5.1) specifies a list of encodings which browsers must support. The HTML standards forbid support of other encodings. The Encoding Standard further stipulates that new formats, new protocols (even when existing formats are used) and authors of new documents are required to use UTF-8 exclusively.
+
+Besides UTF-8, the following encodings are explicitly listed in the HTML standard itself, with reference to the Encoding Standard:
+
+The following additional encodings are listed in the Encoding Standard, and support for them is therefore also required:
+
+The following encodings are listed as explicit examples of forbidden encodings:
+
+The standard also defines a "replacement" decoder, which maps all content labelled as certain encodings to the replacement character (�), refusing to process it at all. This is intended to prevent attacks (e.g. cross site scripting) which may exploit a difference between the client and server in what encodings are supported in order to mask malicious content. Although the same security concern applies to ISO-2022-JP and UTF-16, which also allow sequences of ASCII bytes to be interpreted differently, this approach was not seen as feasible for them since they are comparatively more frequently used in deployed content. The following encodings receive this treatment:
+
+Character references
+
+In addition to native character encodings, characters can also be encoded as character references, which can be numeric character references (decimal or hexadecimal) or character entity references. Character entity references are also sometimes referred to as named entities, or HTML entities for HTML. HTML's usage of character references derives from SGML.
+
+HTML character references
+
+A numeric character reference in HTML refers to a character by its Universal Character Set/Unicode code point, and uses the format
+
+&#nnnn;
+or
+&#xhhhh;
+
+where nnnn is the code point in decimal form, and hhhh is the code point in hexadecimal form. The x must be lowercase in XML documents. The nnnn or hhhh may be any number of digits and may include leading zeros. The hhhh may mix uppercase and lowercase, though uppercase is the usual style.
+
+Not all web browsers or email clients used by receivers of HTML documents, or text editors used by authors of HTML documents, will be able to render all HTML characters. Most modern software is able to display most or all of the characters for the user's language, and will draw a box or other clear indicator for characters they cannot render.
+
+For codes from 0 to 127, the original 7-bit ASCII standard set, most of these characters can be used without a character reference. Codes from 160 to 255 can all be created using character entity names. Only a few higher-numbered codes can be created using entity names, but all can be created by decimal number character reference.
+
+Character entity references can also have the format &name; where name is a case-sensitive alphanumeric string. For example, "λ" can also be encoded as &lambda; in an HTML document. The character entity references &lt;, &gt;, &quot; and &amp; are predefined in HTML and SGML, because <, >, "  and & are already used to delimit markup. This notably did not include XML's &apos; (') entity prior to HTML5. For a list of all named HTML character entity references along with the versions in which they were introduced, see List of XML and HTML character entity references.
+
+Unnecessary use of HTML character references may significantly reduce HTML readability. If the character encoding for a web page is chosen appropriately, then HTML character references are usually only required for markup delimiting characters as mentioned above, and for a few special characters (or none at all if a native Unicode encoding like UTF-8 is used). Incorrect HTML entity escaping may also open up security vulnerabilities for injection attacks such as cross-site scripting. If HTML attributes are left unquoted, certain characters, most importantly whitespace, such as space and tab, must be escaped using entities. Other languages related to HTML have their own methods of escaping characters.
+
+XML character references
+Unlike traditional HTML with its large range of character entity references, in XML there are only five predefined character entity references. These are used to escape characters that are markup sensitive in certain contexts:
+
+All other character entity references have to be defined before they can be used. For example, use of &eacute; (which gives é, Latin lower-case E with acute accent, U+00E9 in Unicode) in an XML document will generate an error unless the entity has already been defined. XML also requires that the x in hexadecimal numeric references be in lowercase: for example &#xA1b rather than &#XA1b. XHTML, which is an XML application, supports the HTML entity set, along with XML's predefined entities.
+
+See also 
+ Charset sniffing – used by many browsers when character encoding metadata is not available
+ Unicode and HTML
+ Language code
+ List of XML and HTML character entity references
+
+References
+
+External links 
+ Online HTML entity encoder & decoder tool
+ Character entity references in HTML4
+ The Definitive Guide to Web Character Encoding
+ HTML Entity Encoding chapter of Browser Security Handbook – more information about current browsers and their entity handling
+ The Open Web Application Security Project's wiki article on cross-site scripting (XSS)
+
+HTML
+World Wide Web Consortium standards
+A carbon nanotube (CNT) is a tube made of carbon with a diameter in the nanometer range (nanoscale). They are one of the allotropes of carbon.
+
+Single-walled carbon nanotubes (SWCNTs) have diameters around 0.5–2.0 nanometers, about 100,000 times smaller than the width of a human hair. They can be idealized as cutouts from a two-dimensional graphene sheet rolled up to form a hollow cylinder.
+
+Multi-walled carbon nanotubes (MWCNTs) consist of nested single-wall carbon nanotubes in a nested, tube-in-tube structure. Double- and triple-walled carbon nanotubes are special cases of MWCNT.
+
+Carbon nanotubes can exhibit remarkable properties, such as exceptional tensile strength and thermal conductivity because of their nanostructure and strength of the bonds between carbon atoms. Some SWCNT structures exhibit high electrical conductivity while others are semiconductors. In addition, carbon nanotubes can be chemically modified. These properties are expected to be valuable in many areas of technology, such as electronics, optics, composite materials (replacing or complementing carbon fibers), nanotechnology, and other applications of materials science.
+
+The predicted properties for SWCNTs were tantalizing, but a path to synthesizing them was lacking until 1993, when Iijima and Ichihashi at NEC and Bethune et al. at IBM independently discovered that co-vaporizing carbon and transition metals such as iron and cobalt could specifically catalyze SWCNT formation.  These discoveries triggered research that succeeded in greatly increasing the efficiency of the catalytic production technique, and led to an explosion of work to characterize and find applications for SWCNTs.
+
+Structure of SWNTs
+
+Basic details 
+
+The structure of an ideal (infinitely long) single-walled carbon nanotube is that of a regular hexagonal lattice drawn on an infinite cylindrical surface, whose vertices are the positions of the carbon atoms. Since the length of the carbon-carbon bonds is fairly fixed, there are constraints on the diameter of the cylinder and the arrangement of the atoms on it.
+
+In the study of nanotubes, one defines a zigzag path on a graphene-like lattice as a path that turns 60 degrees, alternating left and right, after stepping through each bond. It is also conventional to define an armchair path as one that makes two left turns of 60 degrees followed by two right turns every four steps. On some carbon nanotubes, there is a closed zigzag path that goes around the tube. One says that the tube is of the zigzag type or configuration, or simply is a zigzag nanotube. If the tube is instead encircled by a closed armchair path, it is said to be of the armchair type, or an armchair nanotube. An infinite nanotube that is of the zigzag (or armchair) type consists entirely of closed zigzag (or armchair) paths, connected to each other.
+
+The zigzag and armchair configurations are not the only structures that a single-walled nanotube can have. To describe the structure of a general infinitely long tube, one should imagine it being sliced open by a cut parallel to its axis, that goes through some atom A, and then unrolled flat on the plane, so that its atoms and bonds coincide with those of an imaginary graphene sheet—more precisely, with an infinitely long strip of that sheet. The two halves of the atom A will end up on opposite edges of the strip, over two atoms A1 and A2 of the graphene. The line from A1 to A2 will correspond to the circumference of the cylinder that went through the atom A, and will be perpendicular to the edges of the strip. In the graphene lattice, the atoms can be split into two classes, depending on the directions of their three bonds. Half the atoms have their three bonds directed the same way, and half have their three bonds rotated 180 degrees relative to the first half. The atoms A1 and A2, which correspond to the same atom A on the cylinder, must be in the same class. It follows that the circumference of the tube and the angle of the strip are not arbitrary, because they are constrained to the lengths and directions of the lines that connect pairs of graphene atoms in the same class.
+
+Let u and v be two linearly independent vectors that connect the graphene atom A1 to two of its nearest atoms with the same bond directions. That is, if one numbers consecutive carbons around a graphene cell with C1 to C6, then u can be the vector from C1 to C3, and v be the vector from C1 to C5. Then, for any other atom A2 with same class as A1, the vector from A1 to A2 can be written as a linear combination n u + m v, where n and m are integers. And, conversely, each pair of integers (n,m) defines a possible position for A2. Given n and m, one can reverse this theoretical operation by drawing the vector w on the graphene lattice, cutting a strip of the latter along lines perpendicular to w through its endpoints A1 and A2, and rolling the strip into a cylinder so as to bring those two points together. If this construction is applied to a pair (k,0), the result is a zigzag nanotube, with closed zigzag paths of 2k atoms. If it is applied to a pair (k,k), one obtains an armchair tube, with closed armchair paths of 4k atoms.
+
+Types 
+The structure of the nanotube is not changed if the strip is rotated by 60 degrees clockwise around A1 before applying the hypothetical reconstruction above. Such a rotation changes the corresponding pair (n,m) to the pair (−2m,n+m). It follows that many possible positions of A2 relative to A1 — that is, many pairs (n,m) — correspond to the same arrangement of atoms on the nanotube. That is the case, for example, of the six pairs (1,2), (−2,3), (−3,1), (−1,−2), (2,−3), and (3,−1). In particular, the pairs (k,0) and (0,k) describe the same nanotube geometry. These redundancies can be avoided by considering only pairs (n,m) such that n > 0 and m ≥ 0; that is, where the direction of the vector w lies between those of u (inclusive) and v (exclusive). It can be verified that every nanotube has exactly one pair (n,m) that satisfies those conditions, which is called the tube's type. Conversely, for every type there is a hypothetical nanotube. In fact, two nanotubes have the same type if and only if one can be conceptually rotated and translated so as to match the other exactly. Instead of the type (n,m), the structure of a carbon nanotube can be specified by giving the length of the vector w (that is, the circumference of the nanotube), and the angle α between the directions of u and w, 
+may range from 0 (inclusive) to 60 degrees clockwise (exclusive). If the diagram is drawn with u horizontal, the latter is the tilt of the strip away from the vertical.
+
+Chirality and mirror symmetry 
+
+A nanotube is chiral if it has type (n,m), with m > 0 and m ≠ n; then its enantiomer (mirror image) has type (m,n), which is different from (n,m). This operation corresponds to mirroring the unrolled strip about the line L through A1 that makes an angle of 30 degrees clockwise from the direction of the u vector (that is, with the direction of the vector u+v). The only types of nanotubes that are achiral are the (k,0) "zigzag" tubes and the (k,k) "armchair" tubes. If two enantiomers are to be considered the same structure, then one may consider only types (n,m) with 0 ≤ m ≤ n and n > 0. Then the angle α between u and w, which may range from 0 to 30 degrees (inclusive both), is called the "chiral angle" of the nanotube.
+
+Circumference and diameter 
+
+From n and m one can also compute the circumference c, which is the length of the vector w, which turns out to be:
+
+ 
+
+in picometres. The diameter  of the tube is then , that is
+
+ 
+
+also in picometres. (These formulas are only approximate, especially for small n and m where the bonds are strained; and they do not take into account the thickness of the wall.)
+
+The tilt angle α between u and w and the circumference c are related to the type indices n and m by:
+
+ 
+
+where arg(x,y) is the clockwise angle between the X-axis and the vector (x,y); a function that is available in many programming languages as atan2(y,x). Conversely, given c and α, one can get the type (n,m) by the formulas:
+
+ 
+which must evaluate to integers.
+
+Physical limits
+
+Narrowest examples 
+
+If n and m are too small, the structure described by the pair (n,m) will describe a molecule that cannot be reasonably called a "tube", and may not even be stable. For example, the structure theoretically described by the pair (1,0) (the limiting "zigzag" type) would be just a chain of carbons. That is a real molecule, the carbyne; which has some characteristics of nanotubes (such as orbital hybridization, high tensile strength, etc.) — but has no hollow space, and may not be obtainable as a condensed phase. The pair (2,0) would theoretically yield a chain of fused 4-cycles; and (1,1), the limiting "armchair" structure, would yield a chain of bi-connected 4-rings. These structures may not be realizable.
+
+The thinnest carbon nanotube proper is the armchair structure with type (2,2), which has a diameter of 0.3 nm. This nanotube was grown inside a multi-walled carbon nanotube. Assigning of the carbon nanotube type was done by a combination of high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and density functional theory (DFT) calculations.
+
+The thinnest freestanding single-walled carbon nanotube is about 0.43 nm in diameter. Researchers suggested that it can be either (5,1) or (4,2) SWCNT, but the exact type of the carbon nanotube remains questionable. (3,3), (4,3), and (5,1) carbon nanotubes (all about 0.4 nm in diameter) were unambiguously identified using aberration-corrected high-resolution transmission electron microscopy inside double-walled CNTs.
+
+Length
+
+The observation of the longest carbon nanotubes grown so far, around 0.5 metre (550 mm) long, was reported in 2013. These nanotubes were grown on silicon substrates using an improved chemical vapor deposition (CVD) method and represent electrically uniform arrays of single-walled carbon nanotubes.
+
+The shortest carbon nanotube can be considered to be the organic compound cycloparaphenylene, which was synthesized in 2008 by Ramesh Jasti. Other small molecule carbon nanotubes have been synthesized since.
+
+Density
+The highest density of CNTs was achieved in 2013, grown on a conductive titanium-coated copper surface that was coated with co-catalysts cobalt and molybdenum at lower than typical temperatures of 450 °C. The tubes averaged a height of 380 nm and a mass density of 1.6 g cm−3. The material showed ohmic conductivity (lowest resistance ~22 kΩ).
+
+Variants 
+There is no consensus on some terms describing carbon nanotubes in scientific literature: both "-wall" and "-walled" are being used in combination with "single", "double", "triple", or "multi", and the letter C is often omitted in the abbreviation, for example, multi-walled carbon nanotube (MWNT). The International Standards Organization uses single-wall or multi-wall in its documents.
+
+Multi-walled 
+
+Multi-walled nanotubes (MWNTs) consist of multiple rolled layers (concentric tubes) of graphene. There are two models that can be used to describe the structures of multi-walled nanotubes. In the Russian Doll model, sheets of graphite are arranged in concentric cylinders, e.g., a (0,8) single-walled nanotube (SWNT) within a larger (0,17) single-walled nanotube. In the Parchment model, a single sheet of graphite is rolled in around itself, resembling a scroll of parchment or a rolled newspaper. The interlayer distance in multi-walled nanotubes is close to the distance between graphene layers in graphite, approximately 3.4 Å. The Russian Doll structure is observed more commonly. Its individual shells can be described as SWNTs, which can be metallic or semiconducting. Because of statistical probability and restrictions on the relative diameters of the individual tubes, one of the shells, and thus the whole MWNT, is usually a zero-gap metal.
+
+Double-walled carbon nanotubes (DWNTs) form a special class of nanotubes because their morphology and properties are similar to those of SWNTs but they are more resistant to attacks by chemicals. This is especially important when it is necessary to graft chemical functions to the surface of the nanotubes (functionalization) to add properties to the CNT. Covalent functionalization of SWNTs will break some C=C double bonds, leaving "holes" in the structure on the nanotube and thus modifying both its mechanical and electrical properties. In the case of DWNTs, only the outer wall is modified. DWNT synthesis on the gram-scale by the CCVD technique was first proposed in 2003 from the selective reduction of oxide solutions in methane and hydrogen.
+
+The telescopic motion ability of inner shells and their unique mechanical properties will permit the use of multi-walled nanotubes as the main movable arms in upcoming nanomechanical devices. The retraction force that occurs to telescopic motion is caused by the Lennard-Jones interaction between shells, and its value is about 1.5 nN.
+
+Junctions and crosslinking 
+
+ Junctions between two or more nanotubes have been widely discussed theoretically. Such junctions are quite frequently observed in samples prepared by arc discharge as well as by chemical vapor deposition. The electronic properties of such junctions were first considered theoretically by Lambin et al., who pointed out that a connection between a metallic tube and a semiconducting one would represent a nanoscale heterojunction. Such a junction could therefore form a component of a nanotube-based electronic circuit. The adjacent image shows a junction between two multiwalled nanotubes.
+Junctions between nanotubes and graphene have been considered theoretically and studied experimentally. Nanotube-graphene junctions form the basis of pillared graphene, in which parallel graphene sheets are separated by short nanotubes. Pillared graphene represents a class of three-dimensional carbon nanotube architectures.
+
+Recently, several studies have highlighted the prospect of using carbon nanotubes as building blocks to fabricate three-dimensional macroscopic (>100 nm in all three dimensions) all-carbon devices. Lalwani et al. have reported a novel radical-initiated thermal crosslinking method to fabricate macroscopic, free-standing, porous, all-carbon scaffolds using single- and multi-walled carbon nanotubes as building blocks. These scaffolds possess macro-, micro-, and nano-structured pores, and the porosity can be tailored for specific applications. These 3D all-carbon scaffolds/architectures may be used for the fabrication of the next generation of energy storage, supercapacitors, field emission transistors, high-performance catalysis, photovoltaics, and biomedical devices, implants, and sensors.
+
+Other morphologies 
+
+Carbon nanobuds are a newly created material combining two previously discovered allotropes of carbon: carbon nanotubes and fullerenes. In this new material, fullerene-like "buds" are covalently bonded to the outer sidewalls of the underlying carbon nanotube. This hybrid material has useful properties of both fullerenes and carbon nanotubes. In particular, they have been found to be exceptionally good field emitters. In composite materials, the attached fullerene molecules may function as molecular anchors preventing slipping of the nanotubes, thus improving the composite's mechanical properties.
+
+A carbon peapod is a novel hybrid carbon material which traps fullerene inside a carbon nanotube. It can possess interesting magnetic properties with heating and irradiation. It can also be applied as an oscillator during theoretical investigations and predictions.
+
+In theory, a nanotorus is a carbon nanotube bent into a torus (doughnut shape). Nanotori are predicted to have many unique properties, such as magnetic moments 1000 times larger than that previously expected for certain specific radii. Properties such as magnetic moment, thermal stability, etc. vary widely depending on the radius of the torus and the radius of the tube.
+
+Graphenated carbon nanotubes are a relatively new hybrid that combines graphitic foliates grown along the sidewalls of multiwalled or bamboo style CNTs. The foliate density can vary as a function of deposition conditions (e.g., temperature and time) with their structure ranging from a few layers of graphene (< 10) to thicker, more graphite-like. The fundamental advantage of an integrated graphene-CNT structure is the high surface area three-dimensional framework of the CNTs coupled with the high edge density of graphene. Depositing a high density of graphene foliates along the length of aligned CNTs can significantly increase the total charge capacity per unit of nominal area as compared to other carbon nanostructures.
+
+Cup-stacked carbon nanotubes (CSCNTs) differ from other quasi-1D carbon structures, which normally behave as quasi-metallic conductors of electrons. CSCNTs exhibit semiconducting behavior because of the stacking microstructure of graphene layers.
+
+Properties 
+Many properties of single-walled carbon nanotubes depend significantly on the (n,m) type, and this dependence is non-monotonic (see Kataura plot). In particular, the band gap can vary from zero to about 2 eV and the electrical conductivity can show metallic or semiconducting behavior.
+
+Mechanical 
+
+Carbon nanotubes are the strongest and stiffest materials yet discovered in terms of tensile strength and elastic modulus. This strength results from the covalent sp2 bonds formed between the individual carbon atoms. In 2000, a multiwalled carbon nanotube was tested to have a tensile strength of . (For illustration, this translates into the ability to endure tension of a weight equivalent to  on a cable with cross-section of ). Further studies, such as one conducted in 2008, revealed that individual CNT shells have strengths of up to ≈, which is in agreement with quantum/atomistic models. Because carbon nanotubes have a low density for a solid of 1.3 to 1.4 g/cm3, its specific strength of up to 48,000 kN·m·kg−1 is the best of known materials, compared to high-carbon steel's 154 kN·m·kg−1.
+
+Although the strength of individual CNT shells is extremely high, weak shear interactions between adjacent shells and tubes lead to significant reduction in the effective strength of multiwalled carbon nanotubes and carbon nanotube bundles down to only a few GPa. This limitation has been recently addressed by applying high-energy electron irradiation, which crosslinks inner shells and tubes, and effectively increases the strength of these materials to ≈60 GPa for multiwalled carbon nanotubes and ≈17 GPa for double-walled carbon nanotube bundles. CNTs are not nearly as strong under compression. Because of their hollow structure and high aspect ratio, they tend to undergo buckling when placed under compressive, torsional, or bending stress.
+
+On the other hand, there was evidence that in the radial direction they are rather soft. The first transmission electron microscope observation of radial elasticity suggested that even van der Waals forces can deform two adjacent nanotubes. Later, nanoindentations with an atomic force microscope were performed by several groups to quantitatively measure radial elasticity of multiwalled carbon nanotubes and tapping/contact mode atomic force microscopy was also performed on single-walled carbon nanotubes. Young's modulus of on the order of several GPa showed that CNTs are in fact very soft in the radial direction.
+
+It was reported in 2020, CNT-filled polymer nanocomposites with 4 wt% and 6 wt% loadings are the most optimal concentrations, as they provide a good balance between mechanical properties and resilience of mechanical properties against UV exposure for the offshore umbilical sheathing layer.
+
+Electrical 
+
+Unlike graphene, which is a two-dimensional semimetal, carbon nanotubes are either metallic or semiconducting along the tubular axis. For a given (n,m) nanotube, if n = m, the nanotube is metallic; if n − m is a multiple of 3 and n ≠ m, then the nanotube is quasi-metallic with a very small band gap, otherwise the nanotube is a moderate semiconductor.
+Thus, all armchair (n = m) nanotubes are metallic, and nanotubes (6,4), (9,1), etc. are semiconducting.
+Carbon nanotubes are not semimetallic because the degenerate point (the point where the π [bonding] band meets the π* [anti-bonding] band, at which the energy goes to zero) is slightly shifted away from the K point in the Brillouin zone because of the curvature of the tube surface, causing hybridization between the σ* and π* anti-bonding bands, modifying the band dispersion.
+
+The rule regarding metallic versus semiconductor behavior has exceptions because curvature effects in small-diameter tubes can strongly influence electrical properties. Thus, a (5,0) SWCNT that should be semiconducting in fact is metallic according to the calculations. Likewise, zigzag and chiral SWCNTs with small diameters that should be metallic have a finite gap (armchair nanotubes remain metallic). In theory, metallic nanotubes can carry an electric current density of 4 × 109 A/cm2, which is more than 1,000 times greater than those of metals such as copper, where for copper interconnects, current densities are limited by electromigration. Carbon nanotubes are thus being explored as interconnects and conductivity-enhancing components in composite materials, and many groups are attempting to commercialize highly conducting electrical wire assembled from individual carbon nanotubes. There are significant challenges to be overcome however, such as undesired current saturation under voltage, and the much more resistive nanotube-to-nanotube junctions and impurities, all of which lower the electrical conductivity of the macroscopic nanotube wires by orders of magnitude, as compared to the conductivity of the individual nanotubes.
+
+Because of its nanoscale cross-section, electrons propagate only along the tube's axis. As a result, carbon nanotubes are frequently referred to as one-dimensional conductors. The maximum electrical conductance of a single-walled carbon nanotube is 2G0, where G0 = 2e2/h is the conductance of a single ballistic quantum channel.
+
+Because of the role of the π-electron system in determining the electronic properties of graphene, doping in carbon nanotubes differs from that of bulk crystalline semiconductors from the same group of the periodic table (e.g., silicon). Graphitic substitution of carbon atoms in the nanotube wall by boron or nitrogen dopants leads to p-type and n-type behavior, respectively, as would be expected in silicon. However, some non-substitutional (intercalated or adsorbed) dopants introduced into a carbon nanotube, such as alkali metals and electron-rich metallocenes, result in n-type conduction because they donate electrons to the π-electron system of the nanotube. By contrast, π-electron acceptors such as FeCl3 or electron-deficient metallocenes function as p-type dopants because they draw π-electrons away from the top of the valence band.
+
+Intrinsic superconductivity has been reported, although other experiments found no evidence of this, leaving the claim a subject of debate.
+
+In 2021, Michael Strano, the Carbon P. Dubbs Professor of Chemical Engineering at MIT, published department findings on the use of carbon nanotubes to create an electric current. By immersing the structures in an organic solvent, the liquid drew electrons out of the carbon particles. Strano was quoted as saying, "This allows you to do electrochemistry, but with no wires," and represents a significant breakthrough in the technology. Future applications include powering micro- or nanoscale robots, as well as driving alcohol oxidation reactions, which are important in the chemicals industry.
+
+Crystallographic defects also affect the tube's electrical properties. A common result is lowered conductivity through the defective region of the tube. A defect in metallic armchair-type tubes (which can conduct electricity) can cause the surrounding region to become semiconducting, and single monatomic vacancies induce magnetic properties.
+
+Optical 
+Carbon nanotubes have useful absorption, photoluminescence (fluorescence), and Raman spectroscopy properties. Spectroscopic methods offer the possibility of quick and non-destructive characterization of relatively large amounts of carbon nanotubes. There is a strong demand for such characterization from the industrial point of view: numerous parameters of nanotube synthesis can be changed, intentionally or unintentionally, to alter the nanotube quality, such as the non-tubular carbon content, structure (chirality) of the produced nanotubes, and structural defects. These features then determine nearly all other significant optical, mechanical, and electrical properties.
+
+Carbon nanotube optical properties have been explored for use in applications such as for light-emitting diodes (LEDs) and photo-detectors based on a single nanotube have been produced in the lab. Their unique feature is not the efficiency, which is yet relatively low, but the narrow selectivity in the wavelength of emission and detection of light and the possibility of its fine tuning through the nanotube structure. In addition, bolometer and optoelectronic memory devices have been realised on ensembles of single-walled carbon nanotubes. Nanotube fluorescence has been investigated for the purposes of imaging and sensing in biomedical applications.
+
+Thermal 
+
+All nanotubes are expected to be very good thermal conductors along the tube, exhibiting a property known as "ballistic conduction", but good insulators lateral to the tube axis. Measurements show that an individual SWNT has a room-temperature thermal conductivity along its axis of about 3500 W·m−1·K−1; compare this to copper, a metal well known for its good thermal conductivity, which transmits 385 W·m−1·K−1. An individual SWNT has a room-temperature thermal conductivity lateral to its axis (in the radial direction) of about 1.52 W·m−1·K−1, which is about as thermally conductive as soil. Macroscopic assemblies of nanotubes such as films or fibres have reached up to 1500 W·m−1·K−1 so far. Networks composed of nanotubes demonstrate different values of thermal conductivity, from the level of thermal insulation with the thermal conductivity of 0.1 W·m−1·K−1 to such high values. That is dependent on the amount of contribution to the thermal resistance of the system caused by the presence of impurities, misalignments and other factors. The temperature stability of carbon nanotubes is estimated to be up to 2800 °C in vacuum and about 750 °C in air.
+
+Crystallographic defects strongly affect the tube's thermal properties. Such defects lead to phonon scattering, which in turn increases the relaxation rate of the phonons. This reduces the mean free path and reduces the thermal conductivity of nanotube structures. Phonon transport simulations indicate that substitutional defects such as nitrogen or boron will primarily lead to scattering of high-frequency optical phonons. However, larger-scale defects such as Stone–Wales defects cause phonon scattering over a wide range of frequencies, leading to a greater reduction in thermal conductivity.
+
+Synthesis 
+
+Techniques have been developed to produce nanotubes in sizeable quantities, including arc discharge, laser ablation, chemical vapor deposition (CVD) and high-pressure carbon monoxide disproportionation (HiPCO). Among these arc discharge, laser ablation are batch by batch process, Chemical Vapor Deposition can be used both for batch by batch or continuous processes, and HiPCO is gas phase continuous process. Most of these processes take place in a vacuum or with process gases. The CVD growth method is popular, as it yields high quantity and has a degree of control over diameter, length and morphology. Using particulate catalysts, large quantities of nanotubes can be synthesized by these methods, and industrialisation is well on its way, with several CNT and CNT fibers factory in the world. One problem of CVD processes is the high variability in the nanotube's characteristics  The HiPCO process advances in catalysis and continuous growth are making CNTs more commercially viable. The HiPCO process helps in producing high purity single walled carbon nanotubes in higher quantity. The HiPCO reactor operates at high temperature 900-1100 °C and high pressure ~30-50 bar. It uses carbon monoxide as the carbon source and iron pentacarbonyl or nickel tetracarbonyl as a catalyst. These catalysts provide a nucleation site for the nanotubes to grow, while cheaper iron based catalysts like Ferrocene can be used for CVD process.
+
+Vertically aligned carbon nanotube arrays are also grown by thermal chemical vapor deposition. A substrate (quartz, silicon, stainless steel, carbon fibers, etc.) is coated with a catalytic metal (Fe, Co, Ni) layer. Typically that layer is iron and is deposited via sputtering to a thickness of 1–5 nm. A 10–50 nm underlayer of alumina is often also put down on the substrate first. This imparts controllable wetting and good interfacial properties.
+When the substrate is heated to the growth temperature (~600 to 850 °C), the continuous iron film breaks up into small islands with each island then nucleating a carbon nanotube. The sputtered thickness controls the island size and this in turn determines the nanotube diameter. Thinner iron layers drive down the diameter of the islands and drive down the diameter of the nanotubes grown. The amount of time the metal island can sit at the growth temperature is limited as they are mobile and can merge into larger (but fewer) islands. Annealing at the growth temperature reduces the site density (number of CNT/mm2) while increasing the catalyst diameter.
+
+The as-prepared carbon nanotubes always have impurities such as other forms of carbon (amorphous carbon, fullerene, etc.) and non-carbonaceous impurities (metal used for catalyst). These impurities need to be removed to make use of the carbon nanotubes in applications.
+
+Functionalization 
+CNTs are known to have weak dispersibility in many solvents such as water as a consequence of strong intermolecular p–p interactions. This hinders the processability of CNTs in industrial applications. In order to tackle the issue, various techniques have been developed to modify the surface of CNTs in order to improve their stability and solubility in water. This enhances the processing and manipulation of insoluble CNTs rendering them useful for synthesizing innovative CNT nanofluids with impressive properties that are tunable for a wide range of applications.
+Chemical routes such as covalent functionalization have been studied extensively, which involves the oxidation of CNTs via strong acids (e.g. sulfuric acid, nitric acid, or a mixture of both) in order to set the carboxylic groups onto the surface of the CNTs as the final product or for further modification by esterification or amination. Free radical grafting is a promising technique among covalent functionalization methods, in which alkyl or aryl peroxides, substituted anilines, and diazonium salts are used as the starting agents.
+
+Free radical grafting of macromolecules (as the functional group) onto the surface of CNTs can improve the solubility of CNTs compared to common acid treatments which involve the attachment of small molecules such as hydroxyl onto the surface of CNTs. The solubility of CNTs can be improved significantly by free-radical grafting because the large functional molecules facilitate the dispersion of CNTs in a variety of solvents even at a low degree of functionalization. Recently an innovative environmentally friendly approach has been developed for the covalent functionalization of multi-walled carbon nanotubes (MWCNTs) using clove buds. This approach is innovative and green because it does not use toxic and hazardous acids which are typically used in common carbon nanomaterial functionalization procedures. The MWCNTs are functionalized in one pot using a free radical grafting reaction. The clove-functionalized MWCNTs are then dispersed in water producing a highly stable multi-walled carbon nanotube aqueous suspension (nanofluids).
+
+Modeling 
+
+Carbon nanotubes are modelled in a similar manner as traditional composites in which a reinforcement phase is surrounded by a matrix phase. Ideal models such as cylindrical, hexagonal and square models are common. The size of the micromechanics model is highly function of the studied mechanical properties. The concept of representative volume element (RVE) is used to determine the appropriate size and configuration of computer model to replicate the actual behavior of CNT reinforced nanocomposite. Depending on the material property of interest (thermal, electrical, modulus, creep), one RVE might predict the property better than the alternatives. While the implementation of ideal model is computationally efficient, they do not represent microstructural features observed in scanning electron microscopy of actual nanocomposites. To incorporate realistic modeling, computer models are also generated to incorporate variability such as waviness, orientation and agglomeration of multiwall or single wall carbon nanotubes.
+
+Metrology 
+There are many metrology standards and reference materials available for carbon nanotubes.
+
+For single-wall carbon nanotubes, ISO/TS 10868 describes a measurement method for the diameter, purity, and fraction of metallic nanotubes through optical absorption spectroscopy, while ISO/TS 10797 and ISO/TS 10798 establish methods to characterize the morphology and elemental composition of single-wall carbon nanotubes, using transmission electron microscopy and scanning electron microscopy respectively, coupled with energy dispersive X-ray spectrometry analysis.
+
+NIST SRM 2483 is a soot of single-wall carbon nanotubes used as a reference material for elemental analysis, and was characterized using thermogravimetric analysis, prompt gamma activation analysis, induced neutron activation analysis, inductively coupled plasma mass spectroscopy, resonant Raman scattering, UV-visible-near infrared fluorescence spectroscopy and absorption spectroscopy, scanning electron microscopy, and transmission electron microscopy. The Canadian National Research Council also offers a certified reference material SWCNT-1 for elemental analysis using neutron activation analysis and inductively coupled plasma mass spectroscopy. NIST RM 8281 is a mixture of three lengths of single-wall carbon nanotube.
+
+For multiwall carbon nanotubes, ISO/TR 10929 identifies the basic properties and the content of impurities, while ISO/TS 11888 describes morphology using scanning electron microscopy, transmission electron microscopy, viscometry, and light scattering analysis. ISO/TS 10798 is also valid for multiwall carbon nanotubes.
+
+Chemical modification 
+
+Carbon nanotubes can be functionalized to attain desired properties that can be used in a wide variety of applications. The two main methods of carbon nanotube functionalization are covalent and non-covalent modifications. Because of their apparent hydrophobic nature, carbon nanotubes tend to agglomerate hindering their dispersion in solvents or viscous polymer melts. The resulting nanotube bundles or aggregates reduce the mechanical performance of the final composite. The surface of the carbon nanotubes can be modified to reduce the hydrophobicity and improve interfacial adhesion to a bulk polymer through chemical attachment.
+
+The surface of carbon nanotubes can be chemically modified by coating spinel nanoparticles by hydrothermal synthesis and can be used for water oxidation purposes.
+
+In addition, the surface of carbon nanotubes can be fluorinated or halofluorinated by heating while in contact with a fluoroorganic substance, thereby forming partially fluorinated carbons (so called Fluocar materials) with grafted (halo)fluoroalkyl functionality.
+
+Applications 
+
+ 
+Carbon nanotubes are currently used in multiple industrial and consumer applications. These include battery components, polymer composites, to improve the mechanical, thermal and electrical properties of the bulk product, and as a highly absorptive black paint. Many other applications are under development, including field effect transistors for electronics, high-strength fabrics, biosensors for biomedical and agricultural applications, and many others.
+
+Current industrial applications
+
+ Easton-Bell Sports, Inc. have been in partnership with Zyvex Performance Materials, using CNT technology in a number of their bicycle components – including flat and riser handlebars, cranks, forks, seatposts, stems and aero bars.
+ Amroy Europe Oy manufactures Hybtonite carbon nano-epoxy resins where carbon nanotubes have been chemically activated to bond to epoxy, resulting in a composite material that is 20% to 30% stronger than other composite materials. It has been used for wind turbines, marine paints and a variety of sports gear such as skis, ice hockey sticks, baseball bats, hunting arrows, and surfboards.
+ Surrey NanoSystems synthesizes carbon nanotubes to create vantablack ultra-absorptive black paint.
+ "Gecko tape" (also called "nano tape") is often commercially sold as double-sided adhesive tape. It can be used to hang lightweight items such as pictures and decorative items on smooth walls without punching holes in the wall. The carbon nanotube arrays comprising the synthetic setae leave no residue after removal and can stay sticky in extreme temperatures.
+ Tips for atomic force microscope probes.
+
+Applications under development
+
+Applications of nanotubes in development in academia and industry include:
+
+ Utilizing carbon nanotubes as the channel material of carbon nanotube field-effect transistors.
+ Using carbon nanotubes as a scaffold for diverse microfabrication techniques. 
+ Energy dissipation in self-organized nanostructures under influence of an electric field. 
+ Using carbon nanotubes for environmental monitoring due to their active surface area and their ability to absorb gases.
+Jack Andraka used carbon nanotubes in his pancreatic cancer test. His method of testing won the Intel International Science and Engineering Fair Gordon E. Moore Award in the spring of 2012.
+ The Boeing Company has patented the use of carbon nanotubes for structural health monitoring of composites used in aircraft structures. This technology will greatly reduce the risk of an in-flight failure caused by structural degradation of aircraft.
+ Zyvex Technologies has also built a 54' maritime vessel, the Piranha Unmanned Surface Vessel, as a technology demonstrator for what is possible using CNT technology. CNTs help improve the structural performance of the vessel, resulting in a lightweight 8,000 lb boat that can carry a payload of 15,000 lb over a range of 2,500 miles.
+ IMEC is using carbon nanotubes for pellicles in semiconductor lithography.
+ In tissue engineering, carbon nanotubes have been used as scaffolding for bone growth.
+
+Carbon nanotubes can serve as additives to various structural materials. For instance, nanotubes form a tiny portion of the material(s) in some (primarily carbon fiber) baseball bats, golf clubs, car parts, or damascus steel.
+
+IBM expected carbon nanotube transistors to be used on Integrated Circuits by 2020.
+
+Potential/Future 
+
+The strength and flexibility of carbon nanotubes makes them of potential use in controlling other nanoscale structures, which suggests they will have an important role in nanotechnology engineering. The highest tensile strength of an individual multi-walled carbon nanotube has been tested to be 63 GPa. Carbon nanotubes were found in Damascus steel from the 17th century, possibly helping to account for the legendary strength of the swords made of it. Recently, several studies have highlighted the prospect of using carbon nanotubes as building blocks to fabricate three-dimensional macroscopic (>1mm in all three dimensions) all-carbon devices. Lalwani et al. have reported a novel radical initiated thermal crosslinking method to fabricated macroscopic, free-standing, porous, all-carbon scaffolds using single- and multi-walled carbon nanotubes as building blocks. These scaffolds possess macro-, micro-, and nano- structured pores and the porosity can be tailored for specific applications. These 3D all-carbon scaffolds/architectures may be used for the fabrication of the next generation of energy storage, supercapacitors, field emission transistors, high-performance catalysis, photovoltaics, and biomedical devices and implants.
+
+CNTs are potential candidates for future via and wire material in nano-scale VLSI circuits. Eliminating electromigration reliability concerns that plague today's Cu interconnects, isolated (single and multi-wall) CNTs can carry current densities in excess of 1000 MA/cm2 without electromigration damage.
+
+Single-walled nanotubes are likely candidates for miniaturizing electronics. The most basic building block of these systems is an electric wire, and SWNTs with diameters of an order of a nanometre can be excellent conductors. One useful application of SWNTs is in the development of the first intermolecular field-effect transistors (FET). The first intermolecular logic gate using SWCNT FETs was made in 2001. A logic gate requires both a p-FET and an n-FET. Because SWNTs are p-FETs when exposed to oxygen and n-FETs otherwise, it is possible to expose half of an SWNT to oxygen and protect the other half from it. The resulting SWNT acts as a not logic gate with both p- and n-type FETs in the same molecule.
+
+Large quantities of pure CNTs can be made into a freestanding sheet or film by surface-engineered tape-casting (SETC) fabrication technique which is a scalable method to fabricate flexible and foldable sheets with superior properties. Another reported form factor is CNT fiber (a.k.a. filament) by wet spinning. The fiber is either directly spun from the synthesis pot or spun from pre-made dissolved CNTs. Individual fibers can be turned into a yarn. Apart from its strength and flexibility, the main advantage is making an electrically conducting yarn. The electronic properties of individual CNT fibers (i.e. bundle of individual CNT) are governed by the two-dimensional structure of CNTs. The fibers were measured to have a resistivity only one order of magnitude higher than metallic conductors at 300K. By further optimizing the CNTs and CNT fibers, CNT fibers with improved electrical properties could be developed.
+
+CNT-based yarns are suitable for applications in energy and electrochemical water treatment when coated with an ion-exchange membrane. Also, CNT-based yarns could replace copper as a winding material. Pyrhönen et al. (2015) have built a motor using CNT winding.
+
+Safety and health 
+
+The National Institute for Occupational Safety and Health (NIOSH) is the leading United States federal agency conducting research and providing guidance on the occupational safety and health implications and applications of nanomaterials. Early scientific studies have indicated that nanoscale particles may pose a greater health risk than bulk materials due to a relative increase in surface area per unit mass. Increase in length and diameter of CNT is correlated to increased toxicity and pathological alterations in lung. The biological interactions of nanotubes are not well understood, and the field is open to continued toxicological studies. It is often difficult to separate confounding factors, and since carbon is relatively biologically inert, some of the toxicity attributed to carbon nanotubes may be instead due to residual metal catalyst contamination. In previous studies, only Mitsui-7 was reliably demonstrated to be carcinogenic, although for unclear/unknown reasons. Unlike many common mineral fibers (such as asbestos), most SWCNTs and MWCNTs do not fit the size and aspect-ratio criteria to be classified as respirable fibers. In 2013, given that the long-term health effects have not yet been measured, NIOSH published a Current Intelligence Bulletin detailing the potential hazards and recommended exposure limit for carbon nanotubes and fibers. The U.S. National Institute for Occupational Safety and Health has determined non-regulatory recommended exposure limits (RELs) of 1 μg/m3 for carbon nanotubes and carbon nanofibers as background-corrected elemental carbon as an 8-hour time-weighted average (TWA) respirable mass concentration. Although CNT caused pulmonary inflammation and toxicity in mice, exposure to aerosols generated from sanding of composites containing polymer-coated MWCNTs, representative of the actual end-product, did not exert such toxicity.
+
+As of October 2016, single wall carbon nanotubes have been registered through the European Union's Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulations, based on evaluation of the potentially hazardous properties of SWCNT. Based on this registration, SWCNT commercialization is allowed in the EU up to 10 metric tons. Currently, the type of SWCNT registered through REACH is limited to the specific type of single wall carbon nanotubes manufactured by OCSiAl, which submitted the application.
+
+History
+
+The true identity of the discoverers of carbon nanotubes is a subject of some controversy. A 2006 editorial written by Marc Monthioux and Vladimir Kuznetsov in the journal Carbon described the origin of the carbon nanotube. A large percentage of academic and popular literature attributes the discovery of hollow, nanometre-size tubes composed of graphitic carbon to Sumio Iijima of NEC in 1991. His paper initiated a flurry of excitement and could be credited with inspiring the many scientists now studying applications of carbon nanotubes. Though Iijima has been given much of the credit for discovering carbon nanotubes, it turns out that the timeline of carbon nanotubes goes back much further than 1991.
+
+In 1952, L. V. Radushkevich and V. M. Lukyanovich published clear images of 50 nanometre diameter tubes made of carbon in the Journal of Physical Chemistry Of Russia. This discovery was largely unnoticed, as the article was published in Russian, and Western scientists' access to Soviet press was limited during the Cold War. Monthioux and Kuznetsov mentioned in their Carbon editorial: 
+
+In 1976, Morinobu Endo of CNRS observed hollow tubes of rolled up graphite sheets synthesised by a chemical vapour-growth technique. The first specimens observed would later come to be known as single-walled carbon nanotubes (SWNTs). Endo, in his early review of vapor-phase-grown carbon fibers (VPCF), also reminded us that he had observed a hollow tube, linearly extended with parallel carbon layer faces near the fiber core. This appears to be the observation of multi-walled carbon nanotubes at the center of the fiber. The mass-produced MWCNTs today are strongly related to the VPGCF developed by Endo. In fact, they call it the "Endo-process", out of respect for his early work and patents. In 1979, John Abrahamson presented evidence of carbon nanotubes at the 14th Biennial Conference of Carbon at Pennsylvania State University. The conference paper described carbon nanotubes as carbon fibers that were produced on carbon anodes during arc discharge. A characterization of these fibers was given, as well as hypotheses for their growth in a nitrogen atmosphere at low pressures.
+
+In 1981, a group of Soviet scientists published the results of chemical and structural characterization of carbon nanoparticles produced by a thermocatalytic disproportionation of carbon monoxide. Using TEM images and XRD patterns, the authors suggested that their "carbon multi-layer tubular crystals" were formed by rolling graphene layers into cylinders. They speculated that via this rolling, many different arrangements of graphene hexagonal nets are possible. They suggested two such possible arrangements: circular arrangement (armchair nanotube); and a spiral, helical arrangement (chiral tube).
+
+In 1987, Howard G. Tennent of Hyperion Catalysis was issued a U.S. patent for the production of "cylindrical discrete carbon fibrils" with a "constant diameter between about 3.5 and about 70 nanometers..., length 102 times the diameter, and an outer region of multiple essentially continuous layers of ordered carbon atoms and a distinct inner core...."
+
+Helping to create the initial excitement associated with carbon nanotubes were Iijima's 1991 discovery of multi-walled carbon nanotubes in the insoluble material of arc-burned graphite rods; and Mintmire, Dunlap, and White's independent prediction that if single-walled carbon nanotubes could be made, they would exhibit remarkable conducting properties. Nanotube research accelerated greatly following the independent discoveries by Iijima and Ichihashi at NEC and Bethune et al. at IBM of methods to specifically produce single-walled carbon nanotubes by adding transition-metal catalysts to the carbon in an arc discharge. Thess et al. refined this catalytic method by vaporizing the carbon/transition-metal combination in a high temperature furnace, which greatly improved the yield and purity of the SWNTs and made them widely available for characterization and application experiments. The arc discharge technique, well known to produce the famed Buckminsterfullerene , thus played a role in the discoveries of both multi- and single-wall nanotubes, extending the run of serendipitous discoveries relating to fullerenes.  The discovery of nanotubes remains a contentious issue. Many believe that Iijima's report in 1991 is of particular importance because it brought carbon nanotubes into the awareness of the scientific community as a whole.
+
+In 2020, during archaeological excavation of Keezhadi in Tamil Nadu, India, ~2600-year-old pottery was discovered whose coatings appear to contain carbon nanotubes.  The robust mechanical properties of the nanotubes are partially why the coatings have lasted for so many years, say the scientists.
+
+See also 
+ Buckypaper
+ Carbide-derived carbon
+ Carbon nanocone
+ Carbon nanofibers
+ Carbon nanoscrolls
+ Carbon nanotube computer
+ Carbon nanotubes in photovoltaics
+ Colossal carbon tube
+ Diamond nanothread
+ Filamentous carbon
+ Molecular modelling
+ Nanoflower
+ Ninithi (nanotube modelling software)
+ Optical properties of carbon nanotubes
+ Organic semiconductor
+
+References 
+This article incorporates public domain text from National Institute of Environmental Health Sciences (NIEHS) as quoted.
+
+External links 
+
+ Nanocarbon: From Graphene to Buckyballs. Interactive 3D models of cyclohexane, benzene, graphene, graphite, chiral & non-chiral nanotubes, and C60 Buckyballs - WeCanFigureThisOut.org. 
+ The Nanotube site . Last updated 2013.04.12
+ EU Marie Curie Network CARBIO: Multifunctional carbon nanotubes for biomedical applications
+ C60 and Carbon Nanotubes a short video explaining how nanotubes can be made from modified graphite sheets and the three different types of nanotubes that are formed
+ Learning module for Bandstructure of Carbon Nanotubes and Nanoribbons
+ Selection of free-download articles on carbon nanotubes
+ WOLFRAM Demonstrations Project: Electronic Band Structure of a Single-Walled Carbon Nanotube by the Zone-Folding Method
+ WOLFRAM Demonstrations Project: Electronic Structure of a Single-Walled Carbon Nanotube in Tight-Binding Wannier Representation
+ Electrospinning
+
+Allotropes of carbon
+ 
+Emerging technologies
+Transparent electrodes
+Refractory materials
+Space elevator
+Discovery and invention controversies
+Nanomaterials
+The Czech Republic, also known as Czechia, is a landlocked country in Central Europe. Historically known as Bohemia, it is bordered by Austria to the south, Germany to the west, Poland to the northeast, and Slovakia to the southeast. The Czech Republic has a hilly landscape that covers an area of  with a mostly temperate continental and oceanic climate. The capital and largest city is Prague; other major cities and urban areas include Brno, Ostrava, Plzeň and Liberec.
+
+The Duchy of Bohemia was founded in the late 9th century under Great Moravia. It was formally recognized as an Imperial State of the Holy Roman Empire in 1002 and became a kingdom in 1198. Following the Battle of Mohács in 1526, all of the Crown lands of Bohemia were gradually integrated into the Habsburg monarchy. Nearly a hundred years later, the Protestant Bohemian Revolt led to the Thirty Years' War. After the Battle of White Mountain, the Habsburgs consolidated their rule. With the dissolution of the Holy Roman Empire in 1806, the Crown lands became part of the Austrian Empire.
+
+In the 19th century, the Czech lands became more industrialized, and in 1918 most of it became part of the First Czechoslovak Republic following the collapse of Austria-Hungary after World War I. Czechoslovakia was the only country in Central and Eastern Europe to remain a parliamentary democracy during the entirety of the interwar period. After the Munich Agreement in 1938, Nazi Germany systematically took control over the Czech lands. Czechoslovakia was restored in 1945 and three years later became an Eastern Bloc communist state following a coup d'état in 1948. Attempts to liberalize the government and economy were suppressed by a Soviet-led invasion of the country during the Prague Spring in 1968. In November 1989, the Velvet Revolution ended communist rule in the country and restored democracy. On 31 December 1992, Czechoslovakia was peacefully dissolved, with its constituent states becoming the independent states of the Czech Republic and Slovakia.
+
+The Czech Republic is a unitary parliamentary republic and developed country with an advanced, high-income social market economy. It is a welfare state with a European social model, universal health care and free-tuition university education. It ranks 32nd in the Human Development Index. The Czech Republic is a member of the United Nations, NATO, the European Union, the OECD, the OSCE, the Council of Europe and the Visegrád Group.
+
+Name
+
+The traditional English name "Bohemia" derives from Latin: Boiohaemum, which means "home of the Boii" (a Gallic tribe). The current English name ultimately comes from the Czech word . The name comes from the Slavic tribe () and, according to legend, their leader Čech, who brought them to Bohemia, to settle on Říp Mountain. The etymology of the word  can be traced back to the Proto-Slavic root , meaning "member of the people; kinsman", thus making it cognate to the Czech word  (a person).
+
+The country has been traditionally divided into three lands, namely Bohemia () in the west, Moravia () in the east, and Czech Silesia (; the smaller, south-eastern part of historical Silesia, most of which is located within modern Poland) in the northeast. Known as the lands of the Bohemian Crown since the 14th century, a number of other names for the country have been used, including Czech/Bohemian lands, Bohemian Crown, Czechia and the lands of the Crown of Saint Wenceslaus. When the country regained its independence after the dissolution of the Austro-Hungarian empire in 1918, the new name of Czechoslovakia was coined to reflect the union of the Czech and Slovak nations within one country.
+
+After Czechoslovakia dissolved on the last day of 1992,  was adopted as the Czech short name for the new state and  the Ministry of Foreign Affairs of the Czech Republic recommended Czechia for the English-language equivalent. This form was not widely adopted at the time, leading to the long name Czech Republic being used in English in nearly all circumstances. The Czech government directed use of Czechia as the official English short name in 2016. The short name has been listed by the United Nations and is used by other organizations such as the European Union, NATO, the CIA, Google Maps, and the European Broadcasting Union. In 2022, the American AP Stylebook stated in its entry on the country that "Czechia, the Czech Republic. Both are acceptable. The shorter name Czechia is preferred by the Czech government. If using Czechia, clarify in the story that the country is more widely known in English as the Czech Republic."
+
+History
+
+Prehistory 
+
+Archaeologists have found evidence of prehistoric human settlements in the area, dating back to the Paleolithic era.
+
+In the classical era, as a result of the 3rd century BC Celtic migrations, Bohemia became associated with the Boii. The Boii founded an oppidum near the site of modern Prague. Later in the 1st century, the Germanic tribes of the Marcomanni and Quadi settled there.
+
+Slavs from the Black Sea–Carpathian region settled in the area (their migration was pushed by an invasion of peoples from Siberia and Eastern Europe into their area: Huns, Avars, Bulgars and Magyars). In the sixth century, the Huns had moved westwards into Bohemia, Moravia, and some of present-day Austria and Germany.
+
+During the 7th century, the Frankish merchant Samo, supporting the Slavs fighting against nearby settled Avars, became the ruler of the first documented Slavic state in Central Europe, Samo's Empire. The principality of Great Moravia, controlled by Moymir dynasty, arose in the 8th century. It reached its zenith in the 9th (during the reign of Svatopluk I of Moravia), holding off the influence of the Franks. Great Moravia was Christianized, with a role being played by the Byzantine mission of Cyril and Methodius. They codified the Old Church Slavonic language, the first literary and liturgical language of the Slavs, and the Glagolitic script.
+
+Bohemia 
+
+The Duchy of Bohemia emerged in the late 9th century when it was unified by the Přemyslid dynasty. Bohemia was from 1002 until 1806 an Imperial Estate of the Holy Roman Empire.
+
+In 1212, Přemysl Ottokar I extracted the Golden Bull of Sicily from the emperor, confirming Ottokar and his descendants' royal status; the Duchy of Bohemia was raised to a Kingdom. German immigrants settled in the Bohemian periphery in the 13th century. The Mongols in the invasion of Europe carried their raids into Moravia but were defensively defeated at Olomouc.
+
+After a series of dynastic wars, the House of Luxembourg gained the Bohemian throne.
+
+Efforts for a reform of the church in Bohemia started already in the late 14th century. Jan Hus' followers seceded from some practices of the Roman Church and in the Hussite Wars (1419–1434) defeated five crusades organized against them by Sigismund. During the next two centuries, 90% of the population in Bohemia and Moravia were considered Hussites. The pacifist thinker Petr Chelčický inspired the movement of the Moravian Brethren (by the middle of the 15th century) that completely separated from the Roman Catholic Church.
+
+On 21 December 1421, Jan Žižka, a successful military commander and mercenary, led his group of forces in the Battle of Kutná Hora, resulting in a victory for the Hussites. He is honoured to this day as a national hero.
+
+After 1526 Bohemia came increasingly under Habsburg control as the Habsburgs became first the elected and then in 1627 the hereditary rulers of Bohemia. Between 1583 and 1611 Prague was the official seat of the Holy Roman Emperor Rudolf II and his court.
+
+The Defenestration of Prague and subsequent revolt against the Habsburgs in 1618 marked the start of the Thirty Years' War. In 1620, the rebellion in Bohemia was crushed at the Battle of White Mountain and the ties between Bohemia and the Habsburgs' hereditary lands in Austria were strengthened. The leaders of the Bohemian Revolt were executed in 1621. The nobility and the middle class Protestants had to either convert to Catholicism or leave the country.
+
+The following era of 1620 to the late 18th century became known as the "Dark Age". During the Thirty Years' War, the population of the Czech lands declined by a third through the expulsion of Czech Protestants as well as due to the war, disease and famine. The Habsburgs prohibited all Christian confessions other than Catholicism. The flowering of Baroque culture shows the ambiguity of this historical period.
+Ottoman Turks and Tatars invaded Moravia in 1663. In 1679–1680 the Czech lands faced the Great Plague of Vienna and an uprising of serfs.
+
+There were peasant uprisings influenced by famine. Serfdom was abolished between 1781 and 1848. Several battles of the Napoleonic Wars took place on the current territory of the Czech Republic.
+
+The end of the Holy Roman Empire in 1806 led to degradation of the political status of Bohemia which lost its position of an electorate of the Holy Roman Empire as well as its own political representation in the Imperial Diet. Bohemian lands became part of the Austrian Empire. During the 18th and 19th century the Czech National Revival began its rise, with the purpose to revive Czech language, culture, and national identity. The Revolution of 1848 in Prague, striving for liberal reforms and autonomy of the Bohemian Crown within the Austrian Empire, was suppressed.
+
+It seemed that some concessions would be made also to Bohemia, but in the end, the Emperor Franz Joseph I affected a compromise with Hungary only. The Austro-Hungarian Compromise of 1867 and the never realized coronation of Franz Joseph as King of Bohemia led to a disappointment of some Czech politicians. The Bohemian Crown lands became part of the so-called Cisleithania.
+
+The Czech Social Democratic and progressive politicians started the fight for universal suffrage. The first elections under universal male suffrage were held in 1907.
+
+Czechoslovakia 
+In 1918, during the collapse of the Habsburg monarchy at the end of World War I, the independent republic of Czechoslovakia, which joined the winning Allied powers, was created, with Tomáš Garrigue Masaryk in the lead. This new country incorporated the Bohemian Crown.
+
+The First Czechoslovak Republic comprised only 27% of the population of the former Austria-Hungary, but nearly 80% of the industry, which enabled it to compete with Western industrial states. In 1929 compared to 1913, the gross domestic product increased by 52% and industrial production by 41%. In 1938 Czechoslovakia held 10th place in the world industrial production. Czechoslovakia was the only country in Central and Eastern Europe to remain a liberal democracy throughout the entire 
+interwar period. Although the First Czechoslovak Republic was a unitary state, it provided certain rights to its minorities, the largest being Germans (23.6% in 1921), Hungarians (5.6%) and Ukrainians (3.5%).
+
+Western Czechoslovakia was occupied by Nazi Germany, which placed most of the region into the Protectorate of Bohemia and Moravia. The Protectorate was proclaimed part of the Third Reich, and the president and prime minister were subordinated to Nazi Germany's Reichsprotektor. One Nazi concentration camp was located within the Czech territory at Terezín, north of Prague. The vast majority of the Protectorate's Jews were murdered in Nazi-run concentration camps. The Nazi  called for the extermination, expulsion, Germanization or enslavement of most or all Czechs for the purpose of providing more living space for the German people. There was Czechoslovak resistance to Nazi occupation as well as reprisals against the Czechoslovaks for their anti-Nazi resistance. The German occupation ended on 9 May 1945, with the arrival of the Soviet and American armies and the Prague uprising. Most of Czechoslovakia's German-speakers were forcibly expelled from the country, first as a result of local acts of violence and then under the aegis of an "organized transfer" confirmed by the Soviet Union, the United States, and Great Britain at the Potsdam Conference.
+
+In the 1946 elections, the Communist Party gained 38% of the votes and became the largest party in the Czechoslovak parliament, formed a coalition with other parties, and consolidated power. A coup d'état came in 1948 and a single-party government was formed. For the next 41 years, the Czechoslovak Communist state conformed to Eastern Bloc economic and political features. The Prague Spring political liberalization was stopped by the 1968 Warsaw Pact invasion of Czechoslovakia. Analysts believe that the invasion caused the communist movement to fracture, ultimately leading to the Revolutions of 1989.
+
+Czech Republic 
+
+In November 1989, Czechoslovakia again became a liberal democracy through the Velvet Revolution. However, Slovak national aspirations strengthened (Hyphen War) and on 31 December 1992, the country peacefully split into the independent countries of the Czech Republic and Slovakia. Both countries went through economic reforms and privatizations, with the intention of creating a market economy, as they have been trying to do since 1990, when Czechs and Slovaks still shared the common state. This process was largely successful; in 2006 the Czech Republic was recognized by the World Bank as a "developed country", and in 2009 the Human Development Index ranked it as a nation of "Very High Human Development".
+
+From 1991, the Czech Republic, originally as part of Czechoslovakia and since 1993 in its own right, has been a member of the Visegrád Group and from 1995, the OECD. The Czech Republic joined NATO on 12 March 1999 and the European Union on 1 May 2004. On 21 December 2007 the Czech Republic joined the Schengen Area.
+
+Until 2017, either the centre-left Czech Social Democratic Party or the centre-right Civic Democratic Party led the governments of the Czech Republic. In October 2017, the populist movement ANO 2011, led by the country's second-richest man, Andrej Babiš, won the elections with three times more votes than its closest rival, the Civic Democrats. In December 2017, Czech president Miloš Zeman appointed Andrej Babiš as the new prime minister.
+
+In the 2021 elections, ANO 2011 was narrowly defeated and Petr Fiala became the new prime minister. He formed a government coalition of the alliance SPOLU (Civic Democratic Party, KDU-ČSL and TOP 09) and the alliance of Pirates and Mayors. In January 2023, retired general Petr Pavel won the presidential election, becoming new Czech president to succeed Miloš Zeman. Following the 2022 Russian invasion of Ukraine, the country took in half a million Ukrainian refugees, the largest number per capita in the world.
+
+Geography 
+
+The Czech Republic lies mostly between latitudes 48° and 51° N and longitudes 12° and 19° E.
+
+Bohemia, to the west, consists of a basin drained by the Elbe () and the Vltava rivers, surrounded by mostly low mountains, such as the Krkonoše range of the Sudetes. The highest point in the country, Sněžka at , is located here. Moravia, the eastern part of the country, is also hilly. It is drained mainly by the Morava River, but it also contains the source of the Oder River ().
+
+Water from the Czech Republic flows to three different seas: the North Sea, Baltic Sea, and Black Sea. The Czech Republic also leases the Moldauhafen, a  lot in the middle of the Hamburg Docks, which was awarded to Czechoslovakia by Article 363 of the Treaty of Versailles, to allow the landlocked country a place where goods transported down river could be transferred to seagoing ships. The territory reverts to Germany in 2028.
+
+Phytogeographically, the Czech Republic belongs to the Central European province of the Circumboreal Region, within the Boreal Kingdom. According to the World Wide Fund for Nature, the territory of the Czech Republic can be subdivided into four ecoregions: the Western European broadleaf forests, Central European mixed forests, Pannonian mixed forests, and Carpathian montane conifer forests.
+
+There are four national parks in the Czech Republic. The oldest is Krkonoše National Park (Biosphere Reserve), and the others are Šumava National Park (Biosphere Reserve), Podyjí National Park, and Bohemian Switzerland.
+
+The three historical lands of the Czech Republic (formerly some countries of the Bohemian Crown) correspond with the river basins of the Elbe and the Vltava basin for Bohemia, the Morava one for Moravia, and the Oder river basin for Czech Silesia (in terms of the Czech territory).
+
+Climate 
+
+The Czech Republic has a temperate climate, situated in the transition zone between the oceanic and continental climate types, with warm summers and cold, cloudy and snowy winters. The temperature difference between summer and winter is due to the landlocked geographical position.
+
+Temperatures vary depending on the elevation. In general, at higher altitudes, the temperatures decrease and precipitation increases. The wettest area in the Czech Republic is found around Bílý Potok in Jizera Mountains and the driest region is the Louny District to the northwest of Prague. Another factor is the distribution of the mountains.
+
+At the highest peak of Sněžka (), the average temperature is , whereas in the lowlands of the South Moravian Region, the average temperature is as high as . The country's capital, Prague, has a similar average temperature, although this is influenced by urban factors.
+
+The coldest month is usually January, followed by February and December. During these months, there is snow in the mountains and sometimes in the cities and lowlands. During March, April, and May, the temperature usually increases, especially during April, when the temperature and weather tends to vary during the day. Spring is also characterized by higher water levels in the rivers, due to melting snow with occasional flooding.
+
+The warmest month of the year is July, followed by August and June. On average, summer temperatures are about  higher than during winter. Summer is also characterized by rain and storms.
+
+Autumn generally begins in September, which is still warm and dry. During October, temperatures usually fall below  or  and deciduous trees begin to shed their leaves. By the end of November, temperatures usually range around the freezing point.
+
+The coldest temperature ever measured was in Litvínovice near České Budějovice in 1929, at  and the hottest measured, was at  in Dobřichovice in 2012.
+
+Most rain falls during the summer. Sporadic rainfall is throughout the year (in Prague, the average number of days per month experiencing at least  of rain varies from 12 in September and October to 16 in November) but concentrated rainfall (days with more than  per day) are more frequent in the months of May to August (average around two such days per month). Severe thunderstorms, producing damaging straight-line winds, hail, and occasional tornadoes occur, especially during the summer period.
+
+Environment 
+
+As of 2020, the Czech Republic ranks as the 21st most environmentally conscious country in the world in Environmental Performance Index. It had a 2018 Forest Landscape Integrity Index mean score of 1.71/10, ranking it 160th globally out of 172 countries. The Czech Republic has four National Parks (Šumava National Park, Krkonoše National Park, České Švýcarsko National Park, Podyjí National Park) and 25 Protected Landscape Areas.
+
+Government 
+
+The Czech Republic is a pluralist multi-party parliamentary representative democracy. The Parliament (Parlament České republiky) is bicameral, with the Chamber of Deputies (, 200 members) and the Senate (, 81 members). The members of the Chamber of Deputies are elected for a four-year term by proportional representation, with a 5% election threshold. There are 14 voting districts, identical to the country's administrative regions. The Chamber of Deputies, the successor to the Czech National Council, has the powers and responsibilities of the now defunct federal parliament of the former Czechoslovakia. The members of the Senate are elected in single-seat constituencies by two-round runoff voting for a six-year term, with one-third elected every even year in the autumn. This arrangement is modeled on the U.S. Senate, but each constituency is roughly the same size and the voting system used is a two-round runoff.
+
+The president is a formal head of state with limited and specific powers, who appoints the prime minister, as well the other members of the cabinet on a proposal by the prime minister. From 1993 until 2012, the President of the Czech Republic was selected by a joint session of the parliament for a five-year term, with no more than two consecutive terms (2x Václav Havel, 2x Václav Klaus). Since 2013, the president has been elected directly. Some commentators have argued that, with the introduction of direct election of the President, the Czech Republic has moved away from the parliamentary system and towards a semi-presidential one. The Government's exercise of executive power derives from the Constitution. The members of the government are the Prime Minister, Deputy prime ministers and other ministers. The Government is responsible to the Chamber of Deputies. The Prime Minister is the head of government and wields powers such as the right to set the agenda for most foreign and domestic policy and choose government ministers.
+
+|President
+|Petr Pavel
+|Independent
+|9 March 2023
+|-
+|President of the Senate
+|Miloš Vystrčil
+|ODS
+|19 February 2020
+|-
+|President of the Chamber of Deputies
+|Markéta Pekarová Adamová
+|TOP 09
+|10 November 2021
+|-
+|Prime Minister
+|Petr Fiala
+|ODS
+|28 November 2021
+|}
+
+Law 
+
+The Czech Republic is a unitary state, with a civil law system based on the continental type, rooted in Germanic legal culture. The basis of the legal system is the Constitution of the Czech Republic adopted in 1993. The Penal Code is effective from 2010. A new Civil code became effective in 2014. The court system includes district, county, and supreme courts and is divided into civil, criminal, and administrative branches. The Czech judiciary has a triumvirate of supreme courts. The Constitutional Court consists of 15 constitutional judges and oversees violations of the Constitution by either the legislature or by the government. The Supreme Court is formed of 67 judges and is the court of highest appeal for most legal cases heard in the Czech Republic. The Supreme Administrative Court decides on issues of procedural and administrative propriety. It also has jurisdiction over certain political matters, such as the formation and closure of political parties, jurisdictional boundaries between government entities, and the eligibility of persons to stand for public office. The Supreme Court and the Supreme Administrative Court are both based in Brno, as is the Supreme Public Prosecutor's Office.
+
+Foreign relations 
+
+The Czech Republic has ranked as one of the safest or most peaceful countries for the past few decades. It is a member of the United Nations, the European Union, NATO, OECD, Council of Europe and is an observer to the Organization of American States. The embassies of most countries with diplomatic relations with the Czech Republic are located in Prague, while consulates are located across the country.
+
+The Czech passport is restricted by visas. According to the 2018 Henley & Partners Visa Restrictions Index, Czech citizens have visa-free access to 173 countries, which ranks them 7th along with Malta and New Zealand. The World Tourism Organization ranks the Czech passport 24th. The US Visa Waiver Program applies to Czech nationals.
+
+The Prime Minister and Minister of Foreign Affairs have primary roles in setting foreign policy, although the President also has influence and represents the country abroad. Membership in the European Union and NATO is central to the Czech Republic's foreign policy. The Office for Foreign Relations and Information (ÚZSI) serves as the foreign intelligence agency responsible for espionage and foreign policy briefings, as well as protection of Czech Republic's embassies abroad.
+
+The Czech Republic has ties with Slovakia, Poland and Hungary as a member of the Visegrád Group, as well as with Germany, Israel, the United States and the European Union and its members. After 2020, relations with Asian democratic states, such as Taiwan, are being strengthened. On the contrary, the Czech Republic has long had bad relations with Russia, and from 2021 the Czech Republic appears on Russia's official list of enemy countries. The Czech Republic also has problematic relations with China.
+
+Czech officials have supported dissenters in Belarus, Moldova, Myanmar and Cuba.
+
+Famous Czech diplomats of the past included Jaroslav Lev of Rožmitál, Humprecht Jan Czernin, Count Philip Kinsky of Wchinitz and Tettau, Wenzel Anton, Prince of Kaunitz-Rietberg, Prince Karl Philipp Schwarzenberg, Alois Lexa von Aehrenthal, Ottokar Czernin, Edvard Beneš, Jan Masaryk, Jiří Hájek, Jiří Dienstbier, Michael Žantovský, Petr Kolář, Alexandr Vondra, Prince Karel Schwarzenberg and Petr Pavel.
+
+Military 
+
+The Czech armed forces consist of the Czech Land Forces, the Czech Air Force and of specialized support units. The armed forces are managed by the Ministry of Defence. The President of the Czech Republic is Commander-in-chief of the armed forces. In 2004 the army transformed itself into a fully professional organization and compulsory military service was abolished. The country has been a member of NATO since 12 March 1999. Defence spending is approximately 1.28% of the GDP (2021). The armed forces are charged with protecting the Czech Republic and its allies, promoting global security interests, and contributing to NATO.
+
+Currently, as a member of NATO, the Czech military are participating in the Resolute Support and KFOR operations and have soldiers in Afghanistan, Mali, Bosnia and Herzegovina, Kosovo, Egypt, Israel and Somalia. The Czech Air Force also served in the Baltic states and Iceland. The main equipment of the Czech military includes JAS 39 Gripen multi-role fighters, Aero L-159 Alca combat aircraft, Mi-35 attack helicopters, armored vehicles (Pandur II, OT-64, OT-90, BVP-2) and tanks (T-72 and T-72M4CZ).
+
+The most famous Czech, and therefore Czechoslovak, soldiers and military leaders of the past were Ottokar II of Bohemia, John of Bohemia, Jan Žižka, Albrecht von Wallenstein, Karl Philipp, Prince of Schwarzenberg, Joseph Radetzky von Radetz, Josef Šnejdárek, Heliodor Píka, Ludvík Svoboda, Jan Kubiš, Jozef Gabčík, František Fajtl and Petr Pavel.
+
+Human rights 
+
+Human rights in the Czech Republic are guaranteed by the Charter of Fundamental Rights and Freedoms and international treaties on human rights. Nevertheless, there were cases of human rights violations such as discrimination against Roma children, for which the European Commission asked the Czech Republic to provide an explanation, or the illegal sterilization of Roma women, for which the government apologized.
+
+Prague is the seat of Radio Free Europe/Radio Liberty. Today, the station is based in Hagibor. At the beginning of the 1990s, Václav Havel personally invited her to Czechoslovakia.
+
+People of the same sex can enter into a "registered partnership" in the Czech Republic. Conducting same-sex marriage is not legal under current Czech law.
+
+The best-known Czech activists and supporters of human rights include Berta von Suttner, born in Prague, who won the Nobel Peace Prize for her pacifist struggle, philosopher and the first Czechoslovak president Tomáš Garrigue Masaryk, student Jan Palach, who set himself on fire in 1969 in protest against the Soviet occupation, Karel Schwarzenberg, who was chairman of the International Helsinki Committee for Human Rights between 1984 and 1990, Václav Havel, long-time dissident and later president, sociologist and dissident Jiřina Šiklová and Šimon Pánek, founder and director of the People in Need organization.
+
+Administrative divisions 
+
+Since 2000, the Czech Republic has been divided into thirteen regions (Czech: kraje, singular kraj) and the capital city of Prague. Every region has its own elected regional assembly and a regional governor. In Prague, the assembly and presidential powers are executed by the city council and the mayor.
+
+The older seventy-six districts (okresy, singular okres) including three "statutory cities" (without Prague, which had special status) lost most of their importance in 1999 in an administrative reform; they remain as territorial divisions and seats of various branches of state administration.
+
+The smallest administrative units are obce (municipalities). As of 2021, the Czech Republic is divided into 6,254 municipalities. Cities and towns are also municipalities. The capital city of Prague is a region and municipality at the same time.
+
+Economy 
+
+The Czech Republic has a developed, high-income export-oriented social market economy based in services, manufacturing and innovation, that maintains a welfare state and the European social model. The Czech Republic participates in the European Single Market as a member of the European Union and is therefore a part of the economy of the European Union, but uses its own currency, the Czech koruna, instead of the euro. It has a per capita GDP rate that is 91% of the EU average and is a member of the OECD. Monetary policy is conducted by the Czech National Bank, whose independence is guaranteed by the Constitution. The Czech Republic ranks 12th in the UN inequality-adjusted human development and 24th in World Bank Human Capital Index. It was described by The Guardian as "one of Europe's most flourishing economies".
+
+, the country's GDP per capita at purchasing power parity is $51,329 and $29,856 at nominal value. According to Allianz A.G., in 2018 the country was an MWC (mean wealth country), ranking 26th in net financial assets. The country experienced a 4.5% GDP growth in 2017. The 2016 unemployment rate was the lowest in the EU at 2.4%, and the 2016 poverty rate was the second lowest of OECD members. Czech Republic ranks 27th in the 2021 Index of Economic Freedom, 31st in the 2023 Global Innovation Index, down from 24th in the 2016, 29th in the Global Competitiveness Report, and 25th in the Global Enabling Trade Report.
+The Czech Republic has a diverse economy that ranks 7th in the 2016 Economic Complexity Index. The industrial sector accounts for 37.5% of the economy, while services account for 60% and agriculture for 2.5%. The largest trading partner for both export and import is Germany and the EU in general. Dividends worth CZK 270 billion were paid to the foreign owners of Czech companies in 2017, which has become a political issue. The country has been a member of the Schengen Area since 1 May 2004, having abolished border controls, completely opening its borders with all of its neighbors on 21 December 2007.
+
+Industry 
+
+ the largest companies by revenue in the Czech Republic were: automobile manufacturer Škoda Auto, utility company ČEZ Group, conglomerate Agrofert, energy trading company EPH, oil processing company Unipetrol, electronics manufacturer Foxconn CZ and steel producer Moravia Steel. Other Czech transportation companies include: Škoda Transportation (tramways, trolleybuses, metro), Tatra (heavy trucks, the second oldest car maker in the world), Avia (medium trucks), Karosa and SOR Libchavy (buses), Aero Vodochody (military aircraft), Let Kunovice (civil aircraft), Zetor (tractors), Jawa Moto (motorcycles) and Čezeta (electric scooters).
+
+Škoda Transportation is the fourth largest tram producer in the world; nearly one third of all trams in the world come from Czech factories. The Czech Republic is also the world's largest vinyl records manufacturer, with GZ Media producing about 6 million pieces annually in Loděnice. Česká zbrojovka is among the ten largest firearms producers in the world and five who produce automatic weapons.
+
+In the food industry, Czech companies include Agrofert, Kofola and Hamé.
+
+Energy 
+
+Production of Czech electricity exceeds consumption by about 10 TWh per year, the excess being exported. Nuclear power presently provides about 30 percent of the total power needs, its share is projected to increase to 40 percent. In 2005, 65.4 percent of electricity was produced by steam and combustion power plants (mostly coal); 30 percent by nuclear plants; and 4.6 percent came from renewable sources, including hydropower. The largest Czech power resource is Temelín Nuclear Power Station, with another nuclear power plant in Dukovany.
+
+The Czech Republic is reducing its dependence on highly polluting low-grade brown coal as a source of energy. Natural gas is purchased from Norwegian companies and as liquefied gas LNG from the Netherlands and Belgium. In the past, three-quarters of gas supplies came from Russia, but after the outbreak of the war in Ukraine, the government gradually stopped these supplies. Gas consumption (approx. 100 TWh in 2003–2005) is almost double electricity consumption. South Moravia has small oil and gas deposits.
+
+Transportation infrastructure 
+
+ the road network in the Czech Republic is  long, out of which  are motorways. The speed limit is  within towns,  outside of towns and  on motorways.
+
+The Czech Republic has one of the densest rail networks in the world.  the country has  of lines. Of that number,  is electrified,  are single-line tracks and  are double and multiple-line tracks. The length of tracks is , out of which  is electrified.
+
+České dráhy (the Czech Railways) is the main railway operator in the country, with about 180 million passengers carried yearly. Maximum speed is limited to .
+
+Václav Havel Airport in Prague is the main international airport in the country. In 2019, it handled 17.8 million passengers. In total, the Czech Republic has 91 airports, six of which provide international air services. The public international airports are in Brno, Karlovy Vary, Mnichovo Hradiště, Mošnov (near Ostrava), Pardubice and Prague. The non-public international airports capable of handling airliners are in Kunovice and Vodochody.
+
+Russia, via pipelines through Ukraine and to a lesser extent, Norway, via pipelines through Germany, supply the Czech Republic with liquid and natural gas.
+
+Communications and IT 
+
+The Czech Republic ranks in the top 10 countries worldwide with the fastest average internet speed. By the beginning of 2008, there were over 800 mostly local WISPs, with about 350,000 subscribers in 2007. Plans based on either GPRS, EDGE, UMTS or CDMA2000 are being offered by all three mobile phone operators (T-Mobile, O2, Vodafone) and internet provider U:fon. Government-owned Český Telecom slowed down broadband penetration. At the beginning of 2004, local-loop unbundling began and alternative operators started to offer ADSL and also SDSL. This and later privatization of Český Telecom helped drive down prices.
+
+On 1 July 2006, Český Telecom was acquired by globalized company (Spain-owned) Telefónica group and adopted the new name Telefónica O2 Czech Republic. , VDSL and ADSL2+ are offered in variants, with download speeds of up to 50 Mbit/s and upload speeds of up to 5 Mbit/s. Cable internet is gaining more popularity with its higher download speeds ranging from 50 Mbit/s to 1 Gbit/s.
+
+Two computer security companies, Avast and AVG, were founded in the Czech Republic. In 2016, Avast led by Pavel Baudiš bought rival AVG for US$1.3 billion, together at the time, these companies had a user base of about 400 million people and 40% of the consumer market outside of China. Avast is the leading provider of antivirus software, with a 20.5% market share.
+
+Tourism 
+
+Prague is the fifth most visited city in Europe after London, Paris, Istanbul and Rome. In 2001, the total earnings from tourism reached 118 billion CZK, making up 5.5% of GNP and 9% of overall export earnings. The industry employs more than 110,000 people – over 1% of the population.
+Guidebooks and tourists reporting overcharging by taxi drivers and pickpocketing problems are mainly in Prague, though the situation has improved recently. Since 2005, Prague's mayor, Pavel Bém, has worked to improve this reputation by cracking down on petty crime and, aside from these problems, Prague is a "safe" city. The Czech Republic's crime rate is described by the United States State department as "low".
+
+One of the tourist attractions in the Czech Republic is the Nether district Vítkovice in Ostrava.
+
+The Czech Republic boasts 16 UNESCO World Heritage Sites, 3 of them are transnational. , further 14 sites are on the tentative list.
+
+Architectural heritage is an object of interest to visitors – it includes castles and châteaux from different historical epoques, namely Karlštejn Castle, Český Krumlov and the Lednice–Valtice Cultural Landscape. There are 12 cathedrals and 15 churches elevated to the rank of basilica by the Pope, calm monasteries.
+
+Away from the towns, areas such as Bohemian Paradise, Bohemian Forest and the Giant Mountains attract visitors seeking outdoor pursuits. There is a number of beer festivals.
+
+The country is also known for its various museums. Puppetry and marionette exhibitions are with a number of puppet festivals throughout the country. Aquapalace Prague in Čestlice is the largest water park in the country.
+
+Science 
+
+The Czech lands have a long and well-documented history of scientific innovation. Today, the Czech Republic has a highly sophisticated, developed, high-performing, innovation-oriented scientific community supported by the government, industry, and leading universities. Czech scientists are embedded members of the global scientific community. They contribute annually to multiple international academic journals and collaborate with their colleagues across boundaries and fields. The Czech Republic was ranked 24th in the Global Innovation Index in 2020 and 2021, up from 26th in 2019.
+
+Historically, the Czech lands, especially Prague, have been the seat of scientific discovery going back to early modern times, including Tycho Brahe, Nicolaus Copernicus, and Johannes Kepler. In 1784 the scientific community was first formally organized under the charter of the Royal Czech Society of Sciences. Currently, this organization is known as the Czech Academy of Sciences. Similarly, the Czech lands have a well-established history of scientists, including Nobel laureates biochemists Gerty and Carl Ferdinand Cori, chemists Jaroslav Heyrovský and Otto Wichterle, physicists Ernst Mach and Peter Grünberg, physiologist Jan Evangelista Purkyně and chemist Antonín Holý. Sigmund Freud, the founder of psychoanalysis, was born in Příbor, Gregor Mendel, the founder of genetics, was born in Hynčice and spent most of his life in Brno, logician and mathematician Kurt Gödel was born in Brno.
+
+Historically, most scientific research was recorded in Latin, but from the 18th century onwards increasingly in German and later in Czech, archived in libraries supported and managed by religious groups and other denominations as evidenced by historical locations of international renown and heritage such as the Strahov Monastery and the Clementinum in Prague. Increasingly, Czech scientists publish their work and that of their history in English.
+
+The current important scientific institution is the already mentioned Academy of Sciences of the Czech Republic, the CEITEC Institute in Brno or the HiLASE and Eli Beamlines centers with the most powerful laser in the world in Dolní Břežany. Prague is the seat of the administrative center of the GSA Agency operating the European navigation system Galileo and the European Union Agency for the Space Programme.
+
+Demographics 
+
+The total fertility rate (TFR) in 2020 was estimated at 1.71 children per woman, which is below the replacement rate of 2.1. The Czech Republic's population has an average age of 43.3 years. The life expectancy in 2021 was estimated to be 79.5 years (76.55 years male, 82.61 years female). About 77,000 people immigrate to the Czech Republic annually. Vietnamese immigrants began settling in the country during the Communist period, when they were invited as guest workers by the Czechoslovak government. In 2009, there were about 70,000 Vietnamese in the Czech Republic. Most decide to stay in the country permanently.
+
+According to results of the 2021 census, the majority of the inhabitants of the Czech Republic are Czechs (57.3%), followed by Moravians (3.4%), Slovaks (0.9%), Ukrainians (0.7%), Viets (0.3%), Poles (0.3%), Russians (0.2%), Silesians (0.1%) and Germans (0.1%). Another 4.0% declared combination of two nationalities (3.6% combination of Czech and other nationality). As the 'nationality' was an optional item, a number of people left this field blank (31.6%). According to some estimates, there are about 250,000 Romani people in the Czech Republic. The Polish minority resides mainly in the Trans-Olza region.
+
+There were 658,564 foreigners residing in the country in 2021, according to the Czech Statistical Office, with the largest groups being Ukrainian (22%), Slovak (22%), Vietnamese (12%), Russian (7%) and German (4%). Most of the foreign population lives in Prague (37.3%) and Central Bohemia Region (13.2%).
+
+The Jewish population of Bohemia and Moravia, 118,000 according to the 1930 census, was nearly annihilated by the Nazi Germans during the Holocaust. There were approximately 3,900 Jews in the Czech Republic in 2021. The former Czech prime minister, Jan Fischer, is of Jewish faith.
+
+Nationality of residents, who answered the question in the Census 2021:
+
+Largest cities
+
+Religion 
+
+About 75% to 79% of residents of the Czech Republic do not declare having any religion or faith in surveys, and the proportion of convinced atheists (30%) is the third highest in the world behind those of China (47%) and Japan (31%). The Czech people have been historically characterized as "tolerant and even indifferent towards religion". The religious identity of the country has changed drastically since the first half of the 20th century, when more than 90% of Czechs were Christians.
+
+Christianization in the 9th and 10th centuries introduced Catholicism. After the Bohemian Reformation, most Czechs became followers of Jan Hus, Petr Chelčický and other regional Protestant Reformers. Taborites and Utraquists were Hussite groups. Towards  the end of the Hussite Wars, the Utraquists changed sides and allied with the Catholic Church. Following the joint Utraquist—Catholic victory, Utraquism was accepted as a distinct form of Christianity to be practiced in Bohemia by the Catholic Church while all remaining Hussite groups were prohibited. After the Reformation, some Bohemians went with the teachings of Martin Luther, especially Sudeten Germans. In the wake of the Reformation, Utraquist Hussites took a renewed increasingly anti-Catholic stance, while some of the defeated Hussite factions were revived. After the Habsburgs regained control of Bohemia, the whole population was forcibly converted to Catholicism—even the Utraquist Hussites. Going forward, Czechs have become more wary and pessimistic of religion as such. A history of resistance to the Catholic Church followed. It suffered a schism with the neo-Hussite Czechoslovak Hussite Church in 1920, lost the bulk of its adherents during the Communist era and continues to lose in the modern, ongoing secularization. Protestantism never recovered after the Counter-Reformation was introduced by the Austrian Habsburgs in 1620. Prior to the Holocaust, the Czech Republic had a sizable Jewish community of around 100,000. There are many historically important and culturally relevant Synagogues in the Czech Republic such as Europe's oldest active Synagogue, The Old New Synagogue and the second largest Synagogue in Europe, the Great Synagogue (Plzeň). The Holocaust decimated Czech Jewry and the Jewish population as of 2021 is 3,900.
+
+According to the 2011 census, 34% of the population stated they had no religion, 10.3% was Catholic, 0.8% was Protestant (0.5% Czech Brethren and 0.4% Hussite), and 9% followed other forms of religion both denominational or not (of which 863 people answered they are Pagan). 45% of the population did not answer the question about religion. From 1991 to 2001 and further to 2011 the adherence to Catholicism decreased from 39% to 27% and then to 10%; Protestantism similarly declined from 3.7% to 2% and then to 0.8%. The Muslim population is estimated to be 20,000 representing 0.2% of the population.
+
+The proportion of religious believers varies significantly across the country, from 55% in Zlín Region to 16% in Ústí nad Labem Region.
+
+Education and health care 
+
+Education in the Czech Republic is compulsory for nine years and citizens have access to a free-tuition university education, while the average number of years of education is 13.1. Additionally, the Czech Republic has a "relatively equal" educational system in comparison with other countries in Europe. Founded in 1348, Charles University was the first university in Central Europe. Other major universities in the country are Masaryk University, Czech Technical University, Palacký University, Academy of Performing Arts and University of Economics.
+
+The Programme for International Student Assessment, coordinated by the OECD, currently ranks the Czech education system as the 15th most successful in the world, higher than the OECD average. The UN Education Index ranks the Czech Republic 10th  (positioned behind Denmark and ahead of South Korea).
+
+Health care in the Czech Republic is similar in quality to that of other developed nations. The Czech universal health care system is based on a compulsory insurance model, with fee-for-service care funded by mandatory employment-related insurance plans. According to the 2016 Euro health consumer index, a comparison of healthcare in Europe, the Czech healthcare is 13th, ranked behind Sweden and two positions ahead of the United Kingdom.
+
+Culture
+
+Art 
+
+Venus of Dolní Věstonice is the treasure of prehistoric art. Theodoric of Prague was a painter in the Gothic era who decorated the castle Karlstejn. In the Baroque era, there were Wenceslaus Hollar, Jan Kupecký, Karel Škréta, Anton Raphael Mengs or Petr Brandl, sculptors Matthias Braun and Ferdinand Brokoff. In the first half of the 19th century, Josef Mánes joined the romantic movement. In the second half of the 19th century had the main say the so-called "National Theatre generation": sculptor Josef Václav Myslbek and painters Mikoláš Aleš, Václav Brožík, Vojtěch Hynais or Julius Mařák. At the end of the century came a wave of Art Nouveau. Alfons Mucha became the main representative. He is known for Art Nouveau posters and his cycle of 20 large canvases named the Slav Epic, which depicts the history of Czechs and other Slavs.
+, the Slav Epic can be seen in the Veletržní Palace of the National Gallery in Prague, which manages the largest collection of art in the Czech Republic. Max Švabinský was another Art nouveau painter. The 20th century brought an avant-garde revolution. In the Czech lands mainly expressionist and cubist: Josef Čapek, Emil Filla, Bohumil Kubišta, Jan Zrzavý. Surrealism emerged particularly in the work of Toyen, Josef Šíma and Karel Teige. In the world, however, he pushed mainly František Kupka, a pioneer of abstract painting. As illustrators and cartoonists in the first half of the 20th century gained fame Josef Lada, Zdeněk Burian or Emil Orlík. Art photography has become a new field (František Drtikol, Josef Sudek, later Jan Saudek or Josef Koudelka).
+
+The Czech Republic is known for its individually made, mouth-blown, and decorated Bohemian glass.
+
+Architecture 
+
+The earliest preserved stone buildings in Bohemia and Moravia date back to the time of the Christianization in the 9th and 10th centuries. Since the Middle Ages, the Czech lands have been using the same architectural styles as most of Western and Central Europe. The oldest still standing churches were built in the Romanesque style. During the 13th century, it was replaced by the Gothic style. In the 14th century, Emperor Charles IV invited architects from France and Germany, Matthias of Arras and Peter Parler, to his court in Prague. During the Middle Ages, some fortified castles were built by the king and aristocracy, as well as some monasteries.
+
+The Renaissance style penetrated the Bohemian Crown in the late 15th century when the older Gothic style started to be mixed with Renaissance elements. An example of pure Renaissance architecture in Bohemia is the Queen Anne's Summer Palace, which was situated in the garden of Prague Castle. Evidence of the general reception of the Renaissance in Bohemia, involving an influx of Italian architects, can be found in spacious chateaus with arcade courtyards and geometrically arranged gardens. Emphasis was placed on comfort, and buildings that were built for entertainment purposes also appeared.
+
+In the 17th century, the Baroque style spread throughout the Crown of Bohemia.
+
+In the 18th century, Bohemia produced an architectural peculiarity – the Baroque Gothic style, a synthesis of the Gothic and Baroque styles.
+
+During the 19th century stands the revival architectural styles. Some churches were restored to their presumed medieval appearance and there were constructed buildings in the Neo-Romanesque, Neo-Gothic and Neo-Renaissance styles. At the turn of the 19th and 20th centuries, the new art style appeared in the Czech lands – Art Nouveau.
+
+Bohemia contributed an unusual style to the world's architectural heritage when Czech architects attempted to transpose the Cubism of painting and sculpture into architecture.
+
+Between World Wars I and II, Functionalism, with its sober, progressive forms, took over as the main architectural style.
+
+After World War II and the Communist coup in 1948, art in Czechoslovakia became Soviet-influenced. The Czechoslovak avant-garde artistic movement is known as the Brussels style came up in the time of political liberalization of Czechoslovakia in the 1960s. Brutalism dominated in the 1970s and 1980s.
+
+The Czech Republic is not shying away from the more modern trends of international architecture, an example is the Dancing House (Tančící dům) in Prague, Golden Angel in Prague or Congress Centre in Zlín.
+
+Influential Czech architects include Peter Parler, Benedikt Rejt, Jan Santini Aichel, Kilian Ignaz Dientzenhofer, Josef Fanta, Josef Hlávka, Josef Gočár, Pavel Janák, Jan Kotěra, Věra Machoninová, Karel Prager, Karel Hubáček, Jan Kaplický, Eva Jiřičná or Josef Pleskot.
+
+Literature 
+
+The literature from the area of today's Czech Republic was mostly written in Czech, but also in Latin and German or even Old Church Slavonic. Franz Kafka, although a competent user of Czech, wrote in his mother tongue, German. His included: (The Trial and The Castle).
+
+In the second half of the 13th century, the royal court in Prague became one of the centers of German Minnesang and courtly literature. The Czech German-language literature can be seen in the first half of the 20th century.
+
+Bible translations played a role in the development of Czech literature. The oldest Czech translation of the Psalms originated in the late 13th century and the first complete Czech translation of the Bible was finished around 1360. The first complete printed Czech Bible was published in 1488. The first complete Czech Bible translation from the original languages was published between 1579 and 1593. The Codex Gigas from the 12th century is the largest extant medieval manuscript in the world.
+
+Czech-language literature can be divided into several periods: the Middle Ages; the Hussite period; the Renaissance humanism; the Baroque period; the Enlightenment and Czech reawakening in the first half of the 19th century, modern literature in the second half of the 19th century; the avant-garde of the interwar period; the years under Communism; and the Czech Republic.
+
+The antiwar comedy novel The Good Soldier Švejk is the most translated Czech book in history.
+
+The international literary award the Franz Kafka Prize is awarded in the Czech Republic.
+
+The Czech Republic has the densest network of libraries in Europe.
+
+Czech literature and culture played a role on at least two occasions when Czechs lived under oppression and political activity was suppressed. On both of these occasions, in the early 19th century and then again in the 1960s, the Czechs used their cultural and literary effort to strive for political freedom, establishing a confident, politically aware nation.
+
+Music 
+
+The musical tradition of the Czech lands arose from the first church hymns, whose first evidence is suggested at the break of the 10th and 11th centuries. Some pieces of Czech music include two chorales, which in their time performed the function of anthems: "Lord, Have Mercy on Us" and the hymn "Saint Wenceslaus" or "Saint Wenceslaus Chorale". The authorship of the anthem "Lord, Have Mercy on Us" is ascribed by some historians to Saint Adalbert of Prague (sv.Vojtěch), bishop of Prague, living between 956 and 997.
+
+The wealth of musical culture lies in the classical music tradition during all historical periods, especially in the Baroque, Classicism, Romantic, modern classical music and in the traditional folk music of Bohemia, Moravia and Silesia. Since the early era of artificial music, Czech musicians and composers have been influenced the folk music of the region and dance.
+
+Czech music can be considered to have been "beneficial" in both the European and worldwide context, several times co-determined or even determined a newly arriving era in musical art, above all of Classical era, as well as by original attitudes in Baroque, Romantic and modern classical music. Some Czech musical works are The Bartered Bride, New World Symphony, Sinfonietta and Jenůfa.
+
+A music festival in the country is Prague Spring International Music Festival of classical music, a permanent showcase for performing artists, symphony orchestras and chamber music ensembles of the world.
+
+Theatre 
+
+The roots of Czech theatre can be found in the Middle Ages, especially in the cultural life of the Gothic period. In the 19th century, the theatre played a role in the national awakening movement and later, in the 20th century, it became a part of modern European theatre art. The original Czech cultural phenomenon came into being at the end of the 1950s. This project called Laterna magika, resulting in productions that combined theater, dance, and film in a poetic manner, considered the first multimedia art project in an international context.
+
+A drama is Karel Čapek's play R.U.R., which introduced the word "robot".
+
+The country has a tradition of puppet theater. In 2016, Czech and Slovak Puppetry was included on the UNESCO Intangible Cultural Heritage Lists.
+
+Film 
+
+The tradition of Czech cinematography started in the second half of the 1890s. Peaks of the production in the era of silent movies include the historical drama The Builder of the Temple and the social and erotic drama Erotikon directed by Gustav Machatý. The early Czech sound film era was productive, above all in mainstream genres, with the comedies of Martin Frič or Karel Lamač. There were dramatic movies sought internationally.
+
+Hermína Týrlová was a prominent Czech animator, screenwriter, and film director. She was often called the mother of Czech animation. Over the course of her career, she produced over 60 animated children's short films using puppets and the technique of stop motion animation.
+
+Before the German occupation, in 1933, filmmaker and animator  established the first Czech animation studio "IRE Film" with her husband Karel Dodal.
+
+After the period of Nazi occupation and early communist official dramaturgy of socialist realism in movies at the turn of the 1940s and 1950s with fewer exceptions such as Krakatit or Men without wings (awarded by  in 1946), an era of the Czech film began with animated films, performed in anglophone countries under the name "The Fabulous World of Jules Verne" from 1958, which combined acted drama with animation, and Jiří Trnka, the founder of the modern puppet film. This began a tradition of animated films (Mole etc.).
+
+In the 1960s, the hallmark of Czechoslovak New Wave's films were improvised dialogues, black and absurd humor and the occupation of non-actors. Directors are trying to preserve natural atmosphere without refinement and artificial arrangement of scenes. A personality of the 1960s and the beginning of the 1970s with original manuscript and psychological impact is František Vláčil. Another international author is Jan Švankmajer, a filmmaker and artist whose work spans several media. He is a self-labeled surrealist known for animations and features.
+
+The Barrandov Studios in Prague are the largest film studios with film locations in the country. Filmmakers have come to Prague to shoot scenery no longer found in Berlin, Paris and Vienna. The city of Karlovy Vary was used as a location for the 2006 James Bond film Casino Royale.
+
+The Czech Lion is the highest Czech award for film achievement. Karlovy Vary International Film Festival is one of the film festivals that have been given competitive status by the FIAPF. Other film festivals held in the country include Febiofest, Jihlava International Documentary Film Festival, One World Film Festival, Zlín Film Festival and Fresh Film Festival.
+
+Media 
+
+Czech journalists and media enjoy a degree of freedom. There are restrictions against writing in support of Nazism, racism or violating Czech law. The Czech press was ranked as the 40th most free press in the World Freedom Index by Reporters Without Borders in 2021. Radio Free Europe/Radio Liberty has its headquarters in Prague.
+
+The national public television service is Czech Television that operates the 24-hour news channel ČT24 and the news website ct24.cz. As of 2020, Czech Television is the most watched television, followed by private televisions TV Nova and Prima TV. However, TV Nova has the most watched main news program and prime time program. Other public services include the Czech Radio and the Czech News Agency.
+
+The best-selling daily national newspapers in 2020/21 are Blesk (average 703,000 daily readers), Mladá fronta DNES (average 461,000 daily readers), Právo (average 182,000 daily readers), Lidové noviny (average 163,000 daily readers) and Hospodářské noviny (average 162,000 daily readers).
+
+Most Czechs (87%) read their news online, with Seznam.cz, iDNES.cz, Novinky.cz, iPrima.cz and Seznam Zprávy.cz being the most visited as of 2021.
+
+Cuisine 
+
+Czech cuisine is marked by an emphasis on meat dishes with pork, beef, and chicken. Goose, duck, rabbit, and venison are served. Fish is less common, with the occasional exception of fresh trout and carp, which is served at Christmas.
+
+There is a variety of local sausages, wurst, pâtés, and smoked and cured meats. Czech desserts include a variety of whipped cream, chocolate, and fruit pastries and tarts, crêpes, creme desserts and cheese, poppy-seed-filled and other types of traditional cakes such as buchty, koláče and štrúdl.
+
+Czech beer has a history extending more than a millennium; the earliest known brewery existed in 993. Today the Czech Republic has the highest beer consumption per capita in the world. The pilsner style beer (pils) originated in Plzeň, where the world's first blond lager Pilsner Urquell is still produced. It has served as the inspiration for more than two-thirds of the beer produced in the world today. The city of České Budějovice has similarly lent its name to its beer, known as Budweiser Budvar.
+
+The South Moravian region has been producing wine since the Middle Ages; about 94% of vineyards in the Czech Republic are Moravian. Aside from beer, slivovitz and wine, the Czech Republic also produces two liquors, Fernet Stock and Becherovka. Kofola is a non-alcoholic domestic cola soft drink which competes with Coca-Cola and Pepsi.
+
+Sport 
+
+The two leading sports in the Czech Republic are football and ice hockey. The most watched sporting events are the Olympic tournament and World Championships of ice hockey. Other most popular sports include tennis, volleyball, floorball, golf, ball hockey, athletics, basketball and skiing.
+
+The country has won 15 gold medals in the Summer Olympics and nine in the Winter Games. (See Olympic history.) The Czech ice hockey team won the gold medal at the 1998 Winter Olympics and has won twelve gold medals at the World Championships, including three straight from 1999 to 2001.
+
+The Škoda Motorsport is engaged in competition racing since 1901 and has gained a number of titles with various vehicles around the world. MTX automobile company was formerly engaged in the manufacture of racing and formula cars since 1969.
+
+Hiking is a popular sport. The word for 'tourist' in Czech, turista, also means 'trekker' or 'hiker'. For hikers, thanks to the more than 120-year-old tradition, there is the Czech Hiking Markers System of trail blazing, that has been adopted by countries worldwide. There is a network of around 40,000 km of marked short- and long-distance trails crossing the whole country and all the Czech mountains.
+
+See also 
+
+ List of Czech Republic-related topics
+ Outline of the Czech Republic
+
+Notes
+
+References
+
+Citations
+
+General sources
+
+Further reading 
+ 
+ Hochman, Jiří (1998). Historical dictionary of the Czech State. Scarecrow Press. 
+ Bryant, Chad. Prague: Belonging and the Modern City. Cambridge MA: Harvard University Press, 2021.
+
+External links 
+ Governmental website
+ Presidential website
+ Senate
+ Portal of the Public Administration
+ #VisitCzechia – official tourist portal of the Czech Republic
+ Czechia – Central Intelligence Agency: The World Factbook
+ 
+ 
+
+ 
+Central Europe
+Countries in Europe
+Landlocked countries
+Member states of NATO
+Member states of the European Union
+Member states of the United Nations
+Member states of the Three Seas Initiative
+Republics
+Member states of the Council of Europe
+States and territories established in 1993
+OECD members
+Czechoslovakia (; Czech and , Česko-Slovensko) was a landlocked state in Central Europe, created in 1918, when it declared its independence from Austria-Hungary. In 1938, after the Munich Agreement, the Sudetenland became part of Nazi Germany, while the country lost further territories to Hungary and Poland (Carpathian Ruthenia to Hungary and Zaolzie to Poland). Between 1939 and 1945, the state ceased to exist, as Slovakia proclaimed its independence and the remaining territories in the east became part of Hungary, while in the remainder of the Czech Lands, the German Protectorate of Bohemia and Moravia was proclaimed. In 1939, after the outbreak of World War II, former Czechoslovak President Edvard Beneš formed a government-in-exile and sought recognition from the Allies.
+
+After World War II, Czechoslovakia was reestablished under its pre-1938 borders, with the exception of Carpathian Ruthenia, which became part of the Ukrainian SSR (a republic of the Soviet Union). The Communist Party seized power in a coup in 1948. From 1948 to 1989, Czechoslovakia was part of the Eastern Bloc with a planned economy. Its economic status was formalized in membership of Comecon from 1949 and its defense status in the Warsaw Pact of 1955. A period of political liberalization in 1968, the Prague Spring, ended violently when the Soviet Union, assisted by other Warsaw Pact countries, invaded Czechoslovakia. In 1989, as Marxist–Leninist governments and communism were ending all over Central and Eastern Europe, Czechoslovaks peacefully deposed their communist government during the Velvet Revolution, which began on 17 November 1989 and ended 11 days later on 28 November when all of the top Communist leaders and Communist party itself resigned. On 31 December 1992, Czechoslovakia peacefully split into the two sovereign states of the Czech Republic and Slovakia.
+
+Characteristics
+Form of state
+1918–1937: A democratic republic championed by Tomáš Masaryk.
+1938–1939: After the annexation of Sudetenland by Nazi Germany in 1938, the region gradually turned into a state with loosened connections among the Czech, Slovak, and Ruthenian parts. A strip of southern Slovakia and Carpathian Ruthenia was redeemed by Hungary, and the Trans-Olza region was annexed by Poland.
+1939–1945: The remainder of the state was dismembered and became split into the Protectorate of Bohemia and Moravia and the Slovak Republic, while the rest of Carpathian Ruthenia was occupied and annexed by Hungary. A government-in-exile continued to exist in London, supported by the United Kingdom, United States and their Allies; after the German invasion of Soviet Union, it was also recognized by the Soviet Union. Czechoslovakia adhered to the Declaration by United Nations and was a founding member of the United Nations.
+1946–1948: The country was governed by a coalition government with communist ministers, including the prime minister and the minister of interior. Carpathian Ruthenia was ceded to the Soviet Union.
+1948–1989: The country became a Marxist-Leninist state under Soviet domination with a command economy. In 1960, the country officially became a socialist republic, the Czechoslovak Socialist Republic. It was a satellite state of the Soviet Union.
+1989–1990: Czechoslovakia formally became a federal republic comprising the Czech Socialist Republic and the Slovak Socialist Republic. In late 1989, the communist rule came to an end during the Velvet Revolution followed by the re-establishment of a democratic parliamentary republic.
+1990–1992: Shortly after the Velvet Revolution, the state was renamed the Czech and Slovak Federative Republic, consisting of the Czech Republic and the Slovak Republic (Slovakia) until the peaceful dissolution on 31  December 1992.
+
+Neighbors
+Austria 1918–1938, 1945–1992
+Germany (both predecessors, West Germany and East Germany, were neighbors between 1949 and 1990)
+Hungary
+Poland
+Romania 1918–1938
+Soviet Union 1945–1991
+Ukraine 1991–1992 (Soviet Union member until 1991)
+Topography
+The country was of generally irregular terrain. The western area was part of the north-central European uplands. The eastern region was composed of the northern reaches of the Carpathian Mountains and lands of the Danube River basin.
+
+Climate
+The weather is mild winters and mild summers. Influenced by the Atlantic Ocean from the west, the Baltic Sea from the north, and Mediterranean Sea from the south. There is no continental weather.
+
+Names
+
+1918–1938: Czechoslovak Republic (abbreviated ČSR), or Czechoslovakia, before the formalization of the name in 1920, also known as Czecho-Slovakia or the Czecho-Slovak state
+1938–1939: Czecho-Slovak Republic, or Czecho-Slovakia
+1945–1960: Czechoslovak Republic (ČSR), or Czechoslovakia
+1960–1990: Czechoslovak Socialist Republic (ČSSR), or Czechoslovakia
+1990: Czechoslovak Federative Republic (ČSFR)
+1990–1992: Czech and Slovak Federative Republic (ČSFR), or Czechoslovakia
+
+History
+
+Origins
+
+The area was part of the Austro-Hungarian Empire until it collapsed at the end of World War I. The new state was founded by Tomáš Garrigue Masaryk, who served as its first president from 14 November 1918 to 14 December 1935. He was succeeded by his close ally Edvard Beneš (1884–1948).
+
+The roots of Czech nationalism go back to the 19th century, when philologists and educators, influenced by Romanticism, promoted the Czech language and pride in the Czech people. Nationalism became a mass movement in the second half of the 19th century. Taking advantage of the limited opportunities for participation in political life under Austrian rule, Czech leaders such as historian František Palacký (1798–1876) founded various patriotic, self-help organizations which provided a chance for many of their compatriots to participate in communal life before independence. Palacký supported Austro-Slavism and worked for a reorganized federal Austrian Empire, which would protect the Slavic speaking peoples of Central Europe against Russian and German threats.
+
+An advocate of democratic reform and Czech autonomy within Austria-Hungary, Masaryk was elected twice to the Reichsrat (Austrian Parliament), from 1891 to 1893 for the Young Czech Party, and from 1907 to 1914 for the Czech Realist Party, which he had founded in 1889 with Karel Kramář and Josef Kaizl.
+
+During World War I a number of Czechs and Slovaks, the Czechoslovak Legions, fought with the Allies in France and Italy, while large numbers deserted to Russia in exchange for its support for the independence of Czechoslovakia from the Austrian Empire. With the outbreak of World War I, Masaryk began working for Czech independence in a union with Slovakia. With Edvard Beneš and Milan Rastislav Štefánik, Masaryk visited several Western countries and won support from influential publicists. The Czechoslovak National Council was the main organization that advanced the claims for a Czechoslovak state.
+
+First Czechoslovak Republic
+
+Formation
+
+The Bohemian Kingdom ceased to exist in 1918 when it was incorporated into Czechoslovakia. Czechoslovakia was founded in October 1918, as one of the successor states of the Austro-Hungarian Empire at the end of World War I and as part of the Treaty of Saint-Germain-en-Laye. It consisted of the present day territories of Bohemia, Moravia, Slovakia and Carpathian Ruthenia. Its territory included some of the most industrialized regions of the former Austria-Hungary. The land consisted of modern day Czechia, Slovakia, and a region of Ukraine called Carpathian Ruthenia
+
+Ethnicity 
+
+The new country was a multi-ethnic state, with Czechs and Slovaks as constituent peoples. The population consisted of Czechs (51%), Slovaks (16%), Germans (22%), Hungarians (5%) and Rusyns (4%). Many of the Germans, Hungarians, Ruthenians and Poles and some Slovaks, felt oppressed because the political elite did not generally allow political autonomy for minority ethnic groups. This policy led to unrest among the non-Czech population, particularly in German-speaking Sudetenland, which initially had proclaimed itself part of the Republic of German-Austria in accordance with the self-determination principle.
+
+The state proclaimed the official ideology that there were no separate Czech and Slovak nations, but only one nation of Czechoslovaks (see Czechoslovakism), to the disagreement of Slovaks and other ethnic groups. Once a unified Czechoslovakia was restored after World War II (after the country had been divided during the war), the conflict between the Czechs and the Slovaks surfaced again. The governments of Czechoslovakia and other Central European nations deported ethnic Germans, reducing the presence of minorities in the nation. Most of the Jews had been killed during the war by the Nazis.
+
+*Jews identified themselves as Germans or Hungarians (and Jews only by religion not ethnicity), the sum is, therefore, more than 100%.
+
+Interwar period 
+During the period between the two world wars Czechoslovakia was a democratic state. The population was generally literate, and contained fewer alienated groups. The influence of these conditions was augmented by the political values of Czechoslovakia's leaders and the policies they adopted. Under Tomas Masaryk, Czech and Slovak politicians promoted progressive social and economic conditions that served to defuse discontent.
+
+Foreign minister Beneš became the prime architect of the Czechoslovak-Romanian-Yugoslav alliance (the "Little Entente", 1921–38) directed against Hungarian attempts to reclaim lost areas. Beneš worked closely with France. Far more dangerous was the German element, which after 1933 became allied with the Nazis in Germany.
+
+Czech-Slovak relations came to be a central issue in Czechoslovak politics during the 1930s. The increasing feeling of inferiority among the Slovaks,  who were hostile to the more numerous Czechs, weakened the country in the late 1930s. Slovakia became autonomous in the fall of 1938, and by mid-1939, Slovakia had become independent, with the First Slovak Republic set up as a satellite state of Nazi Germany and the far-right Slovak People's Party in power .
+
+After 1933, Czechoslovakia remained the only democracy in central and eastern Europe.
+
+Munich Agreement, and Two-Step German Occupation
+
+In September 1938, Adolf Hitler demanded control of the Sudetenland. On 29 September 1938, Britain and France ceded control in the Appeasement at the Munich Conference; France ignored the military alliance it had with Czechoslovakia. During October 1938, Nazi Germany occupied the Sudetenland border region, effectively crippling Czechoslovak defences.
+
+The First Vienna Award assigned a strip of southern Slovakia and Carpathian Ruthenia to Hungary. Poland occupied Zaolzie, an area whose population was majority Polish, in October 1938.
+
+On 14 March 1939, the remainder ("rump") of Czechoslovakia was dismembered by the proclamation of the Slovak State, the next day the rest of Carpathian Ruthenia was occupied and annexed by Hungary, while the following day the German Protectorate of Bohemia and Moravia was proclaimed.
+
+The eventual goal of the German state under Nazi leadership was to eradicate Czech nationality through assimilation, deportation, and extermination of the Czech intelligentsia; the intellectual elites and middle class made up a considerable number of the 200,000 people who passed through concentration camps and the 250,000 who died during German occupation. Under , it was assumed that around 50% of Czechs would be fit for Germanization. The Czech intellectual elites were to be removed not only from Czech territories but from Europe completely. The authors of Generalplan Ost believed it would be best if they emigrated overseas, as even in Siberia they were considered a threat to German rule. Just like Jews, Poles, Serbs, and several other nations, Czechs were considered to be untermenschen by the Nazi state. In 1940, in a secret Nazi plan for the Germanization of the Protectorate of Bohemia and Moravia it was declared that those considered to be of racially Mongoloid origin and the Czech intelligentsia were not to be Germanized.
+
+The deportation of Jews to concentration camps was organized under the direction of Reinhard Heydrich, and the fortress town of Terezín was made into a ghetto way station for Jewish families. On 4 June 1942 Heydrich died after being wounded by an assassin in Operation Anthropoid. Heydrich's successor, Colonel General Kurt Daluege, ordered mass arrests and executions and the destruction of the villages of Lidice and Ležáky. In 1943 the German war effort was accelerated. Under the authority of Karl Hermann Frank, German minister of state for Bohemia and Moravia, some 350,000 Czech laborers were dispatched to the Reich. Within the protectorate, all non-war-related industry was prohibited. Most of the Czech population obeyed quiescently up until the final months preceding the end of the war, while thousands were involved in the resistance movement.
+
+For the Czechs of the Protectorate Bohemia and Moravia, German occupation was a period of brutal oppression. Czech losses resulting from political persecution and deaths in concentration camps totaled between 36,000 and 55,000. The Jewish populations of Bohemia and Moravia (118,000 according to the 1930 census) were virtually annihilated. Many Jews emigrated after 1939; more than 70,000 were killed; 8,000 survived at Terezín. Several thousand Jews managed to live in freedom or in hiding throughout the occupation.
+
+Despite the estimated 136,000 deaths at the hands of the Nazi regime, the population in the Reichsprotektorate saw a net increase during the war years of approximately 250,000 in line with an increased birth rate.
+
+On 6 May 1945, the third US Army of General Patton entered Pilsen from the south west. On 9 May 1945, Soviet Red Army troops entered Prague.
+
+Communist Czechoslovakia
+
+After World War II, prewar Czechoslovakia was reestablished, with the exception of Subcarpathian Ruthenia, which was annexed by the Soviet Union and incorporated into the Ukrainian Soviet Socialist Republic. The Beneš decrees were promulgated concerning ethnic Germans (see Potsdam Agreement) and ethnic Hungarians. Under the decrees, citizenship was abrogated for people of German and Hungarian ethnic origin who had accepted German or Hungarian citizenship during the occupations. In 1948, this provision was cancelled for the Hungarians, but only partially for the Germans. The government then confiscated the property of the Germans and expelled about 90% of the ethnic German population, over 2 million people. Those who remained were collectively accused of supporting the Nazis after the Munich Agreement, as 97.32% of Sudeten Germans had voted for the NSDAP in the December 1938 elections. Almost every decree explicitly stated that the sanctions did not apply to antifascists. Some 250,000 Germans, many married to Czechs, some antifascists, and also those required for the post-war reconstruction of the country, remained in Czechoslovakia. The Beneš Decrees still cause controversy among nationalist groups in the Czech Republic, Germany, Austria and Hungary.
+
+Following the expulsion of the ethnic German population from Czechoslovakia, parts of the former Sudetenland, especially around Krnov and the surrounding villages of the Jesenik mountain region in northeastern Czechoslovakia, were settled in 1949 by Communist refugees from Northern Greece who had left their homeland as a result of the Greek Civil War. These Greeks made up a large proportion of the town and region's population until the late 1980s/early 1990s. Although defined as "Greeks", the Greek Communist community of Krnov and the Jeseniky region actually consisted of an ethnically diverse population, including Greek Macedonians, Macedonians, Vlachs, Pontic Greeks and Turkish speaking Urums or Caucasus Greeks.
+
+Carpathian Ruthenia (Podkarpatská Rus) was occupied by (and in June 1945 formally ceded to) the Soviet Union. In the 1946 parliamentary election, the Communist Party of Czechoslovakia was the winner in the Czech lands, and the Democratic Party won in Slovakia. In February 1948 the Communists seized power. Although they would maintain the fiction of political pluralism through the existence of the National Front, except for a short period in the late 1960s (the Prague Spring) the country had no liberal democracy. Since citizens lacked significant electoral methods of registering protest against government policies, periodically there were street protests that became violent. For example, there were riots in the town of Plzeň in 1953, reflecting economic discontent. Police and army units put down the rebellion, and hundreds were injured but no one was killed. While its economy remained more advanced than those of its neighbors in Eastern Europe, Czechoslovakia grew increasingly economically weak relative to Western Europe.
+
+The currency reform of 1953 caused dissatisfaction among Czechoslovak laborers. To equalize the wage rate, Czechoslovaks had to turn in their old money for new at a decreased value. The banks also confiscated savings and bank deposits to control the amount of money in circulation. In the 1950s, Czechoslovakia experienced high economic growth (averaging 7% per year), which allowed for a substantial increase in wages and living standards, thus promoting the stability of the regime.
+
+In 1968, when the reformer Alexander Dubček was appointed to the key post of First Secretary of the Czechoslovak Communist Party, there was a brief period of liberalization known as the Prague Spring. In response, after failing to persuade the Czechoslovak leaders to change course, five other members of the Warsaw Pact invaded. Soviet tanks rolled into Czechoslovakia on the night of 20–21 August 1968. Soviet Communist Party General Secretary Leonid Brezhnev viewed this intervention as vital for the preservation of the Soviet, socialist system and vowed to intervene in any state that sought to replace Marxism-Leninism with capitalism.
+
+In the week after the invasion there was a spontaneous campaign of civil resistance against the occupation. This resistance involved a wide range of acts of non-cooperation and defiance: this was followed by a period in which the Czechoslovak Communist Party leadership, having been forced in Moscow to make concessions to the Soviet Union, gradually put the brakes on their earlier liberal policies.
+
+Meanwhile, one plank of the reform program had been carried out: in 1968–69, Czechoslovakia was turned into a federation of the Czech Socialist Republic and Slovak Socialist Republic. The theory was that under the federation, social and economic inequities between the Czech and Slovak halves of the state would be largely eliminated. A number of ministries, such as education, now became two formally equal bodies in the two formally equal republics. However, the centralized political control by the Czechoslovak Communist Party severely limited the effects of federalization.
+
+The 1970s saw the rise of the dissident movement in Czechoslovakia, represented among others by Václav Havel. The movement sought greater political participation and expression in the face of official disapproval, manifested in limitations on work activities, which went as far as a ban on professional employment, the refusal of higher education for the dissidents' children, police harassment and prison.
+
+During the 1980s, Czechoslovakia became one of the most tightly controlled Communist regimes in the Warsaw Pact in resistance to the mitigation of controls notified by Soviet president Mikhail Gorbachev.
+
+After 1989
+
+In 1989, the Velvet Revolution restored democracy. This occurred around the same time as the fall of communism in Romania, Bulgaria, Hungary, East Germany and Poland.
+
+The word "socialist" was removed from the country's full name on 29 March 1990 and replaced by "federal".
+
+Pope John Paul II made a papal visit to Czechoslovakia on 21 April 1990, hailing it as a symbolic step of reviving Christianity in the newly-formed post-communist state.
+
+Czechoslovakia participated in the Gulf War with a small force of 200 troops under the command of the U.S.-led coalition.
+
+In 1992, because of growing nationalist tensions in the government, Czechoslovakia was peacefully dissolved by parliament. On 31 December 1992 it formally separated into two independent countries, the Czech Republic and the Slovak Republic.
+
+Government and politics 
+
+After World War II, a political monopoly was held by the Communist Party of Czechoslovakia (KSČ). The leader of the KSČ was de facto the most powerful person in the country during this period. Gustáv Husák was elected first secretary of the KSČ in 1969 (changed to general secretary in 1971) and president of Czechoslovakia in 1975. Other parties and organizations existed but functioned in subordinate roles to the KSČ. All political parties, as well as numerous mass organizations, were grouped under umbrella of the National Front. Human rights activists and religious activists were severely repressed.
+
+Constitutional development
+
+Czechoslovakia had the following constitutions during its history (1918–1992):
+Temporary constitution of 14 November 1918 (democratic): see History of Czechoslovakia (1918–1938)
+The 1920 constitution (The Constitutional Document of the Czechoslovak Republic), democratic, in force until 1948, several amendments
+The Communist 1948 Ninth-of-May Constitution
+The Communist 1960 Constitution of the Czechoslovak Socialist Republic with major amendments in 1968 (Constitutional Law of Federation), 1971, 1975, 1978, and 1989 (at which point the leading role of the Communist Party was abolished). It was amended several more times during 1990–1992 (for example, 1990, name change to Czecho-Slovakia, 1991 incorporation of the human rights charter)
+
+Heads of state and government 
+
+List of presidents of Czechoslovakia
+List of prime ministers of Czechoslovakia
+
+Foreign policy
+
+International agreements and membership
+In the 1930s, the nation formed a military alliance with France, which collapsed in the Munich Agreement of 1938. After World War II, an active participant in Council for Mutual Economic Assistance (Comecon), Warsaw Pact, United Nations and its specialized agencies; signatory of conference on Security and Cooperation in Europe.
+
+Administrative divisions
+
+1918–1923: Different systems in former Austrian territory (Bohemia, Moravia, a small part of Silesia) compared to former Hungarian territory (Slovakia and Ruthenia): three lands (země) (also called district units (kraje)): Bohemia, Moravia, Silesia, plus 21 counties (župy) in today's Slovakia and three counties in today's Ruthenia; both lands and counties were divided into districts (okresy).
+1923–1927: As above, except that the Slovak and Ruthenian counties were replaced by six (grand) counties ((veľ)župy) in Slovakia and one (grand) county in Ruthenia, and the numbers and boundaries of the okresy were changed in those two territories.
+1928–1938: Four lands (Czech: země, Slovak: krajiny): Bohemia, Moravia-Silesia, Slovakia and Sub-Carpathian Ruthenia, divided into districts (okresy).
+Late 1938 – March 1939: As above, but Slovakia and Ruthenia gained the status of "autonomous lands". Slovakia was called Slovenský štát, with its own currency and government.
+1945–1948: As in 1928–1938, except that Ruthenia became part of the Soviet Union.
+1949–1960: 19 regions (kraje) divided into 270 okresy.
+1960–1992: 10 kraje, Prague, and (from 1970) Bratislava (capital of Slovakia); these were divided into 109–114 okresy; the kraje were abolished temporarily in Slovakia in 1969–1970 and for many purposes from 1991 in Czechoslovakia; in addition, the Czech Socialist Republic and the Slovak Socialist Republic were established in 1969 (without the word Socialist from 1990).
+
+Population and ethnic groups
+
+Economy
+
+Before World War II, the economy was about the fourth in all industrial countries in Europe. The state was based on strong economy, manufacturing cars (Škoda, Tatra), trams, aircraft (Aero, Avia), ships, ship engines (Škoda), cannons, shoes (Baťa), turbines, guns (Zbrojovka Brno). It was the industrial workshop for the Austro-Hungarian empire. The Slovak lands relied more heavily on agriculture than the Czech lands.
+
+After World War II, the economy was centrally planned, with command links controlled by the communist party, similarly to the Soviet Union. The large metallurgical industry was dependent on imports of iron and non-ferrous ores.
+Industry: Extractive industry and manufacturing dominated the sector, including machinery, chemicals, food processing, metallurgy, and textiles. The sector was wasteful in its use of energy, materials, and labor and was slow to upgrade technology, but the country was a major supplier of high-quality machinery, instruments, electronics, aircraft, airplane engines and arms to other socialist countries.
+Agriculture: Agriculture was a minor sector, but collectivized farms of large acreage and relatively efficient mode of production enabled the country to be relatively self-sufficient in the food supply. The country depended on imports of grains (mainly for livestock feed) in years of adverse weather. Meat production was constrained by a shortage of feed, but the country still recorded high per capita consumption of meat.
+Foreign Trade: Exports were estimated at US$17.8 billion in 1985. Exports were machinery (55%), fuel and materials (14%), and manufactured consumer goods (16%). Imports stood at an estimated US$17.9 billion in 1985, including fuel and materials (41%), machinery (33%), and agricultural and forestry products (12%). In 1986, about 80% of foreign trade was with other socialist countries.
+Exchange rate: Official, or commercial, the rate was crowns (Kčs) 5.4 per US$1 in 1987. Tourist, or non-commercial, the rate was Kčs 10.5 per US$1. Neither rate reflected purchasing power. The exchange rate on the black market was around Kčs 30 per US$1, which became the official rate once the currency became convertible in the early 1990s.
+Fiscal year: Calendar year.
+Fiscal policy: The state was the exclusive owner of means of production in most cases. Revenue from state enterprises was the primary source of revenues followed by turnover tax. The government spent heavily on social programs, subsidies, and investment. The budget was usually balanced or left a small surplus.
+
+Resource base
+
+After World War II, the country was short of energy, relying on imported crude oil and natural gas from the Soviet Union, domestic brown coal, and nuclear and hydroelectric energy. Energy constraints were a major factor in the 1980s.
+
+Transport and communications
+
+Slightly after the foundation of Czechoslovakia in 1918, there was a lack of essential infrastructure in many areas – paved roads, railways, bridges, etc. Massive improvement in the following years enabled Czechoslovakia to develop its industry. Prague's civil airport in Ruzyně became one of the most modern terminals in the world when it was finished in 1937. Tomáš Baťa, a Czech entrepreneur and visionary, outlined his ideas in the publication "Budujme stát pro 40 milionů lidí", where he described the future motorway system. Construction of the first motorways in Czechoslovakia begun in 1939, nevertheless, they were stopped after German occupation during World War II.
+
+Society
+
+Education
+
+Education was free at all levels and compulsory from ages 6 to 15. The vast majority of the population was literate. There was a highly developed system of apprenticeship training and vocational schools supplemented general secondary schools and institutions of higher education.
+
+Religion
+
+In 1991, 46% of the population were Roman Catholics, 5.3% were Evangelical Lutheran, 30% were Atheist, and other religions made up 17% of the country, but there were huge differences in religious practices between the two constituent republics; see Czech Republic and Slovakia.
+
+Health, social welfare and housing
+
+After World War II, free health care was available to all citizens. National health planning emphasized preventive medicine; factory and local health care centres supplemented hospitals and other inpatient institutions. There was a substantial improvement in rural health care during the 1960s and 1970s.
+
+Mass media
+
+During the era between the World Wars, Czechoslovak democracy and liberalism facilitated conditions for free publication. The most significant daily newspapers in these times were Lidové noviny, Národní listy, Český deník and Československá Republika.
+
+During Communist rule, the mass media in Czechoslovakia were controlled by the Communist Party. Private ownership of any publication or agency of the mass media was generally forbidden, although churches and other organizations published small periodicals and newspapers. Even with this information monopoly in the hands of organizations under KSČ control, all publications were reviewed by the government's Office for Press and Information.
+
+Sports
+
+The Czechoslovakia national football team was a consistent performer on the international scene, with eight appearances in the FIFA World Cup Finals, finishing in second place in 1934 and 1962. The team also won the European Football Championship in 1976, came in third in 1980 and won the Olympic gold in 1980.
+
+Well-known football players such as Pavel Nedvěd, Antonín Panenka, Milan Baroš, Tomáš Rosický, Vladimír Šmicer or Petr Čech were all born in Czechoslovakia.
+
+The International Olympic Committee code for Czechoslovakia is TCH, which is still used in historical listings of results.
+
+The Czechoslovak national ice hockey team won many medals from the world championships and Olympic Games. Peter Šťastný, Jaromír Jágr, Dominik Hašek, Peter Bondra, Petr Klíma, Marián Gáborík, Marián Hossa, Miroslav Šatan and Pavol Demitra all come from Czechoslovakia.
+
+Emil Zátopek, winner of four Olympic gold medals in athletics, is considered one of the top athletes in Czechoslovak history.
+
+Věra Čáslavská was an Olympic gold medallist in gymnastics, winning seven gold medals and four silver medals. She represented Czechoslovakia in three consecutive Olympics.
+
+Several accomplished professional tennis players including Jaroslav Drobný, Ivan Lendl, Jan Kodeš, Miloslav Mečíř, Hana Mandlíková, Martina Hingis, Martina Navratilova, Jana Novotna, Petra Kvitová and Daniela Hantuchová were born in Czechoslovakia.
+
+Culture
+Czech RepublicSlovakia
+List of CzechsList of Slovaks
+MDŽ (International Women's Day)
+Jazz in dissident Czechoslovakia
+
+Postage stamps
+Postage stamps and postal history of Czechoslovakia
+Czechoslovakia stamp reused by Slovak Republic after 18 January 1939 by overprinting country and value
+
+See also
+Effects on the environment in Czechoslovakia from Soviet influence during the Cold War
+Former countries in Europe after 1815
+List of former sovereign states
+
+Notes
+
+References
+
+Sources
+
+Further reading
+
+Heimann, Mary. Czechoslovakia: The State That Failed (2009). 
+Hermann, A. H. A History of the Czechs (1975).
+Kalvoda, Josef. The Genesis of Czechoslovakia (1986).
+Leff, Carol Skalnick. National Conflict in Czechoslovakia: The Making and Remaking of a State, 1918–87 (1988).
+Mantey, Victor. A History of the Czechoslovak Republic (1973).
+Myant, Martin. The Czechoslovak Economy, 1948–88 (1989).
+Naimark, Norman, and Leonid Gibianskii, eds. The Establishment of Communist Regimes in Eastern Europe, 1944–1949 (1997) online edition
+Orzoff, Andrea. Battle for the Castle: The Myth of Czechoslovakia in Europe 1914–1948 (Oxford University Press, 2009); online review  online
+Paul, David. Czechoslovakia: Profile of a Socialist Republic at the Crossroads of Europe (1990).
+Renner, Hans. A History of Czechoslovakia since 1945 (1989).
+Seton-Watson, R. W. A History of the Czechs and Slovaks (1943).
+Stone, Norman, and E. Strouhal, eds.Czechoslovakia: Crossroads and Crises, 1918–88 (1989).
+Wheaton, Bernard; Zdenek Kavav. "The Velvet Revolution: Czechoslovakia, 1988–1991" (1992).
+Williams, Kieran, "Civil Resistance in Czechoslovakia: From Soviet Invasion to "Velvet Revolution", 1968–89",in Adam Roberts and Timothy Garton Ash (eds.), Civil Resistance and Power Politics: The Experience of Non-violent Action from Gandhi to the Present (Oxford University Press, 2009).
+Windsor, Philip, and Adam Roberts, Czechoslovakia 1968: Reform, Repression and Resistance (1969).
+Wolchik, Sharon L. Czechoslovakia: Politics, Society, and Economics (1990).
+
+External links
+
+Online books and articles 
+U.S. Library of Congress Country Studies, "Czechoslovakia"
+English/Czech: Orders and Medals of Czechoslovakia including Order of the White Lion
+Czechoslovakia by Encyclopædia Britannica
+ Katrin Boeckh: Crumbling of Empires and Emerging States: Czechoslovakia and Yugoslavia as (Multi)national Countries, in: 1914-1918-online. International Encyclopedia of the First World War.
+
+Maps with Hungarian-language rubrics:
+Border changes after the creation of Czechoslovakia
+Interwar Czechoslovakia
+Czechoslovakia after Munich Agreement
+
+ 
+Eastern Bloc
+Former republics
+Geography of Europe
+History of Central Europe
+1918 establishments in Czechoslovakia
+1939 disestablishments in Czechoslovakia
+1945 establishments in Czechoslovakia
+1992 disestablishments in Czechoslovakia
+States and territories established in 1918
+States and territories disestablished in 1939
+States and territories established in 1945
+States and territories disestablished in 1992
+1918 establishments in Europe
+1992 disestablishments in Europe
+Former member states of the United Nations
+Computer science is the study of computation, information, and automation. Computer science spans theoretical disciplines (such as algorithms, theory of computation, and information theory) to applied disciplines (including the design and implementation of hardware and software). Though more often considered an academic discipline, computer science is closely related to computer programming.
+
+Algorithms and data structures are central to computer science.
+
+The theory of computation concerns abstract models of computation and general classes of problems that can be solved using them. The fields of cryptography and computer security involve studying the means for secure communication and for preventing security vulnerabilities. Computer graphics and computational geometry address the generation of images. Programming language theory considers different ways to describe computational processes, and database theory concerns the management of repositories of data. Human–computer interaction investigates the interfaces through which humans and computers interact, and software engineering focuses on the design and principles behind developing software. Areas such as operating systems, networks and embedded systems investigate the principles and design behind complex systems. Computer architecture describes the construction of computer components and computer-operated equipment. Artificial intelligence and machine learning aim to synthesize goal-orientated processes such as problem-solving, decision-making, environmental adaptation, planning and learning found in humans and animals. Within artificial intelligence, computer vision aims to understand and process image and video data, while natural language processing aims to understand and process textual and linguistic data.
+
+The fundamental concern of computer science is determining what can and cannot be automated. The Turing Award is generally recognized as the highest distinction in computer science.
+
+History
+
+The earliest foundations of what would become computer science predate the invention of the modern digital computer. Machines for calculating fixed numerical tasks such as the abacus have existed since antiquity, aiding in computations such as multiplication and division. Algorithms for performing computations have existed since antiquity, even before the development of sophisticated computing equipment.
+
+Wilhelm Schickard designed and constructed the first working mechanical calculator in 1623. In 1673, Gottfried Leibniz demonstrated a digital mechanical calculator, called the Stepped Reckoner. Leibniz may be considered the first computer scientist and information theorist, because of various reasons, including the fact that he documented the binary number system. In 1820, Thomas de Colmar launched the mechanical calculator industry when he invented his simplified arithmometer, the first calculating machine strong enough and reliable enough to be used daily in an office environment. Charles Babbage started the design of the first automatic mechanical calculator, his Difference Engine, in 1822, which eventually gave him the idea of the first programmable mechanical calculator, his Analytical Engine. He started developing this machine in 1834, and "in less than two years, he had sketched out many of the salient features of the modern computer". "A crucial step was the adoption of a punched card system derived from the Jacquard loom" making it infinitely programmable. In 1843, during the translation of a French article on the Analytical Engine, Ada Lovelace wrote, in one of the many notes she included, an algorithm to compute the Bernoulli numbers, which is considered to be the first published algorithm ever specifically tailored for implementation on a computer. Around 1885, Herman Hollerith invented the tabulator, which used punched cards to process statistical information; eventually his company became part of IBM. Following Babbage, although unaware of his earlier work, Percy Ludgate in 1909 published the 2nd of the only two designs for mechanical analytical engines in history. In 1914, the Spanish engineer Leonardo Torres Quevedo published his Essays on Automatics, and designed, inspired by Babbage, a theoretical electromechanical calculating machine which was to be controlled by a read-only program. The paper also introduced the idea of floating-point arithmetic. In 1920, to celebrate the 100th anniversary of the invention of the arithmometer, Torres presented in Paris the  Electromechanical Arithmometer, a prototype that demonstrated the feasibility of an electromechanical analytical engine, on which commands could be typed and the results printed automatically. In 1937, one hundred years after Babbage's impossible dream, Howard Aiken convinced IBM, which was making all kinds of punched card equipment and was also in the calculator business to develop his giant programmable calculator, the ASCC/Harvard Mark I, based on Babbage's Analytical Engine, which itself used cards and a central computing unit. When the machine was finished, some hailed it as "Babbage's dream come true".
+
+During the 1940s, with the development of new and more powerful computing machines such as the Atanasoff–Berry computer and ENIAC, the term computer came to refer to the machines rather than their human predecessors. As it became clear that computers could be used for more than just mathematical calculations, the field of computer science broadened to study computation in general. In 1945, IBM founded the Watson Scientific Computing Laboratory at Columbia University in New York City. The renovated fraternity house on Manhattan's West Side was IBM's first laboratory devoted to pure science. The lab is the forerunner of IBM's Research Division, which today operates research facilities around the world. Ultimately, the close relationship between IBM and Columbia University was instrumental in the emergence of a new scientific discipline, with Columbia offering one of the first academic-credit courses in computer science in 1946. Computer science began to be established as a distinct academic discipline in the 1950s and early 1960s. The world's first computer science degree program, the Cambridge Diploma in Computer Science, began at the University of Cambridge Computer Laboratory in 1953. The first computer science department in the United States was formed at Purdue University in 1962. Since practical computers became available, many applications of computing have become distinct areas of study in their own rights.
+
+Etymology
+
+Although first proposed in 1956, the term "computer science" appears in a 1959 article in Communications of the ACM,
+in which Louis Fein argues for the creation of a Graduate School in Computer Sciences analogous to the creation of Harvard Business School in 1921. Louis justifies the name by arguing that, like management science, the subject is applied and interdisciplinary in nature, while having the characteristics typical of an academic discipline.
+His efforts, and those of others such as numerical analyst George Forsythe, were rewarded: universities went on to create such departments, starting with Purdue in 1962. Despite its name, a significant amount of computer science does not involve the study of computers themselves. Because of this, several alternative names have been proposed. Certain departments of major universities prefer the term computing science, to emphasize precisely that difference. Danish scientist Peter Naur suggested the term datalogy, to reflect the fact that the scientific discipline revolves around data and data treatment, while not necessarily involving computers. The first scientific institution to use the term was the Department of Datalogy at the University of Copenhagen, founded in 1969, with Peter Naur being the first professor in datalogy. The term is used mainly in the Scandinavian countries. An alternative term, also proposed by Naur, is data science; this is now used for a multi-disciplinary field of data analysis, including statistics and databases.
+
+In the early days of computing, a number of terms for the practitioners of the field of computing were suggested in the Communications of the ACM—turingineer, turologist, flow-charts-man, applied meta-mathematician, and applied epistemologist. Three months later in the same journal, comptologist was suggested, followed next year by hypologist. The term computics has also been suggested. In Europe, terms derived from contracted translations of the expression "automatic information" (e.g. "informazione automatica" in Italian) or "information and mathematics" are often used, e.g. informatique (French), Informatik (German), informatica (Italian, Dutch), informática (Spanish, Portuguese), informatika (Slavic languages and Hungarian) or pliroforiki (πληροφορική, which means informatics) in Greek. Similar words have also been adopted in the UK (as in the School of Informatics, University of Edinburgh). "In the U.S., however, informatics is linked with applied computing, or computing in the context of another domain."
+
+A folkloric quotation, often attributed to—but almost certainly not first formulated by—Edsger Dijkstra, states that "computer science is no more about computers than astronomy is about telescopes." The design and deployment of computers and computer systems is generally considered the province of disciplines other than computer science. For example, the study of computer hardware is usually considered part of computer engineering, while the study of commercial computer systems and their deployment is often called information technology or information systems. However, there has been exchange of ideas between the various computer-related disciplines. Computer science research also often intersects other disciplines, such as cognitive science, linguistics, mathematics, physics, biology, Earth science, statistics, philosophy, and logic.
+
+Computer science is considered by some to have a much closer relationship with mathematics than many scientific disciplines, with some observers saying that computing is a mathematical science. Early computer science was strongly influenced by the work of mathematicians such as Kurt Gödel, Alan Turing, John von Neumann, Rózsa Péter and Alonzo Church and there continues to be a useful interchange of ideas between the two fields in areas such as mathematical logic, category theory, domain theory, and algebra.
+
+The relationship between computer science and software engineering is a contentious issue, which is further muddied by disputes over what the term "software engineering" means, and how computer science is defined. David Parnas, taking a cue from the relationship between other engineering and science disciplines, has claimed that the principal focus of computer science is studying the properties of computation in general, while the principal focus of software engineering is the design of specific computations to achieve practical goals, making the two separate but complementary disciplines.
+
+The academic, political, and funding aspects of computer science tend to depend on whether a department is formed with a mathematical emphasis or with an engineering emphasis. Computer science departments with a mathematics emphasis and with a numerical orientation consider alignment with computational science. Both types of departments tend to make efforts to bridge the field educationally if not across all research.
+
+Philosophy
+
+Epistemology of computer science
+Despite the word "science" in its name, there is debate over whether or not computer science is a discipline of science, mathematics, or engineering. Allen Newell and Herbert A. Simon argued in 1975,  It has since been argued that computer science can be classified as an empirical science since it makes use of empirical testing to evaluate the correctness of programs, but a problem remains in defining the laws and theorems of computer science (if any exist) and defining the nature of experiments in computer science. Proponents of classifying computer science as an engineering discipline argue that the reliability of computational systems is investigated in the same way as bridges in civil engineering and airplanes in aerospace engineering. They also argue that while empirical sciences observe what presently exists, computer science observes what is possible to exist and while scientists discover laws from observation, no proper laws have been found in computer science and it is instead concerned with creating phenomena.
+
+Proponents of classifying computer science as a mathematical discipline argue that computer programs are physical realizations of mathematical entities and programs can be deductively reasoned through mathematical formal methods. Computer scientists Edsger W. Dijkstra and Tony Hoare regard instructions for computer programs as mathematical sentences and interpret formal semantics for programming languages as mathematical axiomatic systems.
+
+Paradigms of computer science
+A number of computer scientists have argued for the distinction of three separate paradigms in computer science. Peter Wegner argued that those paradigms are science, technology, and mathematics. Peter Denning's working group argued that they are theory, abstraction (modeling), and design. Amnon H. Eden described them as the "rationalist paradigm" (which treats computer science as a branch of mathematics, which is prevalent in theoretical computer science, and mainly employs deductive reasoning), the "technocratic paradigm" (which might be found in engineering approaches, most prominently in software engineering), and the "scientific paradigm" (which approaches computer-related artifacts from the empirical perspective of natural sciences, identifiable in some branches of artificial intelligence).
+Computer science focuses on methods involved in design, specification, programming, verification, implementation and testing of human-made computing systems.
+
+Fields
+
+As a discipline, computer science spans a range of topics from theoretical studies of algorithms and the limits of computation to the practical issues of implementing computing systems in hardware and software.
+CSAB, formerly called Computing Sciences Accreditation Board—which is made up of representatives of the Association for Computing Machinery (ACM), and the IEEE Computer Society (IEEE CS)—identifies four areas that it considers crucial to the discipline of computer science: theory of computation, algorithms and data structures, programming methodology and languages, and computer elements and architecture. In addition to these four areas, CSAB also identifies fields such as software engineering, artificial intelligence, computer networking and communication, database systems, parallel computation, distributed computation, human–computer interaction, computer graphics, operating systems, and numerical and symbolic computation as being important areas of computer science.
+
+Theoretical computer science
+
+Theoretical Computer Science is mathematical and abstract in spirit, but it derives its motivation from the practical and everyday computation. Its aim is to understand the nature of computation and, as a consequence of this understanding, provide more efficient methodologies.
+
+Theory of computation
+
+According to Peter Denning, the fundamental question underlying computer science is, "What can be automated?" Theory of computation is focused on answering fundamental questions about what can be computed and what amount of resources are required to perform those computations. In an effort to answer the first question, computability theory examines which computational problems are solvable on various theoretical models of computation. The second question is addressed by computational complexity theory, which studies the time and space costs associated with different approaches to solving a multitude of computational problems.
+
+The famous P = NP? problem, one of the Millennium Prize Problems, is an open problem in the theory of computation.
+
+Information and coding theory
+
+Information theory, closely related to probability and statistics, is related to the quantification of information. This was developed by Claude Shannon to find fundamental limits on signal processing operations such as compressing data and on reliably storing and communicating data.
+Coding theory is the study of the properties of codes (systems for converting information from one form to another) and their fitness for a specific application. Codes are used for data compression, cryptography, error detection and correction, and more recently also for network coding. Codes are studied for the purpose of designing efficient and reliable data transmission methods.
+
+Data structures and algorithms
+
+Data structures and algorithms are the studies of commonly used computational methods and their computational efficiency.
+
+Programming language theory and formal methods
+
+Programming language theory is a branch of computer science that deals with the design, implementation, analysis, characterization, and classification of programming languages and their individual features. It falls within the discipline of computer science, both depending on and affecting mathematics, software engineering, and linguistics. It is an active research area, with numerous dedicated academic journals.
+
+Formal methods are a particular kind of mathematically based technique for the specification, development and verification of software and hardware systems. The use of formal methods for software and hardware design is motivated by the expectation that, as in other engineering disciplines, performing appropriate mathematical analysis can contribute to the reliability and robustness of a design. They form an important theoretical underpinning for software engineering, especially where safety or security is involved. Formal methods are a useful adjunct to software testing since they help avoid errors and can also give a framework for testing. For industrial use, tool support is required. However, the high cost of using formal methods means that they are usually only used in the development of high-integrity and life-critical systems, where safety or security is of utmost importance. Formal methods are best described as the application of a fairly broad variety of theoretical computer science fundamentals, in particular logic calculi, formal languages, automata theory, and program semantics, but also type systems and algebraic data types to problems in software and hardware specification and verification.
+
+Applied computer science
+
+Computer graphics and visualization
+
+Computer graphics is the study of digital visual contents and involves the synthesis and manipulation of image data. The study is connected to many other fields in computer science, including computer vision, image processing, and computational geometry, and is heavily applied in the fields of special effects and video games.
+
+Image and sound processing
+
+Information can take the form of images, sound, video or other multimedia. Bits of information can be streamed via signals. Its processing is the central notion of informatics, the European view on computing, which studies information processing algorithms independently of the type of information carrier – whether it is electrical, mechanical or biological. This field plays important role in information theory, telecommunications, information engineering and has applications in medical image computing and speech synthesis, among others. What is the lower bound on the complexity of fast Fourier transform algorithms? is one of unsolved problems in theoretical computer science.
+
+Computational science, finance and engineering
+
+Scientific computing (or computational science) is the field of study concerned with constructing mathematical models and quantitative analysis techniques and using computers to analyze and solve scientific problems. A major usage of scientific computing is simulation of various processes, including computational fluid dynamics, physical, electrical, and electronic systems and circuits, as well as societies and social situations (notably war games) along with their habitats, among many others. Modern computers enable optimization of such designs as complete aircraft. Notable in electrical and electronic circuit design are SPICE, as well as software for physical realization of new (or modified) designs. The latter includes essential design software for integrated circuits.
+
+Social computing and human–computer interaction
+
+Social computing is an area that is concerned with the intersection of social behavior and computational systems. Human–computer interaction research develops theories, principles, and guidelines for user interface designers.
+
+Software engineering
+
+Software engineering is the study of designing, implementing, and modifying the software in order to ensure it is of high quality, affordable, maintainable, and fast to build. It is a systematic approach to software design, involving the application of engineering practices to software. Software engineering deals with the organizing and analyzing of software—it does not just deal with the creation or manufacture of new software, but its internal arrangement and maintenance. For example software testing, systems engineering, technical debt and software development processes.
+
+Artificial intelligence
+
+Artificial intelligence (AI) aims to or is required to synthesize goal-orientated processes such as problem-solving, decision-making, environmental adaptation, learning, and communication found in humans and animals. From its origins in cybernetics and in the Dartmouth Conference (1956), artificial intelligence research has been necessarily cross-disciplinary, drawing on areas of expertise such as applied mathematics, symbolic logic, semiotics, electrical engineering, philosophy of mind, neurophysiology, and social intelligence. AI is associated in the popular mind with robotic development, but the main field of practical application has been as an embedded component in areas of software development, which require computational understanding. The starting point in the late 1940s was Alan Turing's question "Can computers think?", and the question remains effectively unanswered, although the Turing test is still used to assess computer output on the scale of human intelligence. But the automation of evaluative and predictive tasks has been increasingly successful as a substitute for human monitoring and intervention in domains of computer application involving complex real-world data.
+
+Computer systems
+
+Computer architecture and organization
+
+Computer architecture, or digital computer organization, is the conceptual design and fundamental operational structure of a computer system. It focuses largely on the way by which the central processing unit performs internally and accesses addresses in memory. Computer engineers study computational logic and design of computer hardware, from individual processor components, microcontrollers, personal computers to supercomputers and embedded systems. The term "architecture" in computer literature can be traced to the work of Lyle R. Johnson and Frederick P. Brooks, Jr., members of the Machine Organization department in IBM's main research center in 1959.
+
+Concurrent, parallel and distributed computing
+
+Concurrency is a property of systems in which several computations are executing simultaneously, and potentially interacting with each other. A number of mathematical models have been developed for general concurrent computation including Petri nets, process calculi and the Parallel Random Access Machine model. When multiple computers are connected in a network while using concurrency, this is known as a distributed system. Computers within that distributed system have their own private memory, and information can be exchanged to achieve common goals.
+
+Computer networks
+
+This branch of computer science aims to manage networks between computers worldwide.
+
+Computer security and cryptography
+
+Computer security is a branch of computer technology with the objective of protecting information from unauthorized access, disruption, or modification while maintaining the accessibility and usability of the system for its intended users.
+
+Historical cryptography is the art of writing and deciphering secret messages. Modern cryptography is the scientific study of problems relating to distributed computations that can be attacked. Technologies studied in modern cryptography include symmetric and asymmetric encryption, digital signatures, cryptographic hash functions, key-agreement protocols, blockchain, zero-knowledge proofs, and garbled circuits.
+
+Databases and data mining
+
+A database is intended to organize, store, and retrieve large amounts of data easily. Digital databases are managed using database management systems to store, create, maintain, and search data, through database models and query languages. Data mining is a process of discovering patterns in large data sets.
+
+Discoveries
+The philosopher of computing Bill Rapaport noted three Great Insights of Computer Science:
+ Gottfried Wilhelm Leibniz's, George Boole's, Alan Turing's, Claude Shannon's, and Samuel Morse's insight: there are only two objects that a computer has to deal with in order to represent "anything".
+ All the information about any computable problem can be represented using only 0 and 1 (or any other bistable pair that can flip-flop between two easily distinguishable states, such as "on/off", "magnetized/de-magnetized", "high-voltage/low-voltage", etc.).
+
+ Alan Turing's insight: there are only five actions that a computer has to perform in order to do "anything".
+ Every algorithm can be expressed in a language for a computer consisting of only five basic instructions:
+ move left one location;
+ move right one location;
+ read symbol at current location;
+ print 0 at current location;
+ print 1 at current location.
+
+ Corrado Böhm and Giuseppe Jacopini's insight: there are only three ways of combining these actions (into more complex ones) that are needed in order for a computer to do "anything".
+
+ Only three rules are needed to combine any set of basic instructions into more complex ones:
+sequence: first do this, then do that;
+  selection: IF such-and-such is the case, THEN do this, ELSE do that;
+ repetition: WHILE such-and-such is the case, DO this.
+ The three rules of Boehm's and Jacopini's insight can be further simplified with the use of goto (which means it is more elementary than structured programming).
+
+Programming paradigms
+
+Programming languages can be used to accomplish different tasks in different ways. Common programming paradigms include:
+ Functional programming, a style of building the structure and elements of computer programs that treats computation as the evaluation of mathematical functions and avoids state and mutable data. It is a declarative programming paradigm, which means programming is done with expressions or declarations instead of statements.
+ Imperative programming, a programming paradigm that uses statements that change a program's state. In much the same way that the imperative mood in natural languages expresses commands, an imperative program consists of commands for the computer to perform. Imperative programming focuses on describing how a program operates.
+ Object-oriented programming, a programming paradigm based on the concept of "objects", which may contain data, in the form of fields, often known as attributes; and code, in the form of procedures, often known as methods. A feature of objects is that an object's procedures can access and often modify the data fields of the object with which they are associated. Thus object-oriented computer programs are made out of objects that interact with one another.
+ Service-oriented programming, a programming paradigm that uses "services" as the unit of computer work, to design and implement integrated business applications and mission critical software programs
+
+Many languages offer support for multiple paradigms, making the distinction more a matter of style than of technical capabilities.
+
+Research
+
+Conferences are important events for computer science research. During these conferences, researchers from the public and private sectors present their recent work and meet. Unlike in most other academic fields, in computer science, the prestige of conference papers is greater than that of journal publications. One proposed explanation for this is the quick development of this relatively new field requires rapid review and distribution of results, a task better handled by conferences than by journals.
+
+Education
+
+Computer Science, known by its near synonyms, Computing, Computer Studies, has been taught in UK schools since the days of batch processing, mark sensitive cards and paper tape but usually to a select few students. In 1981, the BBC produced a micro-computer and classroom network and Computer Studies became common for GCE O level students (11–16-year-old), and Computer Science to A level students. Its importance was recognised, and it became a compulsory part of the National Curriculum, for Key Stage 3 & 4. In September 2014 it became an entitlement for all pupils over the age of 4.
+
+In the US, with 14,000 school districts deciding the curriculum, provision was fractured. According to a 2010 report by the Association for Computing Machinery (ACM) and Computer Science Teachers Association (CSTA), only 14 out of 50 states have adopted significant education standards for high school computer science. According to a 2021 report, only 51% of high schools in the US offer computer science.
+
+Israel, New Zealand, and South Korea have included computer science in their national secondary education curricula, and several others are following.
+
+See also
+
+ Glossary of computer science
+ List of computer scientists
+ List of computer science awards
+ List of pioneers in computer science
+ Outline of computer science
+
+Notes
+
+References
+
+Further reading
+
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ Peter J. Denning. Is computer science science?, Communications of the ACM, April 2005.
+ Peter J. Denning, Great principles in computing curricula, Technical Symposium on Computer Science Education, 2004.
+
+External links
+
+ DBLP Computer Science Bibliography
+ Association for Computing Machinery
+ Institute of Electrical and Electronics Engineers
+Catalan may refer to:
+
+Catalonia
+From, or related to Catalonia:
+ Catalan language, a Romance language
+ Catalans, an ethnic group formed by the people from, or with origins in, Northern or southern Catalonia
+
+Places
+ 13178 Catalan, asteroid #13178, named "Catalan"
+ Catalán (crater), a lunar crater named for Miguel Ángel Catalán
+ Çatalan, İvrindi, a village in Balıkesir province, Turkey
+ Çatalan, Karaisalı, a village in Adana Province, Turkey
+ Catalan Bay, Gibraltar
+ Catalan Sea, more commonly known as the Balearic Sea
+ Catalan Mediterranean System, the Catalan Mountains
+
+Facilities and structures
+ Çatalan Bridge, Adana, Turkey
+ Çatalan Dam, Adana, Turkey
+ Catalan Batteries, Gibraltar
+
+People
+ Catalan, Lord of Monaco (1415–1457), Lord of Monaco from 1454 until 1457
+ Alfredo Catalán (born 1968), Venezuelan politician
+ Alex Catalán (born 1968), Spanish filmmaker
+ Arnaut Catalan (1219–1253), troubador
+ Diego Catalán (1928–2008), Spanish philologist
+ Emilio Arenales Catalán (1922–1969) Guatemalan politician
+ Eugène Charles Catalan (1814–1894), French and Belgian mathematician
+ Miguel A. Catalán (1894–1957), Spanish spectroscopist
+ Moses Chayyim Catalan (died 1661), Italian rabbi
+ Sergio Catalán (born 1991) Chilean soccer player
+
+Mathematics
+Mathematical concepts named after mathematician Eugène Catalan:
+ Catalan numbers, a sequence of natural numbers that occur in various counting problems
+ Catalan solids, a family of polyhedra
+ Catalan's constant, a number that occurs in estimates in combinatorics
+ Catalan's conjecture
+
+Wine
+ Catalan (grape), another name for the wine grape Mourvèdre
+ Catalan wine, an alternative name used in France for wine made from the Carignan grape
+ Carignan, a wine grape that is also known as Catalan
+
+Sports and games
+ Catalan Opening, in chess
+ Catalan Open, golf tournament
+ Catalans Dragons, a rugby league team often known simply as Catalan
+ XIII Catalan, a rugby league team from Perpignan, France
+
+Other uses
+ Battle of Catalán (1817) in Uruguay 
+ Catalan Sheepdog
+ Catalan Company, medieval mercenary company
+ Catalan vault, architectural design element
+ The Catalans, a 1953 novel by Patrick O'Brian
+
+See also
+
+ 
+
+Catalonia (disambiguation)
+Catalunya (disambiguation)
+ Catalan exonyms
+ Anti-Catalanism
+
+Language and nationality disambiguation pages
+Ethnonymic surnames
+Creationism is the religious belief that nature, and aspects such as the universe, Earth, life, and humans, originated with supernatural acts of divine creation.  In its broadest sense, creationism includes a continuum of religious views, which vary in their acceptance or rejection of scientific explanations such as evolution that describe the origin and development of natural phenomena.
+
+The term creationism most often refers to belief in special creation; the claim that the universe and lifeforms were created as they exist today by divine action, and that the only true explanations are those which are compatible with a Christian fundamentalist literal interpretation of the creation myth found in the Bible's Genesis creation narrative. Since the 1970s, the most common form of this has been Young Earth creationism which posits special creation of the universe and lifeforms within the last 10,000 years on the basis of flood geology, and promotes pseudoscientific creation science. From the 18th century onward, Old Earth creationism accepted geological time harmonized with Genesis through gap or day-age theory, while supporting anti-evolution. Modern old-Earth creationists support progressive creationism and continue to reject evolutionary explanations. Following political controversy, creation science was reformulated as intelligent design and neo-creationism.
+
+Mainline Protestants and the Catholic Church reconcile modern science with their faith in Creation through forms of theistic evolution which hold that God purposefully created through the laws of nature, and accept evolution. Some groups call their belief evolutionary creationism. Less prominently, there are also members of the Islamic and Hindu faiths who are creationists. Use of the term "creationist" in this context dates back to Charles Darwin's unpublished 1842 sketch draft for what became On the Origin of Species, and he used the term later in letters to colleagues. In 1873, Asa Gray published an article in The Nation saying a "special creationist" who held that species "were supernaturally originated just as they are, by the very terms of his doctrine places them out of the reach of scientific explanation."
+
+Biblical basis
+The basis for many creationists' beliefs is a literal or quasi-literal interpretation of the Book of Genesis. The Genesis creation narratives (Genesis 1–2) describe how God brings the Universe into being in a series of creative acts over six days and places the first man and woman (Adam and Eve) in the Garden of Eden. This story is the basis of creationist cosmology and biology. The Genesis flood narrative (Genesis 6–9) tells how God destroys the world and all life through a great flood, saving representatives of each form of life by means of Noah's Ark. This forms the basis of creationist geology, better known as flood geology.
+
+Recent decades have seen attempts to de-link creationism from the Bible and recast it as science; these include creation science and intelligent design.
+
+Types
+To counter the common misunderstanding that the creation–evolution controversy was a simple dichotomy of views, with "creationists" set against "evolutionists", Eugenie Scott of the National Center for Science Education produced a diagram and description of a continuum of religious views as a spectrum ranging from extreme literal biblical creationism to materialist evolution, grouped under main headings. This was used in public presentations, then published in 1999 in Reports of the NCSE. Other versions of a taxonomy of creationists were produced, and comparisons made between the different groupings. In 2009 Scott produced a revised continuum taking account of these issues, emphasizing that intelligent design creationism overlaps other types, and each type is a grouping of various beliefs and positions. The revised diagram is labelled to shows a spectrum relating to positions on the age of the Earth, and the part played by special creation as against evolution. This was published in the book Evolution Vs. Creationism: An Introduction, and the NCSE website rewritten on the basis of the book version.
+
+The main general types are listed below.
+
+Young Earth creationism
+
+Young Earth creationists such as Ken Ham and Doug Phillips believe that God created the Earth within the last ten thousand years, with a literalist interpretation of the Genesis creation narrative, within the approximate time-frame of biblical genealogies. Most young Earth creationists believe that the universe has a similar age as the Earth. A few assign a much older age to the universe than to Earth. Young Earth creationism gives the universe an age consistent with the Ussher chronology and other young Earth time frames. Other young Earth creationists believe that the Earth and the universe were created with the appearance of age, so that the world appears to be much older than it is, and that this appearance is what gives the geological findings and other methods of dating the Earth and the universe their much longer timelines.
+
+The Christian organizations Answers in Genesis (AiG), Institute for Creation Research (ICR) and the Creation Research Society (CRS) promote young Earth creationism in the United States. Carl Baugh's Creation Evidence Museum in Texas, United States AiG's Creation Museum and Ark Encounter in Kentucky, United States were opened to promote young Earth creationism. Creation Ministries International promotes young Earth views in Australia, Canada, South Africa, New Zealand, the United States, and the United Kingdom.
+
+Among Roman Catholics, the Kolbe Center for the Study of Creation promotes similar ideas.
+
+Old Earth creationism
+
+Old Earth creationism holds that the physical universe was created by God, but that the creation event described in the Book of Genesis is to be taken figuratively. This group generally believes that the age of the universe and the age of the Earth are as described by astronomers and geologists, but that details of modern evolutionary theory are questionable.
+
+Old Earth creationism itself comes in at least three types:
+
+Gap creationism
+
+Gap creationism (also known as ruin-restoration creationism, restoration creationism, or the Gap Theory) is a form of old Earth creationism that posits that the six-yom creation period, as described in the Book of Genesis, involved six literal 24-hour days, but that there was a gap of time between two distinct creations in the first and the second verses of Genesis, which the theory states explains many scientific observations, including the age of the Earth. Thus, the six days of creation (verse 3 onwards) start sometime after the Earth was "without form and void." This allows an indefinite gap of time to be inserted after the original creation of the universe, but prior to the Genesis creation narrative, (when present biological species and humanity were created). Gap theorists can therefore agree with the scientific consensus regarding the age of the Earth and universe, while maintaining a literal interpretation of the biblical text.
+
+Some gap creationists expand the basic version of creationism by proposing a "primordial creation" of biological life within the "gap" of time. This is thought to be "the world that then was" mentioned in 2 Peter 3:3–6. Discoveries of fossils and archaeological ruins older than 10,000 years are generally ascribed to this "world that then was," which may also be associated with Lucifer's rebellion.
+
+Day-age creationism
+
+Day-age creationism, a type of old Earth creationism, is a metaphorical interpretation of the creation accounts in Genesis. It holds that the six days referred to in the Genesis account of creation are not ordinary 24-hour days, but are much longer periods (from thousands to billions of years). The Genesis account is then reconciled with the age of the Earth. Proponents of the day-age theory can be found among both theistic evolutionists, who accept the scientific consensus on evolution, and progressive creationists, who reject it. The theories are said to be built on the understanding that the Hebrew word yom is also used to refer to a time period, with a beginning and an end and not necessarily that of a 24-hour day.
+
+The day-age theory attempts to reconcile the Genesis creation narrative and modern science by asserting that the creation "days" were not ordinary 24-hour days, but actually lasted for long periods of time (as day-age implies, the "days" each lasted an age). According to this view, the sequence and duration of the creation "days" may be paralleled to the scientific consensus for the age of the earth and the universe.
+
+Progressive creationism
+
+Progressive creationism is the religious belief that God created new forms of life gradually over a period of hundreds of millions of years. As a form of old Earth creationism, it accepts mainstream geological and cosmological estimates for the age of the Earth, some tenets of biology such as microevolution as well as archaeology to make its case. In this view creation occurred in rapid bursts in which all "kinds" of plants and animals appear in stages lasting millions of years. The bursts are followed by periods of stasis or equilibrium to accommodate new arrivals. These bursts represent instances of God creating new types of organisms by divine intervention. As viewed from the archaeological record, progressive creationism holds that "species do not gradually appear by the steady transformation of its ancestors; [but] appear all at once and "fully formed."
+
+The view rejects macroevolution, claiming it is biologically untenable and not supported by the fossil record, as well as rejects the concept of common descent from a last universal common ancestor. Thus the evidence for macroevolution is claimed to be false, but microevolution is accepted as a genetic parameter designed by the Creator into the fabric of genetics to allow for environmental adaptations and survival. Generally, it is viewed by proponents as a middle ground between literal creationism and evolution. Organizations such as Reasons To Believe, founded by Hugh Ross, promote this version of creationism.
+
+Progressive creationism can be held in conjunction with hermeneutic approaches to the Genesis creation narrative such as the day-age creationism or framework/metaphoric/poetic views.
+
+Philosophic and scientific creationism
+
+Creation science
+
+Creation science, or initially scientific creationism, is a pseudoscience that emerged in the 1960s with proponents aiming to have young Earth creationist beliefs taught in school science classes as a counter to teaching of evolution. Common features of creation science argument include: creationist cosmologies which accommodate a universe on the order of thousands of years old, criticism of radiometric dating through a technical argument about radiohalos, explanations for the fossil record as a record of the Genesis flood narrative (see flood geology), and explanations for the present diversity as a result of pre-designed genetic variability and partially due to the rapid degradation of the perfect genomes God placed in "created kinds" or "baramins" due to mutations.
+
+Neo-creationism
+
+Neo-creationism is a pseudoscientific movement which aims to restate creationism in terms more likely to be well received by the public, by policy makers, by educators and by the scientific community. It aims to re-frame the debate over the origins of life in non-religious terms and without appeals to scripture. This comes in response to the 1987 ruling by the United States Supreme Court in Edwards v. Aguillard that creationism is an inherently religious concept and that advocating it as correct or accurate in public-school curricula violates the Establishment Clause of the First Amendment.
+
+One of the principal claims of neo-creationism propounds that ostensibly objective orthodox science, with a foundation in naturalism, is actually a dogmatically atheistic religion. Its proponents argue that the scientific method excludes certain explanations of phenomena, particularly where they point towards supernatural elements, thus effectively excluding religious insight from contributing to understanding the universe. This leads to an open and often hostile opposition to what neo-creationists term "Darwinism", which they generally mean to refer to evolution, but which they may extend to include such concepts as abiogenesis, stellar evolution and the Big Bang theory.
+
+Unlike their philosophical forebears, neo-creationists largely do not believe in many of the traditional cornerstones of creationism such as a young Earth, or in a dogmatically literal interpretation of the Bible.
+
+Intelligent design
+
+Intelligent design (ID) is the pseudoscientific view that "certain features of the universe and of living things are best explained by an intelligent cause, not an undirected process such as natural selection." All of its leading proponents are associated with the Discovery Institute, a think tank whose wedge strategy aims to replace the scientific method with "a science consonant with Christian and theistic convictions" which accepts supernatural explanations. It is widely accepted in the scientific and academic communities that intelligent design is a form of creationism, and is sometimes referred to as "intelligent design creationism."
+
+ID originated as a re-branding of creation science in an attempt to avoid a series of court decisions ruling out the teaching of creationism in American public schools, and the Discovery Institute has run a series of campaigns to change school curricula. In Australia, where curricula are under the control of state governments rather than local school boards, there was a public outcry when the notion of ID being taught in science classes was raised by the Federal Education Minister Brendan Nelson; the minister quickly conceded that the correct forum for ID, if it were to be taught, is in religious or philosophy classes.
+
+In the US, teaching of intelligent design in public schools has been decisively ruled by a federal district court to be in violation of the Establishment Clause of the First Amendment to the United States Constitution. In Kitzmiller v. Dover, the court found that intelligent design is not science and "cannot uncouple itself from its creationist, and thus religious, antecedents," and hence cannot be taught as an alternative to evolution in public school science classrooms under the jurisdiction of that court. This sets a persuasive precedent, based on previous US Supreme Court decisions in Edwards v. Aguillard and Epperson v. Arkansas (1968), and by the application of the Lemon test, that creates a legal hurdle to teaching intelligent design in public school districts in other federal court jurisdictions.
+
+Geocentrism
+
+In astronomy, the geocentric model (also known as geocentrism, or the Ptolemaic system), is a description of the cosmos where Earth is at the orbital center of all celestial bodies. This model served as the predominant cosmological system in many ancient civilizations such as ancient Greece. As such, they assumed that the Sun, Moon, stars, and naked eye planets circled Earth, including the noteworthy systems of Aristotle (see Aristotelian physics) and Ptolemy.
+
+Articles arguing that geocentrism was the biblical perspective appeared in some early creation science newsletters associated with the Creation Research Society pointing to some passages in the Bible, which, when taken literally, indicate that the daily apparent motions of the Sun and the Moon are due to their actual motions around the Earth rather than due to the rotation of the Earth about its axis. For example,  where the Sun and Moon are said to stop in the sky, and  where the world is described as immobile. Contemporary advocates for such religious beliefs include Robert Sungenis, co-author of the self-published Galileo Was Wrong: The Church Was Right (2006). These people subscribe to the view that a plain reading of the Bible contains an accurate account of the manner in which the universe was created and requires a geocentric worldview. 
+Most contemporary creationist organizations reject such perspectives.
+
+Omphalos hypothesis 
+
+The Omphalos hypothesis is one attempt to reconcile the scientific evidence that the universe is billions of years old with a literal interpretation of the Genesis creation narrative, which implies that the Earth is only a few thousand years old. It is based on the religious belief that the universe was created by a divine being, within the past six to ten thousand years (in keeping with flood geology), and that the presence of objective, verifiable evidence that the universe is older than approximately ten millennia is due to the creator introducing false evidence that makes the universe appear significantly older.
+
+The idea was named after the title of an 1857 book, Omphalos by Philip Henry Gosse, in which Gosse argued that in order for the world to be functional God must have created the Earth with mountains and canyons, trees with growth rings, Adam and Eve with fully grown hair, fingernails, and navels (ὀμφαλός omphalos is Greek for "navel"), and all living creatures with fully formed evolutionary features, etc..., and that, therefore, no empirical evidence about the age of the Earth or universe can be taken as reliable.
+
+Various supporters of Young Earth creationism have given different explanations for their belief that the universe is filled with false evidence of the universe's age, including a belief that some things needed to be created at a certain age for the ecosystems to function, or their belief that the creator was deliberately planting deceptive evidence. The idea has seen some revival in the 20th century by some modern creationists, who have extended the argument to address the "starlight problem". The idea has been criticised as Last Thursdayism, and on the grounds that it requires a deliberately deceptive creator.
+
+Theistic evolution
+
+Theistic evolution, or evolutionary creation, is a belief that "the personal God of the Bible created the universe and life through evolutionary processes." According to the American Scientific Affiliation:
+
+Through the 19th century the term creationism most commonly referred to direct creation of individual souls, in contrast to traducianism. Following the publication of Vestiges of the Natural History of Creation, there was interest in ideas of Creation by divine law. In particular, the liberal theologian Baden Powell argued that this illustrated the Creator's power better than the idea of miraculous creation, which he thought ridiculous. When On the Origin of Species was published, the cleric Charles Kingsley wrote of evolution as "just as noble a conception of Deity." Darwin's view at the time was of God creating life through the laws of nature, and the book makes several references to "creation," though he later regretted using the term rather than calling it an unknown process. In America, Asa Gray argued that evolution is the secondary effect, or modus operandi, of the first cause, design, and published a pamphlet defending the book in theistic terms, Natural Selection not inconsistent with Natural Theology. Theistic evolution, also called, evolutionary creation, became a popular compromise, and St. George Jackson Mivart was among those accepting evolution but attacking Darwin's naturalistic mechanism. Eventually it was realised that supernatural intervention could not be a scientific explanation, and naturalistic mechanisms such as neo-Lamarckism were favoured as being more compatible with purpose than natural selection.
+
+Some theists took the general view that, instead of faith being in opposition to biological evolution, some or all classical religious teachings about Christian God and creation are compatible with some or all of modern scientific theory, including specifically evolution; it is also known as "evolutionary creation." In Evolution versus Creationism, Eugenie Scott and Niles Eldredge state that it is in fact a type of evolution.
+
+It generally views evolution as a tool used by God, who is both the first cause and immanent sustainer/upholder of the universe; it is therefore well accepted by people of strong theistic (as opposed to deistic) convictions. Theistic evolution can synthesize with the day-age creationist interpretation of the Genesis creation narrative; however most adherents consider that the first chapters of the Book of Genesis should not be interpreted as a "literal" description, but rather as a literary framework or allegory.
+
+From a theistic viewpoint, the underlying laws of nature were designed by God for a purpose, and are so self-sufficient that the complexity of the entire physical universe evolved from fundamental particles in processes such as stellar evolution, life forms developed in biological evolution, and in the same way the origin of life by natural causes has resulted from these laws.
+
+In one form or another, theistic evolution is the view of creation taught at the majority of mainline Protestant seminaries. For Roman Catholics, human evolution is not a matter of religious teaching, and must stand or fall on its own scientific merits. Evolution and the Roman Catholic Church are not in conflict. The Catechism of the Catholic Church comments positively on the theory of evolution, which is neither precluded nor required by the sources of faith, stating that scientific studies "have splendidly enriched our knowledge of the age and dimensions of the cosmos, the development of life-forms and the appearance of man." Roman Catholic schools teach evolution without controversy on the basis that scientific knowledge does not extend beyond the physical, and scientific truth and religious truth cannot be in conflict. Theistic evolution can be described as "creationism" in holding that divine intervention brought about the origin of life or that divine laws govern formation of species, though many creationists (in the strict sense) would deny that the position is creationism at all. In the creation–evolution controversy, its proponents generally take the "evolutionist" side. This sentiment was expressed by Fr. George Coyne, (the Vatican's chief astronomer between 1978 and 2006):...in America, creationism has come to mean some fundamentalistic, literal, scientific interpretation of Genesis. Judaic-Christian faith is radically creationist, but in a totally different sense. It is rooted in a belief that everything depends upon God, or better, all is a gift from God.
+
+While supporting the methodological naturalism inherent in modern science, the proponents of theistic evolution reject the implication taken by some atheists that this gives credence to ontological materialism. In fact, many modern philosophers of science, including atheists, refer to the long-standing convention in the scientific method that observable events in nature should be explained by natural causes, with the distinction that it does not assume the actual existence or non-existence of the supernatural.
+
+Religious views
+There are also non-Christian forms of creationism, notably Islamic creationism and Hindu creationism.
+
+Bahá'í Faith
+
+In the creation myth taught by Bahá'u'lláh, the Bahá'í Faith founder, the universe has "neither beginning nor ending," and that the component elements of the material world have always existed and will always exist. With regard to evolution and the origin of human beings, 'Abdu'l-Bahá gave extensive comments on the subject when he addressed western audiences in the beginning of the 20th century. Transcripts of these comments can be found in Some Answered Questions, Paris Talks and The Promulgation of Universal Peace. 'Abdu'l-Bahá described the human species as having evolved from a primitive form to modern man, but that the capacity to form human intelligence was always in existence.
+
+Buddhism
+
+Buddhism denies a creator deity and posits that mundane deities such as Mahabrahma are sometimes misperceived to be a creator. While Buddhism includes belief in divine beings called devas, it holds that they are mortal, limited in their power, and that none of them are creators of the universe. In the Saṃyutta Nikāya, the Buddha also states that the cycle of rebirths stretches back hundreds of thousands of eons, without discernible beginning.
+
+Major Buddhist Indian philosophers such as Nagarjuna, Vasubandhu, Dharmakirti and Buddhaghosa, consistently critiqued Creator God views put forth by Hindu thinkers.
+
+Christianity
+
+, most Christians around the world accepted evolution as the most likely explanation for the origins of species, and did not take a literal view of the Genesis creation narrative. The United States is an exception where belief in religious fundamentalism is much more likely to affect attitudes towards evolution than it is for believers elsewhere. Political partisanship affecting religious belief may be a factor because political partisanship in the US is highly correlated with fundamentalist thinking, unlike in Europe.
+
+Most contemporary Christian leaders and scholars from mainstream churches, such as Anglicans and Lutherans, consider that there is no conflict between the spiritual meaning of creation and the science of evolution. According to the former archbishop of Canterbury, Rowan Williams, "for most of the history of Christianity, and I think this is fair enough, most of the history of the Christianity there's been an awareness that a belief that everything depends on the creative act of God, is quite compatible with a degree of uncertainty or latitude about how precisely that unfolds in creative time."
+
+Leaders of the Anglican and Roman Catholic churches have made statements in favor of evolutionary theory, as have scholars such as the physicist John Polkinghorne, who argues that evolution is one of the principles through which God created living beings. Earlier supporters of evolutionary theory include Frederick Temple, Asa Gray and Charles Kingsley who were enthusiastic supporters of Darwin's theories upon their publication, and the French Jesuit priest and geologist Pierre Teilhard de Chardin saw evolution as confirmation of his Christian beliefs, despite condemnation from Church authorities for his more speculative theories. Another example is that of Liberal theology, not providing any creation models, but instead focusing on the symbolism in beliefs of the time of authoring Genesis and the cultural environment.
+
+Many Christians and Jews had been considering the idea of the creation history as an allegory (instead of historical) long before the development of Darwin's theory of evolution. For example, Philo, whose works were taken up by early Church writers, wrote that it would be a mistake to think that creation happened in six days, or in any set amount of time. Augustine of the late fourth century who was also a former neoplatonist argued that everything in the universe was created by God at the same moment in time (and not in six days as a literal reading of the Book of Genesis would seem to require); It appears that both Philo and Augustine felt uncomfortable with the idea of a seven-day creation because it detracted from the notion of God's omnipotence. In 1950, Pope Pius XII stated limited support for the idea in his encyclical . In 1996, Pope John Paul II stated that "new knowledge has led to the recognition of the theory of evolution as more than a hypothesis," but, referring to previous papal writings, he concluded that "if the human body takes its origin from pre-existent living matter, the spiritual soul is immediately created by God."
+
+In the US, Evangelical Christians have continued to believe in a literal Genesis. , members of evangelical Protestant (70%), Mormon (76%) and Jehovah's Witnesses (90%) denominations were the most likely to reject the evolutionary interpretation of the origins of life.
+
+Jehovah's Witnesses adhere to a combination of gap creationism and day-age creationism, asserting that scientific evidence about the age of the universe is compatible with the Bible, but that the 'days' after Genesis 1:1 were each thousands of years in length.
+
+The historic Christian literal interpretation of creation requires the harmonization of the two creation stories, Genesis 1:1–2:3 and Genesis 2:4–25, for there to be a consistent interpretation. They sometimes seek to ensure that their belief is taught in science classes, mainly in American schools. Opponents reject the claim that the literalistic biblical view meets the criteria required to be considered scientific. Many religious groups teach that God created the Cosmos. From the days of the early Christian Church Fathers there were allegorical interpretations of the Book of Genesis as well as literal aspects.
+
+Christian Science, a system of thought and practice derived from the writings of Mary Baker Eddy, interprets the Book of Genesis figuratively rather than literally. It holds that the material world is an illusion, and consequently not created by God: the only real creation is the spiritual realm, of which the material world is a distorted version. Christian Scientists regard the story of the creation in the Book of Genesis as having symbolic rather than literal meaning. According to Christian Science, both creationism and evolution are false from an absolute or "spiritual" point of view, as they both proceed from a (false) belief in the reality of a material universe. However, Christian Scientists do not oppose the teaching of evolution in schools, nor do they demand that alternative accounts be taught: they believe that both material science and literalist theology are concerned with the illusory, mortal and material, rather than the real, immortal and spiritual. With regard to material theories of creation, Eddy showed a preference for Darwin's theory of evolution over others.
+
+Hinduism
+
+Hindu creationists claim that species of plants and animals are material forms adopted by pure consciousness which live an endless cycle of births and rebirths. Ronald Numbers says that: "Hindu Creationists have insisted on the antiquity of humans, who they believe appeared fully formed as long, perhaps, as trillions of years ago." Hindu creationism is a form of old Earth creationism, according to Hindu creationists the universe may even be older than billions of years. These views are based on the Vedas, the creation myths of which depict an extreme antiquity of the universe and history of the Earth.
+
+In Hindu cosmology, time cyclically repeats general events of creation and destruction, with many "first man", each known as Manu, the progenitor of mankind. Each Manu successively reigns over a 306.72 million year period known as a , each ending with the destruction of mankind followed by a  (period of non-activity) before the next . 120.53million years have elapsed in the current  (current mankind) according to calculations on Hindu units of time. The universe is cyclically created at the start and destroyed at the end of a  (day of Brahma), lasting for 4.32billion years, which is followed by a  (period of dissolution) of equal length. 1.97billion years have elapsed in the current  (current universe). The universal elements or building blocks (unmanifest matter) exists for a period known as a , lasting for 311.04trillion years, which is followed by a  (period of great dissolution) of equal length. 155.52trillion years have elapsed in the current .
+
+Islam
+
+Islamic creationism is the belief that the universe (including humanity) was directly created by God as explained in the Quran. It usually views the Book of Genesis as a corrupted version of God's message. The creation myths in the Quran are vaguer and allow for a wider range of interpretations similar to those in other Abrahamic religions.
+
+Islam also has its own school of theistic evolutionism, which holds that mainstream scientific analysis of the origin of the universe is supported by the Quran. Some Muslims believe in evolutionary creation, especially among liberal movements within Islam.
+
+Writing for The Boston Globe, Drake Bennett noted: "Without a Book of Genesis to account for[...] Muslim creationists have little interest in proving that the age of the Earth is measured in the thousands rather than the billions of years, nor do they show much interest in the problem of the dinosaurs. And the idea that animals might evolve into other animals also tends to be less controversial, in part because there are passages of the Koran that seem to support it. But the issue of whether human beings are the product of evolution is just as fraught among Muslims." Khalid Anees, president of the Islamic Society of Britain, states that Muslims do not agree that one species can develop from another.
+
+Since the 1980s, Turkey has been a site of strong advocacy for creationism, supported by American adherents.
+
+There are several verses in the Qur'an which some modern writers have interpreted as being compatible with the expansion of the universe, Big Bang and Big Crunch theories:
+
+Ahmadiyya
+The Ahmadiyya movement actively promotes evolutionary theory. Ahmadis interpret scripture from the Qur'an to support the concept of macroevolution and give precedence to scientific theories. Furthermore, unlike orthodox Muslims, Ahmadis believe that humans have gradually evolved from different species. Ahmadis regard Adam as being the first Prophet of Godas opposed to him being the first man on Earth. Rather than wholly adopting the theory of natural selection, Ahmadis promote the idea of a "guided evolution," viewing each stage of the evolutionary process as having been selectively woven by God. Mirza Tahir Ahmad, Fourth Caliph of the Ahmadiyya Muslim Community has stated in his magnum opus Revelation, Rationality, Knowledge & Truth (1998) that evolution did occur but only through God being the One who brings it about. It does not occur itself, according to the Ahmadiyya Muslim Community.
+
+Judaism
+
+For Orthodox Jews who seek to reconcile discrepancies between science and the creation myths in the Bible, the notion that science and the Bible should even be reconciled through traditional scientific means is questioned. To these groups, science is as true as the Torah and if there seems to be a problem, epistemological limits are to blame for apparently irreconcilable points. They point to discrepancies between what is expected and what actually is to demonstrate that things are not always as they appear. They note that even the root word for 'world' in the Hebrew language, , means 'hidden' (). Just as they know from the Torah that God created man and trees and the light on its way from the stars in their observed state, so too can they know that the world was created in its over the six days of Creation that reflects progression to its currently-observed state, with the understanding that physical ways to verify this may eventually be identified. This knowledge has been advanced by Rabbi Dovid Gottlieb, former philosophy professor at Johns Hopkins University. Relatively old Kabbalistic sources from well before the scientifically apparent age of the universe was first determined are also in close concord with modern scientific estimates of the age of the universe, according to Rabbi Aryeh Kaplan, and based on Sefer Temunah, an early kabbalistic work attributed to the first-century Tanna Nehunya ben HaKanah. Many kabbalists accepted the teachings of the Sefer HaTemunah, including the medieval Jewish scholar Nahmanides, his close student Isaac ben Samuel of Acre, and David ben Solomon ibn Abi Zimra. Other parallels are derived, among other sources, from Nahmanides, who expounds that there was a Neanderthal-like species with which Adam mated (he did this long before Neanderthals had even been discovered scientifically). Reform Judaism does not take the Torah as a literal text, but rather as a symbolic or open-ended work.
+
+Some contemporary writers such as Rabbi Gedalyah Nadel have sought to reconcile the discrepancy between the account in the Torah, and scientific findings by arguing that each day referred to in the Bible was not 24 hours, but billions of years long. Others claim that the Earth was created a few thousand years ago, but was deliberately made to look as if it was five billion years old, e.g. by being created with ready made fossils. The best known exponent of this approach being Rabbi Menachem Mendel Schneerson. Others state that although the world was physically created in six 24-hour days, the Torah accounts can be interpreted to mean that there was a period of billions of years before the six days of creation.
+
+Prevalence
+
+Most vocal literalist creationists are from the US, and strict creationist views are much less common in other developed countries. According to a study published in Science, a survey of the US, Turkey, Japan and Europe showed that public acceptance of evolution is most prevalent in Iceland, Denmark and Sweden at 80% of the population. There seems to be no significant correlation between believing in evolution and understanding evolutionary science.
+
+Australia
+A 2009 Nielsen poll showed that 23% of Australians believe "the biblical account of human origins," 42%  believe in a "wholly scientific" explanation for the origins of life, while 32% believe in an evolutionary process "guided by God".
+
+A 2013 survey conducted by Auspoll and the Australian Academy of Science found that 80% of Australians believe in evolution (70% believe it is currently occurring, 10% believe in evolution but do not think it is currently occurring), 12% were not sure and 9% stated they do not believe in evolution.
+
+Brazil
+A 2011 Ipsos survey found that 47% of responders in Brazil identified themselves as "creationists and believe that human beings were in fact created by a spiritual force such as the God they believe in and do not believe that the origin of man came from evolving from other species such as apes".
+
+In 2004, IBOPE conducted a poll in Brazil that asked questions about creationism and the teaching of creationism in schools. When asked if creationism should be taught in schools, 89% of people said that creationism should be taught in schools. When asked if the teaching of creationism should replace the teaching of evolution in schools, 75% of people said that the teaching of creationism should replace the teaching of evolution in schools.
+
+Canada
+
+A 2012 survey, by Angus Reid Public Opinion revealed that 61 percent of Canadians believe in evolution. The poll asked "Where did human beings come fromdid we start as singular cells millions of year ago and evolve into our present form, or did God create us in his image 10,000 years ago?"
+
+In 2019, a Research Co. poll asked people in Canada if creationism "should be part of the school curriculum in their province". 38% of Canadians said that creationism should be part of the school curriculum, 39% of Canadians said that it should not be part of the school curriculum, and 23% of Canadians were undecided.
+
+In 2023, a Research Co. poll found that 21% of Canadians "believe God created human beings in their present form within the last 10,000 years". The poll also found that "More than two-in-five Canadians (43%) think creationism should be part of the school curriculum in their province."
+
+Europe
+In Europe, literalist creationism is more widely rejected, though regular opinion polls are not available. Most people accept that evolution is the most widely accepted scientific theory as taught in most schools. In countries with a Roman Catholic majority, papal acceptance of evolutionary creationism as worthy of study has essentially ended debate on the matter for many people.
+
+In the UK, a 2006 poll on the "origin and development of life", asked participants to choose between three different perspectives on the origin of life: 22% chose creationism, 17% opted for intelligent design, 48% selected evolutionary theory, and the rest did not know. A subsequent 2010 YouGov poll on the correct explanation for the origin of humans found that 9% opted for creationism, 12% intelligent design, 65% evolutionary theory and 13% didn't know. The former Archbishop of Canterbury Rowan Williams, head of the worldwide Anglican Communion, views the idea of teaching creationism in schools as a mistake. In 2009, an Ipsos Mori survey in the United Kingdom found that 54% of Britons agreed with the view: "Evolutionary theories should be taught in science lessons in schools together with other possible perspectives, such as intelligent design and creationism."
+
+In Italy, Education Minister Letizia Moratti wanted to retire evolution from the secondary school level; after one week of massive protests, she reversed her opinion.
+
+There continues to be scattered and possibly mounting efforts on the part of religious groups throughout Europe to introduce creationism into public education. In response, the Parliamentary Assembly of the Council of Europe has released a draft report titled The dangers of creationism in education on June 8, 2007, reinforced by a further proposal of banning it in schools dated October 4, 2007.
+
+Serbia suspended the teaching of evolution for one week in September 2004, under education minister Ljiljana Čolić, only allowing schools to reintroduce evolution into the curriculum if they also taught creationism. "After a deluge of protest from scientists, teachers and opposition parties" says the BBC report, Čolić's deputy made the statement, "I have come here to confirm Charles Darwin is still alive" and announced that the decision was reversed. Čolić resigned after the government said that she had caused "problems that had started to reflect on the work of the entire government."
+
+Poland saw a major controversy over creationism in 2006, when the Deputy Education Minister, Mirosław Orzechowski, denounced evolution as "one of many lies" taught in Polish schools. His superior, Minister of Education Roman Giertych, has stated that the theory of evolution would continue to be taught in Polish schools, "as long as most scientists in our country say that it is the right theory." Giertych's father, Member of the European Parliament Maciej Giertych, has opposed the teaching of evolution and has claimed that dinosaurs and humans co-existed.
+
+A June 2015 - July 2016 Pew poll of Eastern European countries found that 56% of people from Armenia say that humans and other living things have "Existed in present state since the beginning of time". Armenia is followed by 52% from Bosnia, 42% from Moldova, 37% from Lithuania, 34% from Georgia and Ukraine, 33% from Croatia and Romania, 31% from Bulgaria, 29% from Greece and Serbia, 26% from Russia, 25% from Latvia, 23% from Belarus and Poland, 21% from Estonia and Hungary, and 16% from the Czech Republic.
+
+South Africa
+A 2011 Ipsos survey found that 56% of responders in South Africa identified themselves as "creationists and believe that human beings were in fact created by a spiritual force such as the God they believe in and do not believe that the origin of man came from evolving from other species such as apes".
+
+South Korea
+In 2009, an EBS survey in South Korea found that 63% of people believed that creation and evolution should both be taught in schools simultaneously.
+
+United States
+
+A 2017 poll by Pew Research found that 62% of Americans believe humans have evolved over time and 34% of Americans believe humans and other living things have existed in their present form since the beginning of time.   A 2019 Gallup creationism survey found that 40% of adults in the United States inclined to the view that "God created humans in their present form at one time within the last 10,000 years" when asked for their views on the origin and development of human beings.
+
+According to a 2014 Gallup poll, about 42% of Americans believe that "God created human beings pretty much in their present form at one time within the last 10,000 years or so."  Another 31% believe that "human beings have developed over millions of years from less advanced forms of life, but God guided this process,"and 19% believe that "human beings have developed over millions of years from less advanced forms of life, but God had no part in this process."
+
+Belief in creationism is inversely correlated to education; of those with postgraduate degrees, 74% accept evolution. In 1987, Newsweek reported: "By one count there are some 700 scientists with respectable academic credentials (out of a total of 480,000 U.S. earth and life scientists) who give credence to creation-science, the general theory that complex life forms did not evolve but appeared 'abruptly.'"
+
+A 2000 poll for People for the American Way found 70% of the US public felt that evolution was compatible with a belief in God.
+
+According to a study published in Science, between 1985 and 2005 the number of adult North Americans who accept evolution declined from 45% to 40%, the number of adults who reject evolution declined from 48% to 39% and the number of people who were unsure increased from 7% to 21%. Besides the US the study also compared data from 32 European countries, Turkey, and Japan. The only country where acceptance of evolution was lower than in the US was Turkey (25%).
+
+According to a 2011 Fox News poll, 45% of Americans believe in creationism, down from 50% in a similar poll in 1999. 21% believe in 'the theory of evolution as outlined by Darwin and other scientists' (up from 15% in 1999), and 27% answered that both are true (up from 26% in 1999).
+
+In September 2012, educator and television personality Bill Nye spoke with the Associated Press and aired his fears about acceptance of creationism, believing that teaching children that creationism is the only true answer without letting them understand the way science works will prevent any future innovation in the world of science. In February 2014, Nye defended evolution in the classroom in a debate with creationist Ken Ham on the topic of whether creation is a viable model of origins in today's modern, scientific era.
+
+Education controversies
+
+In the US, creationism has become centered in the political controversy over creation and evolution in public education, and whether teaching creationism in science classes conflicts with the separation of church and state. Currently, the controversy comes in the form of whether advocates of the intelligent design movement who wish to "Teach the Controversy" in science classes have conflated science with religion.
+
+People for the American Way polled 1500 North Americans about the teaching of evolution and creationism in November and December 1999. They found that most North Americans were not familiar with creationism, and most North Americans had heard of evolution, but many did not fully understand the basics of the theory. The main findings were:
+
+In such political contexts, creationists argue that their particular religiously based origin belief is superior to those of other belief systems, in particular those made through secular or scientific rationale. Political creationists are opposed by many individuals and organizations who have made detailed critiques and given testimony in various court cases that the alternatives to scientific reasoning offered by creationists are opposed by the consensus of the scientific community.
+
+Criticism
+
+Christian criticism
+Most Christians disagree with the teaching of creationism as an alternative to evolution in schools. Several religious organizations, among them the Catholic Church, hold that their faith does not conflict with the scientific consensus regarding evolution. The Clergy Letter Project, which has collected more than 13,000 signatures, is an "endeavor designed to demonstrate that religion and science can be compatible."
+
+In his 2002 article "Intelligent Design as a Theological Problem," George Murphy argues against the view that life on Earth, in all its forms, is direct evidence of God's act of creation (Murphy quotes Phillip E. Johnson's claim that he is speaking "of a God who acted openly and left his fingerprints on all the evidence."). Murphy argues that this view of God is incompatible with the Christian understanding of God as "the one revealed in the cross and resurrection of Christ." The basis of this theology is Isaiah 45:15, "Verily thou art a God that hidest thyself, O God of Israel, the Saviour."
+
+Murphy observes that the execution of a Jewish carpenter by Roman authorities is in and of itself an ordinary event and did not require divine action. On the contrary, for the crucifixion to occur, God had to limit or "empty" himself. It was for this reason that Paul the Apostle wrote, in Philippians 2:5-8:
+
+Let this mind be in you, which was also in Christ Jesus: Who, being in the form of God, thought it not robbery to be equal with God: But made himself of no reputation, and took upon him the form of a servant, and was made in the likeness of men: And being found in fashion as a man, he humbled himself, and became obedient unto death, even the death of the cross.
+
+Murphy concludes that,Just as the Son of God limited himself by taking human form and dying on a cross, God limits divine action in the world to be in accord with rational laws which God has chosen. This enables us to understand the world on its own terms, but it also means that natural processes hide God from scientific observation.For Murphy, a theology of the cross requires that Christians accept a methodological naturalism, meaning that one cannot invoke God to explain natural phenomena, while recognizing that such acceptance does not require one to accept a metaphysical naturalism, which proposes that nature is all that there is.
+
+The Jesuit priest George Coyne has stated that it is "unfortunate that, especially here in America, creationism has come to mean...some literal interpretation of Genesis." He argues that "...Judaic-Christian faith is radically creationist, but in a totally different sense. It is rooted in belief that everything depends on God, or better, all is a gift from God."
+
+Teaching of creationism
+Other Christians have expressed qualms about teaching creationism. In March 2006, then Archbishop of Canterbury Rowan Williams, the leader of the world's Anglicans, stated his discomfort about teaching creationism, saying that creationism was "a kind of category mistake, as if the Bible were a theory like other theories." He also said: "My worry is creationism can end up reducing the doctrine of creation rather than enhancing it." The views of the Episcopal Churcha major American-based branch of the Anglican Communionon teaching creationism resemble those of Williams.
+
+The National Science Teachers Association is opposed to teaching creationism as a science, as is the Association for Science Teacher Education, the National Association of Biology Teachers, the American Anthropological Association, the American Geosciences Institute, the Geological Society of America, the American Geophysical Union, and numerous other professional teaching and scientific societies.
+
+In April 2010, the American Academy of Religion issued Guidelines for Teaching About Religion in K‐12 Public Schools in the United States, which included guidance that creation science or intelligent design should not be taught in science classes, as "Creation science and intelligent design represent worldviews that fall outside of the realm of science that is defined as (and limited to) a method of inquiry based on gathering observable and measurable evidence subject to specific principles of reasoning." However, they, as well as other "worldviews that focus on speculation regarding the origins of life represent another important and relevant form of human inquiry that is appropriately studied in literature or social sciences courses. Such study, however, must include a diversity of worldviews representing a variety of religious and philosophical perspectives and must avoid privileging one view as more legitimate than others."
+
+Randy Moore and Sehoya Cotner, from the biology program at the University of Minnesota, reflect on the relevance of teaching creationism in the article "The Creationist Down the Hall: Does It Matter When Teachers Teach Creationism?", in which they write: "Despite decades of science education reform, numerous legal decisions declaring the teaching of creationism in public-school science classes to be unconstitutional, overwhelming evidence supporting evolution, and the many denunciations of creationism as nonscientific by professional scientific societies, creationism remains popular throughout the United States."
+
+Scientific criticism
+
+Science is a system of knowledge based on observation, empirical evidence, and the development of theories that yield testable explanations and predictions of natural phenomena. By contrast, creationism is often based on literal interpretations of the narratives of particular religious texts. Creationist beliefs involve purported forces that lie outside of nature, such as supernatural intervention, and often do not allow predictions at all. Therefore, these can neither be confirmed nor disproved by scientists. However, many creationist beliefs can be framed as testable predictions about phenomena such as the age of the Earth, its geological history and the origins, distributions and relationships of living organisms found on it. Early science incorporated elements of these beliefs, but as science developed these beliefs were gradually falsified and were replaced with understandings based on accumulated and reproducible evidence that often allows the accurate prediction of future results.
+
+Some scientists, such as Stephen Jay Gould, consider science and religion to be two compatible and complementary fields, with authorities in distinct areas of human experience, so-called non-overlapping magisteria. This view is also held by many theologians, who believe that ultimate origins and meaning are addressed by religion, but favor verifiable scientific explanations of natural phenomena over those of creationist beliefs. Other scientists, such as Richard Dawkins, reject the non-overlapping magisteria and argue that, in disproving literal interpretations of creationists, the scientific method also undermines religious texts as a source of truth. Irrespective of this diversity in viewpoints, since creationist beliefs are not supported by empirical evidence, the scientific consensus is that any attempt to teach creationism as science should be rejected.
+
+Organizations
+
+See also
+
+ Biblical inerrancy
+ Biogenesis
+ Evolution of complexity
+ Flying Spaghetti Monster
+ History of creationism
+ Religious cosmology
+
+Notes
+
+References
+
+Citations
+
+Works cited
+
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+  "Presented as a Paleontological Society short course at the annual meeting of the Geological Society of America, Denver, Colorado, October 24, 1999."
+
+Further reading
+
+External links
+
+ "Creationism" at the Stanford Encyclopedia of Philosophy by Michael Ruse
+ "How Creationism Works" at HowStuffWorks by Julia Layton
+ "TIMELINE: Evolution, Creationism and Intelligent Design" Focuses on major historical and recent events in the scientific and political debate
+   by Warren D. Allmon, Director of the Museum of the Earth
+ "What is creationism?" at talk.origins by Mark Isaak
+ "The Creation/Evolution Continuum" by Eugenie Scott
+ "15 Answers to Creationist Nonsense" by John Rennie, editor in chief of Scientific American magazine
+ "Race, Evolution and the Science of Human Origins" by Allison Hopper, Scientific American (July 5, 2021).
+ Human Timeline (Interactive) Smithsonian, National Museum of Natural History (August 2016)
+
+ 
+Christian terminology
+Creation myths
+Denialism
+Obsolete biology theories
+Origin of life
+Pseudoscience
+Religious cosmologies
+Theism
+Chad (; ), officially the Republic of Chad, is a landlocked country in Central Africa. It borders Libya to the north, Sudan to the east, the Central African Republic to the south, Cameroon and Nigeria to the southwest, and Niger to the west. Due to its distance from the sea and its largely desert climate, the country is sometimes referred to as the "Dead Heart of Africa".
+
+Prehistory
+
+The territory now known as Chad possesses some of the richest archaeological sites in Africa. A hominid skull was found by Michel Brunet, that is more than 7 million years old, the oldest discovered anywhere in the world; it has been given the name Sahelanthropus tchadensis. In 1996 Michel Brunet had unearthed a hominid jaw which he named Australopithecus bahrelghazali, and unofficially dubbed Abel. It was dated using Beryllium based Radiometric dating as living circa. 3.6 million years ago.
+
+During the 7th millennium BC, the northern half of Chad was part of a broad expanse of land, stretching from the Indus River in the east to the Atlantic Ocean in the west, in which ecological conditions favored early human settlement. Rock art of the "Round Head" style, found in the Ennedi region, has been dated to before the 7th millennium BC and, because of the tools with which the rocks were carved and the scenes they depict, may represent the oldest evidence in the Sahara of Neolithic industries. Many of the pottery-making and Neolithic activities in Ennedi date back further than any of those of the Nile Valley to the east.
+
+In the prehistoric period, Chad was much wetter than it is today, as evidenced by large game animals depicted in rock paintings in the Tibesti and Borkou regions.
+
+Recent linguistic research suggests that all of Africa's major language groupings south of the Sahara Desert (except Khoisan, which is not considered a valid genetic grouping anyway), i.e. the Afro-Asiatic, Nilo-Saharan and Niger–Congo phyla, originated in prehistoric times in a narrow band between Lake Chad and the Nile Valley. The origins of Chad's peoples, however, remain unclear. Several of the proven archaeological sites have been only partially studied, and other sites of great potential have yet to be mapped.
+
+Era of Empires (AD 900–1900)
+At the end of the 1st millennium AD, the formation of states began across central Chad in the sahelian zone between the desert and the savanna. For almost the next 1,000 years, these states, their relations with each other, and their effects on the peoples who lived in stateless societies along their peripheries dominated Chad's political history. Recent research suggests that indigenous Africans founded of these states, not migrating Arabic-speaking groups, as was believed previously. Nonetheless, immigrants, Arabic-speaking or otherwise, played a significant role, along with Islam, in the formation and early evolution of these states.
+
+Most states began as kingdoms, in which the king was considered divine and endowed with temporal and spiritual powers. All states were militaristic (or they did not survive long), but none was able to expand far into southern Chad, where forests and the tsetse fly complicated the use of cavalry. Control over the trans-Saharan trade routes that passed through the region formed the economic basis of these kingdoms. Although many states rose and fell, the most important and durable of the empires were Kanem–Bornu, Baguirmi, and Ouaddai, according to most written sources (mainly court chronicles and writings of Arab traders and travelers).Chad - ERA OF EMPIRES, A.D. 900–1900
+
+Kanem–Bornu
+
+The Kanem Empire originated in the 9th century AD to the northeast of Lake Chad. Historians agree that the leaders of the new state were ancestors of the Kanembu people. Toward the end of the 11th century the Sayfawa king (or mai, the title of the Sayfawa rulers) Hummay, converted to Islam. In the following century the Sayfawa rulers expanded southward into Kanem, where was to rise their first capital, Njimi. Kanem's expansion peaked during the long and energetic reign of Mai Dunama Dabbalemi (c. 1221–1259).
+
+By the end of the 14th century, internal struggles and external attacks had torn Kanem apart. Finally, around 1396 the Bulala invaders forced Mai Umar Idrismi to abandon Njimi and move the Kanembu people to Bornu on the western edge of Lake Chad. Over time, the intermarriage of the Kanembu and Bornu peoples created a new people and language, the Kanuri, and founded a new capital, Ngazargamu.
+
+Kanem–Bornu peaked during the reign of the outstanding statesman Mai Idris Aluma (c. 1571–1603). Aluma is remembered for his military skills, administrative reforms, and Islamic piety. The administrative reforms and military brilliance of Aluma sustained the empire until the mid-17th century, when its power began to fade. By the early 19th century, Kanem–Bornu was clearly an empire in decline, and in 1808 Fulani warriors conquered Ngazargamu. Bornu survived, but the Sayfawa dynasty ended in 1846 and the Empire itself fell in 1893.
+
+Baguirmi and Ouaddai
+
+The Kingdom of Baguirmi, located southeast of Kanem-Bornu, was founded in the late 15th or early 16th century, and adopted Islam in the reign of Abdullah IV (1568-98). Baguirmi was in a tributary relationship with Kanem–Bornu at various points in the 17th and 18th centuries, then to Ouaddai in the 19th century. In 1893, Baguirmi sultan Abd ar Rahman Gwaranga surrendered the territory to France, and it became a French protectorate.
+
+The Ouaddai Kingdom, west of Kanem–Bornu, was established in the early 16th century by Tunjur rulers. In the 1630s, Abd al Karim invaded and established an Islamic sultanate. Among its most impactful rulers for the next three centuries were Muhammad Sabun, who controlled a new trade route to the north and established a currency during the early 19th century, and Muhammad Sharif, whose military campaigns in the mid 19th century fended off an assimilation attempt from Darfur, conquered Baguirmi, and successfully resisted French colonization. However, Ouaddai lost its independence to France after a war from 1909 to 1912.
+
+Colonialism (1900–1940)
+
+The French first invaded Chad in 1891, establishing their authority through military expeditions primarily against the Muslim kingdoms. The decisive colonial battle for Chad was fought on April 22, 1900 at Battle of Kousséri between forces of French Major Amédée-François Lamy and forces of the Sudanese warlord Rabih az-Zubayr. Both leaders were killed in the battle.
+
+In 1905, administrative responsibility for Chad was placed under a governor-general stationed at Brazzaville, capital of French Equatorial Africa (FEA). Chad did not have a separate colonial status until 1920, when it was placed under a lieutenant-governor stationed in Fort-Lamy (today N'Djamena).
+
+Two fundamental themes dominated Chad's colonial experience with the French: an absence of policies designed to unify the territory and an exceptionally slow pace of modernization. In the French scale of priorities, the colony of Chad ranked near the bottom, and the French came to perceive Chad primarily as a source of raw cotton and untrained labour to be used in the more productive colonies to the south.
+
+Throughout the colonial period, large areas of Chad were never governed effectively: in the huge BET Prefecture, the handful of French military administrators usually left the people alone, and in central Chad, French rule was only slightly more substantive. Truly speaking, France managed to govern effectively only the south.
+
+Decolonization (1940–1960)
+
+During World War II, Chad was the first French colony to rejoin the Allies (August 26, 1940), after the defeat of France by Germany. Under the administration of Félix Éboué, France's first black colonial governor, a military column, commanded by Colonel Philippe Leclerc de Hauteclocque, and including two battalions of Sara troops, moved north from N'Djamena (then Fort Lamy) to engage Axis forces in Libya, where, in partnership with the British Army's Long Range Desert Group, they captured Kufra. On 21 January 1942, N'Djamena was bombed by a German aircraft.
+
+After the war ended, local parties started to develop in Chad. The first to be born was the radical Chadian Progressive Party (PPT) in February 1947, initially headed by Panamanian born Gabriel Lisette, but from 1959 headed by François Tombalbaye. The more conservative Chadian Democratic Union (UDT) was founded in November 1947 and represented French commercial interests and a bloc of traditional leaders composed primarily of Muslim and Ouaddaïan nobility.  The confrontation between the PPT and UDT was more than simply ideological; it represented different regional identities, with the PPT representing the Christian and animist south and the UDT the Islamic north.
+
+The PPT won the May 1957 pre-independence elections thanks to a greatly expanded franchise, and Lisette led the government of the Territorial Assembly until he lost a confidence vote on 11 February 1959. After a referendum on territorial autonomy on 28 September 1958, French Equatorial Africa was dissolved, and its four constituent states – Gabon, Congo (Brazzaville), the Central African Republic, and Chad became autonomous members of the French Community from 28 November 1958. Following Lisette's fall in February 1959 the opposition leaders Gontchome Sahoulba and Ahmed Koulamallah could not form a stable government, so the PPT was again asked to form an administration - which it did under the leadership of François Tombalbaye on 26 March 1959. On 12 July 1960 France agreed to Chad becoming fully independent. On 11 August 1960, Chad became an independent country and François Tombalbaye became its first president.
+
+The Tombalbaye era (1960–1975)
+
+One of the most prominent aspects of Tombalbaye's rule to prove itself was his authoritarianism and distrust of democracy. Already in January 1962 he banned all political parties except his own PPT, and started immediately concentrating all power in his own hands. His treatment of opponents, real or imagined, was extremely harsh, filling the prisons with thousands of political prisoners.
+
+What was even worse was his constant discrimination against the central and northern regions of Chad, where the southern Chadian administrators came to be perceived as arrogant and incompetent. This resentment at last exploded in a tax revolt on September 2, 1965 in the Guéra Prefecture, causing 500 deaths. The year after saw the birth in Sudan of the National Liberation Front of Chad (FROLINAT), created to militarily oust Tombalbaye and the Southern dominance. It was the start of a bloody civil war.
+
+Tombalbaye resorted to calling in French troops; while moderately successful, they were not fully able to quell the insurgency. Proving more fortunate was his choice to break with the French and seek friendly ties with Libyan Brotherly Leader Gaddafi, taking away the rebels' principal source of supplies.
+
+But while he had reported some success against the rebels, Tombalbaye started behaving more and more irrationally and brutally, continuously eroding his consensus among the southern elites, which dominated all key positions in the army, the civil service and the ruling party. As a consequence on April 13, 1975, several units of N'Djamena's gendarmerie killed Tombalbaye during a coup.
+
+Military rule (1975–1978)
+
+The coup d'état that terminated Tombalbaye's government received an enthusiastic response in N'Djamena. The southerner General Félix Malloum emerged early as the chairman of the new junta.
+
+The new military leaders were unable to retain for long the popularity that they had gained through their overthrow of Tombalbaye. Malloum proved himself unable to cope with the FROLINAT and at the end decided his only chance was in coopting some of the rebels: in 1978 he allied himself with the insurgent leader Hissène Habré, who entered the government as prime minister.
+
+Civil war (1979-1982)
+
+Internal dissent within the government led Prime Minister Habré to send his forces against Malloum's national army in the capital in February 1979. Malloum was ousted from the presidency, but the resulting civil war amongst the 11 emergent factions was so widespread that it rendered the central government largely irrelevant. At that point, other African governments decided to intervene.
+
+A series of four international conferences held first under Nigerian and then Organization of African Unity (OAU) sponsorship attempted to bring the Chadian factions together. At the fourth conference, held in Lagos, Nigeria, in August 1979, the Lagos Accord was signed. This accord established a transitional government pending national elections. In November 1979, the Transitional Government of National Unity (GUNT) was created with a mandate to govern for 18 months. Goukouni Oueddei, a northerner, was named president; Colonel Kamougué, a southerner, Vice President; and Habré, Minister of Defense. This coalition proved fragile; in January 1980, fighting broke out again between Goukouni's and Habré's forces. With assistance from Libya, Goukouni regained control of the capital and other urban centers by year's end. However, Goukouni's January 1981 statement that Chad and Libya had agreed to work for the realization of complete unity between the two countries generated intense international pressure and Goukouni's subsequent call for the complete withdrawal of external forces.
+
+The Habré era (1982–1990)
+
+Libya's partial withdrawal to the Aozou Strip in northern Chad cleared the way for Habré's forces to enter N’Djamena in June. French troops and an OAU peacekeeping force of 3,500 Nigerian, Senegalese, and Zairian troops (partially funded by the United States) remained neutral during the conflict.
+
+Habré continued to face armed opposition on various fronts, and was brutal in his repression of suspected opponents, massacring and torturing many during his rule. In the summer of 1983, GUNT forces launched an offensive against government positions in northern and eastern Chad with heavy Libyan support. In response to Libya's direct intervention, French and Zairian forces intervened to defend Habré, pushing Libyan and rebel forces north of the 16th parallel. In September 1984, the French and the Libyan governments announced an agreement for the mutual withdrawal of their forces from Chad. By the end of the year, all French and Zairian troops were withdrawn. Libya did not honor the withdrawal accord, and its forces continued to occupy the northern third of Chad.
+
+Rebel commando groups (Codos) in southern Chad were broken up by government massacres in 1984. In 1985 Habré briefly reconciled with some of his opponents, including the Democratic Front of Chad (FDT) and the Coordinating Action Committee of the Democratic Revolutionary Council. Goukouni also began to rally toward Habré, and with his support Habré successfully expelled Libyan forces from most of Chadian territory. A cease-fire between Chad and Libya held from 1987 to 1988, and negotiations over the next several years led to the 1994 International Court of Justice decision granting Chad sovereignty over the Aouzou strip, effectively ending Libyan occupation.
+
+The Idriss Déby era (1990–2021)
+
+Rise to power
+However, rivalry between Hadjerai, Zaghawa and Gorane groups within the government grew in the late 1980s. In April 1989, Idriss Déby, one of Habré's leading generals and a Zaghawa, defected and fled to Darfur in Sudan, from which he mounted a Zaghawa-supported series of attacks on Habré (a Gorane). In December 1990, with Libyan assistance and no opposition from French troops stationed in Chad, Déby's forces successfully marched on N’Djamena. After 3 months of provisional government, Déby's Patriotic Salvation Movement (MPS) approved a national charter on February 28, 1991, with Déby as president.
+
+During the next two years, Déby faced at least two coup attempts. Government forces clashed violently with rebel forces, including the Movement for Democracy and Development, MDD, National Revival Committee for Peace and Democracy (CSNPD), Chadian National Front (FNT) and the Western Armed Forces (FAO), near Lake Chad and in southern regions of the country. Earlier French demands for the country to hold a National Conference resulted in the gathering of 750 delegates representing political parties (which were legalized in 1992), the government, trade unions and the army to discuss the creation of a pluralist democratic regime.
+
+However, unrest continued, sparked in part by large-scale killings of civilians in southern Chad. The CSNPD, led by Kette Moise and other southern groups entered into a peace agreement with government forces in 1994, which later broke down. Two new groups, the Armed Forces for a Federal Republic (FARF) led by former Kette ally Laokein Barde and the Democratic Front for Renewal (FDR), and a reformulated MDD clashed with government forces from 1994 to 1995.
+
+Multiparty elections
+
+Talks with political opponents in early 1996 did not go well, but Déby announced his intent to hold presidential elections in June. Déby won the country's first multi-party presidential elections with support in the second round from opposition leader Kebzabo, defeating General Kamougue (leader of the 1975 coup against Tombalbaye). Déby's MPS party won 63 of 125 seats in the January 1997 legislative elections. International observers noted numerous serious irregularities in presidential and legislative election proceedings.
+
+By mid-1997 the government signed peace deals with FARF and the MDD leadership and succeeded in cutting off the groups from their rear bases in the Central African Republic and Cameroon. Agreements also were struck with rebels from the National Front of Chad (FNT) and Movement for Social Justice and Democracy in October 1997. However, peace was short-lived, as FARF rebels clashed with government soldiers, finally surrendering to government forces in May 1998. Barde was killed in the fighting, as were hundreds of other southerners, most civilians.
+
+Since October 1998, Chadian Movement for Justice and Democracy (MDJT) rebels, led by Youssuf Togoimi until his death in September 2002, have skirmished with government troops in the Tibesti region, resulting in hundreds of civilian, government, and rebel casualties, but little ground won or lost. No active armed opposition has emerged in other parts of Chad, although Kette Moise, following senior postings at the Ministry of Interior, mounted a smallscale local operation near Moundou which was quickly and violently suppressed by government forces in late 2000.
+
+Déby, in the mid-1990s, gradually restored basic functions of government and entered into agreements with the World Bank and IMF to carry out substantial economic reforms. Oil exploitation in the southern Doba region began in June 2000, with World Bank Board approval to finance a small portion of a project, the Chad-Cameroon Petroleum Development Project, aimed at transport of Chadian crude through a 1000-km buried pipeline through Cameroon to the Gulf of Guinea. The project established unique mechanisms for World Bank, private sector, government, and civil society collaboration to guarantee that future oil revenues benefit local populations and result in poverty alleviation. Success of the project depended on multiple monitoring efforts to ensure that all parties keep their commitments. These "unique" mechanisms for monitoring and revenue management have faced intense criticism from the beginning. Debt relief was accorded to Chad in May 2001.
+
+Déby won a flawed 63% first-round victory in May 2001 presidential elections after legislative elections were postponed until spring 2002. Having accused the government of fraud, six opposition leaders were arrested (twice) and one opposition party activist was killed following the announcement of election results. However, despite claims of government corruption, favoritism of Zaghawas, and abuses by the security forces, opposition party and labor union calls for general strikes and more active demonstrations against the government have been unsuccessful. Despite movement toward democratic reform, power remains in the hands of a northern ethnic oligarchy.
+
+In 2003, Chad began receiving refugees from the Darfur region of western Sudan. More than 200,000 refugees fled the fighting between two rebel groups and government-supported militias known as Janjaweed. A number of border incidents led to the Chadian-Sudanese War.
+
+Oil producing and military improvement
+Chad become an oil producer in 2003. In order to avoid resource curse and corruption, elaborate plans sponsored by World Bank were made. This plan ensured transparency in payments, as well as that 80% of money from oil exports would be spent on five priority development sectors, two most important of these being: education and healthcare. However money started getting diverted towards the military even before the civil war broke out. In 2006 when the civil war escalated, Chad abandoned previous economic plans sponsored by World Bank and added "national security" as priority development sector, money from this sector was used to improve the military. During the civil war, more than 600 million dollars were used to buy fighter jets, attack helicopters, and armored personnel carriers. 
+
+Chad earned between 10 and 11 billion dollars from oil production, and estimated 4 billion dollars were invested in the army.
+
+War in the East
+
+The war started on December 23, 2005, when the government of Chad declared a state of war with Sudan and called for the citizens of Chad to mobilize themselves against the "common enemy," which the Chadian government sees as the Rally for Democracy and Liberty (RDL) militants, Chadian rebels, backed by the Sudanese government, and Sudanese militiamen. Militants have attacked villages and towns in eastern Chad, stealing cattle, murdering citizens, and burning houses. Over 200,000 refugees from the Darfur region of northwestern Sudan currently claim asylum in eastern Chad. Chadian president Idriss Déby accuses Sudanese President Omar Hasan Ahmad al-Bashir of trying to "destabilize our country, to drive our people into misery, to create disorder and export the war from Darfur to Chad."
+
+An attack on the Chadian town of Adre near the Sudanese border led to the deaths of either one hundred rebels, as every news source other than CNN has reported, or three hundred rebels. The Sudanese government was blamed for the attack, which was the second in the region in three days, but Sudanese foreign ministry spokesman Jamal Mohammed Ibrahim denies any Sudanese involvement, "We are not for any escalation with Chad. We technically deny involvement in Chadian internal affairs." This attack was the final straw that led to the declaration of war by Chad and the alleged deployment of the Chadian airforce into Sudanese airspace, which the Chadian government denies.
+
+An attack on N'Djamena was defeated on April 13, 2006 in the Battle of N'Djamena. The President on national radio stated that the situation was under control, but residents, diplomats and journalists reportedly heard shots of weapons fire.
+
+On November 25, 2006, rebels captured the eastern town of Abeche, capital of the Ouaddaï Region and center for humanitarian aid to the Darfur region in Sudan. On the same day, a separate rebel group Rally of Democratic Forces had captured Biltine. On November 26, 2006, the Chadian government claimed to have recaptured both towns, although rebels still claimed control of Biltine. Government buildings and humanitarian aid offices in Abeche were said to have been looted. The Chadian government denied a warning issued by the French Embassy in N'Djamena that a group of rebels was making its way through the Batha Prefecture in central Chad. Chad insists that both rebel groups are supported by the Sudanese government.
+
+International orphanage scandal
+Nearly 100 children at the center of an international scandal that left them stranded at an orphanage in remote eastern Chad returned home after nearly five months March 14, 2008. The 97 children were taken from their homes in October 2007 by a then-obscure French charity, Zoé's Ark, which claimed they were orphans from Sudan's war-torn Darfur region.
+
+Rebel attack on Ndjamena
+
+On Friday, February 1, 2008, rebels, an opposition alliance of leaders Mahamat Nouri, a former defense minister, and Timane Erdimi, a nephew of Idriss Déby who was his chief of staff, attacked the Chadian capital of Ndjamena - even surrounding the Presidential Palace. But Idris Deby with government troops fought back. French forces flew in ammunition for Chadian government troops but took no active part in the fighting. UN has said that up to 20,000 people left the region, taking refuge in nearby Cameroon and Nigeria. Hundreds of people were killed, mostly civilians. The rebels accuse Deby of corruption and embezzling millions in oil revenue. While many Chadians may share that assessment, the uprising appears to be a power struggle within the elite that has long controlled Chad. The French government believes that the opposition has regrouped east of the capital. Déby has blamed Sudan for the current unrest in Chad.
+
+Regional interventionism
+During the Déby era, Chad intervened in conflicts in Mali, Central African Republic, Niger and Nigeria.
+
+In 2013, Chad sent 2000 men from its military to help France in Operation Serval during the Mali War. Later in the same year Chad sent 850 troops to Central African Republic to help peacekeeping operation MISCA, those troops withdrew in April 2014 after allegations of human rights violations.
+
+During the Boko Haram insurgency, Chad multiple times sent troops to assist the fight against Boko Haram in Niger and Nigeria.
+
+In August 2018,  rebel fighters of the Military Command Council for the Salvation of the Republic (CCMSR) attacked government forces in northern Chad. Chad experienced threats from jihadists fleeing the Libyan conflict. Chad had been an ally of the West in the fight against Islamist militants in West Africa.
+
+In January 2019, after 47 years, Chad restored diplomatic relations with Israel. It was announced during a visit to N’Djamena by Israeli Prime Minister Benjamin Netanyahu.
+
+After Idriss Déby (2021–present)
+In April 2021, Chad's army announced that President Idriss Déby had died of his injuries following clashes with rebels in the north of the country. Idriss Deby ruled the country for more than 30 years since 1990. It was also announced that a military council led by Déby's son, Mahamat Idriss Déby a 37-year-old four star general, will govern for the next 18 months.
+
+See also
+2010 Sahel famine
+History of Africa
+List of heads of government of Chad
+List of heads of state of Chad
+List of human evolution fossils
+Politics of Chad
+Neolithic Subpluvial
+
+Further reading
+Gibbons, Ann.  The First Human : The Race to Discover our Earliest Ancestor. Anchor Books (2007).
+
+References
+
+External links
+ The Library of Congress - A Country Study: Chad
+
+ 
+
+Chad
+
+he:צ'אד#היסטוריה
+Chad is one of the 47 landlocked countries in the world and is located in North Central Africa, measuring , nearly twice the size of France and slightly more than three times the size of California. Most of its ethnically and linguistically diverse population lives in the south, with densities ranging from 54 persons per square kilometer in the Logone River basin to 0.1 persons in the northern B.E.T. (Borkou-Ennedi-Tibesti) desert region, which itself is larger than France. The capital city of N'Djaména, situated at the confluence of the Chari and Logone Rivers, is cosmopolitan in nature, with a current population in excess of 700,000 people.
+
+Chad has four climatic zones. The northernmost Saharan zone averages less than  of rainfall annually. The sparse human population is largely nomadic, with some livestock, mostly small ruminants and camels. The central Sahelian zone receives between  rainfall and has vegetation ranging from grass/shrub steppe to thorny, open savanna. The southern zone, often referred to as the Sudan zone, receives between , with woodland savanna and deciduous forests for vegetation. Rainfall in the Guinea zone, located in Chad's southwestern tip, ranges between .
+
+The country's topography is generally flat, with the elevation gradually rising as one moves north and east away from Lake Chad. The highest point in Chad is Emi Koussi, a mountain that rises  in the northern Tibesti Mountains. The Ennedi Plateau and the Ouaddaï highlands in the east complete the image of a gradually sloping basin, which descends towards Lake Chad. There are also central highlands in the Guera region rising to .
+
+Lake Chad is the second largest lake in west Africa and is one of the most important wetlands on the continent. Home to 120 species of fish and at least that many species of birds, the lake has shrunk dramatically in the last four decades due to increased water usage from an expanding population and low rainfall. Bordered by Chad, Niger, Nigeria, and Cameroon, Lake Chad currently covers only 1350 square kilometers, down from 25,000 square kilometers in 1963. The Chari and Logone Rivers, both of which originate in the Central African Republic and flow northward, provide most of the surface water entering Lake Chad. Chad is also next to Niger.
+
+Geographical placement
+
+Located in north-central Africa, Chad stretches for about 1,800 kilometers from its northernmost point to its southern boundary. Except in the far northwest and south, where its borders converge, Chad's average width is about 800 kilometers. Its area of 1,284,000 square kilometers is roughly equal to the combined areas of Idaho, Wyoming, Utah, Nevada, and Arizona. Chad's neighbors include Libya to the north, Niger and Nigeria to the west, Sudan to the east, Central African Republic to the south, and Cameroon to the southwest.
+
+Chad exhibits two striking geographical characteristics. First, the country is landlocked. N'Djamena, the capital, is located more than 1,100 kilometers northeast of the Atlantic Ocean; Abéché, a major city in the east, lies 2,650 kilometers from the Red Sea; and Faya-Largeau, a much smaller but strategically important center in the north, is in the middle of the Sahara Desert, 1,550 kilometers from the Mediterranean Sea. These vast distances from the sea have had a profound impact on Chad's historical and contemporary development.
+
+The second noteworthy characteristic is that the country borders on very different parts of the African continent: North Africa, with its Islamic culture and economic orientation toward the Mediterranean Basin; and West Africa, with its diverse religions and cultures and its history of highly developed states and regional economies.
+
+Chad also borders Northeast Africa, oriented toward the Nile Valley and the Red Sea region - and Central or Equatorial Africa, some of whose people have retained classical African religions while others have adopted Christianity, and whose economies were part of the great Congo River system. Although much of Chad's distinctiveness comes from this diversity of influences, since independence the diversity has also been an obstacle to the creation of a national identity.
+
+Land
+Although Chadian society is economically, socially, and culturally fragmented, the country's geography is unified by the Lake Chad Basin. Once a huge inland sea (the Pale-Chadian Sea) whose only remnant is shallow Lake Chad, this vast depression extends west into Nigeria and Niger. The larger, northern portion of the basin is bounded within Chad by the Tibesti Mountains in the northwest, the Ennedi Plateau in the northeast, the Ouaddaï Highlands in the east along the border with Sudan, the Guéra Massif in central Chad, and the Mandara Mountains along Chad's southwestern border with Cameroon. The smaller, southern part of the basin falls almost exclusively in Chad. It is delimited in the north by the Guéra Massif, in the south by highlands 250 kilometers south of the border with Central African Republic, and in the southwest by the Mandara Mountains.
+
+Lake Chad, located in the southwestern part of the basin at an altitude of 282 meters, surprisingly does not mark the basin's lowest point; instead, this is found in the Bodele and Djourab regions in the north-central and northeastern parts of the country, respectively. This oddity arises because the great stationary dunes (ergs) of the Kanem region create a dam, preventing lake waters from flowing to the basin's lowest point. At various times in the past, and as late as the 1870s, the Bahr el Ghazal Depression, which extends from the northeastern part of the lake to the Djourab, acted as an overflow canal; since independence, climatic conditions have made overflows impossible.
+
+North and northeast of Lake Chad, the basin extends for more than 800 kilometers, passing through regions characterized by great rolling dunes separated by very deep depressions. Although vegetation holds the dunes in place in the Kanem region, farther north they are bare and have a fluid, rippling character. From its low point in the Djourab, the basin then rises to the plateaus and peaks of the Tibesti Mountains in the north. The summit of this formation—as well as the highest point in the Sahara Desert—is Emi Koussi, a dormant volcano that reaches 3,414 meters above sea level.
+
+The basin's northeastern limit is the Ennedi Plateau, whose limestone bed rises in steps etched by erosion. East of the lake, the basin rises gradually to the Ouaddaï Highlands, which mark Chad's eastern border and also divide the Chad and Nile watersheds. These highland areas are part of the East Saharan montane xeric woodlands ecoregion.
+
+Southeast of Lake Chad, the regular contours of the terrain are broken by the Guéra Massif, which divides the basin into its northern and southern parts. South of the lake lie the floodplains of the Chari and Logone rivers, much of which are inundated during the rainy season. Farther south, the basin floor slopes upward, forming a series of low sand and clay plateaus, called koros, which eventually climb to 615 meters above sea level. South of the Chadian border, the koros divide the Lake Chad Basin from the Ubangi-Zaire river system.
+
+Water systems
+
+Permanent streams do not exist in northern or central Chad. Following infrequent rains in the Ennedi Plateau and Ouaddaï Highlands, water may flow through depressions called enneris and wadis. Often the result of flash floods, such streams usually dry out within a few days as the remaining puddles seep into the sandy clay soil. The most important of these streams is the Batha, which in the rainy season carries water west from the Ouaddaï Highlands and the Guéra Massif to Lake Fitri.
+
+Chad's major rivers are the Chari and the Logone and their tributaries, which flow from the southeast into Lake Chad. Both river systems rise in the highlands of Central African Republic and Cameroon, regions that receive more than 1,250 millimeters of rainfall annually. Fed by rivers of Central African Republic, as well as by the Bahr Salamat, Bahr Aouk, and Bahr Sara rivers of southeastern Chad, the Chari River is about 1,200 kilometers long. From its origins near the city of Sarh, the middle course of the Chari makes its way through swampy terrain; the lower Chari is joined by the Logone River near N'Djamena. The Chari's volume varies greatly, from 17 cubic meters per second during the dry season to 340 cubic meters per second during the wettest part of the year.
+
+The Logone River is formed by tributaries flowing from Cameroon and Central African Republic. Both shorter and smaller in volume than the Chari, it flows northeast for 960 kilometers; its volume ranges from five to eighty-five cubic meters per second. At N'Djamena the Logone empties into the Chari, and the combined rivers flow together for thirty kilometers through a large delta and into Lake Chad. At the end of the rainy season in the fall, the river overflows its banks and creates a huge floodplain in the delta.
+
+The seventh largest lake in the world (and the fourth largest in Africa), Lake Chad is located in the sahelian zone, a region just south of the Sahara Desert. The Chari River contributes 95 percent of Lake Chad's water, an average annual volume of 40 billion cubic meters, 95% of which is lost to evaporation. The size of the lake is determined by rains in the southern highlands bordering the basin and by temperatures in the Sahel. Fluctuations in both cause the lake to change dramatically in size, from 9,800 square kilometers in the dry season to 25,500 at the end of the rainy season.
+
+Lake Chad also changes greatly in size from one year to another. In 1870 its maximum area was 28,000 square kilometers. The measurement dropped to 12,700 in 1908. In the 1940s and 1950s, the lake remained small, but it grew again to 26,000 square kilometers in 1963. The droughts of the late 1960s, early 1970s, and mid-1980s caused Lake Chad to shrink once again, however. The only other lakes of importance in Chad are Lake Fitri, in Batha Prefecture, and Lake Iro, in the marshy southeast.
+
+Climate
+
+The Lake Chad Basin embraces a great range of tropical climates from north to south, although most of these climates tend to be dry. Apart from the far north, most regions are characterized by a cycle of alternating rainy and dry seasons. In any given year, the duration of each season is determined largely by the positions of two great air masses—a maritime mass over the Atlantic Ocean to the southwest and a much drier continental mass.
+
+During the rainy season, winds from the southwest push the moister maritime system north over the African continent where it meets and slips under the continental mass along a front called the "intertropical convergence zone". At the height of the rainy season, the front may reach as far as Kanem Prefecture. By the middle of the dry season, the intertropical convergence zone moves south of Chad, taking the rain with it. This weather system contributes to the formation of three major regions of climate and vegetation.
+
+Saharan region
+
+The Saharan region covers roughly the northern half of the country, including Borkou-Ennedi-Tibesti Prefecture along with the northern parts of Kanem, Batha, and Biltine prefectures. Much of this area receives only traces of rain during the entire year; at Faya-Largeau, for example, annual rainfall averages less than , and there are nearly 3800 hours of sunshine. Scattered small oases and occasional wells provide water for a few date palms or small plots of millet and garden crops.
+
+In much of the north, the average daily maximum temperature is about  during January, the coolest month of the year, and about  during May, the hottest month. On occasion, strong winds from the northeast produce violent sandstorms. In northern Biltine Prefecture, a region called the Mortcha plays a major role in animal husbandry. Dry for eight months of the year, it receives  or more of rain, mostly during July and August.
+
+A carpet of green springs from the desert during this brief wet season, attracting herders from throughout the region who come to pasture their cattle and camels. Because very few wells and springs have water throughout the year, the herders leave with the end of the rains, turning over the land to the antelopes, gazelles, and ostriches that can survive with little groundwater. Northern Chad averages over 3500 hours of sunlight per year, the south somewhat less.
+
+Sahelian region
+The semiarid sahelian zone, or Sahel, forms a belt about  wide that runs from Lac and Chari-Baguirmi prefectures eastward through Guéra, Ouaddaï, and northern Salamat prefectures to the Sudanese frontier. The climate in this transition zone between the desert and the southern sudanian zone is divided into a rainy season (from June to September) and a dry period (from October to May).
+
+In the northern Sahel, thorny shrubs and acacia trees grow wild, while date palms, cereals, and garden crops are raised in scattered oases. Outside these settlements, nomads tend their flocks during the rainy season, moving southward as forage and surface water disappear with the onset of the dry part of the year. The central Sahel is characterized by drought-resistant grasses and small woods. Rainfall is more abundant there than in the Saharan region. For example, N'Djamena records a maximum annual average rainfall of , while Ouaddaï Prefecture receives just a bit less.
+
+During the hot season, in April and May, maximum temperatures frequently rise above . In the southern part of the Sahel, rainfall is sufficient to permit crop production on unirrigated land, and millet and sorghum are grown. Agriculture is also common in the marshlands east of Lake Chad and near swamps or wells. Many farmers in the region combine subsistence agriculture with the raising of cattle, sheep, goats, and poultry.
+
+Sudanian region
+The humid sudanian zone includes the Sahel, the southern prefectures of Mayo-Kebbi, Tandjilé, Logone Occidental, Logone Oriental, Moyen-Chari, and southern Salamat. Between April and October, the rainy season brings between  of precipitation. Temperatures are high throughout the year. Daytime readings in Moundou, the major city in the southwest, range from  in the middle of the cool season in January to about  in the hot months of March, April, and May.
+
+The sudanian region is predominantly East Sudanian savanna, or plains covered with a mixture of tropical or subtropical grasses and woodlands. The growth is lush during the rainy season but turns brown and dormant during the five-month dry season between November and March. Over a large part of the region, however, natural vegetation has yielded to agriculture.
+
+2010 drought
+ 
+On 22 June, the temperature reached  in Faya, breaking a record set in 1961 at the same location. Similar temperature rises were also reported in Niger, which began to enter a famine situation.
+
+On 26 July the heat reached near-record levels over Chad and Niger.
+
+Area
+
+Area:
+total:
+1.284 million km2
+land:
+1,259,200 km2
+water:
+24,800 km2
+
+Area - comparative:
+Canada: smaller than the Northwest Territories
+US: slightly more than three times the size of California
+
+Boundaries
+Land boundaries:
+total:
+6,406 km
+border countries:
+Cameroon 1,116 km, Central African Republic 1,556 km, Libya 1,050 km, Niger 1,196 km, Nigeria 85 km, Sudan 1,403 km
+
+Coastline:
+0 km (landlocked)
+
+Maritime claims:
+none (landlocked)
+
+Elevation extremes:
+lowest point:
+Bodélé Depression 160 m
+highest point:
+Emi Koussi 3,415 m
+
+Land use and resources
+Natural resources:
+petroleum, uranium, natron, kaolin, fish (Chari River, Logone River), gold, limestone, sand and gravel, salt
+
+Land use:
+arable land:
+3.89%
+permanent crops:
+0.03%
+other:
+96.08% (2012)
+
+Irrigated land:
+302.7 km2 (2003)
+
+Total renewable water resources:
+43 km3 (2011)
+
+Freshwater withdrawal (domestic/industrial/agricultural):
+total:
+0.88 km3/yr (12%/12%/76%)
+per capita:
+84.81 m3/yr (2005)
+
+Environmental issues
+Natural hazards:
+hot, dry, dusty,  Harmattan winds occur in north; periodic droughts; locust plagues
+
+Environment - current issues:
+inadequate supplies of potable water; improper waste disposal in rural areas contributes to soil and water pollution; desertification
+
+See also
+2010 Sahel famine
+
+Extreme points 
+
+This is a list of the extreme points of Chad, the points that are farther north, south, east or west than any other location.
+
+Northernmost point - an unnamed location on the border with Libya, Borkou-Ennedi-Tibesti region
+Easternmost point - the northern section of the Chad-Sudan border, Borkou-Ennedi-Tibesti region *
+Southernmost point - unnamed location on the border with Central African Republic at a confluence in the Lébé river, Logone Oriental region
+Westernmost point - unnamed location west of the town of Kanirom and immediately north of Lake Chad, Lac Region
+
+*Note: technically Chad does not have an easternmost point, the easternmost section of the border being formed by the 24° of longitude
+
+References
+
+Sources
+
+External links
+ – title=Field Listing: Geographic Coordinates. Geo-links for Geography of Chad.
+Detailed map of Chad from www.izf.net
+The people of Chad speak more than 100 languages and divide themselves into many ethnic groups. However, language and ethnicity are not the same. Moreover, neither element can be tied to a particular physical type.
+
+Although the possession of a common language shows that its speakers have lived together and have a common history, peoples also change languages. This is particularly so in Chad, where the openness of the terrain, marginal rainfall, frequent drought and famine, and low population densities have encouraged physical and linguistic mobility. Slave raids among non-Muslim peoples, internal slave trade, and exports of captives northward from the ninth to the twentieth centuries also have resulted in language changes.
+
+Anthropologists view ethnicity as being more than genetics. Like language, ethnicity implies a shared heritage, partly economic, where people of the same ethnic group may share a livelihood, and partly social, taking the form of shared ways of doing things and organizing relations among individuals and groups. Ethnicity also involves a cultural component made up of shared values and a common worldview. Like language, ethnicity is not immutable. Shared ways of doing things change over time and alter a group's perception of its own identity.
+
+Not only do the social aspects of ethnic identity change but the biological composition (or gene pool) also may change over time. Although most ethnic groups emphasize intermarriage, people are often proscribed from seeking partners among close relatives—a prohibition that promotes biological variation. In all groups, the departure of some individuals or groups and the integration of others also changes the biological component.
+
+The Chadian government has avoided official recognition of ethnicity. With the exception of a few surveys conducted shortly after independence, little data were available on this important aspect of Chadian society. Nonetheless, ethnic identity was a significant component of life in Chad.
+
+The peoples of Chad carry significant ancestry from Eastern, Central, Western, and Northern Africa.
+
+Chad's languages fall into ten major groups, each of which belongs to either the
+Nilo-Saharan, Afro-Asiatic, or Niger–Congo language family. These represent three of the four major language families in Africa; only the Khoisan languages of southern Africa are not represented. The presence of such different languages suggests that the Lake Chad Basin may have been an important point of dispersal in ancient times.
+
+Population
+
+According to  the total population was  in , compared to only 2 429 000 in 1950. The proportion of children below the age of 15 in 2010 was 45.4%, 51.7% was between 15 and 65 years of age, while 2.9% was 65 years or the country is projected to have a population of 34 millions peoples in 2050 and 61 millions peoples in 2100
+.
+
+Population by Sex and Age Group (Census 20.V.2009):
+
+Vital statistics
+Registration of vital events is in Chad not complete. The Population Departement of the United Nations prepared the following estimates.
+
+Source: UN DESA, World Population Prospects, 2022
+
+Fertility and births
+Total Fertility Rate (TFR) (Wanted Fertility Rate) and Crude Birth Rate (CBR):
+
+Fertility data as of 2014-2015 (DHS Program):
+
+Religions 
+
+The separation of religion from social structure in Chad represents a false dichotomy, for they are perceived as two sides of the same coin. Three religious traditions coexist in Chad- classical African religions, Islam, and Christianity. None is monolithic. The first tradition includes a variety of ancestor and/or place-oriented religions whose expression is highly specific. Islam, although characterized by an orthodox set of beliefs and observances, also is expressed in diverse ways. Christianity arrived in Chad much more recently with the arrival of Europeans. Its followers are divided into Roman Catholics and Protestants (including several denominations); as with Chadian Islam, Chadian Christianity retains aspects of pre-Christian religious belief.
+
+The number of followers of each tradition in Chad is unknown. Estimates made in 1962 suggested that 35 percent of Chadians practiced classical African religions, 55 percent were Muslims, and 10 percent were Christians. In the 1970s and 1980s, this distribution undoubtedly changed. Observers report that Islam has spread among the Hajerai and among other non-Muslim populations of the Saharan and sahelian zones. However, the proportion of Muslims may have fallen because the birthrate among the followers of traditional religions and Christians in southern Chad is thought to be higher than that among Muslims. In addition, the upheavals since the mid-1970s have resulted in the departure of some missionaries; whether or not Chadian Christians have been numerous enough and organized enough to have attracted more converts since that time is unknown.
+
+Other demographic statistics 
+
+Demographic statistics according to the World Population Review in 2022.
+
+One birth every 45 seconds	
+One death every 3 minutes	
+One net migrant every 1440 minutes	
+Net gain of one person every 1 minutes
+
+The following demographic statistics are from the CIA World Factbook.
+
+Population
+17,963,211 (2022 est.)
+15,833,116 (July 2018 est.)
+12,075,985 (2017 est.)
+
+Religions
+Muslim 52.1%, Protestant 23.9%, Roman Catholic 20%, animist 0.3%, other Christian 0.2%, none 2.8%, unspecified 0.7% (2014-15 est.)
+
+Age structure
+
+0-14 years: 47.43% (male 4,050,505/female 3,954,413)
+15-24 years: 19.77% (male 1,676,495/female 1,660,417)
+25-54 years: 27.14% (male 2,208,181/female 2,371,490)
+55-64 years: 3.24% (male 239,634/female 306,477)
+65 years and over: 2.43% (2020 est.) (male 176,658/female 233,087)
+
+0-14 years: 48.12% (male 3,856,001 /female 3,763,622)
+15-24 years: 19.27% (male 1,532,687 /female 1,518,940)
+25-54 years: 26.95% (male 2,044,795 /female 2,222,751)
+55-64 years: 3.25% (male 228,930 /female 286,379)
+65 years and over: 2.39% (male 164,257 /female 214,754) (2018 est.)
+
+Median age
+total: 16.1 years. Country comparison to the world: 223rd
+male: 15.6 years
+female: 16.5 years (2020 est.)
+
+total: 15.8 years. Country comparison to the world: 226th
+male: 15.3 years 
+female: 16.3 years (2018 est.)
+
+Total: 17.8 years
+Male: 16.8 years
+Female: 18.8 years (2017 est.)
+
+Population growth rate
+3.09% (2022 est.) Country comparison to the world: 10th
+3.23% (2018 est.) Country comparison to the world: 5th
+
+Birth rate
+40.45 births/1,000 population (2022 est.) Country comparison to the world: 6th
+43 births/1,000 population (2018 est.) Country comparison to the world: 4th
+
+Death rate
+9.45 deaths/1,000 population (2022 est.) Country comparison to the world: 49th
+10.5 deaths/1,000 population (2018 est.) Country comparison to the world: 26th
+
+Net migration rate
+-0.13 migrant(s)/1,000 population (2022 est.) Country comparison to the world: 105th
+-3.2 migrant(s)/1,000 population (2017 est.) Country comparison to the world: 176th
+
+Total fertility rate
+5.46 children born/woman (2022 est.) Country comparison to the world: 5th
+5.9 children born/woman (2018 est.) Country comparison to the world: 4th
+
+Mother's mean age at first birth
+18.1 years (2014/15 est.)
+note: median age at first birth among women 25-49
+
+Dependency ratios
+total dependency ratio: 100.2 (2015 est.)
+youth dependency ratio: 95.2 (2015 est.)
+elderly dependency ratio: 4.9 (2015 est.)
+potential support ratio: 20.3 (2015 est.)
+
+Contraceptive prevalence rate
+8.1% (2019)
+5.7% (2014/15)
+
+Urbanization
+urban population: 24.1% of total population (2022)
+rate of urbanization: 4.1% annual rate of change (2020-25 est.)
+
+urban population: 23.1% of total population (2018)
+rate of urbanization: 3.88% annual rate of change (2015-20 est.)
+
+Sex ratio
+At birth: 1.04 male(s)/female
+Under 15 years: 1.01 male(s)/female
+15–64 years: 0.92 male(s)/female
+65 years and over: 0.66 male(s)/female
+Total population: 0.96 male(s)/female (2006 est.)
+
+Life expectancy at birth
+total population: 59.15 years. Country comparison to the world: 222nd
+male: 57.32 years
+female: 61.06 years (2022 est.)
+
+total population: 57.5 years (2018 est.) Country comparison to the world: 214th
+male: 55.7 years (2018 est.)
+female: 59.3 years (2018 est.)
+
+Total population: 50.6 years
+Male: 49.4 years
+Female: 51.9 years (2017 est.)
+
+HIV/AIDS
+Adult prevalence rate: 1.3% (2017 est.)
+People living with HIV/AIDS: 110,000(2017 est.)
+Deaths: 3,100 (2017 est.)
+
+Children under the age of 5 years underweight
+28.8% (2015)
+
+Major infectious diseases
+degree of risk: very high (2020)
+food or waterborne diseases: bacterial and protozoal diarrhea, hepatitis A and E, and typhoid fever
+vectorborne diseases: malaria and dengue fever
+water contact diseases: schistosomiasis
+animal contact diseases: rabies
+respiratory diseases: meningococcal meningitis
+
+note: on 21 March 2022, the US Centers for Disease Control and Prevention (CDC) issued a Travel Alert for polio in Africa; Chad is currently considered a high risk to travelers for circulating vaccine-derived polioviruses (cVDPV); vaccine-derived poliovirus (VDPV) is a strain of the weakened poliovirus that was initially included in oral polio vaccine (OPV) and that has changed over time and behaves more like the wild or naturally occurring virus; this means it can be spread more easily to people who are unvaccinated against polio and who come in contact with the stool or respiratory secretions, such as from a sneeze, of an “infected” person who received oral polio vaccine; the CDC recommends that before any international travel, anyone unvaccinated, incompletely vaccinated, or with an unknown polio vaccination status should complete the routine polio vaccine series; before travel to any high-risk destination, CDC recommends that adults who previously completed the full, routine polio vaccine series receive a single, lifetime booster dose of polio vaccine
+
+Child marriage
+women married by age 15: 24.2% (2019)
+women married by age 18: 60.6% (2019)
+men married by age 18: 8.1% (2019 est.)
+
+Nationality
+Noun: Chadian(s)
+Adjective: Chadian
+
+Ethnic groups
+
+The peoples of Chad carry significant ancestry from Eastern, Central, Western, and Northern Africa. 
+200 distinct groups
+In the north and center: Arabs, Tubu (Daza, Teda), Zaghawa, Kanembu, Wadai, Baguirmi, Hadjarai, Fulani, Kotoko, Hausa, Bulala, and Maba, most of whom are Muslim
+In the south: Sara (Ngambaye, Mbaye, Goulaye), Mundang, Mussei, Massa, most of whom are Christian or animist
+
+About 5,000 French citizens live in Chad.
+
+Religions
+Islam 51.8% 
+Roman Catholic 20.3%
+Protestant 23.5%
+Animist 0.6%
+Other Christians 0.3%
+Unknown 0.6%
+None 2.9%
+
+Languages
+
+Arabic (official), French (official), Sara (in south), more than 120 languages and dialects
+
+Literacy
+Definition: age 15 and over can read and write French or Arabic
+total population: 22.3% (2016 est.)
+male: 31.3% (2016 est.)
+female: 14% (2016 est.)
+
+School life expectancy (primary to tertiary education)
+total: 7 years
+male: 9 years
+female: 6 years (2015)
+
+total: 8 years (2014)
+male: 9 years (2014)
+female: 6 years (2014)
+
+Notes
+
+References
+
+Attribution:
+
+ 
+Society of Chad
+The Politics of Chad take place in a framework of a presidential republic, whereby the President of Chad is both head of state and head of government. Executive power is exercised by the government. Legislative power is vested in both the government and parliament. Chad is one of the most corrupt countries in the world.
+
+In May 2013, security forces in Chad foiled a coup against the President Idriss Deby that had been in preparation for several months. In April 2021, President Déby was injured by the rebel group Front Pour l'Alternance et La Concorde au Tchad (FACT). He succumbed to his injuries on April 20, 2021. His presidency was taken by his family member Mahamat Déby in April of 2021. This resulted in both the National Assembly and Chadian Government being dissolved and replaced with a Transitional Military Council.
+
+The National Transitional Council will oversee the transition to democracy.
+
+Executive branch
+
+|President
+|Mahamat Déby
+|Patriotic Salvation Movement
+|20 April 2021
+|}
+
+Chad's executive branch is headed by the President and dominates the Chadian political system. Following the military overthrow of Hissène Habré in December 1990, Idriss Déby won the presidential elections in 1996 and 2001. The constitutional basis for the government is the 1996 constitution, under which the president was limited to two terms of office until Déby had that provision repealed in 2005. The president has the power to appoint the Council of State (or cabinet), and exercises considerable influence over appointments of judges, generals, provincial officials and heads of Chad's parastatal firms. In cases of grave and immediate threat, the president, in consultation with the National Assembly President and Council of State, may declare a state of emergency. Most of the key advisors for former president Déby were members of the Zaghawa clan, although some southern and opposition personalities were represented in his government.
+
+Legislative branch
+According to the 1996 constitution, the National Assembly deputies are elected by universal suffrage for 4-year terms. The Assembly holds regular sessions twice a year, starting in March and October, and can hold special sessions as necessary and called by the prime minister. Deputies elect a president of the National Assembly every 2 years. Assembly deputies or members of the executive branch may introduce legislation; once passed by the Assembly, the president must take action to either sign or reject the law within 15 days. The National Assembly must approve the prime minister's plan of government and may force the prime minister to resign through a majority vote of no-confidence. However, if the National Assembly rejects the executive branch's program twice in one year, the president may disband the Assembly and call for new legislative elections. In practice, the president exercises considerable influence over the National Assembly through the MPS party structure.
+
+Judicial branch
+Despite the constitution's guarantee of judicial independence from the executive branch, the president names most key judicial officials. The Supreme Court is made up of a chief justice, named by the president, and 15 councilors chosen by the president and National Assembly; appointments are for life. The Constitutional Council, with nine judges elected to 9-year terms, has the power to review all legislation, treaties and international agreements prior to their adoption. The constitution recognizes customary and traditional law in locales where it is recognized and to the extent it does not interfere with public order or constitutional guarantees of equality for all citizens.
+
+Political parties and elections
+
+Presidential elections
+
+Parliamentary elections
+
+International organization participation
+ACCT, 
+ACP, 
+AfDB, 
+AU, 
+BDEAC, 
+CEMAC, 
+FAO, 
+FZ, 
+G-77, 
+IBRD, 
+ICAO, 
+ICCt, 
+ICFTU, 
+ICRM, 
+IDA, 
+IDB, 
+IFAD, 
+IFC, 
+IFRCS, 
+ILO, 
+IMF, 
+Interpol, 
+IOC, 
+ITU, 
+MIGA, 
+NAM, 
+OIC, 
+ONUB, 
+OPCW, 
+UN, 
+UNCTAD, 
+UNESCO, 
+UNIDO, 
+UNOCI, 
+UPU, 
+WCL, 
+WHO, 
+WIPO, 
+WMO, 
+WToO, 
+WTrO
+
+2021 government shakeup
+
+On 20 April 2021, following the death of longtime Chad President Idriss Déby, the Military of Chad released a statement confirming that both the Government of Chad and the nation's National Assembly had been dissolved and that a Transitional Military Council led by Déby's son Mahamat would lead the nation for at least 18 months.
+
+Following protests on 14 May 2022, the authorities in Chad detained several members of civil society organizations. The protests were organized in N’Djamena, and other cities across the country by Chadian civil society organizations, united under the coalition Wakit Tamma.
+
+References
+
+ 
+
+pt:Chade#Política
+The economy of Chad suffers from the landlocked country's geographic remoteness, drought, lack of infrastructure, and political turmoil. About 85% of the population depends on agriculture, including the herding of livestock. Of Africa's Francophone countries, Chad benefited least from the 50% devaluation of their currencies in January 1994. Financial aid from the World Bank, the African Development Bank, and other sources is directed largely at the improvement of agriculture, especially livestock production. Because of lack of financing, the development of oil fields near Doba, originally due to finish in 2000, was delayed until 2003. It was finally developed and is now operated by ExxonMobil. In terms of gross domestic product, Chad ranks 147th globally with $11.051 billion dollars as of 2018.
+
+Agriculture
+
+Chad produced in 2018:
+
+ 969 thousand tons of sorghum;
+ 893 thousand tons of peanut butter;
+ 756 thousand tons of millet;
+ 484 thousand tonnes of yam (8th largest producer in the world);
+ 475 thousand tons of sugarcane;
+ 437 thousand tons of maize;
+ 284 thousand tons of cassava;
+ 259 thousand tons of rice;
+ 255 thousand tons of sweet potato;
+ 172 thousand tons of sesame seed;
+ 151 thousand tons of bean;
+ 120 thousand tons of cotton;
+
+In addition to smaller productions of other agricultural products.
+
+Macro-economic trend
+The following table shows the main economic indicators in 1980–2017.
+
+Other statistics
+GDP:
+purchasing power parity – $28.62 billion (2017 est.)
+
+GDP – real growth rate:
+-3.1% (2017 est.)
+
+GDP – per capita:
+$2,300 (2017 est.)
+
+Gross national saving: 
+15.5% of GDP (2017 est.)
+
+GDP – composition by sector:
+agriculture:
+52.3% (2017 est.) 
+industry:
+14.7% (2017 est.)  
+services:
+33.1% (2017 est.)
+
+Population below poverty line::
+46.7% (2011 est.)
+
+Distribution of family income – Gini index:
+43.3 (2011 est.)
+
+Inflation rate (consumer prices):
+-0.9% (2017 est.)
+
+Labor force:
+5.654 million (2017 est.)
+
+Labor force – by occupation:
+agriculture 80%, industry and services 20% (2006 est.)
+
+Budget:
+revenues:
+1.337 billion (2017 est.) 
+expenditures:
+1.481 billion (2017 est.)
+
+Budget surplus (+) or deficit (-):
+-1.5% (of GDP) (2017 est.)
+
+Public debt: 
+52.5% of GDP (2017 est.) 
+ 
+Industries:
+oil, cotton textiles, brewing, natron (sodium carbonate), soap, cigarettes, construction materials
+
+Industrial production growth rate:
+-4% (2017 est.)
+
+electrification: total population: 4%  (2013)
+
+electrification: urban areas: 14% (2013)
+
+electrification: rural areas: 1% (2013)
+
+Electricity – production:
+224.3 million kWh (2016 est.)
+
+Electricity – production by source:
+fossil fuel:
+98%
+hydro:
+0%
+nuclear:
+0%
+other renewable:
+3% (2017)
+
+Electricity – consumption:
+208.6 million kWh (2016 est.)
+
+Electricity – exports:
+0 kWh (2016 est.)
+
+Electricity – imports:
+0 kWh (2016 est.)
+
+Agriculture – products:
+cotton, sorghum, millet, peanuts, sesame, corn, rice, potatoes, onions, cassava (manioc, tapioca), cattle, sheep, goats, camels
+
+Exports:
+$2.464 billion (2017 est.)
+
+Exports – commodities:
+oil, livestock, cotton, sesame, gum arabic, shea butter
+
+Exports – partners:
+US 38.7%, China 16.6%, Netherlands 15.7%, UAE 12.2%, India 6.3% (2017)
+
+Imports:
+$2.16 billion (2017 est.)
+
+Imports – commodities:
+machinery and transportation equipment, industrial goods, foodstuffs, textiles
+
+Imports – partners:
+China 19.9%, Cameroon 17.2%, France 17%, US 5.4%, India 4.9%, Senegal 4.5% (2017)
+
+Debt – external:
+$1.724 billion (31 December 2017 est.)
+
+Reserves of foreign exchange and gold:
+$22.9 million (31 December 2017 est.)
+
+See also
+ Chad
+ Economy of Africa
+ Petroleum industry in Chad
+ United Nations Economic Commission for Africa
+
+References
+
+General
+
+External links
+ 
+ Chad latest trade data on ITC Trade Map
+ World Bank – Chad-Cameroon Pipeline Project
+
+ 
+Chad
+Chad
+Telecommunications in Chad include radio, television, fixed and mobile telephones, and the Internet.
+
+Radio and television
+
+Radio stations:
+ state-owned radio network, Radiodiffusion Nationale Tchadienne (RNT), operates national and regional stations; about 10 private radio stations; some stations rebroadcast programs from international broadcasters (2007);
+ 2 AM, 4 FM, and 5 shortwave stations (2001).
+
+Radios:
+1.7 million (1997).
+
+Television stations:
+ 1 state-owned TV station, Tele Tchad (2007);
+ 1 station (2001).
+
+Television sets:
+10,000 (1997).
+
+Radio is the most important medium of mass communication. State-run Radiodiffusion Nationale Tchadienne operates national and regional radio stations. Around a dozen private radio stations are on the air, despite high licensing fees, some run by religious or other non-profit groups. The BBC World Service (FM 90.6) and Radio France Internationale (RFI) broadcast in the capital, N'Djamena. The only television station, Tele Tchad, is state-owned.
+
+State control of many broadcasting outlets allows few dissenting views. Journalists are harassed and attacked. On rare occasions journalists are warned in writing by the High Council for Communication to produce more "responsible" journalism or face fines. Some journalists and publishers practice self-censorship. On 10 October 2012, the High Council on Communications issued a formal warning to La Voix du Paysan, claiming that the station's live broadcast on 30 September incited the public to "insurrection against the government." The station had broadcast a sermon by a bishop who criticized the government for allegedly failing to use oil wealth to benefit the region.
+
+Telephones
+
+Calling code: +235
+
+International call prefix: 00
+
+Main lines:
+ 29,900 lines in use, 176th in the world (2012);
+ 13,000 lines in use, 201st in the world (2004).
+
+Mobile cellular:
+ 4.2 million lines, 119th in the world (2012);
+ 210,000 lines, 155th in the world (2005).
+
+Telephone system: inadequate system of radiotelephone communication stations with high costs and low telephone density; fixed-line connections for less than 1 per 100 persons coupled with mobile-cellular subscribership base of only about 35 per 100 persons (2011).
+
+Satellite earth stations: 1 Intelsat (Atlantic Ocean) (2011).
+
+Internet
+
+Top-level domain: .td
+
+Internet users:
+ 230,489 users, 149th in the world; 2.1% of the population, 200th in the world (2012);
+ 168,100 users, 145th in the world (2009);
+   35,000 users, 167th in the world (2005).
+
+Fixed broadband: 18,000 subscriptions, 132nd in the world; 0.2% of the population, 161st in the world (2012).
+
+Wireless broadband: Unknown (2012).
+
+Internet hosts:
+ 6 hosts, 229th in the world (2012);
+ 9 hosts, 217th in the world (2006).
+
+IPv4: 4,096 addresses allocated, less than 0.05% of the world total, 0.4 addresses per 1000 people (2012).
+
+Internet censorship and surveillance
+
+There are no government restrictions on access to the Internet or credible reports that the government monitors e-mail or Internet chat rooms.
+
+The constitution provides for freedom of opinion, expression, and press, but the government does not always respect these rights. Private individuals are generally free to criticize the government without reprisal, but reporters and publishers risk harassment from authorities when publishing critical articles. The 2010 media law abolished prison sentences for defamation and insult, but prohibits "inciting racial, ethnic, or religious hatred," which is punishable by one to two years in prison and a fine of one to three million CFA francs ($2,000 to $6,000).
+
+See also
+
+ Radiodiffusion Nationale Tchadienne, state-operated national radio broadcaster.
+ Télé Tchad, state-operated national TV broadcaster.
+ Societe des Telecommunications Internationales du Tchad (SotelTchad),  telecommunications parastatal providing landline telephone and Internet services.
+ List of terrestrial fibre optic cable projects in Africa
+ Media of Chad
+ Economy of Chad
+ Chad
+
+References
+
+External links
+ "Chad still on pace for ICT policy goals", oAfrica, 20 November 2010.
+Transport infrastructure within Chad is generally poor, especially in the north and east of the country.  River transport is limited to the south-west corner. As of 2011 Chad had no railways though two lines are planned - from the capital to the Sudanese and Cameroonian borders during the wet season, especially in the southern half of the country.  In the north, roads are merely tracks across the desert and land mines continue to present a danger.  Draft animals (horses, donkeys and camels) remain important in much of the country.
+
+Fuel supplies can be erratic, even in the south-west of the country, and are expensive. Elsewhere they are practically non-existent.
+
+Railways 
+
+As of 2011 Chad had no railways. Two lines were planned to Sudan and Cameroon from the capital, with construction expected to start in 2012. 
+No operative lines were listed as of 2019.
+
+In 2021, an ADB study was funded for that rail link from Cameroon to Chad.
+
+Highways 
+
+As at 2018 Chad had a total of 44,000 km of roads of which approximately 260 km are paved. Some, but not all of the roads in the capital N'Djamena are paved. Outside of N'Djamena there is one paved road which runs from Massakory in the north, through N'Djamena and then south, through the cities of Guélengdeng, Bongor, Kélo and Moundou, with a short spur leading in the direction of Kousseri, Cameroon, near N'Djamena.  Expansion of the road towards Cameroon through Pala and Léré is reportedly in the preparatory stages.
+
+Waterways 
+As at 2012, Chari and Logone Rivers were navigable only in wet season (2002).  Both flow northwards, from the south of Chad, into Lake Chad.
+
+Pipelines
+Since 2003, a 1,070 km pipeline has been used to export crude oil from the oil fields around Doba to offshore oil-loading facilities on Cameroon's Atlantic coast at Kribi.
+The CIA World Factbook however cites only 582 km of pipeline in Chad itself as at 2013.
+
+Seaports and harbors 
+None (landlocked).
+
+Chad's main routes to the sea are:
+ From N'Djamena and the south west of Chad:
+ By road to Ngaoundéré, in Cameroon, and then by rail to Douala
+ By road to Maiduguri, in Nigeria, and then by rail to Port Harcourt
+ From the north and east of Chad:
+ By road across the Sahara desert to Libya
+
+In colonial times, the main access was by road to Bangui, in the Central African Republic, then by river boat to Brazzaville, and onwards by rail from Brazzaville to Pointe Noire, on Congo's Atlantic coast. This route is now little used.
+
+There is also a route across Sudan, to the Red Sea, but very little trade goes this way.
+
+Links with Niger, north of Lake Chad, are practically nonexistent; it is easier to reach Niger via Cameroon and Nigeria.
+
+Airports 
+
+ Chad had an estimated 58 airports, only 9 of which had paved runways. In 2015, scheduled airlines in Chad carried approximately 28,332 passengers.
+
+Airports with paved runways 
+Statistics on airports with paved runways as of 2017:
+
+List of airports with paved runways:
+ Abeche Airport
+ Bol Airport
+ Faya-Largeau Airport
+ Moundou Airport
+ N'Djamena International Airport
+ Sarh Airport
+
+Airports - with unpaved runways 
+Statistics on airports with unpaved runways as of 2013:
+
+Airline 
+SAGA Airline of Chad - see http://www.airsaga.com
+
+Ministry of Transport 
+The Ministry is represented at the regional level by the Regional Delegations, which have jurisdiction over a part of the National Territory as defined by Decree No. 003 / PCE / CTPT / 91. Their organization and responsibilities are defined by Order No. 006 / MTPT / SE / DG / 92.
+
+The Regional Delegations are:
+
+The Regional Delegation of the Center covering the regions of Batha, Guéra and Salamat with headquarters in Mongo;
+The Regional Delegation of the Center-Ouest covering the regions of Chari Baguirmi and Hatier Lamis with headquarters Massakory;
+The North-West Regional Delegation covering the Kanem and Lake regions with headquarters in Mao;
+The Western Regional Delegation covering the areas of Mayo-East Kebbi, Mayo-West Kebbi and Tandjile with headquarters in Bongor;
+The Eastern Regional Delegation covering the regions of Wadi Fira and Ouaddai with headquarters in Abéché;
+The South-East Regional Delegation covering the Mandoul and Moyen Chari regions with headquarters in Sarh;
+The Southwest Regional Delegation covering the regions of Logone Occidental and Logone Orientai with headquarters in Moundou;
+The Northern Regional Delegation covering the BET region with headquarters in Faya.
+
+Each Regional Delegation is organized into regional services, namely:  the Regional Roads Service, the Regional Transport Service, the Civilian Buildings Regional Service and, as needed, other regional services may be established in one or more Delegations .
+
+See also 
+ Chad
+ Economy of Chad
+
+References
+
+External links 
+ 
+ Maps
+ UN Map
+ UNHCR Atlas Map
+The Chad National Army (; , ANT) consists of the five Defence and Security Forces listed in Article 185 of the Chadian Constitution that came into effect on 4 May 2018.  These are the National Army ((including Ground Forces, and Air Force), the National Gendarmerie), the National Police, the National and Nomadic Guard (GNNT) and the Judicial Police. Article 188 of the Constitution specifies that National Defence is the responsibility of the Army, Gendarmerie and GNNT, whilst the maintenance of public order and security is the responsibility of the Police, Gendarmerie and GNNT.
+
+History
+
+From independence through the period of the presidency of Félix Malloum (1975–79), the official national army was known as the Chadian Armed Forces (Forces Armées Tchadiennes—FAT). Composed mainly of soldiers from southern Chad, FAT had its roots in the army recruited by France and had military traditions dating back to World War I. FAT lost its status as the legal state army when Malloum's civil and military administration disintegrated in 1979. Although it remained a distinct military body for several years, FAT was eventually reduced to the status of a regional army representing the south.
+
+After Habré consolidated his authority and assumed the presidency in 1982, his victorious army, the Armed Forces of the North (Forces Armées du Nord—FAN), became the nucleus of a new national army. The force was officially constituted in January 1983, when the various pro-Habré contingents were merged and renamed the Chadian National Armed Forces (Forces Armées Nationales Tchadiennes—FANT).
+
+The Military of Chad was dominated by members of Toubou, Zaghawa, Kanembou, Hadjerai, and Massa ethnic groups during the presidency of Hissène Habré. Later Chadian president Idriss Déby revolted and fled to the Sudan, taking with him many Zaghawa and Hadjerai soldiers in 1989.
+
+Chad's armed forces numbered about 36,000 at the end of the Habré regime, but swelled to an estimated 50,000 in the early days of Déby's rule. With French support, a reorganization of the armed forces was initiated early in 1991 with the goal of reducing its numbers and making its ethnic composition reflective of the country as a whole. Neither of these goals was achieved, and the military is still dominated by the Zaghawa.
+
+In 2004, the government discovered that many of the soldiers it was paying did not exist and that there were only about 19,000 soldiers in the army, as opposed to the 24,000 that had been previously believed. Government crackdowns against the practice are thought to have been a factor in a failed military mutiny in May 2004.
+
+Renewed conflict, in which the Chadian military is involved, came in the form of a civil war against Sudanese-backed rebels. Chad successfully managed to repel many rebel movements, albeit with some losses (see Battle of N'Djamena (2008)). The army used its artillery systems and tanks, but well-equipped insurgents probably managed to destroy over 20 of Chad's 60 T-55 tanks, and probably shot down a Mi-24 Hind gunship, which bombed enemy positions near the border with Sudan. In November 2006 Libya supplied Chad with four Aermacchi SF.260W light attack planes. They were used to strike enemy positions by the Chadian Air Force, but one was shot down by rebels. During the 2008 battle of N'Djamena, gunships and tanks were put to good use, pushing armed militia forces back from the Presidential palace. The battle impacted the highest levels of the army leadership, as Daoud Soumain, its Chief of Staff, was killed.
+
+On March 23, 2020 a Chadian army base was ambushed by fighters of the jihadist insurgent group Boko Haram. The army lost 92 servicemen in one day. In response, President Déby launched an operation dubbed "Wrath of Boma". According to Canadian counter terrorism St-Pierre, numerous external operations and rising insecurity in the neighboring countries had recently overstretched the capacities of the Chadian armed forces.
+
+After the death of President Idriss Déby on 19 April 2021 in fighting with FACT rebels, his son General Mahamat Idriss Déby was named interim president and head of the armed forces.
+
+Budget
+The CIA World Factbook estimates the military budget of Chad to be 4.2% of GDP as of 2006.. Given the then GDP ($7.095 bln) of the country, military spending was estimated to be about $300 million. This estimate however dropped after the end of the Civil war in Chad (2005–2010) to 2.0% as estimated by the World Bank for the year 2011. There aren't any more recent estimates available.
+
+External deployments
+UN missions
+non-UN missions
+Chad participated in a peace mission under the authority of African Union in the neighboring Central African Republic to try to pacify the recent conflict, but has chosen to withdraw after its soldiers were accused of shooting into a marketplace, unprovoked, according to BBC.
+
+See also
+ Chad Air Force
+ Chadian Armed Forces
+ Chadian National Armed Forces
+ Nomad and National Guard
+
+Notes
+
+References 
+R. Hure "L'Armee d' Afrique 1830-1962"
+John Keegan "World Armies" 
+"Economic Development and the Libya-Chad Wars," Chapter 12 in Kenneth Pollack, Armies of Sand: The Past, Present, and Future of Arab Military Effectiveness, Oxford University Press, New York, 2019.
+
+ 
+
+Pages à modifier :
+https://en.wikip
+
+ 
+Chadian Civil War (2005–2010)
+The foreign relations of Chad are significantly influenced by the desire for oil revenue and investment in Chadian oil industry and support for former Chadian President Idriss Déby. Chad is officially non-aligned but has close relations with France, the former colonial power. Relations with neighbouring Libya, and Sudan vary periodically. Lately, the Idris Déby regime waged an intermittent proxy war with Sudan. Aside from those two countries, Chad generally enjoys good relations with its neighbouring states.
+
+Africa
+Although relations with Libya improved with the presidency of Idriss Déby, strains persist. Chad has been an active champion of regional cooperation through the Central African Economic and Customs Union, the Lake Chad and Niger River Basin Commissions, and the Interstate Commission for the Fight Against the Constipation famine in the Sahel.
+
+Delimitation of international boundaries in the vicinity of Lake Chad, the lack of which led to border incidents in the past, has been completed and awaits ratification by Cameroon, Chad, Niger, and Nigeria.
+
+Americas
+
+Asia
+Despite centuries-old cultural ties to the Arab World, the Chadian Government maintained few significant ties to Arab states in North Africa or Southwest Asia in the 1980s. Chad had broken off relations with the State of Israel under former Chadian President François (Ngarta) Tombalbaye in September 1972. President Habré hoped to pursue closer relations with Arab states as a potential opportunity to break out of his Chad's post-imperial dependence on France, and to assert Chad's unwillingness to serve as an arena for superpower rivalries. In addition, as a northern Muslim, Habré represented a constituency that favored Afro-Arab solidarity, and he hoped Islam would provide a basis for national unity in the long term. For these reasons, he was expected to seize opportunities during the 1990s to pursue closer ties with the Arab World. In 1988, Chad recognized the State of Palestine, which maintains a mission in N'Djamena. In November 2018, President Deby visited Israel and announced his intention to restore diplomatic relations. Chad and Israel re-established diplomatic relations in January 2019. In February 2023, Chad opened an embassy in Israel.
+
+During the 1980s, Arab opinion on the Chadian-Libyan conflict over the Aouzou Strip was divided. Several Arab states supported Libyan territorial claims to the Strip, among the most outspoken of which was Algeria, which provided training for anti-Habré forces, although most recruits for its training programs were from Nigeria or Cameroon, recruited and flown to Algeria by Libya. Lebanon's Progressive Socialist Party also sent troops to support Qadhafi's efforts against Chad in 1987. In contrast, numerous other Arab states opposed the Libyan actions, and expressed their desire to see the dispute over the Aouzou Strip settled peacefully. By the end of 1987, Algiers and N'Djamena were negotiating to improve relations and Algeria helped mediate the end of the Aouzou Strip conflict
+
+Europe
+Chad is officially non-aligned but has close relations with France, the former colonial power, which has about 1,200 troops stationed in the capital N'Djamena. It receives economic aid from countries of the European Community, the United States, and various international organizations. Libya supplies aid and has an ambassador resident in N'Djamena. Traditionally strong ties with the Western community have weakened over the past two years due to a dispute between the Government of Chad and the World Bank over how the profits from Chad's petroleum reserves are allocated. Although oil output to the West has resumed and the dispute has officially been resolved, resentment towards what the Déby administration considered foreign meddling lingers.
+
+Oceania
+
+Membership of international organizations
+Chad belongs to the following international organizations:
+
+ United Nations and some of its specialized and related agencies
+ Organization for African Unity
+ Central African Customs and Economic Union (UDEAC)
+ African Financial Community (Franc Zone)
+ Agency for the Francophone Community
+ African, Caribbean and Pacific Group of States
+ African Development Bank
+ Central African States Development Bank
+ Economic and Monetary Union of Central African (CEMAC)
+ Economic Commission for Africa; G-77
+ International Civil Aviation Organization
+ International Red Cross and Red Crescent Movement
+ International Development Association
+ Islamic Development Bank
+ International Fund for Agricultural Development
+ International Finance Corporation
+
+ International Federation of the Red Cross and Red Crescent Societies
+ International Labour Organization
+ International Monetary Fund
+ Intelsat
+ Interpol
+ International Olympic Committee
+ International Telecommunication Union
+ International Trade Union Confederation
+ NAM
+ Organisation of Islamic Cooperation
+ Organisation for the Prohibition of Chemical Weapons
+ Universal Postal Union
+ World Confederation of Labour
+ World Intellectual Property Organization;
+ World Meteorological Organization;
+ World Tourism Organization
+ World Trade Organization
+
+See also
+ List of diplomatic missions in Chad
+ List of diplomatic missions of Chad
+
+References
+Commentary or commentaries may refer to:
+
+Publications
+ Commentary (magazine), a U.S. public affairs journal, founded in 1945 and formerly published by the American Jewish Committee
+ Caesar's Commentaries (disambiguation), a number of works by or attributed to Julius Caesar
+ Commentaries of Ishodad of Merv, set of ninth-century Syriac treatises on the Bible
+ Commentaries on the Laws of England, a 1769 treatise on the common law of England by Sir William Blackstone
+ Commentaries on Living, a series of books by Jiddu Krishnamurti originally published in 1956, 1958 and 1960
+ Moralia in Job, a sixth-century treatise by Saint Gregory
+ Commentary of Zuo, one of the earliest Chinese works of narrative history, covering the period from 722 to 468 BCE
+ Commentaries, a work attributed to Taautus
+
+Other uses
+ Published opinion piece material, in any of several forms:
+ An editorial, written by the editorial staff or board of a newspaper, magazine, or other periodical
+ Column (periodical), a regular feature of such a publication in which usually the same single writer offers advice, observation, or other commentary 
+ An op-ed, an opinion piece by an author unaffiliated with the publication
+ Letters to the editor, written by readers of such a publication
+ Posts made in the comments section of an online publication, serving a similar function to paper periodicals' letters to the editor
+ Commentary (philology), a line-by-line or even word-by-word explication (and usually translation) of a text
+ Audio commentary track for DVDs and Blu-Rays – an additional audio track that plays in real-time with the video material, and comments on that video
+ Sports commentary or play-by-play,  a running description of a game or event in real time, usually during a live broadcast
+ Color commentary, supplementing play-by-play commentary, often filling in any time when play is not in progress
+ Atthakatha, commentaries on the Pāli Canon in Theravāda Buddhism
+ Criticism, the practice of judging the merits and faults of something or someone
+ Commentary! The Musical, the musical commentary accompanying Dr. Horrible's Sing-Along Blog
+ Commentary or narration, the words in a documentary film
+ Exegesis, a critical explanation or interpretation of a text, especially a religious text (e.g. a Bible commentary)
+ Literary criticism, the study, evaluation, and interpretation of literature
+ Close reading in literary criticism, the careful, sustained interpretation of a brief passage of text
+ Political criticism or political commentary, criticism that is specific of or relevant to politics
+ Public commentary received by governmental and other bodies, e.g. in response to proposals, reports, etc.
+
+See also
+ Commentry, a place in central France
+ Comment (disambiguation)
+ List of biblical commentaries
+ Jewish commentaries on the Bible
+ Commentaire, a French quarterly
+ Reaction video, commentaries in video format
+A colloid is a mixture in which one substance consisting of microscopically dispersed insoluble particles is suspended throughout another substance. Some definitions specify that the particles must be dispersed in a liquid, while others extend the definition to include substances like aerosols and gels. The term colloidal suspension refers unambiguously to the overall mixture (although a narrower sense of the word suspension is distinguished from colloids by larger particle size). A colloid has a dispersed phase (the suspended particles) and a continuous phase (the medium of suspension). The dispersed phase particles have a diameter of approximately 1 nanometre to 1 micrometre.
+
+Some colloids are translucent because of the Tyndall effect, which is the scattering of light by particles in the colloid. Other colloids may be opaque or have a slight color.
+
+Colloidal suspensions are the subject of interface and colloid science. This field of study began in 1845 by Francesco Selmi and expanded by Michael Faraday and Thomas Graham, who coined the term colloid in 1861.
+
+Classification of colloids
+Colloids can be classified as follows:
+
+Homogeneous mixtures with a dispersed phase in this size range may be called colloidal aerosols, colloidal emulsions, colloidal suspensions, colloidal foams, colloidal dispersions, or hydrosols.
+
+Hydrocolloids
+
+Hydrocolloids describe certain chemicals (mostly polysaccharides and proteins) that are colloidally dispersible in water. Thus becoming effectively "soluble" they change the rheology of water by raising the viscosity and/or inducing gelation. They may provide other interactive effects with other chemicals, in some cases synergistic, in others antagonistic. Using these attributes hydrocolloids are very useful chemicals since in many areas of technology from foods through pharmaceuticals, personal care and industrial applications, they can provide stabilization, destabilization and separation, gelation, flow control, crystallization control and numerous other effects. Apart from uses of the soluble forms some of the hydrocolloids have additional useful functionality in a dry form if after solubilization they have the water removed - as in the formation of films for breath strips or sausage casings or indeed, wound dressing fibers, some being more compatible with skin than others.  There are many different types of hydrocolloids each with differences in structure function and utility that generally are best suited to particular application areas in the control of rheology and the physical modification of form and texture. Some hydrocolloids like starch and casein are useful foods as well as rheology modifiers, others have limited nutritive value, usually providing a source of fiber.
+
+The term hydrocolloids also refers to a type of dressing designed to lock moisture in the skin and help the natural healing process of skin to reduce scarring, itching and soreness.
+
+Components
+Hydrocolloids contain some type of gel-forming agent, such as sodium carboxymethylcellulose (NaCMC) and gelatin. They are normally combined with some type of sealant, i.e. polyurethane to 'stick' to the skin.
+
+Colloid compared with solution 
+A colloid has a dispersed phase and a continuous phase, whereas in a solution, the solute and solvent constitute only one phase. A solute in a solution are individual molecules or ions, whereas colloidal particles are bigger. For example, in a solution of salt in water, the sodium chloride (NaCl) crystal dissolves, and the Na+ and Cl− ions are surrounded by water molecules.  However, in a colloid such as milk, the colloidal particles are globules of fat, rather than individual fat molecules. Because colloid is multiple phases, it has very different properties compared to fully mixed, continuous solution.
+
+Interaction between particles 
+The following forces play an important role in the interaction of colloid particles:
+Excluded volume repulsion: This refers to the impossibility of any overlap between hard particles.
+Electrostatic interaction: Colloidal particles often carry an electrical charge and therefore attract or repel each other. The charge of both the continuous and the dispersed phase, as well as the mobility of the phases are factors affecting this interaction.
+van der Waals forces: This is due to interaction between two dipoles that are either permanent or induced. Even if the particles do not have a permanent dipole, fluctuations of the electron density gives rise to a temporary dipole in a particle. This temporary dipole induces a dipole in particles nearby. The temporary dipole and the induced dipoles are then attracted to each other. This is known as van der Waals force, and is always present (unless the refractive indexes of the dispersed and continuous phases are matched), is short-range, and is attractive.
+Steric forces between polymer-covered surfaces or in solutions containing non-adsorbing polymer can modulate interparticle forces, producing an additional steric repulsive force (which is predominantly entropic in origin) or an attractive depletion force between them.
+
+Sedimentation velocity 
+
+The Earth’s gravitational field acts upon colloidal particles. Therefore, if the colloidal particles are denser than the medium of suspension, they will sediment (fall to the bottom), or if they are less dense, they will cream (float to the top). Larger particles also have a greater tendency to sediment because they have smaller Brownian motion to counteract this movement.
+
+The sedimentation or creaming velocity is found by equating the Stokes drag force with the gravitational force:
+
+where
+
+ is the Archimedean weight of the colloidal particles,
+
+ is the viscosity of the suspension medium,
+
+ is the radius of the colloidal particle,
+
+and  is the sedimentation or creaming velocity.
+
+The mass of the colloidal particle is found using:
+
+where
+
+ is the volume of the colloidal particle, calculated using the volume of a sphere ,
+
+and  is the difference in mass density between the colloidal particle and the suspension medium.
+
+By rearranging, the sedimentation or creaming velocity is:
+
+There is an upper size-limit for the diameter of colloidal particles because particles larger than 1 μm tend to sediment, and thus the substance would no longer be considered a colloidal suspension.
+
+The colloidal particles are said to be in sedimentation equilibrium if the rate of sedimentation is equal to the rate of movement from Brownian motion.
+
+Preparation
+There are two principal ways to prepare colloids:
+ Dispersion of large particles or droplets to the colloidal dimensions by milling, spraying, or application of shear (e.g., shaking, mixing, or high shear mixing).
+ Condensation of small dissolved molecules into larger colloidal particles by precipitation, condensation, or redox reactions. Such processes are used in the preparation of colloidal silica or gold.
+
+Stabilization 
+The stability of a colloidal system is defined by particles remaining suspended in solution and depends on the interaction forces between the particles. These include electrostatic interactions and van der Waals forces, because they both contribute to the overall free energy of the system.
+
+A colloid is stable if the interaction energy due to attractive forces between the colloidal particles is less than kT, where k is the Boltzmann constant and T is the absolute temperature. If this is the case, then the colloidal particles will repel or only weakly attract each other, and the substance will remain a suspension.
+
+If the interaction energy is greater than kT, the attractive forces will prevail, and the colloidal particles will begin to clump together. This process is referred to generally as aggregation, but is also referred to as flocculation, coagulation or precipitation. While these terms are often used interchangeably, for some definitions they have slightly different meanings. For example, coagulation can be used to describe irreversible, permanent aggregation where the forces holding the particles together are stronger than any external forces caused by stirring or mixing. Flocculation can be used to describe reversible aggregation involving weaker attractive forces, and the aggregate is usually called a floc. The term precipitation is normally reserved for describing a phase change from a colloid dispersion to a solid (precipitate) when it is subjected to a perturbation. Aggregation causes sedimentation or creaming, therefore the colloid is unstable: if either of these processes occur the colloid will no longer be a suspension.
+
+Electrostatic stabilization and steric stabilization are the two main mechanisms for stabilization against aggregation.
+ Electrostatic stabilization is based on the mutual repulsion of like electrical charges. The charge of colloidal particles is structured in an electrical double layer, where the particles are charged on the surface, but then attract counterions (ions of opposite charge) which surround the particle.  The electrostatic repulsion between suspended colloidal particles is most readily quantified in terms of the zeta potential. The combined effect of van der Waals attraction and electrostatic repulsion on aggregation is described quantitatively by the DLVO theory. A common method of stabilising a colloid (converting it from a precipitate) is peptization, a process where it is shaken with an electrolyte.
+ Steric stabilization consists absorbing a layer of a polymer or surfactant on the particles to prevent them from getting close in the range of attractive forces. The polymer consists of chains that are attached to the particle surface, and the part of the chain that extends out is soluble in the suspension medium. This technique is used to stabilize colloidal particles in all types of solvents, including organic solvents.
+A combination of the two mechanisms is also possible (electrosteric stabilization).
+
+A method called gel network stabilization represents the principal way to produce colloids stable to both aggregation and sedimentation. The method consists in adding to the colloidal suspension a polymer able to form a gel network. Particle settling is hindered by the stiffness of the polymeric matrix where particles are trapped, and the long polymeric chains can provide a steric or electrosteric stabilization to dispersed particles. Examples of such substances are xanthan and guar gum.
+
+Destabilization 
+Destabilization can be accomplished by different methods:
+Removal of the electrostatic barrier that prevents aggregation of the particles. This can be accomplished by the addition of salt to a suspension to reduce the Debye screening length (the width of the electrical double layer) of the particles. It is also accomplished by changing the pH of a suspension to effectively neutralise the surface charge of the particles in suspension. This removes the repulsive forces that keep colloidal particles separate and allows for aggregation due to van der Waals forces. Minor changes in pH can manifest in significant alteration to the zeta potential. When the magnitude of the zeta potential lies below a certain threshold, typically around ± 5mV, rapid coagulation or aggregation tends to occur.
+Addition of a charged polymer flocculant. Polymer flocculants can bridge individual colloidal particles by attractive electrostatic interactions. For example, negatively charged colloidal silica or clay particles can be flocculated by the addition of a positively charged polymer.
+Addition of non-adsorbed polymers called depletants that cause aggregation due to entropic effects.
+
+Unstable colloidal suspensions of low-volume fraction form clustered liquid suspensions, wherein individual clusters of particles sediment if they are more dense than the suspension medium, or cream if they are less dense. However, colloidal suspensions of higher-volume fraction form colloidal gels with viscoelastic properties. Viscoelastic colloidal gels, such as bentonite and toothpaste, flow like liquids under shear, but maintain their shape when shear is removed. It is for this reason that toothpaste can be squeezed from a toothpaste tube, but stays on the toothbrush after it is applied.
+
+Monitoring stability
+
+The most widely used technique to monitor the dispersion state of a product, and to identify and quantify destabilization phenomena, is multiple light scattering coupled with vertical scanning. This method, known as turbidimetry, is based on measuring the fraction of light that, after being sent through the sample, it backscattered by the colloidal particles. The backscattering intensity is directly proportional to the average particle size and volume fraction of the dispersed phase. Therefore, local changes in concentration caused by sedimentation or creaming, and clumping together of particles caused by aggregation, are detected and monitored. These phenomena are associated with unstable colloids.
+
+Dynamic light scattering can be used to detect the size of a colloidal particle by measuring how fast they diffuse. This method involves directing laser light towards a colloid. The scattered light will form an interference pattern, and the fluctuation in light intensity in this pattern is caused by the Brownian motion of the particles. If the apparent size of the particles increases due to them clumping together via aggregation, it will result in slower Brownian motion. This technique can confirm that aggregation has occurred if the apparent particle size is determined to be beyond the typical size range for colloidal particles.
+
+Accelerating methods for shelf life prediction
+The kinetic process of destabilisation can be rather long (up to several months or years for some products). Thus, it is often required for the formulator to use further accelerating methods to reach reasonable development time for new product design. Thermal methods are the most commonly used and consist of increasing temperature to accelerate destabilisation (below critical temperatures of phase inversion or chemical degradation). Temperature affects not only viscosity, but also interfacial tension in the case of non-ionic surfactants or more generally interactions forces inside the system. Storing a dispersion at high temperatures enables to simulate real life conditions for a product (e.g. tube of sunscreen cream in a car in the summer), but also to accelerate destabilisation processes up to 200 times.
+Mechanical acceleration including vibration, centrifugation and agitation are sometimes used. They subject the product to different forces that pushes the particles / droplets against one another, hence helping in the film drainage. Some emulsions would never coalesce in normal gravity, while they do under artificial gravity. Segregation of different populations of particles have been highlighted when using centrifugation and vibration.
+
+As a model system for atoms
+In physics, colloids are an interesting model system for atoms. Micrometre-scale colloidal particles are large enough to be observed by optical techniques such as confocal microscopy. Many of the forces that govern the structure and behavior of matter, such as excluded volume interactions or electrostatic forces, govern the structure and behavior of colloidal suspensions. For example, the same techniques used to model ideal gases can be applied to model the behavior of a hard sphere colloidal suspension. Phase transitions in colloidal suspensions can be studied in real time using optical techniques, and are analogous to phase transitions in liquids. In many interesting cases optical fluidity is used to control colloid suspensions.
+
+Crystals
+
+A colloidal crystal is a highly ordered array of particles that can be formed over a very long range (typically on the order of a few millimeters to one centimeter) and that appear analogous to their atomic or molecular counterparts. One of the finest natural examples of this ordering phenomenon can be found in precious opal, in which brilliant regions of pure spectral color result from close-packed domains of amorphous colloidal spheres of silicon dioxide (or silica, SiO2). These spherical particles precipitate in highly siliceous pools in Australia and elsewhere, and form these highly ordered arrays after years of sedimentation and compression under hydrostatic and gravitational forces. The periodic arrays of submicrometre spherical particles provide similar arrays of interstitial voids, which act as a natural diffraction grating for visible light waves, particularly when the interstitial spacing is of the same order of magnitude as the incident lightwave.
+
+Thus, it has been known for many years that, due to repulsive Coulombic interactions, electrically charged macromolecules in an aqueous environment can exhibit long-range crystal-like correlations with interparticle separation distances, often being considerably greater than the individual particle diameter. In all of these cases in nature, the same brilliant iridescence (or play of colors) can be attributed to the diffraction and constructive interference of visible lightwaves that satisfy Bragg’s law, in a matter analogous to the scattering of X-rays in crystalline solids.
+
+The large number of experiments exploring the physics and chemistry of these so-called "colloidal crystals" has emerged as a result of the relatively simple methods that have evolved in the last 20 years for preparing synthetic monodisperse colloids (both polymer and mineral) and, through various mechanisms, implementing and preserving their long-range order formation.
+
+In biology
+Colloidal phase separation is an important organising principle for compartmentalisation of both the cytoplasm and nucleus of cells into biomolecular condensates—similar in importance to compartmentalisation via lipid bilayer membranes, a type of liquid crystal. The term biomolecular condensate has been used to refer to clusters of macromolecules that arise via liquid-liquid or liquid-solid phase separation within cells. Macromolecular crowding strongly enhances colloidal phase separation and formation of biomolecular condensates.
+
+In the environment
+Colloidal particles can also serve as transport vector
+of diverse contaminants in the surface water (sea water, lakes, rivers, fresh water bodies) and in underground water circulating in fissured rocks
+(e.g. limestone, sandstone, granite). Radionuclides and heavy metals easily sorb onto colloids suspended in water. Various types of colloids are recognised: inorganic colloids (e.g. clay particles, silicates, iron oxy-hydroxides), organic colloids (humic and fulvic substances). When heavy metals or radionuclides form their own pure colloids, the term "eigencolloid" is used to designate pure phases, i.e., pure Tc(OH)4, U(OH)4, or Am(OH)3. Colloids have been suspected for the long-range transport of plutonium on the Nevada Nuclear Test Site. They have been the subject of detailed studies for many years. However, the mobility of inorganic colloids is very low in compacted bentonites and in deep clay formations
+because of the process of ultrafiltration occurring in dense clay membrane.
+The question is less clear for small organic colloids often mixed in porewater with truly dissolved organic molecules.
+
+In soil science, the colloidal fraction in soils consists of tiny clay and humus particles that are less than 1μm in diameter and carry either positive and/or negative electrostatic charges that vary depending on the chemical conditions of the soil sample, i.e. soil pH.
+
+Intravenous therapy
+Colloid solutions used in intravenous therapy belong to a major group of volume expanders, and can be used for intravenous fluid replacement. Colloids preserve a high colloid osmotic pressure in the blood, and therefore, they should theoretically preferentially increase the intravascular volume, whereas other types of volume expanders called crystalloids also increase the interstitial volume and intracellular volume. However, there is still controversy to the actual difference in efficacy by this difference, and much of the research related to this use of colloids is based on fraudulent research by Joachim Boldt. Another difference is that crystalloids generally are much cheaper than colloids.
+
+References
+
+ 
+Chemical mixtures
+Colloidal chemistry
+Condensed matter physics
+Soft matter
+Dosage forms
+Chinese may refer to:
+ Something related to China
+ Chinese people, people identified with China, through nationality, citizenship, and/or ethnicity
+Han Chinese, East Asian ethnic group native to China.
+Zhonghua minzu, the supra-ethnic concept of the Chinese nation
+ List of ethnic groups in China, people of various ethnicities in contemporary China
+ Ethnic minorities in China, people of non-Han Chinese ethnicities in modern China
+ Ethnic groups in Chinese history, people of various ethnicities in historical China
+ Nationals of the People's Republic of China
+ Nationals of the Republic of China 
+ Overseas Chinese, Chinese people residing outside the territories of mainland China, Hong Kong, Macau, and Taiwan
+ Sinitic languages, the major branch of the Sino-Tibetan language family
+ Chinese language, a group of related languages spoken predominantly in China, sharing a written script (Chinese characters in traditional and simplified forms)
+ Standard Chinese, the standard form of Mandarin Chinese in mainland China, similar to forms of Mandarin Chinese in Taiwan and Singapore
+ Varieties of Chinese, topolects grouped under Chinese languages
+ Written Chinese, writing scripts used for Chinese languages
+Chinese characters, logograms used for the writing of East Asian languages
+ Chinese cuisine, styles of food originating from China or their derivatives
+"Chinese", a song about take out meals by Lily Allen from It's Not Me, It's You
+
+See also
+ Chinese citizen (disambiguation)
+ Tang Chinese (disambiguation)
+ 
+
+Language and nationality disambiguation pages
+"Riding shotgun" was a phrase used to describe the bodyguard who rides alongside a stagecoach driver, typically armed with a break-action shotgun, called a coach gun, to ward off bandits or hostile Native Americans. In modern use, it refers to the practice of sitting alongside the driver in a moving vehicle. The coining of this phrase dates to 1905 at the latest.
+
+Etymology
+The expression "riding shotgun" is derived from "shotgun messenger", a colloquial term for "express messenger", when stagecoach travel was popular during the American Wild West and the Colonial period in Australia. The person rode alongside the driver. The first known use of the phrase "riding shotgun" was in the 1905 novel The Sunset Trail by Alfred Henry Lewis. 
+
+It was later used in print and especially film depiction of stagecoaches and wagons in the Old West in danger of being robbed or attacked by bandits. A special armed employee of the express service using the stage for transportation of bullion or cash would sit beside the driver, carrying a short shotgun (or alternatively a rifle), to provide an armed response in case of threat to the cargo, which was usually a strongbox. Absence of an armed person in that position often signaled that the stage was not carrying a strongbox, but only passengers.
+
+Historical examples
+
+Tombstone, Arizona Territory
+On the evening of March 15, 1881, a Kinnear & Company stagecoach carrying US$26,000 in silver bullion () was en route from the boom town of Tombstone, Arizona Territory to Benson, Arizona, the nearest freight terminal. Bob Paul, who had run for Pima County Sheriff and was contesting the election he lost due to ballot-stuffing, was temporarily working once again as the Wells Fargo shotgun messenger. He had taken the reins and driver's seat in Contention City because the usual driver, a well-known and popular man named Eli "Budd" Philpot, was ill. Philpot was riding shotgun.
+
+Near Drew's Station, just outside Contention City, a man stepped into the road and commanded them to "Hold!" Three cowboys attempted to rob the stage. Paul, in the driver's seat, fired his shotgun and emptied his revolver at the robbers, wounding a cowboy later identified as Bill Leonard in the groin. Philpot, riding shotgun, and passenger Peter Roerig, riding in the rear dickey seat, were both shot and killed. The horses spooked and Paul wasn't able to bring the stage under control for almost a mile, leaving the robbers with nothing. Paul, who normally rode shotgun, later said he thought the first shot killing Philpot had been meant for him.
+
+When Wyatt Earp first arrived in Tombstone in December 1879, he initially took a job as a stagecoach shotgun messenger for Wells Fargo, guarding shipments of silver bullion. When Earp was appointed Pima County Deputy Sheriff on July 27, 1881, his brother Morgan Earp took over his job.
+
+Historical weapon
+When Wells, Fargo & Co. began regular stagecoach service from Tipton, Missouri to San Francisco, California in 1858, they issued shotguns to its drivers and guards for defense along the perilous 2,800 mile route. The guard was called a shotgun messenger and they were issued a Coach gun, typically a 10-gauge or 12-gauge, short, double-barreled shotgun.
+
+Modern usage
+More recently, the term has been applied to a game, usually played by groups of friends to determine who rides beside the driver in a car. Typically, this involves claiming the right to ride shotgun by being the first person to call out "shotgun" when everyone is in view of the vehicle; in some regions, calling shotgun too early disqualifies one from the game. The game creates an environment that is fair by forgetting and leaving out most seniority except that parents and significant others automatically get shotgun, and this meanwhile leaves out any conflicts that may have previously occurred when deciding who gets to ride shotgun.
+
+See also
+
+ Coach gun
+ Drive-by shooting
+ Shotgun messenger
+
+References
+
+American cultural conventions
+Car games
+Western (genre) staples and terminology
+Cooking, also known as cookery or professionally as the culinary arts, is the art, science and craft of using heat to make food more palatable, digestible, nutritious, or safe. Cooking techniques and ingredients vary widely, from grilling food over an open fire to using electric stoves, to baking in various types of ovens, reflecting local conditions.
+
+Types of cooking also depend on the skill levels and training of the cooks. Cooking is done both by people in their own dwellings and by professional cooks and chefs in restaurants and other food establishments.
+
+Preparing food with heat or fire is an activity unique to humans. Archeological evidence of cooking fires from at least 300,000 years ago exists, but some estimate that humans started cooking up to 2 million years ago.
+
+The expansion of agriculture, commerce, trade, and transportation between civilizations in different regions offered cooks many new ingredients. New inventions and technologies, such as the invention of pottery for holding and boiling of water, expanded cooking techniques. Some modern cooks apply advanced scientific techniques to food preparation to further enhance the flavor of the dish served.
+
+History
+
+Phylogenetic analysis suggests that early hominids may have adopted cooking 1 million to 2 million years ago.  of burnt bone fragments and plant ashes from the Wonderwerk Cave in South Africa has provided evidence supporting control of fire by early humans by 1 million years ago. In his seminal work Catching Fire: How Cooking Made Us Human, Richard Wrangham suggested that evolution of bipedalism and a large cranial capacity meant that early Homo habilis regularly cooked food. However, unequivocal evidence in the archaeological record for the controlled use of fire begins at 400,000 BCE, long after Homo erectus. Archaeological evidence from 300,000 years ago, in the form of ancient hearths, earth ovens, burnt animal bones, and flint, are found across Europe and the Middle East. The oldest evidence (via heated fish teeth from a deep cave) of controlled use of fire to cook food by archaic humans was dated to ~780,000 years ago. Anthropologists think that widespread cooking fires began about 250,000 years ago when hearths first appeared.
+
+Recently, the earliest hearths have been reported to be at least 790,000 years old.
+
+Communication between the Old World and the New World in the Columbian Exchange influenced the history of cooking. The movement of foods across the Atlantic from the New World, such as potatoes, tomatoes, maize, beans, bell pepper, chili pepper, vanilla, pumpkin, cassava, avocado, peanut, pecan, cashew, pineapple, blueberry, sunflower, chocolate, gourds, and squash, had a profound effect on Old World cooking. The movement of foods across the Atlantic from the Old World, such as cattle, sheep, pigs, wheat, oats, barley, rice, apples, pears, peas, chickpeas, green beans, mustard, and carrots, similarly changed New World cooking.
+
+In the 17th and 18th centuries, food was a classic marker of identity in Europe. In the 19th-century "Age of Nationalism", cuisine became a defining symbol of national identity.
+
+The Industrial Revolution brought mass-production, mass-marketing, and standardization of food. Factories processed, preserved, canned, and packaged a wide variety of foods, and processed cereals quickly became a defining feature of the American breakfast. In the 1920s, freezing methods, cafeterias, and fast food restaurants emerged.
+
+Ingredients
+Most ingredients in cooking are derived from living organisms. Vegetables, fruits, grains and nuts as well as herbs and spices come from plants, while meat, eggs, and dairy products come from animals. Mushrooms and the yeast used in baking are kinds of fungi. Cooks also use water and minerals such as salt. Cooks can also use wine or spirits.
+
+Naturally occurring ingredients contain various amounts of molecules called proteins, carbohydrates and fats. They also contain water and minerals. Cooking involves a manipulation of the chemical properties of these molecules.
+
+Carbohydrates
+
+Carbohydrates include the common sugar, sucrose (table sugar), a disaccharide, and such simple sugars as glucose (made by enzymatic splitting of sucrose) and fructose (from fruit), and starches from sources such as cereal flour, rice, arrowroot and potato.
+
+The interaction of heat and carbohydrate is complex. Long-chain sugars such as starch tend to break down into more digestible simpler sugars. If the sugars are heated so that all water of crystallisation is driven off, caramelization starts, with the sugar undergoing thermal decomposition with the formation of carbon, and other breakdown products producing caramel. Similarly, the heating of sugars and proteins causes the Maillard reaction, a basic flavor-enhancing technique.
+
+An emulsion of starch with fat or water can, when gently heated, provide thickening to the dish being cooked. In European cooking, a mixture of butter and flour called a roux is used to thicken liquids to make stews or sauces. In Asian cooking, a similar effect is obtained from a mixture of rice or corn starch and water. These techniques rely on the properties of starches to create simpler mucilaginous saccharides during cooking, which causes the familiar thickening of sauces. This thickening will break down, however, under additional heat.
+
+Fats
+
+Types of fat include vegetable oils, animal products such as butter and lard, as well as fats from grains, including maize and flax oils. Fats are used in a number of ways in cooking and baking. To prepare stir fries, grilled cheese or pancakes, the pan or griddle is often coated with fat or oil. Fats are also used as an ingredient in baked goods such as cookies, cakes and pies. Fats can reach temperatures higher than the boiling point of water, and are often used to conduct high heat to other ingredients, such as in frying, deep frying or sautéing. Fats are used to add flavor to food (e.g., butter or bacon fat), prevent food from sticking to pans and create a desirable texture.
+
+Proteins
+
+Edible animal material, including muscle, offal, milk, eggs and egg whites, contains substantial amounts of protein. Almost all vegetable matter (in particular legumes and seeds) also includes proteins, although generally in smaller amounts. Mushrooms have high protein content. Any of these may be sources of essential amino acids. When proteins are heated they become denatured (unfolded) and change texture. In many cases, this causes the structure of the material to become softer or more friable – meat becomes cooked and is more friable and less flexible. In some cases, proteins can form more rigid structures, such as the coagulation of albumen in egg whites. The formation of a relatively rigid but flexible matrix from egg white provides an important component in baking cakes, and also underpins many desserts based on meringue.
+
+Water
+
+Cooking often involves water, and water-based liquids. These can be added in order to immerse the substances being cooked (this is typically done with water, stock or wine). Alternatively, the foods themselves can release water. A favorite method of adding flavor to dishes is to save the liquid for use in other recipes. Liquids are so important to cooking that the name of the cooking method used is often based on how the liquid is combined with the food, as in steaming, simmering, boiling, braising and blanching. Heating liquid in an open container results in rapidly increased evaporation, which concentrates the remaining flavor and ingredients; this is a critical component of both stewing and sauce making.
+
+Vitamins and minerals
+
+Vitamins and minerals are required for normal metabolism; and what the body cannot manufacture itself must come from external sources. Vitamins come from several sources including fresh fruit and vegetables (Vitamin C), carrots, liver (Vitamin A), cereal bran, bread, liver (B vitamins), fish liver oil (Vitamin D) and fresh green vegetables (Vitamin K). Many minerals are also essential in small quantities including iron, calcium, magnesium, sodium chloride and sulfur; and in very small quantities copper, zinc and selenium. The micronutrients, minerals, and vitamins in fruit and vegetables may be destroyed or eluted by cooking. Vitamin C is especially prone to oxidation during cooking and may be completely destroyed by protracted cooking. The bioavailability of some vitamins such as thiamin, vitamin B6, niacin, folate, and carotenoids are increased with cooking by being freed from the food microstructure. Blanching or steaming vegetables is a way of minimizing vitamin and mineral loss in cooking.
+
+Methods
+
+There are many methods of cooking, most of which have been known since antiquity. These include baking, roasting, frying, grilling, barbecuing, smoking, boiling, steaming and braising. A more recent innovation is microwaving. Various methods use differing levels of heat and moisture and vary in cooking time. The method chosen greatly affects the result because some foods are more appropriate to some methods than others. Some major hot cooking techniques include:
+
+Roasting
+Roasting – Barbecuing – Grilling/Broiling – Rotisserie – Searing
+Baking
+Baking – Baking Blind – Flashbaking
+Boiling
+Boiling – Blanching – Braising – Coddling – Double steaming – Infusion – Poaching – Pressure cooking – Simmering – Smothering – Steaming – Steeping – Stewing – Stone boiling –  Vacuum flask cooking
+Frying
+Fry – Air frying — Deep frying – Gentle frying – Hot salt frying – Hot sand frying – Pan frying – Pressure frying – Sautéing  – Shallow frying – Stir frying – Vacuum frying
+Steaming
+Steaming works by boiling water continuously, causing it to vaporise into steam; the steam then carries heat to the nearby food, thus cooking the food.  By many it is considered a healthy form of cooking, holding nutrients within the vegetable or meat being cooked.
+ En papillote – The food is put into a pouch and then baked, allowing its own moisture to steam the food.
+Smoking
+Smoking is the process of flavoring, cooking, or preserving food by exposing it to smoke from burning or smoldering material, most often wood.
+
+Health and safety
+
+Indoor air pollution 
+
+As of 2021, over 2.6 billion people cook using open fires or inefficient stoves using kerosene, biomass, and coal as fuel. These cooking practices use fuels and technologies that produce high levels of household air pollution, causing 3.8 million premature deaths annually. Of these deaths, 27% are from pneumonia, 27% from ischaemic heart disease, 20% from chronic obstructive pulmonary disease, 18% from stroke, and 8% from lung cancer. Women and young children are disproportionately affected, since they spend the most time near the hearth.
+
+Security while cooking 
+Hazards while cooking can include
+ Unseen slippery surfaces (such as from oil stains, water droplets, or items that have fallen on the floor)
+ Cuts; about a third of the US's estimated annual 400,000 knife injuries are kitchen-related.
+ Burns or fires
+
+To prevent those injuries there are protections such as cooking clothing, anti-slip shoes, fire extinguisher and more.
+
+Food safety
+
+Cooking can prevent many foodborne illnesses that would otherwise occur if raw food is consumed. When heat is used in the preparation of food, it can kill or inactivate harmful organisms, such as bacteria and viruses, as well as various parasites such as tapeworms and Toxoplasma gondii. Food poisoning and other illness from uncooked or poorly prepared food may be caused by bacteria such as pathogenic strains of Escherichia coli, Salmonella typhimurium and Campylobacter, viruses such as noroviruses, and protozoa such as Entamoeba histolytica. Bacteria, viruses and parasites may be introduced through salad, meat that is uncooked or done rare, and unboiled water.
+
+The sterilizing effect of cooking depends on temperature, cooking time, and technique used. Some food spoilage bacteria such as Clostridium botulinum or Bacillus cereus can form spores that survive boiling, which then germinate and regrow after the food has cooled. This makes it unsafe to reheat cooked food more than once.
+
+Cooking increases the digestibility of many foods which are inedible or poisonous when raw. For example, raw cereal grains are hard to digest, while kidney beans are toxic when raw or improperly cooked due to the presence of phytohaemagglutinin, which is inactivated by cooking for at least ten minutes at .
+
+Food safety depends on the safe preparation, handling, and storage of food. Food spoilage bacteria proliferate in the "Danger zone" temperature range from , food therefore should not be stored in this temperature range. Washing of hands and surfaces, especially when handling different meats, and keeping raw food separate from cooked food to avoid cross-contamination, are good practices in food preparation. Foods prepared on plastic cutting boards may be less likely to harbor bacteria than wooden ones. Washing and disinfecting cutting boards, especially after use with raw meat, poultry, or seafood, reduces the risk of contamination.
+
+Effects on nutritional content of food
+
+Proponents of raw foodism argue that cooking food increases the risk of some of the detrimental effects on food or health. They point out that during cooking of vegetables and fruit containing vitamin C, the vitamin elutes into the cooking water and becomes degraded through oxidation. Peeling vegetables can also substantially reduce the vitamin C content, especially in the case of potatoes where most vitamin C is in the skin. However, research has shown that in the specific case of carotenoids a greater proportion is absorbed from cooked vegetables than from raw vegetables.
+
+Sulforaphane, a glucosinolate breakdown product, is present in vegetables such as broccoli, and is mostly destroyed when the vegetable is boiled. Although there has been some basic research on how sulforaphane might exert beneficial effects in vivo, there is no high-quality evidence for its efficacy against human diseases.
+
+The United States Department of Agriculture has studied retention data for 16 vitamins, 8 minerals, and alcohol for approximately 290 foods across various cooking methods.
+
+Carcinogens
+
+In a human epidemiological analysis by Richard Doll and Richard Peto in 1981, diet was estimated to cause a large percentage of cancers. Studies suggest that around 32% of cancer deaths may be avoidable by changes to the diet. Some of these cancers may be caused by carcinogens in food generated during the cooking process, although it is often difficult to identify the specific components in diet that serve to increase cancer risk.
+
+Several studies published since 1990 indicate that cooking meat at high temperature creates heterocyclic amines (HCAs), which are thought to increase cancer risk in humans. Researchers at the National Cancer Institute found that human subjects who ate beef rare or medium-rare had less than one third the risk of stomach cancer than those who ate beef medium-well or well-done. While avoiding meat or eating meat raw may be the only ways to avoid HCAs in meat fully, the National Cancer Institute states that cooking meat below  creates "negligible amounts" of HCAs. Also, microwaving meat before cooking may reduce HCAs by 90% by reducing the time needed for the meat to be cooked at high heat. Nitrosamines are found in some food, and may be produced by some cooking processes from proteins or from nitrites used as food preservatives; cured meat such as bacon has been found to be carcinogenic, with links to colon cancer. Ascorbate, which is added to cured meat, however, reduces nitrosamine formation.
+
+Baking, grilling or broiling food, especially starchy foods, until a toasted crust is formed generates significant concentrations of acrylamide. This discovery in 2002 led to international health concerns. Subsequent research has however found that it is not likely that the acrylamides in burnt or well-cooked food cause cancer in humans; Cancer Research UK categorizes the idea that burnt food causes cancer as a "myth".
+
+Scientific aspects
+
+The scientific study of cooking has become known as molecular gastronomy. This is a subdiscipline of food science concerning the physical and chemical transformations that occur during cooking.
+
+Important contributions have been made by scientists, chefs and authors such as Hervé This (chemist), Nicholas Kurti (physicist), Peter Barham (physicist), Harold McGee (author), Shirley Corriher (biochemist, author),  Robert Wolke (chemist, author.) It is different for the application of scientific knowledge to cooking, that is "molecular cooking"( (for the technique) or "molecular cuisine" (for a culinary style), for which chefs such as Raymond Blanc, Philippe and Christian Conticini, Ferran Adria, Heston Blumenthal, Pierre Gagnaire (chef).
+
+Chemical processes central to cooking include hydrolysis (in particular beta elimination of pectins, during the thermal treatment of plant tissues), pyrolysis, and glycation reactions wrongly named Maillard reactions.
+
+Cooking foods with heat depends on many factors: the specific heat of an object, thermal conductivity, and (perhaps most significantly) the difference in temperature between the two objects. Thermal diffusivity is the combination of specific heat, conductivity and density that determines how long it will take for the food to reach a certain temperature.
+
+Home-cooking and commercial cooking
+
+Home cooking has traditionally been a process carried out informally in a home or around a communal fire, and can be enjoyed by all members of the family, although in many cultures women bear primary responsibility. Cooking is also often carried out outside of personal quarters, for example at restaurants, or schools. Bakeries were one of the earliest forms of cooking outside the home, and bakeries in the past often offered the cooking of pots of food provided by their customers as an additional service. In the present day, factory food preparation has become common, with many "ready-to-eat" as well as "ready-to-cook" foods being prepared and cooked in factories and home cooks using a mixture of scratch made, and factory made foods together to make a meal. The nutritional value of including more commercially prepared foods has been found to be inferior to home-made foods. Home-cooked meals tend to be healthier with fewer calories, and less saturated fat, cholesterol and sodium on a per calorie basis while providing more fiber, calcium, and iron. The ingredients are also directly sourced, so there is control over authenticity, taste, and nutritional value. The superior nutritional quality of home-cooking could therefore play a role in preventing chronic disease. Cohort studies following the elderly over 10 years show that adults who cook their own meals have significantly lower mortality, even when controlling for confounding variables.
+
+"Home-cooking" may be associated with comfort food, and some commercially produced foods and restaurant meals are presented through advertising or packaging as having been "home-cooked", regardless of their actual origin. This trend began in the 1920s and is attributed to people in urban areas of the U.S. wanting homestyle food even though their schedules and smaller kitchens made cooking harder.
+
+See also
+
+ Carryover cooking
+ Cookbook
+ Cooker
+ Cooking weights and measures
+ Culinary arts
+ Culinary profession
+ Cooking school
+ Dishwashing
+ Food and cooking hygiene
+ Food industry
+ Food preservation
+ Food writing
+ Foodpairing
+ Gourmet Museum and Library
+ High altitude cooking
+ International food terms
+ List of cooking appliances
+ List of cuisines
+ List of films about cooking
+ List of food preparation utensils
+ List of ovens
+ List of stoves
+ Scented water
+ Staple (cooking)
+
+References
+
+External links
+ 
+
+ 
+Articles containing video clips
+Home economics
+Survival skills
+A card game is any game using playing cards as the primary device with which the game is played, be they traditional or game-specific. Countless card games exist, including families of related games (such as poker). A small number of card games played with traditional decks have formally standardized rules with international tournaments being held, but most are folk games whose rules may vary by region, culture, location or from circle to circle.
+
+Traditional card games are played with a deck or pack of playing cards which are identical in size and shape. Each card has two sides, the face and the back. Normally the backs of the cards are indistinguishable. The faces of the cards may all be unique, or there can be duplicates. The composition of a deck is known to each player. In some cases several decks are shuffled together to form a single pack or shoe. Modern card games usually have bespoke decks, often with a vast amount of cards, and can include number or action cards. This type of game is generally regarded as part of the board game hobby.
+
+Games using playing cards exploit the fact that cards are individually identifiable from one side only, so that each player knows only the cards they hold and not those held by anyone else. For this reason card games are often characterized as games of chance or "imperfect information"—as distinct from games of strategy or perfect information, where the current position is fully visible to all players throughout the game. Many games that are not generally placed in the family of card games do in fact use cards for some aspect of their gameplay.
+
+Some games that are placed in the card game genre involve a board. The distinction is that the gameplay of a card game chiefly depends on the use of the cards by players (the board is a guide for scorekeeping or for card placement), while board games (the principal non-card game genre to use cards) generally focus on the players' positions on the board, and use the cards for some secondary purpose.
+
+Types
+
+Trick-taking games
+
+There are two main types of trick-taking game which have different objectives. Both are based on the play of multiple tricks, in each of which each player plays a single card from their hand, and based on the values of played cards one player wins or "takes" the trick.
+
+ Plain-trick games. Many common Anglo-American games fall into this category. The usual objective is to take the most tricks, but variations taking all tricks, making as few tricks (or penalty cards) as possible or taking an exact number of tricks. Bridge, Whist and Spades are popular examples. Hearts, Black Lady and Black Maria are examples of reverse games in which the aim is to avoid certain cards.
+
+ Point-trick games. These are all European or of European origin. Individual cards have specific point values and the objective is usually to amass the majority of points by taking tricks, especially those with higher value cards. The main group is the Ace-Ten family which includes many national games such as German Skat, French Belote, Dutch Klaberjass, Austrian Schnapsen, Spanish Tute, Swiss Jass, Portuguese Sueca, Italian Briscola and Czech Mariáš. Pinochle is an American example of French or Swiss origin. All Tarot card games are of the point-trick variety including German Cego, Austrian Tarock, French Tarot and Italian Minchiate.
+
+Matching games
+
+The object of a matching (or sometimes "melding") game is to acquire particular groups of matching cards before an opponent can do so. In Rummy, this is done through drawing and discarding, and the groups are called melds. Mahjong is a very similar game played with tiles instead of cards. Non-Rummy examples of match-type games generally fall into the "fishing" genre and include the children's games Go Fish and Old Maid.
+
+Shedding games
+
+In a shedding game, players start with a hand of cards, and the object of the game is to be the first player to discard all cards from one's hand. Common shedding games include Crazy Eights (commercialized by Mattel as Uno) and Daihinmin. Some matching-type games are also shedding-type games; some variants of Rummy such as Paskahousu, Phase 10, Rummikub, the bluffing game I Doubt It, and the children's games Musta Maija and Old Maid, fall into both categories.
+
+Catch and collect games
+
+The object of an accumulating game is to acquire all cards in the deck. Examples include most War type games, and games involving slapping a discard pile such as Slapjack. Egyptian Ratscrew has both of these features.
+
+Fishing games
+ 
+
+In fishing games, cards from the hand are played against cards in a layout on the table, capturing table cards if they match.  Fishing games are popular in many nations, including China, where there are many diverse fishing games.  Scopa is considered one of the national card games of Italy.  Cassino is the only fishing game to be widely played in English-speaking countries. Zwicker has been described as a "simpler and jollier version of Cassino", played in Germany. Tablanet (tablić) is a fishing-style game popular in Balkans.
+
+Comparing games
+
+Comparing card games are those where hand values are compared to determine the winner, also known as "vying" or "showdown" games. Poker, blackjack, mus, and baccarat are examples of comparing card games. As seen, nearly all of these games are designed as gambling games.
+
+Patience and solitaire games
+
+Solitaire games are designed to be played by one player. Most games begin with a specific layout of cards, called a tableau, and the object is then either to construct a more elaborate final layout, or to clear the tableau and/or the draw pile or stock by moving all cards to one or more "discard" or "foundation" piles.
+
+Drinking card games
+
+Drinking card games are drinking games using cards, in which the object in playing the game is either to drink or to force others to drink. Many games are ordinary card games with the establishment of "drinking rules"; President, for instance, is virtually identical to Daihinmin but with additional rules governing drinking. Poker can also be played using a number of drinks as the wager. Another game often played as a drinking game is Toepen, quite popular in the Netherlands. Some card games are designed specifically to be played as drinking games.
+
+Compendium games 
+Compendium games consist of a sequence of different contracts played in succession. A common pattern is for a number of reverse deals to be played, in which the aim is to avoid certain cards, followed by a final contract which is a domino-type game. Examples include: Barbu, Herzeln, Lorum and Rosbiratschka. In other games, such as Quodlibet and Rumpel, there is a range of widely varying contracts.
+
+Collectible card games (CCGs)
+
+Collectible card games (CCG) are proprietary playing card games. CCGs are games of strategy between two or more players. Each player has their own deck constructed from a very large pool of unique cards in the commercial market. The cards have different effects, costs, and art. New card sets are released periodically and sold as starter decks or booster packs. Obtaining the different cards makes the game a collectible card game, and cards are sold or traded on the secondary market. Magic: The Gathering, Pokémon, and Yu-Gi-Oh! are well-known collectible card games.
+
+Living card games (LCGs)
+
+Living card games (LCGs) are similar to collectible card games (CCGs), with their most distinguishing feature being a fixed distribution method, which breaks away from the traditional collectible card game format. While new cards for CCGs are usually sold in the form of starter decks or booster packs (the latter being often randomized), LCGs thrive on a model that requires players to acquire one core set in order to play the game, which players can further customize by acquiring extra sets or expansions featuring new content in the form of cards or scenarios. No randomization is involved in the process, thus players that get the same sets or expansions will get the exact same content. The term was popularized by Fantasy Flight Games (FFG) and mainly applies to its products, however some tabletop gaming companies can be seen using a very similar model.
+
+Casino or gambling card games
+
+These games revolve around wagers of money. Though virtually any game in which there are winning and losing outcomes can be wagered on, these games are specifically designed to make the betting process a strategic part of the game. Some of these games involve players betting against each other, such as poker, while in others, like blackjack, players wager against the house.
+
+Poker games
+
+Poker is a family of gambling games in which players bet into a pool, called the pot, the value of which changes as the game progresses that the value of the hand they carry will beat all others according to the ranking system. Variants largely differ on how cards are dealt and the methods by which players can improve a hand. For many reasons, including its age and its popularity among Western militaries, it is one of the most universally known card games in existence.
+
+Other card games
+
+Many other card games have been designed and published on a commercial or amateur basis. In some cases, the game uses the standard 52-card deck, but the object is unique. In Eleusis, for example, players play single cards, and are told whether the play was legal or illegal, in an attempt to discover the underlying rules made up by the dealer.
+
+Most of these games however typically use a specially made deck of cards designed specifically for the game (or variations of it). The decks are thus usually proprietary, but may be created by the game's players. Uno, Phase 10, Set, and 1000 Blank White Cards are popular dedicated-deck card games; 1000 Blank White Cards is unique in that the cards for the game are designed by the players of the game while playing it; there is no commercially available deck advertised as such.
+
+Simulation card games
+A deck of either customised dedicated cards or a standard deck of playing cards with assigned meanings is used to simulate the actions of another activity, for example card football.
+
+Fictional card games
+
+Many games, including card games, are fabricated by science fiction authors and screenwriters to distance a culture depicted in the story from present-day Western culture. They are commonly used as filler to depict background activities in an atmosphere like a bar or rec room, but sometimes the drama revolves around the play of the game. Some of these games become real card games as the holder of the intellectual property develops and markets a suitable deck and ruleset for the game, while others lack sufficient descriptions of rules, or depend on cards or other hardware that are infeasible or physically impossible.
+
+Typical structure of card games
+
+Number and association of players
+
+Any specific card game imposes restrictions on the number of players. The most significant dividing lines run between one-player games and two-player games, and between two-player games and multi-player games. Card games for one player are known as solitaire or patience card games. (See list of solitaire card games.) Generally speaking, they are in many ways special and atypical, although some of them have given rise to two- or multi-player games such as Spite and Malice.
+
+In card games for two players, usually not all cards are distributed to the players, as they would otherwise have perfect information about the game state. Two-player games have always been immensely popular and include some of the most significant card games such as piquet, bezique, sixty-six, klaberjass, gin rummy and cribbage. Many multi-player games started as two-player games that were adapted to a greater number of players. For such adaptations a number of non-obvious choices must be made beginning with the choice of a game orientation.
+
+One way of extending a two-player game to more players is by building two teams of equal size. A common case is four players in two fixed partnerships, sitting crosswise as in whist and contract bridge. Partners sit opposite to each other and cannot see each other's hands. If communication between the partners is allowed at all, then it is usually restricted to a specific list of permitted signs and signals. 17th-century French partnership games such as triomphe were special in that partners sat next to each other and were allowed to communicate freely so long as they did not exchange cards or play out of order.
+
+Another way of extending a two-player game to more players is as a cut-throat or individual game, in which all players play for themselves, and win or lose alone. Most such card games are round games, i.e. they can be played by any number of players starting from two or three, so long as there are enough cards for all.
+
+For some of the most interesting games such as ombre, tarot and skat, the associations between players change from hand to hand. Ultimately players all play on their own, but for each hand, some game mechanism divides the players into two teams. Most typically these are solo games, i.e. games in which one player becomes the soloist and has to achieve some objective against the others, who form a team and win or lose all their points jointly. But in games for more than three players, there may also be a mechanism that selects two players who then have to play against the others.
+
+Direction of play
+The players of a card game normally form a circle around a table or other space that can hold cards. The game orientation or direction of play, which is only relevant for three or more players, can be either clockwise or counterclockwise. It is the direction in which various roles in the game proceed. (In real-time card games, there may be no need for a direction of play.) Most regions have a traditional direction of play, such as:
+
+ Counterclockwise in most of Asia and in Latin America.
+ Clockwise in North America and Australia.
+
+Europe is roughly divided into a clockwise area in the north and a counterclockwise area in the south. The boundary runs between England, Ireland, Netherlands, Germany, Austria (mostly), Slovakia, Ukraine and Russia (clockwise) and France, Switzerland, Spain, Italy, Slovenia, Balkans, Hungary, Romania, Bulgaria, Greece and Turkey (counterclockwise).
+
+Games that originate in a region with a strong preference are often initially played in the original direction, even in regions that prefer the opposite direction. For games that have official rules and are played in tournaments, the direction of play is often prescribed in those rules.
+
+Determining who deals
+Most games have some form of asymmetry between players. The roles of players are normally expressed in terms of the dealer, i.e. the player whose task it is to shuffle the cards and distribute them to the players. Being the dealer can be a (minor or major) advantage or disadvantage, depending on the game. Therefore, after each played hand, the deal normally passes to the next player according to the game orientation.
+
+As it can still be an advantage or disadvantage to be the first dealer, there are some standard methods for determining who is the first dealer. A common method is by cutting, which works as follows. One player shuffles the deck and places it on the table. Each player lifts a packet of cards from the top, reveals its bottom card, and returns it to the deck. The player who reveals the highest (or lowest) card becomes dealer. In the case of a tie, the process is repeated by the tied players. For some games such as whist this process of cutting is part of the official rules, and the hierarchy of cards for the purpose of cutting (which need not be the same as that used otherwise in the game) is also specified. But in general, any method can be used, such as tossing a coin in case of a two-player game, drawing cards until one player draws an ace, or rolling dice.
+
+Hands, rounds and games
+
+A hand, also called a deal, is a unit of the game that begins with the dealer shuffling and dealing the cards as described below, and ends with the players scoring and the next dealer being determined. The set of cards that each player receives and holds in his or her hands is also known as that player's hand.
+
+The hand is over when the players have finished playing their hands. Most often this occurs when one player (or all) has no cards left. The player who sits after the dealer in the direction of play is known as eldest hand (or in two-player games as elder hand) or forehand. A game round consists of as many hands as there are players. After each hand, the deal is passed on in the direction of play, i.e. the previous eldest hand becomes the new dealer. Normally players score points after each hand. A game may consist of a fixed number of rounds. Alternatively it can be played for a fixed number of points. In this case it is over with the hand in which a player reaches the target score.
+
+Shuffling
+
+Shuffling is the process of bringing the cards of a pack into a random order. There are a large number of techniques with various advantages and disadvantages. Riffle shuffling is a method in which the deck is divided into two roughly equal-sized halves that are bent and then released, so that the cards interlace. Repeating this process several times randomizes the deck well, but the method is harder to learn than some others and may damage the cards. The overhand shuffle and the Hindu shuffle are two techniques that work by taking batches of cards from the top of the deck and reassembling them in the opposite order. They are easier to learn but must be repeated more often. A method suitable for small children consists in spreading the cards on a large surface and moving them around before picking up the deck again. This is also the most common method for shuffling tiles such as dominoes.
+
+For casino games that are played for large sums it is vital that the cards be properly randomized, but for many games this is less critical, and in fact player experience can suffer when the cards are shuffled too well. The official skat rules stipulate that the cards are shuffled well, but according to a decision of the German skat court, a one-handed player should ask another player to do the shuffling, rather than use a shuffling machine, as it would shuffle the cards too well. French belote rules go so far as to prescribe that the deck never be shuffled between hands.
+
+Deal
+
+The dealer takes all of the cards in the pack, arranges them so that they are in a uniform stack, and shuffles them. In strict play, the dealer then offers the deck to the previous player (in the sense of the game direction) for cutting. If the deal is clockwise, this is the player to the dealer's right; if counterclockwise, it is the player to the dealer's left. The invitation to cut is made by placing the pack, face downward, on the table near the player who is to cut: who then lifts the upper portion of the pack clear of the lower portion and places it alongside. (Normally the two portions have about equal size. Strict rules often indicate that each portion must contain a certain minimum number of cards, such as three or five.) The formerly lower portion is then replaced on top of the formerly upper portion. Instead of cutting, one may also knock on the deck to indicate that one trusts the dealer to have shuffled fairly.
+
+The actual deal (distribution of cards) is done in the direction of play, beginning with eldest hand. The dealer holds the pack, face down, in one hand, and removes cards from the top of it with his or her other hand to distribute to the players, placing them face down on the table in front of the players to whom they are dealt. The cards may be dealt one at a time, or in batches of more than one card; and either the entire pack or a determined number of cards are dealt out. The undealt cards, if any, are left face down in the middle of the table, forming the stock (also called the talon, widow, skat or kitty depending on the game and region).
+
+Throughout the shuffle, cut, and deal, the dealer should prevent the players from seeing the faces of any of the cards. The players should not try to see any of the faces. Should a player accidentally see a card, other than one's own, proper etiquette would be to admit this. It is also dishonest to try to see cards as they are dealt, or to take advantage of having seen a card. Should a card accidentally become exposed, (visible to all), any player can demand a redeal (all the cards are gathered up, and the shuffle, cut, and deal are repeated) or that the card be replaced randomly into the deck ("burning" it) and a replacement dealt from the top to the player who was to receive the revealed card.
+
+When the deal is complete, all players pick up their cards, or "hand", and hold them in such a way that the faces can be seen by the holder of the cards but not the other players, or vice versa depending on the game. It is helpful to fan one's cards out so that if they have corner indices all their values can be seen at once. In most games, it is also useful to sort one's hand, rearranging the cards in a way appropriate to the game. For example, in a trick-taking game it may be easier to have all one's cards of the same suit together, whereas in a rummy game one might sort them by rank or by potential combinations.
+
+Rules
+
+A new card game starts in a small way, either as someone's invention, or as a modification of an existing game. Those playing it may agree to change the rules as they wish. The rules that they agree on become the "house rules" under which they play the game. A set of house rules may be accepted as valid by a group of players wherever they play, as it may also be accepted as governing all play within a particular house, café, or club.
+
+When a game becomes sufficiently popular, so that people often play it with strangers, there is a need for a generally accepted set of rules. This need is often met when a particular set of house rules becomes generally recognized. For example, when Whist became popular in 18th-century England, players in the Portland Club agreed on a set of house rules for use on its premises. Players in some other clubs then agreed to follow the "Portland Club" rules, rather than go to the trouble of codifying and printing their own sets of rules. The Portland Club rules eventually became generally accepted throughout England and Western cultures.
+
+There is nothing static or "official" about this process. For the majority of games, there is no one set of universal rules by which the game is played, and the most common ruleset is no more or less than that. Many widely played card games, such as Canasta and Pinochle, have no official regulating body. The most common ruleset is often determined by the most popular distribution of rulebooks for card games. Perhaps the original compilation of popular playing card games was collected by Edmund Hoyle, a self-made authority on many popular parlor games. The U.S. Playing Card Company now owns the eponymous Hoyle brand, and publishes a series of rulebooks for various families of card games that have largely standardized the games' rules in countries and languages where the rulebooks are widely distributed. However, players are free to, and often do, invent "house rules" to supplement or even largely replace the "standard" rules.
+
+If there is a sense in which a card game can have an official set of rules, it is when that card game has an "official" governing body. For example, the rules of tournament bridge are governed by the World Bridge Federation, and by local bodies in various countries such as the American Contract Bridge League in the U.S., and the English Bridge Union in England. The rules of skat are governed by The International Skat Players Association and, in Germany,  by the Deutscher Skatverband which publishes the Skatordnung. The rules of French tarot are governed by the Fédération Française de Tarot. The rules of Schafkopf are laid down by the Schafkopfschule in Munich. Even in these cases, the rules must only be followed at games sanctioned by these governing bodies or where the tournament organisers specify them. Players in informal settings are free to implement agreed supplemental or substitute rules. For example, in Schafkopf there are numerous local variants sometimes known as "impure" Schafkopf and specified by assuming the official rules and describing the additions e.g. "with Geier and Bettel, tariff 5/10 cents".
+
+Rule infractions
+An infraction is any action which is against the rules of the game, such as playing a card when it is not one's turn to play or the accidental exposure of a card, informally known as "bleeding."
+
+In many official sets of rules for card games, the rules specifying the penalties for various infractions occupy more pages than the rules specifying how to play correctly. This is tedious but necessary for games that are played seriously. Players who intend to play a card game at a high level generally ensure before beginning that all agree on the penalties to be used. When playing privately, this will normally be a question of agreeing house rules. In a tournament, there will probably be a tournament director who will enforce the rules when required and arbitrate in cases of doubt.
+
+If a player breaks the rules of a game deliberately, this is cheating. The rest of this section is therefore about accidental infractions, caused by ignorance, clumsiness, inattention, etc.
+
+As the same game is played repeatedly among a group of players, precedents build up about how a particular infraction of the rules should be handled. For example, "Sheila just led a card when it wasn't her turn. Last week when Jo did that, we agreed ... etc." Sets of such precedents tend to become established among groups of players, and to be regarded as part of the house rules. Sets of house rules may become formalized, as described in the previous section. Therefore, for some games, there is a "proper" way of handling infractions of the rules. But for many games, without governing bodies, there is no standard way of handling infractions.
+
+In many circumstances, there is no need for special rules dealing with what happens after an infraction. As a general principle, the person who broke a rule should not benefit from it, and the other players should not lose by it. An exception to this may be made in games with fixed partnerships, in which it may be felt that the partner(s) of the person who broke a rule should also not benefit. The penalty for an accidental infraction should be as mild as reasonable, consistent with there being a possible benefit to the person responsible.
+
+Playing cards
+
+The oldest surviving reference to the card game in world history is from the 9th century China, when the Collection of Miscellanea at Duyang, written by Tang-dynasty writer Su E, described Princess Tongchang (daughter of Emperor Yizong of Tang) playing the "leaf game" with members of the Wei clan (the family of the princess's husband) in 868 . The Song dynasty statesman and historian Ouyang Xiu has noted that paper playing cards arose in connection to an earlier development in the book format from scrolls to pages.
+
+Playing cards first appeared in Europe in the last quarter of the 14th century. The earliest European references speak of a Saracen or Moorish game called naib, and in fact an almost complete Mamluk Egyptian deck of 52 cards in a distinct oriental design has survived from around the same time, with the four suits swords, polo sticks, cups and coins and the ranks king, governor, second governor, and ten to one.
+
+The 1430s in Italy saw the invention of the tarot deck, a full Latin-suited deck augmented by suitless cards with painted motifs that played a special role as trumps. Tarot card games are still played with (subsets of) these decks in parts of Central Europe. A full tarot deck contains 14 cards in each suit; low cards labeled 1–10, and court cards  (jack),  (cavalier/knight),  (queen), and  (king), plus the fool or excuse card, and 21 trump cards. In the 18th century the card images of the traditional Italian tarot decks became popular in cartomancy and evolved into "esoteric" decks used primarily for the purpose; today most tarot decks sold in North America are the occult type, and are closely associated with fortune telling. In Europe, "playing tarot" decks remain popular for games, and have evolved since the 18th century to use regional suits (spades, hearts, diamonds and clubs in France; leaves, hearts, bells and acorns in Germany) as well as other familiar aspects of the English-pattern pack such as corner card indices and "stamped" card symbols for non-court cards. Decks differ regionally based on the number of cards needed to play the games; the French tarot consists of the "full" 78 cards, while Germanic, Spanish and Italian Tarot variants remove certain values (usually low suited cards) from the deck, creating a deck with as few as 32 cards.
+
+The French suits were introduced around 1480 and, in France, mostly replaced the earlier Latin suits of swords, clubs, cups and coins. (which are still common in Spanish- and Portuguese-speaking countries as well as in some northern regions of Italy) The suit symbols, being very simple and single-color, could be stamped onto the playing cards to create a deck, thus only requiring special full-color card art for the court cards. This drastically simplifies the production of a deck of cards versus the traditional Italian deck, which used unique full-color art for each card in the deck. The French suits became popular in English playing cards in the 16th century (despite historic animosity between France and England), and from there were introduced to British colonies including North America. The rise of Western culture has led to the near-universal popularity and availability of French-suited playing cards even in areas with their own regional card art.
+
+In Japan, a distinct 48-card hanafuda deck is popular. It is derived from 16th-century Portuguese decks, after undergoing a long evolution driven by laws enacted by the Tokugawa shogunate attempting to ban the use of playing cards
+
+The best-known deck internationally is the English pattern of the 52-card French deck, also called the International or Anglo-American pattern, used for such games as poker and contract bridge. It contains one card for each unique combination of thirteen ranks and the four French suits spades, hearts, diamonds, and clubs. The ranks (from highest to lowest in bridge and poker) are ace, king, queen, jack (or knave), and the numbers from ten down to two (or deuce). The trump cards and knight cards from the French playing tarot are not included.
+
+Originally the term knave was more common than "jack"; the card had been called a jack as part of the terminology of All-Fours since the 17th century, but the word was considered vulgar. (Note the exclamation by Estella in Charles Dickens's novel Great Expectations: "He calls the knaves, Jacks, this boy!") However, because the card abbreviation for knave ("Kn") was so close to that of the king, it was very easy to confuse them, especially after suits and rankings were moved to the corners of the card in order to enable people to fan them in one hand and still see all the values. (The earliest known deck to place suits and rankings in the corner of the card is from 1693, but these cards did not become common until after 1864 when Hart reintroduced them along with the knave-to-jack change.) However, books of card games published in the third quarter of the 19th century evidently still referred to the "knave", and the term with this definition is still recognized in the United Kingdom.
+
+In the 17th century, a French, five-trick, gambling game called Bête became popular and spread to Germany, where it was called La Bete and England where it was named Beast. It was a derivative of Triomphe and was the first card game in history to introduce the concept of bidding.
+
+Chinese handmade mother-of-pearl gaming counters were used in scoring and bidding of card games in the West during the approximate period of 1700–1840. The gaming counters would bear an engraving such as a coat of arms or a monogram to identify a family or individual. Many of the gaming counters also depict Chinese scenes, flowers or animals. Queen Charlotte is one prominent British individual who is known to have played with the Chinese gaming counters. Card games such as Ombre, Quadrille and Pope Joan were popular at the time and required counters for scoring. The production of counters declined after Whist, with its different scoring method, became the most popular card game in the West.
+
+Based on the association of card games and gambling, Pope Benedict XIV banned card games on October 17, 1750.
+
+See also
+
+ Game of chance
+ Game of skill
+ R. F. Foster (games)
+ Henry Jones (writer) who wrote under the pseudonym "Cavendish"
+ John Scarne
+ Dice game
+ List of card games by number of cards
+
+References
+
+External links
+
+ International Playing Card Society
+ Rules for historic card games
+ Collection of rules to many card games
+
+ 
+Tabletop games
+Cross-stitch is a form of sewing and a popular form of counted-thread embroidery in which X-shaped stitches in a tiled, raster-like pattern are used to form a picture. The stitcher counts the threads on a piece of evenweave fabric (such as linen) in each direction so that the stitches are of uniform size and appearance. This form of cross-stitch is also called counted cross-stitch in order to distinguish it from other forms of cross-stitch. Sometimes cross-stitch is done on designs printed on the fabric (stamped cross-stitch); the stitcher simply stitches over the printed pattern. Cross-stitch is often executed on easily countable fabric called aida cloth whose weave creates a plainly visible grid of squares with holes for the needle at each corner.
+
+Fabrics used in cross-stitch include linen, aida cloth, and mixed-content fabrics called 'evenweave' such as jobelan. All cross-stitch fabrics are technically "evenweave" as the term refers to the fact that the fabric is woven to make sure that there are the same number of threads per inch in both the warp and the weft (i.e. vertically and horizontally). Fabrics are categorized by threads per inch (referred to as 'count'), which can range from 11 to 40 count.
+
+Counted cross-stitch projects are worked from a gridded pattern called a chart and can be used on any count fabric; the count of the fabric and the number of threads per stitch determine the size of the finished stitching. For example, if a given design is stitched on a 28 count cross-stitch fabric with each cross worked over two threads, the finished stitching size is the same as it would be on a 14 count aida cloth fabric with each cross worked over one square. These methods are referred to as "2 over 2" (2 embroidery threads used to stitch over 2 fabric threads) and "1 over 1" (1 embroidery thread used to stitch over 1 fabric thread or square), respectively. There are different methods of stitching a pattern, including the cross-country method where one colour is stitched at a time, or the parking method where one block of fabric is stitched at a time and the end of the thread is "parked" at the next point the same colour occurs in the pattern.
+
+History
+
+Cross-stitch can be found all over the world since the middle ages. Many folk museums show examples of clothing decorated with cross-stitch, especially from continental Europe and Asia.
+
+The cross-stitch sampler is called that because it was generally stitched by a young girl to learn how to stitch and to record alphabet and other patterns to be used in her household sewing. These samples of her stitching could be referred back to over the years. Often, motifs and initials were stitched on household items to identify their owner, or simply to decorate the otherwise-plain cloth. The earliest known cross stitch sampler made in the United States is currently housed at Pilgrim Hall in Plymouth, Massachusetts. The sampler was created by Loara Standish, daughter of Captain Myles Standish and pioneer of the Leviathan stitch, circa 1653.
+
+Traditionally, cross-stitch was used to embellish items like household linens, tablecloths, dishcloths, and doilies (only a small portion of which would actually be embroidered, such as a border). Although there are many cross-stitchers who still employ it in this fashion, it is now increasingly popular to work the pattern on pieces of fabric and hang them on the wall for decoration. Cross-stitch is also often used to make greeting cards, pillow tops, or as inserts for box tops, coasters and trivets.
+
+Multicoloured, shaded, painting-like patterns as we know them today are a fairly modern development, deriving from similar shaded patterns of Berlin wool work of the mid-nineteenth century. Besides designs created expressly for cross-stitch, there are software programs that convert a photograph or a fine art image into a chart suitable for stitching. One example of this is in the cross-stitched reproduction of the Sistine Chapel charted and stitched by Joanna Lopianowski-Roberts.
+
+There are many cross-stitching "guilds" and groups across the United States and Europe which offer classes, collaborate on large projects, stitch for charity, and provide other ways for local cross-stitchers to get to know one another. Individually owned local needlework shops (LNS) often have stitching nights at their shops, or host weekend stitching retreats.
+
+Today, cotton floss is the most common embroidery thread. It is a thread made of mercerized cotton, composed of six strands that are only loosely twisted together and easily separable. While there are other manufacturers, the two most-commonly used (and oldest) brands are DMC and Anchor, both of which have been manufacturing embroidery floss since the 1800s.
+
+Other materials used are pearl (or perle) cotton, Danish flower thread, silk and Rayon. Different wool threads, metallic threads or other novelty threads are also used, sometimes for the whole work, but often for accents and embellishments. Hand-dyed cross-stitch floss is created just as the name implies—it is dyed by hand. Because of this, there are variations in the amount of color throughout the thread. Some variations can be subtle, while some can be a huge contrast. Some also have more than one color per thread.
+
+Cross-stitch is widely used in traditional Palestinian dressmaking.
+
+Related stitches and forms of embroidery
+
+The cross-stitch can be executed partially such as in quarter-, half-, and three-quarter-stitches. A single straight stitch, done in the form of backstitching, is often used as an outline, to add detail or definition.
+
+There are many stitches which are related structurally to cross-stitch. The best known are Italian cross-stitch (as seen in Assisi embroidery), long-armed cross-stitch, and Montenegrin stitch. Italian cross-stitch and Montenegrin stitch are reversible, meaning the work looks the same on both sides. These styles have a slightly different look than ordinary cross-stitch. These more difficult stitches are rarely used in mainstream embroidery, but they are still used to recreate historical pieces of embroidery or by the creative and adventurous stitcher. The double cross-stitch, also known as a Leviathan stitch or Smyrna cross-stitch, combines a cross-stitch with an upright cross-stitch.
+
+Berlin wool work and similar petit point stitchery resembles the heavily shaded, opulent styles of cross-stitch, and sometimes also used charted patterns on paper.
+
+Cross-stitch is often combined with other popular forms of embroidery, such as Hardanger embroidery or blackwork embroidery. Cross-stitch may also be combined with other work, such as canvaswork or drawn thread work. Beadwork and other embellishments such as paillettes, charms, small buttons and specialty threads of various kinds may also be used. Cross stitch can often used in needlepoint.
+
+Recent trends for cross stitch
+
+Cross-stitch has become increasingly popular with the younger generation of Europe in recent years. Retailers such as John Lewis experienced a 17% rise in sales of haberdashery products between 2009 and 2010. Hobbycraft, a chain of stores selling craft supplies, also enjoyed an 11% increase in sales over the year to February 22, 2009.
+
+Knitting and cross-stitching have become more popular hobbies for a younger market, in contrast to its traditional reputation as a hobby for retirees. Sewing and craft groups such as Stitch and Bitch London have resurrected the idea of the traditional craft club. At Clothes Show Live 2010 there was a new area called "Sknitch" promoting modern sewing, knitting and embroidery.
+
+In a departure from the traditional designs associated with cross-stitch, there is a current trend for more postmodern or tongue-in-cheek designs featuring retro images or contemporary sayings. It is linked to a concept known as 'subversive cross-stitch', which involves more risque designs, often fusing the traditional sampler style with sayings designed to shock or be incongruous with the old-fashioned image of cross-stitch.
+
+Stitching designs on other materials can be accomplished by using waste canvas. This is a temporary gridded canvas similar to regular canvas used for embroidery that is held together by a water-soluble glue, which is removed after completion of stitch design. Other crafters have taken to cross-stitching on all manner of gridded objects as well including old kitchen strainers or chain-link fences.
+
+Traditionally, it is believed that cross stitch is a woman's craft. But lately there are men who are also addicted to this.
+
+Cross-stitch and feminism 
+In the 21st century, an emphasis on feminist design has emerged within cross-stitch communities. Some cross-stitchers have commented on the way that the practice of embroidery makes them feel connected to the women who practised it before them. There is a push for all embroidery, including cross-stitch, to be respected as a significant art form.
+
+Cross-stitch and computers
+The development of computer technology has also affected such a seemingly conservative craft as cross-stitch. With the help of computer visualization algorithms, it is now possible to create embroidery designs using a photograph or any other picture. Visualisation uses a drawing on a graphical grid, representing colors and / or symbols, which gives the user an indication of the possible use of colors, the position of those colors, and the type of stitch used, such as full cross or quarter stitch.
+
+Flosstube 
+An increasingly popular activity for cross-stitchers is to watch and make YouTube videos detailing their hobby. Flosstubers, as they are known, typically cover WIPs (Works in Progress), FOs (Finished Objects), and Haul (new patterns, thread, and fabric, as well as cross-stitching accessories, such as needle minders). Other accessories include but are not limited to: Floss organizers, thread conditioner, pin cushions, aida cloth or plastic canvas, and embroidery needles.
+
+See also 
+
+ Mosaic
+ Pixel art
+ Embroidery
+
+Notes
+
+References
+ Caulfield, S. F. A., and B. C. Saward, The Dictionary of Needlework, 1885.
+ Enthoven, Jacqueline: The Creative Stitches of Embroidery, Van Norstrand Rheinhold, 1964, .
+ Gillow, John, and Bryan Sentance: World Textiles, Bulfinch Press/Little, Brown, 1999, .
+ Reader's Digest, Complete Guide to Needlework. The Reader's Digest Association, Inc. (March 1992) .
+
+External links
+
+ Articles related to the recent comeback in popularity of cross stitch. "Is Cross Stitch Dead?"
+
+Embroidery stitches
+Sewing stitches
+
+fr:Broderie#Le point de croix
+Games available in most casinos are commonly called casino games. In a casino game, the players gamble cash or casino chips on various possible random outcomes or combinations of outcomes. Casino games are also available in online casinos, where permitted by law. Casino games can also be played outside of casinos for entertainment purposes, like in parties or in school competitions, on machines that simulate gambling.
+
+Categories
+
+There are three general categories of casino games: gaming machines, table games, and random number games. Gaming machines, such as slot machines and pachinko, are usually played by one player at a time and do not require the involvement of casino employees. Tables games, such as blackjack or craps, involve one or more players who are competing against the house (the casino itself) rather than each other. Table games are usually conducted by casino employees known as croupiers or dealers. Random number games are based on the selection of random numbers, either from a computerized random number generator or from other gaming equipment. Random number games may be played at a table or through the purchase of paper tickets or cards, such as keno or bingo.
+
+Some casino games combine multiple of the above aspects; for example, roulette is a table game conducted by a dealer, that involves random numbers. Casinos may also offer other types of gaming, such as hosting poker games or tournaments where players compete against each other.
+
+Common casino games
+Games commonly found at casinos include table games, gaming machines and random number games.
+
+Table games
+In the United States, 'table game' is the term used for games of chance such as blackjack, craps, roulette, and baccarat that are played against the casino and operated by one or more live croupiers, as opposed to those played on a mechanical device like a slot machine or against other players instead of the casino, such as standard poker.
+
+Table games are popularly played in casinos and involve some form of legal gambling, but they are also played privately under varying house rules. The term has significance in that some jurisdictions permit casinos to have only slots and no table games.  In some states, this law has resulted in casinos employing electronic table games, such as roulette, blackjack, and craps.
+
+Table games found in casinos include:
+ Baccarat
+ Blackjack
+ Craps
+ Roulette
+ Poker (Texas hold'em, Five-card draw, Omaha hold'em)
+ Big Six wheel
+ Pool
+
+Gaming machines
+Gaming machines found in casinos include:
+ Pachinko
+ Slot machine
+ Video lottery terminal
+ Video poker
+
+Random numbers games
+Random numbers games found in casinos include:
+ Bingo
+ Keno
+
+House advantage
+
+Casino games typically provide a predictable long-term advantage to the casino, or "house", while offering the players the possibility of a short-term gain that in some cases can be large. Some casino games have a skill element, where the players' decisions have an impact on the results. Players possessing sufficient skills to eliminate the inherent long-term disadvantage (the house edge or vigorish) in a casino game are referred to as advantage players.
+
+The players' disadvantage is a result of the casino not paying winning wagers according to the game's "true odds", which are the payouts that would be expected considering the odds of a wager either winning or losing. For example, if a game is played by wagering on the number that would result from the roll of one die, the true odds would be 6 times the amount wagered since there is a 1 in 6 chance of any single number appearing, assuming that the player gets the original amount wagered back. However, the casino may only pay 4 times the amount wagered for a winning wager.
+
+The house edge, or vigorish, is defined as the casino profit expressed as a percentage of the player's original bet. (In games such as blackjack or Spanish 21, the final bet may be several times the original bet, if the player doubles and splits.)
+
+In American roulette, there are two "zeroes" (0, 00) and 36 non-zero numbers (18 red and 18 black). This leads to a higher house edge compared to European roulette. The chances of a player, who bets 1 unit on red, winning are 18/38 and his chances of losing 1 unit are 20/38. The player's expected value is EV = (18/38 × 1) + (20/38 × (−1)) = 18/38 − 20/38 = −2/38 = −5.26%. Therefore, the house edge is 5.26%. After 10 spins, betting 1 unit per spin, the average house profit will be 10 × 1 × 5.26% = 0.53 units. European roulette wheels have only one "zero" and therefore the house advantage (ignoring the en prison rule) is equal to 1/37 = 2.7%.
+
+The house edge of casino games varies greatly with the game, with some games having an edge as low as 0.3%. Keno can have house edges of up to 25%, slot machines having up to 15%.
+
+The calculation of the roulette house edge is a trivial exercise; for other games, this is not usually the case. Combinatorial analysis and/or computer simulation is necessary to complete the task.
+
+In games that have a skill element, such as blackjack or Spanish 21, the house edge is defined as the house advantage from optimal play (without the use of advanced techniques such as card counting), on the first hand of the shoe (the container that holds the cards). The set of optimal plays for all possible hands is known as "basic strategy" and is highly dependent on the specific rules and even the number of decks used.
+
+Traditionally, the majority of casinos have refused to reveal the house edge information for their slots games, and due to the unknown number of symbols and weightings of the reels, in most cases, it is much more difficult to calculate the house edge than in other casino games. However, due to some online properties revealing this information and some independent research conducted by Michael Shackleford in the offline sector, this pattern is slowly changing.
+
+In games where players are not competing against the house, such as poker, the casino usually earns money via a commission, known as a "rake".
+
+Standard deviation
+
+The luck factor in a casino game is quantified using standard deviations (SD). The standard deviation of a simple game like roulette can be calculated using the binomial distribution. In the binomial distribution, SD = , where n = number of rounds played, p = probability of winning, and q = probability of losing. The binomial distribution assumes a result of 1 unit for a win, and 0 units for a loss, rather than −1 units for a loss, which doubles the range of possible outcomes. Furthermore, if we flat bet at 10 units per round instead of 1 unit, the range of possible outcomes increases 10 fold.
+
+ SD (roulette, even-money bet) = 2b , where b = flat bet per round, n = number of rounds, p = 18/38, and q = 20/38.
+
+For example, after 10 rounds at 1 unit per round, the standard deviation will be 2 × 1 ×  = 3.16 units. After 10 rounds, the expected loss will be 10 × 1 × 5.26% = 0.53. As you can see, standard deviation is many times the magnitude of the expected loss.
+
+The standard deviation for pai gow poker is the lowest out of all common casino games. Many casino games, particularly slot machines, have extremely high standard deviations. The bigger size of the potential payouts, the more the standard deviation may increase.
+
+As the number of rounds increases, eventually, the expected loss will exceed the standard deviation, many times over. From the formula, we can see that the standard deviation is proportional to the square root of the number of rounds played, while the expected loss is proportional to the number of rounds played. As the number of rounds increases, the expected loss increases at a much faster rate. This is why it is impossible for a gambler to win in the long term. It is the high ratio of short-term standard deviation to expected loss that fools gamblers into thinking that they can win.
+
+It is important for a casino to know both the house edge and variance for all of their games. The house edge tells them what kind of profit they will make as a percentage of turnover, and the variance tells them how much they need in the way of cash reserves. The mathematicians and computer programmers that do this kind of work are called gaming mathematicians and gaming analysts. Casinos do not have in-house expertise in this field, so they outsource their requirements to experts in the gaming analysis field.
+
+See also
+ Gambler's fallacy
+
+References
+
+Game
+A video game or computer game is an electronic game that involves interaction with a user interface or input device (such as a joystick, controller, keyboard, or motion sensing device) to generate visual feedback from a display device, most commonly shown in a video format on a television set, computer monitor, flat-panel display or touchscreen on handheld devices, or a virtual reality headset. Most modern video games are audiovisual, with audio complement delivered through speakers or headphones, and sometimes also with other types of sensory feedback (e.g., haptic technology that provides tactile sensations), and some video games also allow microphone and webcam inputs for in-game chatting and livestreaming.
+
+Video games are typically categorized according to their hardware platform, which traditionally includes arcade video games, console games, and computer (PC) games; the latter also encompasses LAN games, online games, and browser games. More recently, the video game industry has expanded onto mobile gaming through mobile devices (such as smartphones and tablet computers), virtual and augmented reality systems, and remote cloud gaming. Video games are also classified into a wide range of genres based on their style of gameplay and target audience.
+
+The first video game prototypes in the 1950s and 1960s were simple extensions of electronic games using video-like output from large, room-sized mainframe computers. The first consumer video game was the arcade video game Computer Space in 1971. In 1972 came the iconic hit game Pong and the first home console, the Magnavox Odyssey. The industry grew quickly during the "golden age" of arcade video games from the late 1970s to early 1980s but suffered from the crash of the North American video game market in 1983 due to loss of publishing control and saturation of the market. Following the crash, the industry matured, was dominated by Japanese companies such as Nintendo, Sega, and Sony, and established practices and methods around the development and distribution of video games to prevent a similar crash in the future, many of which continue to be followed. In the 2000s, the core industry centered on "AAA" games, leaving little room for riskier experimental games. Coupled with the availability of the Internet and digital distribution, this gave room for independent video game development (or "indie games") to gain prominence into the 2010s. Since then, the commercial importance of the video game industry has been increasing. The emerging Asian markets and proliferation of smartphone games in particular are altering player demographics towards casual gaming and increasing monetization by incorporating games as a service.
+
+Today, video game development requires numerous interdisciplinary skills, vision, teamwork, and liaisons between different parties, including developers, publishers, distributors, retailers, hardware manufacturers, and other marketers, to successfully bring a game to its consumers. , the global video game market had estimated annual revenues of  across hardware, software, and services, which is three times the size of the global music industry and four times that of the film industry in 2019, making it a formidable heavyweight across the modern entertainment industry. The video game market is also a major influence behind the electronics industry, where personal computer component, console, and peripheral sales, as well as consumer demands for better game performance, have been powerful driving factors for hardware design and innovation.
+
+Origins
+
+Early video games use interactive electronic devices with various display formats. The earliest example is from 1947—a "cathode-ray tube amusement device" was filed for a patent on 25 January 1947, by Thomas T. Goldsmith Jr. and Estle Ray Mann, and issued on 14 December 1948, as U.S. Patent 2455992. Inspired by radar display technology, it consists of an analog device allowing a user to control the parabolic arc of a dot on the screen to simulate a missile being fired at targets, which are paper drawings fixed to the screen. Other early examples include Christopher Strachey's draughts game, the Nimrod computer at the 1951 Festival of Britain; OXO, a tic-tac-toe computer game by Alexander S. Douglas for the EDSAC in 1952; Tennis for Two, an electronic interactive game engineered by William Higinbotham in 1958; and Spacewar!, written by Massachusetts Institute of Technology students Martin Graetz, Steve Russell, and Wayne Wiitanen's on a DEC PDP-1 computer in 1961. Each game has different means of display: NIMROD has a panel of lights to play the game of Nim, OXO has a graphical display to play tic-tac-toe, Tennis for Two has an oscilloscope to display a side view of a tennis court, and Spacewar! has the DEC PDP-1's vector display to have two spaceships battle each other.
+
+These preliminary inventions paved the way for the origins of video games today. Ralph H. Baer, while working at Sanders Associates in 1966, devised a control system to play a rudimentary game of table tennis on a television screen. With the company's approval, Baer built the prototype "Brown Box". Sanders patented Baer's inventions and licensed them to Magnavox, which commercialized it as the first home video game console, the Magnavox Odyssey, released in 1972. Separately, Nolan Bushnell and Ted Dabney, inspired by seeing Spacewar! running at Stanford University, devised a similar version running in a smaller coin-operated arcade cabinet using a less expensive computer. This was released as Computer Space, the first arcade video game, in 1971. Bushnell and Dabney went on to form Atari, Inc., and with Allan Alcorn, created their second arcade game in 1972, the hit ping pong-style Pong, which was directly inspired by the table tennis game on the Odyssey. Sanders and Magnavox sued Atari for infringement of Baer's patents, but Atari settled out of court, paying for perpetual rights to the patents. Following their agreement, Atari made a home version of Pong, which was released by Christmas 1975. The success of the Odyssey and Pong, both as an arcade game and home machine, launched the video game industry. Both Baer and Bushnell have been titled "Father of Video Games" for their contributions.
+
+Terminology
+The term "video game" was developed to distinguish this class of electronic games that were played on some type of video display rather than on a teletype printer, audio speaker or similar device. This also distinguished from many handheld electronic games like Merlin which commonly used LED lights for indicators but did not use these in combination for imaging purposes.
+
+"Computer game" may also be used as a descriptor, as all these types of games essentially require the use of a computer processor, and in some cases, it is used interchangeably with "video game". Particularly in the United Kingdom and Western Europe, this is common due to the historic relevance of domestically produced microcomputers. Other terms used include digital game, for example by the Australian Bureau of Statistics. However, the term "computer game" can also be used to more specifically refer to games played primarily on personal computers or other type of flexible hardware systems (also known as a PC game), as a way distinguish them from console games, arcade games or mobile games. Other terms such as "television game" or "telegame" had been used in the 1970s and early 1980s, particularly for the home gaming consoles that rely on connection to a television set. In Japan, where consoles like the Odyssey were first imported and then made within the country by the large television manufacturers such as Toshiba and Sharp Corporation, such games are known as "TV games", or TV geemu or terebi geemu. "Electronic game" may also be used to refer to video games, but this also incorporates devices like early handheld electronic games that lack any video output. and the term "TV game" is still commonly used into the 21st century.
+
+The first appearance of the term "video game" emerged around 1973. The Oxford English Dictionary cited a 10 November 1973 BusinessWeek article as the first printed use of the term. Though Bushnell believed the term came from a vending magazine review of Computer Space in 1971, a review of the major vending magazines Vending Times and Cashbox showed that the term came much earlier, appearing first around March 1973 in these magazines in mass usage including by the arcade game manufacturers. As analyzed by video game historian Keith Smith, the sudden appearance suggested that the term had been proposed and readily adopted by those involved. This appeared to trace to Ed Adlum, who ran Cashboxs coin-operated section until 1972 and then later founded RePlay Magazine, covering the coin-op amusement field, in 1975. In a September 1982 issue of RePlay, Adlum is credited with first naming these games as "video games": "RePlay's Eddie Adlum worked at 'Cash Box' when 'TV games' first came out. The personalities in those days were Bushnell, his sales manager Pat Karns and a handful of other 'TV game' manufacturers like Henry Leyser and the McEwan brothers. It seemed awkward to call their products 'TV games', so borrowing a word from Billboards description of movie jukeboxes, Adlum started to refer to this new breed of amusement machine as 'video games.' The phrase stuck." Adlum explained in 1985 that up until the early 1970s, amusement arcades typically had non-video arcade games such as pinball machines and electro-mechanical games. With the arrival of video games in arcades during the early 1970s, there was initially some confusion in the arcade industry over what term should be used to describe the new games. He "wrestled with descriptions of this type of game," alternating between "TV game" and "television game" but "finally woke up one day" and said, "what the hell... video game!"
+
+For many years, the traveling Videotopia exhibit served as the closest representation of such a vital resource. In addition to collecting home video game consoles, the Electronics Conservancy organization set out to locate and restore 400 antique arcade cabinets after realizing that the majority of these games had been destroyed and feared the loss of their historical significance. Video games have significantly began to be seen in the real-world as a purpose to present history in a way of understanding the methodology and terms that are being compared. Researchers have looked at how historical representations affect how the public perceives the past, and digital humanists encourage historians to use video games as primary materials. Video games, considering their past and age, have over time progressed as what a video game really means. Whether played through a monitor, TV, or a hand-held device, there are many ways that video games are being displayed for users to enjoy. People have drawn comparisons between flow-state-engaged video gamers and pupils in conventional school settings. In traditional, teacher-led classrooms, students have little say in what they learn, are passive consumers of the information selected by teachers, are required to follow the pace and skill level of the group (group teaching), and receive brief, imprecise, normative feedback on their work. Video games, as they continue to develop into better graphic definition and genre's, create new terminology when something unknown tends to become known. Yearly, consoles are being created to compete against other brands with similar functioning features that tends to lead the consumer into which they'd like to purchase. Now, companies have moved towards games only the specific console can play to grasp the consumer into purchasing their product compared to when video games first began, there was little to no variety. In 1989, a console war begun with Nintendo, one of the biggest in gaming was up against target, Sega with their brand new Master System which, failed to compete, allowing the Nintendo Emulator System to be one of the most consumed product in the world. More technology continued to be created, as the computer began to be used in people's houses for more than just office and daily use. Games began being implemented into computers and have progressively grown since then with coded robots to play against you. Early games like tic-tac-toe, solitaire, and Tennis for Two were great ways to bring new gaming to another system rather than one specifically meant for gaming.
+
+Definition
+While many games readily fall into a clear, well-understood definition of video games, new genres and innovations in game development have raised the question of what are the essential factors of a video game that separate the medium from other forms of entertainment.
+
+The introduction of interactive films in the 1980s with games like Dragon's Lair, featured games with full motion video played off a form of media but only limited user interaction. This had required a means to distinguish these games from more traditional board games that happen to also use external media, such as the Clue VCR Mystery Game which required players to watch VCR clips between turns. To distinguish between these two, video games are considered to require some interactivity that affects the visual display.
+
+Most video games tend to feature some type of victory or winning conditions, such as a scoring mechanism or a final boss fight. The introduction of walking simulators (adventure games that allow for exploration but lack any objectives) like Gone Home, and empathy games (video games that tend to focus on emotion) like That Dragon, Cancer brought the idea of games that did not have any such type of winning condition and raising the question of whether these were actually games. These are still commonly justified as video games as they provide a game world that the player can interact with by some means.
+
+The lack of any industry definition for a video game by 2021 was an issue during the case Epic Games v. Apple which dealt with video games offered on Apple's iOS App Store. Among concerns raised were games like Fortnite Creative and Roblox which created metaverses of interactive experiences, and whether the larger game and the individual experiences themselves were games or not in relation to fees that Apple charged for the App Store. Judge Yvonne Gonzalez Rogers, recognizing that there was yet an industry standard definition for a video game, established for her ruling that "At a bare minimum, videogames appear to require some level of interactivity or involvement between the player and the medium" compared to passive entertainment like film, music, and television, and "videogames are also generally graphically rendered or animated, as opposed to being recorded live or via motion capture as in films or television". Rogers still concluded that what is a video game "appears highly eclectic and diverse".
+
+Video game terminology
+
+ 
+The gameplay experience varies radically between video games, but many common elements exist. Most games will launch into a title screen and give the player a chance to review options such as the number of players before starting a game. Most games are divided into levels which the player must work the avatar through, scoring points, collecting power-ups to boost the avatar's innate attributes, all while either using special attacks to defeat enemies or moves to avoid them. This information is relayed to the player through a type of on-screen user interface such as a heads-up display atop the rendering of the game itself. Taking damage will deplete their avatar's health, and if that falls to zero or if the avatar otherwise falls into an impossible-to-escape location, the player will lose one of their lives. Should they lose all their lives without gaining an extra life or "1-UP", then the player will reach the "game over" screen. Many levels as well as the game's finale end with a type of boss character the player must defeat to continue on. In some games, intermediate points between levels will offer save points where the player can create a saved game on storage media to restart the game should they lose all their lives or need to stop the game and restart at a later time. These also may be in the form of a passage that can be written down and reentered at the title screen.
+
+Product flaws include software bugs which can manifest as glitches which may be exploited by the player; this is often the foundation of speedrunning a video game. These bugs, along with cheat codes, Easter eggs, and other hidden secrets that were intentionally added to the game can also be exploited. On some consoles, cheat cartridges allow players to execute these cheat codes, and user-developed trainers allow similar bypassing for computer software games. Both of which might make the game easier, give the player additional power-ups, or change the appearance of the game.
+
+Components
+
+To distinguish from electronic games, a video game is generally considered to require a platform, the hardware which contains computing elements, to process player interaction from some type of input device and displays the results to a video output display.
+
+Platform
+
+Video games require a platform, a specific combination of electronic components or computer hardware and associated software, to operate. The term system is also commonly used. Games are typically designed to be played on one or a limited number of platforms, and exclusivity to a platform is used as a competitive edge in the video game market. However, games may be developed for alternative platforms than intended, which are described as ports or conversions. These also may be remasters - where most of the original game's source code is reused and art assets, models, and game levels are updated for modern systems – and remakes, where in addition to asset improvements, significant reworking of the original game and possibly from scratch is performed.
+
+The list below is not exhaustive and excludes other electronic devices capable of playing video games such as PDAs and graphing calculators.
+
+PC games
+PC games involve a player interacting with a personal computer (PC) connected to a video monitor. Personal computers are not dedicated game platforms, so there may be differences running the same game on different hardware. Also, the openness allows some features to developers like reduced software cost, increased flexibility, increased innovation, emulation, creation of modifications or mods, open hosting for online gaming (in which a person plays a video game with people who are in a different household) and others. A gaming computer is a PC or laptop intended specifically for gaming, typically using high-performance, high-cost components. In additional to personal computer gaming, there also exist games that work on mainframe computers and other similarly shared systems, with users logging in remotely to use the computer.
+Home console
+A console game is played on a home console, a specialized electronic device that connects to a common television set or composite video monitor. Home consoles are specifically designed to play games using a dedicated hardware environment, giving developers a concrete hardware target for development and assurances of what features will be available, simplifying development compared to PC game development. Usually consoles only run games developed for it, or games from other platform made by the same company, but never games developed by its direct competitor, even if the same game is available on different platforms. It often comes with a specific game controller. Major console platforms include Xbox, PlayStation and Nintendo.
+Handheld console
+A handheld game console is a small, self-contained electronic device that is portable and can be held in a user's hands. It features the console, a small screen, speakers and buttons, joystick or other game controllers in a single unit. Like consoles, handhelds are dedicated platforms, and share almost the same characteristics. Handheld hardware usually is less powerful than PC or console hardware. Some handheld games from the late 1970s and early 1980s could only play one game. In the 1990s and 2000s, a number of handheld games used cartridges, which enabled them to be used to play many different games. The handheld console has waned in the 2010s as mobile device gaming has become a more dominant factor.
+Arcade video game
+ An arcade video game generally refers to a game played on an even more specialized type of electronic device that is typically designed to play only one game and is encased in a special, large coin-operated cabinet which has one built-in console, controllers (joystick, buttons, etc.), a CRT screen, and audio amplifier and speakers. Arcade games often have brightly painted logos and images relating to the theme of the game. While most arcade games are housed in a vertical cabinet, which the user typically stands in front of to play, some arcade games use a tabletop approach, in which the display screen is housed in a table-style cabinet with a see-through table top. With table-top games, the users typically sit to play. In the 1990s and 2000s, some arcade games offered players a choice of multiple games. In the 1980s, video arcades were businesses in which game players could use a number of arcade video games. In the 2010s, there are far fewer video arcades, but some movie theaters and family entertainment centers still have them.
+Browser game
+A browser game takes advantages of standardizations of technologies for the functionality of web browsers across multiple devices providing a cross-platform environment. These games may be identified based on the website that they appear, such as with Miniclip games. Others are named based on the programming platform used to develop them, such as Java and Flash games.
+Mobile game
+With the introduction of smartphones and tablet computers standardized on the iOS and Android operating systems, mobile gaming has become a significant platform. These games may use unique features of mobile devices that are not necessary present on other platforms, such as accelerometers, global positing information and camera devices to support augmented reality gameplay.
+Cloud gaming
+Cloud gaming requires a minimal hardware device, such as a basic computer, console, laptop, mobile phone or even a dedicated hardware device connected to a display with good Internet connectivity that connects to hardware systems by the cloud gaming provider. The game is computed and rendered on the remote hardware, using a number of predictive methods to reduce the network latency between player input and output on their display device. For example, the Xbox Cloud Gaming and PlayStation Now platforms use dedicated custom server blade hardware in cloud computing centers.
+Virtual reality
+ Virtual reality (VR) games generally require players to use a special head-mounted unit that provides stereoscopic screens and motion tracking to immerse a player within virtual environment that responds to their head movements. Some VR systems include control units for the player's hands as to provide a direct way to interact with the virtual world. VR systems generally require a separate computer, console, or other processing device that couples with the head-mounted unit.
+Emulation
+An emulator enables games from a console or otherwise different system to be run in a type of virtual machine on a modern system, simulating the hardware of the original and allows old games to be played. While emulators themselves have been found to be legal in United States case law, the act of obtaining the game software that one does not already own may violate copyrights. However, there are some official releases of emulated software from game manufacturers, such as Nintendo with its Virtual Console or Nintendo Switch Online offerings.
+Backward compatibility
+Backward compatibility is similar in nature to emulation in that older games can be played on newer platforms, but typically directly though hardware and build-in software within the platform. For example, the PlayStation 2 is capable of playing original PlayStation games simply by inserting the original game media into the newer console, while Nintendo's Wii could play GameCube titles as well in the same manner.
+
+Game media
+
+Early arcade games, home consoles, and handheld games were dedicated hardware units with the game's logic built into the electronic componentry of the hardware. Since then, most video game platforms are considered programmable, having means to read and play multiple games distributed on different types of media or formats. Physical formats include ROM cartridges, magnetic storage including magnetic-tape data storage and floppy discs, optical media formats including CD-ROM and DVDs, and flash memory cards. Furthermore digital distribution over the Internet or other communication methods as well as cloud gaming alleviate the need for any physical media. In some cases, the media serves as the direct read-only memory for the game, or it may be the form of installation media that is used to write the main assets to the player's platform's local storage for faster loading periods and later updates.
+
+Games can be extended with new content and software patches through either expansion packs which are typically available as physical media, or as downloadable content nominally available via digital distribution. These can be offered freely or can be used to monetize a game following its initial release. Several games offer players the ability to create user-generated content to share with others to play. Other games, mostly those on personal computers, can be extended with user-created modifications or mods that alter or add onto the game; these often are unofficial and were developed by players from reverse engineering of the game, but other games provide official support for modding the game.
+
+Input device
+
+Video game can use several types of input devices to translate human actions to a game. Most common are the use of game controllers like gamepads and joysticks for most consoles, and as accessories for personal computer systems along keyboard and mouse controls. Common controls on the most recent controllers include face buttons, shoulder triggers, analog sticks, and directional pads ("d-pads"). Consoles typically include standard controllers which are shipped or bundled with the console itself, while peripheral controllers are available as a separate purchase from the console manufacturer or third-party vendors. Similar control sets are built into handheld consoles and onto arcade cabinets. Newer technology improvements have incorporated additional technology into the controller or the game platform, such as touchscreens and motion detection sensors that give more options for how the player interacts with the game. Specialized controllers may be used for certain genres of games, including racing wheels, light guns and dance pads. Digital cameras and motion detection can capture movements of the player as input into the game, which can, in some cases, effectively eliminate the control, and on other systems such as virtual reality, are used to enhance immersion into the game.
+
+Display and output
+
+By definition, all video games are intended to output graphics to an external video display, such as cathode-ray tube televisions, newer liquid-crystal display (LCD) televisions and built-in screens, projectors or computer monitors, depending on the type of platform the game is played on. Features such as color depth, refresh rate, frame rate, and screen resolution are a combination of the limitations of the game platform and display device and the program efficiency of the game itself. The game's output can range from fixed displays using LED or LCD elements, text-based games, two-dimensional and three-dimensional graphics, and augmented reality displays.
+
+The game's graphics are often accompanied by sound produced by internal speakers on the game platform or external speakers attached to the platform, as directed by the game's programming. This often will include sound effects tied to the player's actions to provide audio feedback, as well as background music for the game.
+
+Some platforms support additional feedback mechanics to the player that a game can take advantage of. This is most commonly haptic technology built into the game controller, such as causing the controller to shake in the player's hands to simulate a shaking earthquake occurring in game.
+
+Classifications
+Video games are frequently classified by a number of factors related to how one plays them.
+
+Genre
+
+A video game, like most other forms of media, may be categorized into genres. However, unlike film or television which use visual or narrative elements, video games are generally categorized into genres based on their gameplay interaction, since this is the primary means which one interacts with a video game. The narrative setting does not impact gameplay; a shooter game is still a shooter game, regardless of whether it takes place in a fantasy world or in outer space. An exception is the horror game genre, used for games that are based on narrative elements of horror fiction, the supernatural, and psychological horror.
+
+Genre names are normally self-describing in terms of the type of gameplay, such as action game, role playing game, or shoot 'em up, though some genres have derivations from influential works that have defined that genre, such as roguelikes from Rogue, Grand Theft Auto clones from Grand Theft Auto III, and battle royale games from the film Battle Royale. The names may shift over time as players, developers and the media come up with new terms; for example, first-person shooters were originally called "Doom clones" based on the 1993 game. A hierarchy of game genres exist, with top-level genres like "shooter game" and "action game" that broadly capture the game's main gameplay style, and several subgenres of specific implementation, such as within the shooter game first-person shooter and third-person shooter. Some cross-genre types also exist that fall until multiple top-level genres such as action-adventure game.
+
+Mode
+
+A video game's mode describes how many players can use the game at the same type. This is primarily distinguished by single-player video games and multiplayer video games. Within the latter category, multiplayer games can be played in a variety of ways, including locally at the same device, on separate devices connected through a local network such as LAN parties, or online via separate Internet connections. Most multiplayer games are based on competitive gameplay, but many offer cooperative and team-based options as well as asymmetric gameplay. Online games use server structures that can also enable massively multiplayer online games (MMOs) to support hundreds of players at the same time.
+
+A small number of video games are zero-player games, in which the player has very limited interaction with the game itself. These are most commonly simulation games where the player may establish a starting state and then let the game proceed on its own, watching the results as a passive observer, such as with many computerized simulations of Conway's Game of Life.
+
+Types
+Most video games are intended for entertainment purposes. Different game types include:
+
+ Core games
+ Core or hard-core games refer to the typical perception of video games, developed for entertainment purposes. These games typically require a fair amount of time to learn and master, in contrast to casual games, and thus are most appealing to gamers rather than a broader audience. Most of the AAA video game industry is based around the delivery of core games.
+
+ Casual games
+ In contrast to core games, casual games are designed for ease of accessibility, simple to understand gameplay and quick to grasp rule sets, and aimed at mass market audience. They frequently support the ability to jump in and out of play on demand, such as during commuting or lunch breaks. Numerous browser and mobile games fall into the casual game area, and casual games often are from genres with low intensity game elements such as match three, hidden object, time management, and puzzle games. Causal games frequently use social-network game mechanics, where players can enlist the help of friends on their social media networks for extra turns or moves each day. Popular casual games include Tetris and Candy Crush Saga. More recent, starting in the late 2010s, are hyper-casual games which use even more simplistic rules for short but infinitely replayable games, such as Flappy Bird.
+ Educational games
+ Education software has been used in homes and classrooms to help teach children and students, and video games have been similarly adapted for these reasons, all designed to provide a form of interactivity and entertainment tied to game design elements. There are a variety of differences in their designs and how they educate the user. These are broadly split between edutainment games that tend to focus on the entertainment value and rote learning but are unlikely to engage in critical thinking, and educational video games that are geared towards problem solving through motivation and positive reinforcement while downplaying the entertainment value. Examples of educational games include The Oregon Trail and the Carmen Sandiego series. Further, games not initially developed for educational purposes have found their way into the classroom after release, such as that feature open worlds or virtual sandboxes like Minecraft, or offer critical thinking skills through puzzle video games like SpaceChem.
+Serious games
+ Further extending from educational games, serious games are those where the entertainment factor may be augmented, overshadowed, or even eliminated by other purposes for the game. Game design is used to reinforce the non-entertainment purpose of the game, such as using video game technology for the game's interactive world, or gamification for reinforcement training. Educational games are a form of serious games, but other types of games include fitness games that incorporate significant physical exercise to help keep the player fit (such as Wii Fit), simulator games that resemble fight simulators to pilot aircraft (such as Microsoft Flight Simulator), advergames that are built around the advertising of a product (such as Pepsiman), and newsgames aimed at conveying a specific advocacy message (such as NarcoGuerra).
+Art games
+Although video games have been considered an art form on their own, games may be developed to try to purposely communicate a story or message, using the medium as a work of art. These art or arthouse games are designed to generate emotion and empathy from the player by challenging societal norms and offering critique through the interactivity of the video game medium. They may not have any type of win condition and are designed to let the player explore through the game world and scenarios. Most art games are indie games in nature, designed based on personal experiences or stories through a single developer or small team. Examples of art games include Passage, Flower, and That Dragon, Cancer.
+
+Content rating
+
+Video games can be subject to national and international content rating requirements. Like with film content ratings, video game ratings typing identify the target age group that the national or regional ratings board believes is appropriate for the player, ranging from all-ages, to a teenager-or-older, to mature, to the infrequent adult-only games. Most content review is based on the level of violence, both in the type of violence and how graphic it may be represented, and sexual content, but other themes such as drug and alcohol use and gambling that can influence children may also be identified. A primary identifier based on a minimum age is used by nearly all systems, along with additional descriptors to identify specific content that players and parents should be aware of.
+
+The regulations vary from country to country but generally are voluntary systems upheld by vendor practices, with penalty and fines issued by the ratings body on the video game publisher for misuse of the ratings. Among the major content rating systems include:
+ Entertainment Software Rating Board (ESRB) that oversees games released in the United States. ESRB ratings are voluntary and rated along a E (Everyone), E10+ (Everyone 10 and older), T (Teen), M (Mature), and AO (Adults Only). Attempts to mandate video games ratings in the U.S. subsequently led to the landmark Supreme Court case, Brown v. Entertainment Merchants Association in 2011 which ruled video games were a protected form of art, a key victory for the video game industry.
+ Pan European Game Information (PEGI) covering the United Kingdom, most of the European Union and other European countries, replacing previous national-based systems. The PEGI system uses content rated based on minimum recommended ages, which include 3+, 8+, 12+, 16+, and 18+.
+ Australian Classification Board (ACB) oversees the ratings of games and other works in Australia, using ratings of G (General), PG (Parental Guidance), M (Mature), MA15+ (Mature Accompanied), R18+ (Restricted), and X (Restricted for pornographic material). ACB can also deny to give a rating to game (RC – Refused Classification). The ACB's ratings are enforceable by law, and importantly, games cannot be imported or purchased digitally in Australia if they have failed to gain a rating or were given the RC rating, leading to a number of notable banned games.
+ Computer Entertainment Rating Organization (CERO) rates games for Japan. Their ratings include A (all ages), B (12 and older), C (15 and over), D (17 and over), and Z (18 and over).
+
+Additionally, the major content system provides have worked to create the International Age Rating Coalition (IARC), a means to streamline and align the content ratings system between different region, so that a publisher would only need to complete the content ratings review for one provider, and use the IARC transition to affirm the content rating for all other regions.
+
+Certain nations have even more restrictive rules related to political or ideological content. Within Germany, until 2018, the Unterhaltungssoftware Selbstkontrolle (Entertainment Software Self-Regulation) would refuse to classify, and thus allow sale, of any game depicting Nazi imagery, and thus often requiring developers to replace such imagery with fictional ones. This ruling was relaxed in 2018 to allow for such imagery for "social adequacy" purposes that applied to other works of art. China's video game segment is mostly isolated from the rest of the world due to the government's censorship, and all games published there must adhere to strict government review, disallowing content such as smearing the image of the Chinese Communist Party. Foreign games published in China often require modification by developers and publishers to meet these requirements.
+
+Development
+
+Video game development and authorship, much like any other form of entertainment, is frequently a cross-disciplinary field. Video game developers, as employees within this industry are commonly referred, primarily include programmers and graphic designers. Over the years this has expanded to include almost every type of skill that one might see prevalent in the creation of any movie or television program, including sound designers, musicians, and other technicians; as well as skills that are specific to video games, such as the game designer. All of these are managed by producers.
+
+In the early days of the industry, it was more common for a single person to manage all of the roles needed to create a video game. As platforms have become more complex and powerful in the type of material they can present, larger teams have been needed to generate all of the art, programming, cinematography, and more. This is not to say that the age of the "one-man shop" is gone, as this is still sometimes found in the casual gaming and handheld markets, where smaller games are prevalent due to technical limitations such as limited RAM or lack of dedicated 3D graphics rendering capabilities on the target platform (e.g., some PDAs).
+
+Video games are programmed like any other piece of computer software. Prior to the mid-1970s, arcade and home consoles were programmed by assembling discrete electro-mechanical components on circuit boards, which limited games to relatively simple logic. By 1975, low-cost microprocessors were available at volume to be used for video game hardware, which allowed game developers to program more detailed games, widening the scope of what was possible. Ongoing improvements in computer hardware technology has expanded what has become possible to create in video games, coupled with convergence of common hardware between console, computer, and arcade platforms to simplify the development process. Today, game developers have a number of commercial and open source tools available for use to make games, often which are across multiple platforms to support portability, or may still opt to create their own for more specialized features and direct control of the game. Today, many games are built around a game engine that handles the bulk of the game's logic, gameplay, and rendering. These engines can be augmented with specialized engines for specific features, such as a physics engine that simulates the physics of objects in real-time. A variety of middleware exists to help developers to access other features, such as for playback of videos within games, network-oriented code for games that communicate via online services, matchmaking for online games, and similar features. These features can be used from a developers' programming language of choice, or they may opt to also use game development kits that minimize the amount of direct programming they have to do but can also limit the amount of customization they can add into a game. Like all software, video games usually undergo quality testing before release to assure there are no bugs or glitches in the product, though frequently developers will release patches and updates.
+
+With the growth of the size of development teams in the industry, the problem of cost has increased. Development studios need the best talent, while publishers reduce costs to maintain profitability on their investment. Typically, a video game console development team ranges from 5 to 50 people, and some exceed 100. In May 2009, Assassin's Creed II was reported to have a development staff of 450. The growth of team size combined with greater pressure to get completed projects into the market to begin recouping production costs has led to a greater occurrence of missed deadlines, rushed games and the release of unfinished products.
+
+While amateur and hobbyist game programming had existed since the late 1970s with the introduction of home computers, a newer trend since the mid-2000s is indie game development. Indie games are made by small teams outside any direct publisher control, their games being smaller in scope than those from the larger "AAA" game studios, and are often experiment in gameplay and art style. Indie game development are aided by larger availability of digital distribution, including the newer mobile gaming marker, and readily-available and low-cost development tools for these platforms.
+
+Game theory and studies
+
+Although departments of computer science have been studying the technical aspects of video games for years, theories that examine games as an artistic medium are a relatively recent development in the humanities. The two most visible schools in this emerging field are ludology and narratology. Narrativists approach video games in the context of what Janet Murray calls "Cyberdrama". That is to say, their major concern is with video games as a storytelling medium, one that arises out of interactive fiction. Murray puts video games in the context of the Holodeck, a fictional piece of technology from Star Trek, arguing for the video game as a medium in which the player is allowed to become another person, and to act out in another world. This image of video games received early widespread popular support, and forms the basis of films such as Tron, eXistenZ and The Last Starfighter.
+
+Ludologists break sharply and radically from this idea. They argue that a video game is first and foremost a game, which must be understood in terms of its rules, interface, and the concept of play that it deploys. Espen J. Aarseth argues that, although games certainly have plots, characters, and aspects of traditional narratives, these aspects are incidental to gameplay. For example, Aarseth is critical of the widespread attention that narrativists have given to the heroine of the game Tomb Raider, saying that "the dimensions of Lara Croft's body, already analyzed to death by film theorists, are irrelevant to me as a player, because a different-looking body would not make me play differently... When I play, I don't even see her body, but see through it and past it." Simply put, ludologists reject traditional theories of art because they claim that the artistic and socially relevant qualities of a video game are primarily determined by the underlying set of rules, demands, and expectations imposed on the player.
+
+While many games rely on emergent principles, video games commonly present simulated story worlds where emergent behavior occurs within the context of the game. The term "emergent narrative" has been used to describe how, in a simulated environment, storyline can be created simply by "what happens to the player." However, emergent behavior is not limited to sophisticated games. In general, any place where event-driven instructions occur for AI in a game, emergent behavior will exist. For instance, take a racing game in which cars are programmed to avoid crashing, and they encounter an obstacle in the track: the cars might then maneuver to avoid the obstacle causing the cars behind them to slow or maneuver to accommodate the cars in front of them and the obstacle. The programmer never wrote code to specifically create a traffic jam, yet one now exists in the game.
+
+Intellectual property for video games
+
+Most commonly, video games are protected by copyright, though both patents and trademarks have been used as well.
+
+Though local copyright regulations vary to the degree of protection, video games qualify as copyrighted visual-audio works, and enjoy cross-country protection under the Berne Convention. This typically only applies to the underlying code, as well as to the artistic aspects of the game such as its writing, art assets, and music. Gameplay itself is generally not considered copyrightable; in the United States among other countries, video games are considered to fall into the idea–expression distinction in that it is how the game is presented and expressed to the player that can be copyrighted, but not the underlying principles of the game.
+
+Because gameplay is normally ineligible for copyright, gameplay ideas in popular games are often replicated and built upon in other games. At times, this repurposing of gameplay can be seen as beneficial and a fundamental part of how the industry has grown by building on the ideas of others. For example Doom (1993) and Grand Theft Auto III (2001) introduced gameplay that created popular new game genres, the first-person shooter and the Grand Theft Auto clone, respectively, in the few years after their release. However, at times and more frequently at the onset of the industry, developers would intentionally create video game clones of successful games and game hardware with few changes, which led to the flooded arcade and dedicated home console market around 1978. Cloning is also a major issue with countries that do not have strong intellectual property protection laws, such as within China. The lax oversight by China's government and the difficulty for foreign companies to take Chinese entities to court had enabled China to support a large grey market of cloned hardware and software systems. The industry remains challenged to distinguish between creating new games based on refinements of past successful games to create a new type of gameplay, and intentionally creating a clone of a game that may simply swap out art assets.
+
+Industry
+
+History
+The early history of the video game industry, following the first game hardware releases and through 1983, had little structure. Video games quickly took off during the golden age of arcade video games from the late 1970s to early 1980s, but the newfound industry was mainly composed of game developers with little business experience. This led to numerous companies forming simply to create clones of popular games to try to capitalize on the market. Due to loss of publishing control and oversaturation of the market, the North American home video game market crashed in 1983, dropping from revenues of around  in 1983 to  by 1985. Many of the North American companies created in the prior years closed down. Japan's growing game industry was briefly shocked by this crash but had sufficient longevity to withstand the short-term effects, and Nintendo helped to revitalize the industry with the release of the Nintendo Entertainment System in North America in 1985. Along with it, Nintendo established a number of core industrial practices to prevent unlicensed game development and control game distribution on their platform, methods that continue to be used by console manufacturers today.
+
+The industry remained more conservative following the 1983 crash, forming around the concept of publisher-developer dichotomies, and by the 2000s, leading to the industry centralizing around low-risk, triple-A games and studios with large development budgets of at least  or more. The advent of the Internet brought digital distribution as a viable means to distribute games, and contributed to the growth of more riskier, experimental independent game development as an alternative to triple-A games in the late 2000s and which has continued to grow as a significant portion of the video game industry.
+
+Industry roles
+Video games have a large network effect that draw on many different sectors that tie into the larger video game industry. While video game developers are a significant portion of the industry, other key participants in the market include:
+ Publishers: Companies generally that oversee bringing the game from the developer to market. This often includes performing the marketing, public relations, and advertising of the game. Publishers frequently pay the developers ahead of time to make their games and will be involved in critical decisions about the direction of the game's progress, and then pay the developers additional royalties or bonuses based on sales performances. Other smaller, boutique publishers may simply offer to perform the publishing of a game for a small fee and a portion of the sales, and otherwise leave the developer with the creative freedom to proceed. A range of other publisher-developer relationships exist between these points. 
+ Distributors: Publishers often are able to produce their own game media and take the role of distributor, but there are also third-party distributors that can mass-produce game media and distribute to retailers. Digital storefronts like Steam and the iOS App Store also serve as distributors and retailers in the digital space.
+ Retailers: Physical storefronts, which include large online retailers, department and electronic stores, and specialty video game stores, sell games, consoles, and other accessories to consumers. This has also including a trade-in market in certain regions, allowing players to turn in used games for partial refunds or credit towards other games. However, with the uprising of digital marketplaces and e-commerce revolution, retailers have been performing worse than in the past.
+ Hardware manufacturers: The video game console manufacturers produce console hardware, often through a value chain system that include numerous component suppliers and contract manufacturer that assemble the consoles. Further, these console manufacturers typically require a license to develop for their platform and may control the production of some games, such as Nintendo does with the use of game cartridges for its systems. In exchange, the manufacturers may help promote games for their system and may seek console exclusivity for certain games. For games on personal computers, a number of manufacturers are devoted to high-performance "gaming computer" hardware, particularly in the graphics card area; several of the same companies overlap with component supplies for consoles. A range of third-party manufacturers also exist to provide equipment and gear for consoles post-sale, such as additional controllers for console or carrying cases and gear for handheld devices.
+ Journalism: While journalism around video games used to be primarily print-based, and focused more on post-release reviews and gameplay strategy, the Internet has brought a more proactive press that use web journalism, covering games in the months prior to release as well as beyond, helping to build excitement for games ahead of release.
+ Influencers: With the rising importance of social media, video game companies have found that the opinions of influencers using streaming media to play through their games has had a significant impact on game sales, and have turned to use influencers alongside traditional journalism as a means to build up attention to their game before release.
+ Esports: Esports is a major function of several multiplayer games with numerous professional leagues established since the 2000s, with large viewership numbers, particularly out of southeast Asia since the 2010s.
+ Trade and advocacy groups: Trade groups like the Entertainment Software Association were established to provide a common voice for the industry in response to governmental and other advocacy concerns. They frequently set up the major trade events and conventions for the industry such as E3.
+ Gamers: Proactive hobbyists who are players and consumers of video games. While their representation in the industry is primarily seen through game sales, many companies follow gamers' comments on social media or on user reviews and engage with them to work to improve their products in addition to other feedback from other parts of the industry. Demographics of the larger player community also impact parts of the market; while once dominated by younger men, the market shifted in the mid-2010s towards women and older players who generally preferred mobile and causal games, leading to further growth in those sectors.
+
+Major regional markets
+
+The industry itself grew out from both the United States and Japan in the 1970s and 1980s before having a larger worldwide contribution. Today, the video game industry is predominantly led by major companies in North America (primarily the United States and Canada), Europe, and southeast Asia including Japan, South Korea, and China. Hardware production remains an area dominated by Asian companies either directly involved in hardware design or part of the production process, but digital distribution and indie game development of the late 2000s has allowed game developers to flourish nearly anywhere and diversify the field.
+
+Game sales
+
+According to the market research firm Newzoo, the global video game industry drew estimated revenues of over  in 2020. Mobile games accounted for the bulk of this, with a 48% share of the market, followed by console games at 28% and personal computer games at 23%.
+
+Sales of different types of games vary widely between countries due to local preferences. Japanese consumers tend to purchase much more handheld games than console games and especially PC games, with a strong preference for games catering to local tastes. Another key difference is that, though having declined in the West, arcade games remain an important sector of the Japanese gaming industry. In South Korea, computer games are generally preferred over console games, especially MMORPG games and real-time strategy games. Computer games are also popular in China.
+
+Effects on society
+
+Culture
+
+Video game culture is a worldwide new media subculture formed around video games and game playing. As computer and video games have increased in popularity over time, they have had a significant influence on popular culture. Video game culture has also evolved over time hand in hand with internet culture as well as the increasing popularity of mobile games. Many people who play video games identify as gamers, which can mean anything from someone who enjoys games to someone who is passionate about it. As video games become more social with multiplayer and online capability, gamers find themselves in growing social networks. Gaming can both be entertainment as well as competition, as a new trend known as electronic sports is becoming more widely accepted. In the 2010s, video games and discussions of video game trends and topics can be seen in social media, politics, television, film and music. The COVID-19 pandemic during 2020–2021 gave further visibility to video games as a pastime to enjoy with friends and family online as a means of social distancing.
+
+Since the mid-2000s there has been debate whether video games qualify as art, primarily as the form's interactivity interfered with the artistic intent of the work and that they are designed for commercial appeal. A significant debate on the matter came after film critic Roger Ebert published an essay "Video Games can never be art", which challenged the industry to prove him and other critics wrong. The view that video games were an art form was cemented in 2011 when the U.S. Supreme Court ruled in the landmark case Brown v. Entertainment Merchants Association that video games were a protected form of speech with artistic merit. Since then, video game developers have come to use the form more for artistic expression, including the development of art games, and the cultural heritage of video games as works of arts, beyond their technical capabilities, have been part of major museum exhibits, including The Art of Video Games at the Smithsonian American Art Museum and toured at other museums from 2012 to 2016.
+
+Video games will inspire sequels and other video games within the same franchise, but also have influenced works outside of the video game medium. Numerous television shows (both animated and live-action), films, comics and novels have been created based on existing video game franchises. Because video games are an interactive medium there has been trouble in converting them to these passive forms of media, and typically such works have been critically panned or treated as children's media. For example, until 2019, no video game film had ever been received a "Fresh" rating on Rotten Tomatoes, but the releases of Detective Pikachu (2019) and Sonic the Hedgehog (2020), both receiving "Fresh" ratings, shows signs of the film industry having found an approach to adapt video games for the large screen. That said, some early video game-based films have been highly successful at the box office, such as 1995's Mortal Kombat and 2001's Lara Croft: Tomb Raider.
+
+More recently since the 2000s, there has also become a larger appreciation of video game music, which ranges from chiptunes composed for limited sound-output devices on early computers and consoles, to fully-scored compositions for most modern games. Such music has frequently served as a platform for covers and remixes, and concerts featuring video game soundtracks performed by bands or orchestras, such as Video Games Live, have also become popular. Video games also frequently incorporate licensed music, particularly in the area of rhythm games, furthering the depth of which video games and music can work together.
+
+Further, video games can serve as a virtual environment under full control of a producer to create new works. With the capability to render 3D actors and settings in real-time, a new type of work machinima (short for "machine cinema") grew out from using video game engines to craft narratives. As video game engines gain higher fidelity, they have also become part of the tools used in more traditional filmmaking. Unreal Engine has been used as a backbone by Industrial Light & Magic for their StageCraft technology for shows like The Mandalorian.
+
+Separately, video games are also frequently used as part of the promotion and marketing for other media, such as for films, anime, and comics. However, these licensed games in the 1990s and 2000s often had a reputation for poor quality, developed without any input from the intellectual property rights owners, and several of them are considered among lists of games with notably negative reception, such as Superman 64. More recently, with these licensed games being developed by triple-A studios or through studios directly connected to the licensed property owner, there has been a significant improvement in the quality of these games, with an early trendsetting example of Batman: Arkham Asylum.
+
+Beneficial uses
+
+Besides their entertainment value, appropriately-designed video games have been seen to provide value in education across several ages and comprehension levels. Learning principles found in video games have been identified as possible techniques with which to reform the U.S. education system. It has been noticed that gamers adopt an attitude while playing that is of such high concentration, they do not realize they are learning, and that if the same attitude could be adopted at school, education would enjoy significant benefits. Students are found to be "learning by doing" while playing video games while fostering creative thinking.
+
+Video games are also believed to be beneficial to the mind and body. It has been shown that action video game players have better hand–eye coordination and visuo-motor skills, such as their resistance to distraction, their sensitivity to information in the peripheral vision and their ability to count briefly presented objects, than nonplayers. Researchers found that such enhanced abilities could be acquired by training with action games, involving challenges that switch attention between different locations, but not with games requiring concentration on single objects. A 2018 systematic review found evidence that video gaming training had positive effects on cognitive and emotional skills in the adult population, especially with young adults. A 2019 systematic review also added support for the claim that video games are beneficial to the brain, although the beneficial effects of video gaming on the brain differed by video games types.
+
+Organisers of video gaming events, such as the organisers of the D-Lux video game festival in Dumfries, Scotland, have emphasised the positive aspects video games can have on mental health. Organisers, mental health workers and mental health nurses at the event emphasised the relationships and friendships that can be built around video games and how playing games can help people learn about others as a precursor to discussing the person's mental health. A study in 2020 from Oxford University also suggested that playing video games can be a benefit to a person's mental health. The report of 3,274 gamers, all over the age of 18, focused on the games Animal Crossing: New Horizons and Plants vs Zombies: Battle for Neighborville and used actual play-time data. The report found that those that played more games tended to report greater "wellbeing". Also in 2020, computer science professor Regan Mandryk of the University of Saskatchewan said her research also showed that video games can have health benefits such as reducing stress and improving mental health. The university's research studied all age groups – "from pre-literate children through to older adults living in long term care homes" – with a main focus on 18 to 55-year-olds.
+
+A study of gamers attitudes towards gaming which was reported about in 2018 found that millennials use video games as a key strategy for coping with stress. In the study of 1,000 gamers, 55% said that it "helps them to unwind and relieve stress ... and half said they see the value in gaming as a method of escapism to help them deal with daily work pressures".
+
+Controversies
+
+Video games have caused controversy since the 1970s. Parents and children's advocates regularly raise concerns that violent video games can influence young players into performing those violent acts in real life, and events such as the Columbine High School massacre in 1999 in which the perpetrators specifically alluded to using video games to plot out their attack, raised further fears. Medical experts and mental health professionals have also raised concerned that video games may be addictive, and the World Health Organization has included "gaming disorder" in the 11th revision of its International Statistical Classification of Diseases. Other health experts, including the American Psychiatric Association, have stated that there is insufficient evidence that video games can create violent tendencies or lead to addictive behavior, though agree that video games typically use a compulsion loop in their core design that can create dopamine that can help reinforce the desire to continue to play through that compulsion loop and potentially lead into violent or addictive behavior. Even with case law establishing that video games qualify as a protected art form, there has been pressure on the video game industry to keep their products in check to avoid over-excessive violence particularly for games aimed at younger children. The potential addictive behavior around games, coupled with increased used of post-sale monetization of video games, has also raised concern among parents, advocates, and government officials about gambling tendencies that may come from video games, such as controversy around the use of loot boxes in many high-profile games.
+
+Numerous other controversies around video games and its industry have arisen over the years, among the more notable incidents include the 1993 United States Congressional hearings on violent games like Mortal Kombat which lead to the formation of the ESRB ratings system, numerous legal actions taken by attorney Jack Thompson over violent games such as Grand Theft Auto III and Manhunt from 2003 to 2007, the outrage over the "No Russian" level from Call of Duty: Modern Warfare 2 in 2009 which allowed the player to shoot a number of innocent non-player characters at an airport, and the Gamergate harassment campaign in 2014 that highlighted misogyny from a portion of the player demographic. The industry as a whole has also dealt with issues related to gender, racial, and LGBTQ+ discrimination and mischaracterization of these minority groups in video games. A further issue in the industry is related to working conditions, as development studios and publishers frequently use "crunch time", required extended working hours, in the weeks and months ahead of a game's release to assure on-time delivery.
+
+Collecting and preservation
+
+Players of video games often maintain collections of games. More recently there has been interest in retrogaming, focusing on games from the first decades. Games in retail packaging in good shape have become collectors items for the early days of the industry, with some rare publications having gone for over  . Separately, there is also concern about the preservation of video games, as both game media and the hardware to play them degrade over time. Further, many of the game developers and publishers from the first decades no longer exist, so records of their games have disappeared. Archivists and preservations have worked within the scope of copyright law to save these games as part of the cultural history of the industry.
+
+There are many video game museums around the world, including the National Videogame Museum in Frisco, Texas, which serves as the largest museum wholly dedicated to the display and preservation of the industry's most important artifacts. Europe hosts video game museums such as the Computer Games Museum in Berlin and the Museum of Soviet Arcade Machines in Moscow and Saint-Petersburg. The Museum of Art and Digital Entertainment in Oakland, California is a dedicated video game museum focusing on playable exhibits of console and computer games. The Video Game Museum of Rome is also dedicated to preserving video games and their history. The International Center for the History of Electronic Games at The Strong in Rochester, New York contains one of the largest collections of electronic games and game-related historical materials in the world, including a  exhibit which allows guests to play their way through the history of video games. The Smithsonian Institution in Washington, DC has three video games on permanent display: Pac-Man, Dragon's Lair, and Pong.
+
+The Museum of Modern Art has added a total of 20 video games and one video game console to its permanent Architecture and Design Collection since 2012. In 2012, the Smithsonian American Art Museum ran an exhibition on "The Art of Video Games". However, the reviews of the exhibit were mixed, including questioning whether video games belong in an art museum.
+
+See also
+
+ Lists of video games
+ List of accessories to video games by system
+ Outline of video games
+
+Notes
+
+References
+
+Sources
+
+Further reading 
+
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+
+ The Ultimate History of Video Games: From Pong to Pokemon--The Story Behind the Craze That Touched Our Lives and Changed the World by Steven L. Kent, Crown, 2001, 
+ The Ultimate History of Video Games, Volume 2: Nintendo, Sony, Microsoft, and the Billion-Dollar Battle to Shape Modern Gaming by Steven L. Kent, Crown, 2021,
+
+External links
+
+ Video games bibliography by the French video game research association Ludoscience
+ The Virtual Museum of Computing (VMoC) (archived 10 October 2014)
+
+ 
+Games and sports introduced in 1947
+Digital media
+American inventions
+The Cambrian Period ( ; sometimes symbolized Ꞓ) is the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million years ago (mya) to the beginning of the Ordovician Period  mya. Its subdivisions, and its base, are somewhat in flux. 
+
+The period was established as "Cambrian series" by Adam Sedgwick, who named it after Cambria, the Latin name for 'Cymru' (Wales), where Britain's Cambrian rocks are best exposed. Sedgwick identified the layer as part of his task, along with Roderick Murchison, to subdivide the large "Transition Series", although the two geologists disagreed for a while on the appropriate categorization. 
+
+The Cambrian is unique in its unusually high proportion of  sedimentary deposits, sites of exceptional preservation where "soft" parts of organisms are preserved as well as their more resistant shells. As a result, our understanding of the Cambrian biology surpasses that of some later periods.
+
+The Cambrian marked a profound change in life on Earth: prior to the Cambrian, the majority of living organisms on the whole were small, unicellular and simple (Ediacaran fauna and earlier Tonian Huainan biota being notable exceptions). Complex, multicellular organisms gradually became more common in the millions of years immediately preceding the Cambrian, but it was not until this period that mineralized – hence readily fossilized – organisms became common. 
+
+The rapid diversification of lifeforms in the Cambrian, known as the Cambrian explosion, produced the first representatives of all modern animal phyla. Phylogenetic analysis has supported the view that before the Cambrian radiation, in the Cryogenian or Tonian, animals (metazoans) evolved monophyletically from a single common ancestor: flagellated colonial protists similar to modern choanoflagellates.
+Although diverse life forms prospered in the oceans, the land is thought to have been comparatively barren – with nothing more complex than a microbial soil crust and a few molluscs and arthropods (albeit not terrestrial) that emerged to browse on the microbial biofilm. 
+
+By the end of the Cambrian, myriapods, arachnids, and hexapods started adapting to the land, along with the first plants. Most of the continents were probably dry and rocky due to a lack of vegetation. Shallow seas flanked the margins of several continents created during the breakup of the supercontinent Pannotia. The seas were relatively warm, and polar ice was absent for much of the period.
+
+Stratigraphy 
+
+The Cambrian Period followed the Ediacaran Period and was followed by the Ordovician Period.
+
+The base of the Cambrian lies atop a complex assemblage of trace fossils known as the Treptichnus pedum assemblage.
+The use of Treptichnus pedum, a reference ichnofossil to mark the lower boundary of the Cambrian, is problematic because very similar trace fossils belonging to the Treptichnids group are found well below T. pedum in Namibia, Spain and Newfoundland, and possibly in the western US. The stratigraphic range of T. pedum overlaps the range of the Ediacaran fossils in Namibia, and probably in Spain.
+
+Subdivisions  
+The Cambrian is divided into four epochs (series) and ten ages (stages). Currently only three series and six stages are named and have a GSSP (an internationally agreed-upon stratigraphic reference point).
+
+Because the international stratigraphic subdivision is not yet complete, many local subdivisions are still widely used. In some of these subdivisions the Cambrian is divided into three epochs with locally differing names – the Early Cambrian (Caerfai or Waucoban,  mya), Middle Cambrian (St Davids or Albertan,  mya) and Late Cambrian ( mya; also known as Merioneth or Croixan). 
+Trilobite zones allow biostratigraphic correlation in the Cambrian. Rocks of these epochs are referred to as belonging to the Lower, Middle, or Upper Cambrian.
+
+Each of the local series is divided into several stages. The Cambrian is divided into several regional faunal stages of which the Russian-Kazakhian system is most used in international parlance:
+
+*Most Russian paleontologists define the lower boundary of the Cambrian at the base of the Tommotian Stage, characterized by diversification and global distribution of organisms with mineral skeletons and the appearance of the first Archaeocyath bioherms.
+
+Dating the Cambrian 
+
+The International Commission on Stratigraphy lists the Cambrian Period as beginning at  and ending at .
+
+The lower boundary of the Cambrian was originally held to represent the first appearance of complex life, represented by trilobites. The recognition of small shelly fossils before the first trilobites, and Ediacara biota substantially earlier, led to calls for a more precisely defined base to the Cambrian Period.
+
+Despite the long recognition of its distinction from younger Ordovician rocks and older Precambrian rocks, it was not until 1994 that the Cambrian system/period was internationally ratified. After decades of careful consideration, a continuous sedimentary sequence at Fortune Head, Newfoundland was settled upon as a formal base of the Cambrian Period, which was to be correlated worldwide by the earliest appearance of Treptichnus pedum. Discovery of this fossil a few metres below the GSSP led to the refinement of this statement, and it is the T. pedum ichnofossil assemblage that is now formally used to correlate the base of the Cambrian.
+
+This formal designation allowed radiometric dates to be obtained from samples across the globe that corresponded to the base of the Cambrian. Early dates of  quickly gained favour, though the methods used to obtain this number are now considered to be unsuitable and inaccurate. A more precise date using modern radiometric dating yield a date of . The ash horizon in Oman from which this date was recovered corresponds to a marked fall in the abundance of carbon-13 that correlates to equivalent excursions elsewhere in the world, and to the disappearance of distinctive Ediacaran fossils (Namacalathus, Cloudina). Nevertheless, there are arguments that the dated horizon in Oman does not correspond to the Ediacaran-Cambrian boundary, but represents a facies change from marine to evaporite-dominated strata – which would mean that dates from other sections, ranging from 544 or 542 Ma, are more suitable.
+
+Paleogeography 
+Plate reconstructions suggest a global supercontinent, Pannotia, was in the process of breaking up early in the Cambrian, with Laurentia (North America), Baltica, and Siberia having separated from the main supercontinent of Gondwana to form isolated land masses. Most continental land was clustered in the Southern Hemisphere at this time, but was drifting north. Large, high-velocity rotational movement of Gondwana appears to have occurred in the Early Cambrian.
+
+With a lack of sea ice – the great glaciers of the Marinoan Snowball Earth were long melted – the sea level was high, which led to large areas of the continents being flooded in warm, shallow seas ideal for sea life. The sea levels fluctuated somewhat, suggesting there were "ice ages", associated with pulses of expansion and contraction of a south polar ice cap.
+
+In Baltoscandia a Lower Cambrian transgression transformed large swathes of the Sub-Cambrian peneplain into an epicontinental sea.
+
+Climate 
+Glaciers likely existed during the earliest Cambrian at high and possibly even at middle palaeolatitudes, possibly due to the ancient continent of Gondwana covering the South Pole and cutting off polar ocean currents. Middle Terreneuvian deposits, corresponding to the boundary between the Fortunian and Stage 2, show evidence of glaciation. However, other authors believe these very early, pretrilobitic glacial deposits may not even be of Cambrian age at all but instead date back to the Neoproterozoic, an era characterised by numerous severe icehouse periods. The beginning of Stage 3 was relatively cool, with the period between 521 and 517 Ma being known as the Cambrian Arthropod Radiation Cool Event (CARCE). The Earth was generally very warm during Stage 4; its climate was comparable to the hot greenhouse of the Late Cretaceous and Early Palaeogene, as evidenced by a maximum in continental weathering rates over the last 900 million years and the presence of tropical, lateritic palaeosols at high palaeolatitudes during this time. The Archaecyathid Extinction Warm Event (AEWE), lasting from 511 to 510.5 Ma, was particularly warm. Another warm event, the Redlichiid-Olenid Extinction Warm Event, occurred at the beginning of the Wuliuan. It became even warmer towards the end of the period, and sea levels rose dramatically. This warming trend continued into the Early Ordovician, the start of which was characterised by an extremely hot global climate.
+
+Flora 
+The Cambrian flora was little different from the Ediacaran. The principal taxa were the marine macroalgae Fuxianospira, Sinocylindra, and Marpolia. No calcareous macroalgae are known from the period.
+
+No land plant (embryophyte) fossils are known from the Cambrian. However, biofilms and microbial mats were well developed on Cambrian tidal flats and beaches 500 mya, and microbes forming microbial Earth ecosystems, comparable with modern soil crust of desert regions, contributing to soil formation. Although molecular clock estimates suggest terrestrial plants may have first emerged during the Middle or Late Cambrian, the consequent large-scale removal of the greenhouse gas CO2 from the atmosphere through sequestration did not begin until the Ordovician.
+
+Oceanic life 
+
+The Cambrian explosion was a period of rapid multicellular growth. Most animal life during the Cambrian was aquatic. Trilobites were once assumed to be the dominant life form at that time, but this has proven to be incorrect. Arthropods were by far the most dominant animals in the ocean, but trilobites were only a minor part of the total arthropod diversity. What made them so apparently abundant was their heavy armor reinforced by calcium carbonate (CaCO3), which fossilized far more easily than the fragile chitinous exoskeletons of other arthropods, leaving numerous preserved remains.
+
+The period marked a steep change in the diversity and composition of Earth's biosphere. The Ediacaran biota suffered a mass extinction at the start of the Cambrian Period, which corresponded with an increase in the abundance and complexity of burrowing behaviour. This behaviour had a profound and irreversible effect on the substrate which transformed the seabed ecosystems. Before the Cambrian, the sea floor was covered by microbial mats. By the end of the Cambrian, burrowing animals had destroyed the mats in many areas through bioturbation. As a consequence, many of those organisms that were dependent on the mats became extinct, while the other species adapted to the changed environment that now offered new ecological niches. Around the same time there was a seemingly rapid appearance of representatives of all the mineralized phyla, including the Bryozoa, which were once thought to have only appeared in the Lower Ordovician. However, many of those phyla were represented only by stem-group forms; and since mineralized phyla generally have a benthic origin, they may not be a good proxy for (more abundant) non-mineralized phyla.
+
+While the early Cambrian showed such diversification that it has been named the Cambrian Explosion, this changed later in the period, when there occurred a sharp drop in biodiversity. About 515 million years ago, the number of species going extinct exceeded the number of new species appearing. Five million years later, the number of genera had dropped from an earlier peak of about 600 to just 450. Also, the speciation rate in many groups was reduced to between a fifth and a third of previous levels. 500 million years ago, oxygen levels fell dramatically in the oceans, leading to hypoxia, while the level of poisonous hydrogen sulfide simultaneously increased, causing another extinction. The later half of Cambrian was surprisingly barren and showed evidence of several rapid extinction events; the stromatolites which had been replaced by reef building sponges known as Archaeocyatha, returned once more as the archaeocyathids became extinct. This declining trend did not change until the Great Ordovician Biodiversification Event.
+
+Some Cambrian organisms ventured onto land, producing the trace fossils Protichnites and Climactichnites. Fossil evidence suggests that euthycarcinoids, an extinct group of arthropods, produced at least some of the Protichnites. Fossils of the track-maker of Climactichnites have not been found; however, fossil trackways and resting traces suggest a large, slug-like mollusc.
+
+In contrast to later periods, the Cambrian fauna was somewhat restricted; free-floating organisms were rare, with the majority living on or close to the sea floor; and mineralizing animals were rarer than in future periods, in part due to the unfavourable ocean chemistry.
+
+Many modes of preservation are unique to the Cambrian, and some preserve soft body parts, resulting in an abundance of . These include Sirius Passet, the Sinsk Algal Lens, the Maotianshan Shales, the Emu Bay Shale, and the Burgess Shale,.
+
+Symbol
+The United States Federal Geographic Data Committee uses a "barred capital C"  character to represent the Cambrian Period.
+The Unicode character is .
+
+Gallery
+
+See also 
+ Cambrian–Ordovician extinction event – circa 488 mya
+ Dresbachian extinction event—circa 499 mya
+ End Botomian extinction event—circa 513 mya
+ List of fossil sites (with link directory)
+ Type locality (geology), the locality where a particular rock type, stratigraphic unit, fossil or mineral species is first identified
+
+References
+
+Further reading
+
+External links 
+
+ 
+ Biostratigraphy – includes information on Cambrian trilobite biostratigraphy
+  Sam Gon's trilobite pages (contains numerous Cambrian trilobites)
+ Examples of Cambrian Fossils
+ Paleomap Project
+ Report on the web on Amthor and others from Geology vol. 31
+ Weird Life on the Mats
+ Chronostratigraphy scale v.2018/08 | Cambrian
+
+ 
+Geological periods
+In ontology, the theory of categories concerns itself with the categories of being: the highest genera or kinds of entities according to Amie Thomasson. To investigate the categories of being, or simply categories, is to determine the most fundamental and the broadest classes of entities. A distinction between such categories, in making the categories or applying them, is called an ontological distinction. Various systems of categories have been proposed, they often include categories for substances, properties, relations, states of affairs or events. A representative question within the theory of categories might articulate itself, for example, in a query like, "Are universals prior to particulars?"
+
+Early development
+The process of abstraction required to discover the number and names of the categories of being has been undertaken by many philosophers since Aristotle and involves the careful inspection of each concept to ensure that there is no higher category or categories under which that concept could be subsumed. The scholars of the twelfth and thirteenth centuries developed Aristotle's ideas. For example, Gilbert of Poitiers divides Aristotle's ten categories into two sets, primary and secondary, according to whether they inhere in the subject or not:
+Primary categories: Substance, Relation, Quantity and Quality
+Secondary categories: Place, Time, Situation, Condition, Action, Passion
+Furthermore, following Porphyry’s likening of the classificatory hierarchy to a tree, they concluded that the major classes could be subdivided to form subclasses, for example, Substance could be divided into Genus and Species, and Quality could be subdivided into Property and Accident, depending on whether the property was necessary or contingent. An alternative line of development was taken by Plotinus in the second century who by a process of abstraction reduced Aristotle's list of ten categories to five: Substance, Relation, Quantity, Motion and Quality. Plotinus further suggested that the latter three categories of his list, namely Quantity, Motion and Quality correspond to three different kinds of relation and that these three categories could therefore be subsumed under the category of Relation. This was to lead to the supposition that there were only two categories at the top of the hierarchical tree, namely Substance and Relation. Many supposed that relations only exist in the mind. Substance and Relation, then, are closely commutative with Mind and Matter--this is expressed most clearly in the dualism of René Descartes.
+
+Vaisheshika
+
+Stoic
+
+Aristotle
+
+One of Aristotle’s early interests lay in the classification of the natural world, how for example the genus "animal" could be first divided into "two-footed animal" and then into "wingless, two-footed animal". He realised that the distinctions were being made according to the qualities the animal possesses, the quantity of its parts and the kind of motion that it exhibits. To fully complete the proposition "this animal is ..." Aristotle stated in his work on the Categories that there were ten kinds of predicate where ...
+
+"... each signifies either substance or quantity or quality or relation or where or when or being-in-a-position or having or acting or being acted upon".
+
+He realised that predicates could be simple or complex. The simple kinds consist of a subject and a predicate linked together by the "categorical" or inherent type of relation. For Aristotle the more complex kinds were limited to propositions where the predicate is compounded of two of the above categories for example "this is a horse running". More complex kinds of proposition were only discovered after Aristotle by the Stoic, Chrysippus, who developed the "hypothetical" and "disjunctive" types of syllogism and these were terms which were to be developed through the Middle Ages and were to reappear in Kant's system of categories.
+
+Category came into use with Aristotle's essay Categories, in which he discussed univocal and equivocal terms, predication, and ten categories:
+Substance, essence (ousia) – examples of primary substance: this man, this horse; secondary substance (species, genera): man, horse
+Quantity (poson, how much), discrete or continuous – examples: two cubits long, number, space, (length of) time.
+Quality (poion, of what kind or description) – examples: white, black, grammatical, hot, sweet, curved, straight.
+Relation (pros ti, toward something) – examples: double, half, large, master, knowledge.
+Place (pou, where) – examples: in a marketplace, in the Lyceum
+Time (pote, when) – examples: yesterday, last year
+Position, posture, attitude (keisthai, to lie) – examples: sitting, lying, standing
+State, condition (echein, to have or be) – examples: shod, armed
+Action (poiein, to make or do) – examples: to lance, to heat, to cool (something)
+Affection, passion (paschein, to suffer or undergo) – examples: to be lanced, to be heated, to be cooled
+
+Plotinus
+Plotinus in writing his Enneads around AD 250 recorded that "philosophy at a very early age investigated the number and character of the existents ... some found ten, others less .... to some the genera were the first principles, to others only a generic classification of existents". He realised that some categories were reducible to others saying "why are not Beauty, Goodness and the virtues, Knowledge and Intelligence included among the primary genera?" He concluded that such transcendental categories and even the categories of Aristotle were in some way posterior to the three Eleatic categories first recorded in Plato's dialogue Parmenides and which comprised the following three coupled terms: 
+Unity/Plurality
+Motion/Stability
+Identity/Difference
+
+Plotinus called these "the hearth of reality" deriving from them not only the three categories of Quantity, Motion and Quality but also what came to be known as "the three moments of the Neoplatonic world process":
+First, there existed the "One", and his view that "the origin of things is a contemplation"
+The Second "is certainly an activity ... a secondary phase ... life streaming from life ... energy running through the universe"
+The Third is some kind of Intelligence concerning which he wrote "Activity is prior to Intellection ... and self knowledge"
+
+Plotinus likened the three to the centre, the radii and the circumference of a circle, and clearly thought that the principles underlying the categories were the first principles of creation. "From a single root all being multiplies". Similar ideas were to be introduced into Early Christian thought by, for example, Gregory of Nazianzus who summed it up saying "Therefore, Unity, having from all eternity arrived by motion at duality, came to rest in trinity".
+
+Modern development
+Kant and Hegel accused the Aristotelian table of categories of being 'rhapsodic', derived arbitrarily and in bulk from experience, without any systematic necessity.
+
+The early modern dualism, which has been described above, of Mind and Matter or Subject and Relation, as reflected in the writings of Descartes underwent a substantial revision in the late 18th century. The first objections to this stance were formulated in the eighteenth century by Immanuel Kant who realised that we can say nothing about Substance except through the relation of the subject to other things. 
+
+For example: In the sentence "This is a house" the substantive subject "house" only gains meaning in relation to human use patterns or to other similar houses. The category of Substance disappears from Kant's tables, and under the heading of Relation, Kant lists inter alia the three relationship types of Disjunction, Causality and Inherence. The three older concepts of Quantity, Motion and Quality, as Peirce discovered, could be subsumed under these three broader headings in that Quantity relates to the subject through the relation of Disjunction; Motion relates to the subject through the relation of Causality; and Quality relates to the subject through the relation of Inherence. Sets of three continued to play an important part in the nineteenth century development of the categories, most notably in G.W.F. Hegel's extensive tabulation of categories, and in C.S. Peirce's categories set out in his work on the logic of relations. One of Peirce's contributions was to call the three primary categories Firstness, Secondness and Thirdness which both emphasises their general nature, and avoids the confusion of having the same name for both the category itself and for a concept within that category.
+
+In a separate development, and building on the notion of primary and secondary categories introduced by the Scholastics, Kant introduced the idea that secondary or "derivative" categories could be derived from the primary categories through the combination of one primary category with another. This would result in the formation of three secondary categories: the first, "Community" was an example that Kant gave of such a derivative category; the second, "Modality", introduced by Kant, was a term which Hegel, in developing Kant's dialectical method, showed could also be seen as a derivative category; and the third, "Spirit" or "Will" were terms that Hegel and Schopenhauer were developing separately for use in their own systems. Karl Jaspers in the twentieth century, in his development of existential categories, brought the three together, allowing for differences in terminology, as Substantiality, Communication and Will. This pattern of three primary and three secondary categories was used most notably in the nineteenth century by Peter Mark Roget to form the six headings of his Thesaurus of English Words and Phrases. The headings used were the three objective categories of Abstract Relation, Space (including Motion) and Matter and the three subjective categories of Intellect, Feeling and Volition, and he found that under these six headings all the words of the English language, and hence any possible predicate, could be assembled.
+
+Kant
+
+In the Critique of Pure Reason (1781), Immanuel Kant argued that the categories are part of our own mental structure and consist of a set of a priori concepts through which we interpret the world around us. These concepts correspond to twelve logical functions of the understanding which we use to make judgements and there are therefore two tables given in the Critique, one of the Judgements and a corresponding one for the Categories. To give an example, the logical function behind our reasoning from ground to consequence (based on the Hypothetical relation) underlies our understanding of the world in terms of cause and effect (the Causal relation). In each table the number twelve arises from, firstly, an initial division into two: the Mathematical and the Dynamical; a second division of each of these headings into a further two: Quantity and Quality, and Relation and Modality respectively; and, thirdly, each of these then divides into a further three subheadings as follows.
+
+Table of Judgements
+
+Mathematical
+Quantity
+Universal
+Particular
+Singular
+Quality
+Affirmative
+Negative
+Infinite
+Dynamical
+Relation
+Categorical
+Hypothetical
+Disjunctive
+Modality
+Problematic
+Assertoric
+Apodictic
+
+Table of Categories
+
+Mathematical
+Quantity
+Unity
+Plurality
+Totality
+Quality
+Reality
+Negation
+Limitation
+Dynamical
+Relation
+Inherence and Subsistence (substance and accident)
+Causality and Dependence (cause and effect)
+Community (reciprocity)
+Modality
+Possibility
+Existence
+Necessity
+
+Criticism of Kant's system followed, firstly, by Arthur Schopenhauer, who amongst other things was unhappy with the term "Community", and declared that the tables "do open violence to truth, treating it as nature was treated by old-fashioned gardeners", and secondly, by W.T.Stace who in his book The Philosophy of Hegel suggested that in order to make Kant's structure completely symmetrical a third category would need to be added to the Mathematical and the Dynamical. This, he said, Hegel was to do with his category of concept.
+
+Hegel
+G.W.F. Hegel in his Science of Logic (1812) attempted to provide a more comprehensive system of categories than Kant and developed a structure that was almost entirely triadic. So important were the categories to Hegel that he claimed the first principle of the world, which he called the "absolute", is "a system of categories  the categories must be the reason of which the world is a consequent".
+
+Using his own logical method of sublation, later called the Hegelian dialectic, reasoning from the abstract through the negative to the concrete, he arrived at a hierarchy of some 270 categories, as explained by W. T. Stace. The three very highest categories were "logic", "nature" and "spirit". The three highest categories of "logic", however, he called "being", "essence", and "notion" which he explained as follows:
+
+ Being was differentiated from Nothing by containing with it the concept of the "other", an initial internal division that can be compared with Kant's category of disjunction. Stace called the category of Being the sphere of common sense containing concepts such as consciousness, sensation, quantity, quality and measure.
+ Essence. The "other" separates itself from the "one" by a kind of motion, reflected in Hegel's first synthesis of "becoming". For Stace this category represented the sphere of science containing within it firstly, the thing, its form and properties; secondly, cause, effect and reciprocity, and thirdly, the principles of classification, identity and difference. 
+ Notion. Having passed over into the "Other" there is an almost neoplatonic return into a higher unity that in embracing the "one" and the "other" enables them to be considered together through their inherent qualities. This according to Stace is the sphere of philosophy proper where we find not only the three types of logical proposition: disjunctive, hypothetical, and categorical but also the three transcendental concepts of beauty, goodness and truth.
+
+Schopenhauer's category that corresponded with "notion" was that of "idea", which in his Four-Fold Root of Sufficient Reason he complemented with the category of the "will". The title of his major work was The World as Will and Idea. The two other complementary categories, reflecting one of Hegel's initial divisions, were those of Being and Becoming. At around the same time, Goethe was developing his colour theories in the  of 1810, and introduced similar principles of combination and complementation, symbolising, for Goethe, "the primordial relations which belong both to nature and vision". Hegel in his Science of Logic accordingly asks us to see his system not as a tree but as a circle.
+
+Twentieth-century development
+In the twentieth century the primacy of the division between the subjective and the objective, or between mind and matter, was disputed by, among others, Bertrand Russell and Gilbert Ryle. Philosophy began to move away from the metaphysics of categorisation towards the linguistic problem of trying to differentiate between, and define, the words being used. Ludwig Wittgenstein’s conclusion was that there were no clear definitions which we can give to words and categories but only a "halo" or "corona" of related meanings radiating around each term. Gilbert Ryle thought the problem could be seen in terms of dealing with "a galaxy of ideas" rather than a single idea, and suggested that category mistakes are made when a concept (e.g. "university"), understood as falling under one category (e.g. abstract idea), is used as though it falls under another (e.g. physical object). With regard to the visual analogies being used, Peirce and Lewis, just like Plotinus earlier, likened the terms of propositions to points, and the relations between the terms to lines. Peirce, taking this further, talked of univalent, bivalent and trivalent relations linking predicates to their subject and it is just the number and types of relation linking subject and predicate that determine the category into which a predicate might fall. Primary categories contain concepts where there is one dominant kind of relation to the subject. Secondary categories contain concepts where there are two dominant kinds of relation. Examples of the latter were given by Heidegger in his two propositions "the house is on the creek" where the two dominant relations are spatial location (Disjunction) and cultural association (Inherence), and "the house is eighteenth century" where the two relations are temporal location (Causality) and cultural quality (Inherence). A third example may be inferred from Kant in the proposition "the house is impressive or sublime" where the two relations are spatial or mathematical disposition (Disjunction) and dynamic or motive power (Causality). Both Peirce and Wittgenstein introduced the analogy of colour theory in order to illustrate the shades of meanings of words. Primary categories, like primary colours, are analytical representing the furthest we can go in terms of analysis and abstraction and include Quantity, Motion and Quality. Secondary categories, like secondary colours, are synthetic and include concepts such as Substance, Community and Spirit. 
+
+Apart from these, the categorial scheme of Alfred North Whitehead and his Process Philosophy, alongside Nicolai Hartmann and his Critical Realism, remain one of the most detailed and advanced systems in categorial research in metaphysics.
+
+Peirce
+
+Charles Sanders Peirce, who had read Kant and Hegel closely, and who also had some knowledge of Aristotle, proposed a system of merely three phenomenological categories: Firstness, Secondness, and Thirdness, which he repeatedly invoked in his subsequent writings. Like Hegel, C.S. Peirce attempted to develop a system of categories from a single indisputable principle, in Peirce's case the notion that in the first instance he could only be aware of his own ideas. 
+	"It seems that the true categories of consciousness are first, feeling ... second, a sense of resistance ... and third, synthetic consciousness, or thought".
+	Elsewhere he called the three primary categories: Quality, Reaction and Meaning, and even Firstness, Secondness and Thirdness, saying, "perhaps it is not right to call these categories conceptions, they are so intangible that they are rather tones or tints upon conceptions":     
+Firstness (Quality): "The first is predominant in feeling ... we must think of a quality without parts, e.g. the colour of magenta ... When I say it is a quality I do not mean that it "inheres" in a subject ... The whole content of consciousness is made up of qualities of feeling, as truly as the whole of space is made up of points, or the whole of time by instants".
+Secondness (Reaction): "This is present even in such a rudimentary fragment of experience as a simple feeling ... an action and reaction between our soul and the stimulus ... The idea of second is predominant in the ideas of causation and of statical force ... the real is active; we acknowledge it by calling it the actual".
+Thirdness (Meaning): "Thirdness is essentially of a general nature ... ideas in which thirdness predominate [include] the idea of a sign or representation ... Every genuine triadic relation involves meaning ... the idea of meaning is irreducible to those of quality and reaction ... synthetical consciousness is the consciousness of a third or medium".
+
+Although Peirce's three categories correspond to the three concepts of relation given in Kant's tables, the sequence is now reversed and follows that given by Hegel, and indeed before Hegel of the three moments of the world-process given by Plotinus. Later, Peirce gave a mathematical reason for there being three categories in that although monadic, dyadic and triadic nodes are irreducible, every node of a higher valency is reducible to a "compound of triadic relations". Ferdinand de Saussure, who was developing "semiology" in France just as Peirce was developing "semiotics" in the US, likened each term of a proposition to "the centre of a constellation, the point where other coordinate terms, the sum of which is indefinite, converge".
+
+Others
+Edmund Husserl (1962, 2000) wrote extensively about categorial systems as part of his phenomenology.
+
+For Gilbert Ryle (1949), a category (in particular a "category mistake") is an important semantic concept, but one having only loose affinities to an ontological category.
+
+Contemporary systems of categories have been proposed by John G. Bennett (The Dramatic Universe, 4 vols., 1956–65), Wilfrid Sellars (1974), Reinhardt Grossmann (1983, 1992), Johansson (1989), Hoffman and Rosenkrantz (1994), Roderick Chisholm (1996), Barry Smith (ontologist) (2003), and Jonathan Lowe (2006).
+
+See also
+
+ Categories (Aristotle)
+ Categories (Peirce)
+ Categories (Stoic)
+ Category (Kant)
+ Metaphysics
+ Modal logic
+ Ontology
+ Schema (Kant)
+ Similarity (philosophy)
+
+References
+
+Selected bibliography
+
+Aristotle, 1953. Metaphysics. Ross, W. D., trans. Oxford University Press.
+--------, 2004. Categories, Edghill, E. M., trans. Uni. of Adelaide library.
+John G. Bennett, 1956–1965. The Dramatic Universe. London, Hodder & Stoughton.
+Gustav Bergmann, 1992. New Foundations of Ontology. Madison: Uni. of Wisconsin Press.
+Browning, Douglas, 1990. Ontology and the Practical Arena. Pennsylvania State Uni.
+Butchvarov, Panayot, 1979. Being qua Being: A Theory of Identity, Existence, and Predication. Indiana Uni. Press.
+Roderick Chisholm, 1996. A Realistic Theory of Categories. Cambridge Uni. Press.
+Feibleman, James Kern, 1951. Ontology. The Johns Hopkins Press (reprinted 1968, Greenwood Press, Publishers, New York).
+Grossmann, Reinhardt, 1983. The Categorial Structure of the World. Indiana Uni. Press.
+Grossmann, Reinhardt, 1992. The Existence of the World: An Introduction to Ontology. Routledge.
+Haaparanta, Leila and Koskinen, Heikki J., 2012. Categories of Being: Essays on Metaphysics and Logic. New York: Oxford University Press.
+Hoffman, J., and Rosenkrantz, G. S.,1994. Substance among other Categories. Cambridge Uni. Press.
+Edmund Husserl, 1962. Ideas: General Introduction to Pure Phenomenology. Boyce Gibson, W. R., trans. Collier.
+------, 2000. Logical Investigations, 2nd ed. Findlay, J. N., trans. Routledge.
+Johansson, Ingvar, 1989. Ontological Investigations. Routledge, 2nd ed. Ontos Verlag 2004.
+ Kahn, Charles H., 2009. Essays on Being, Oxford University Press.
+Immanuel Kant, 1998. Critique of Pure Reason. Guyer, Paul, and Wood, A. W., trans. Cambridge Uni. Press.
+Charles Sanders Peirce, 1992, 1998. The Essential Peirce, vols. 1,2. Houser, Nathan et al., eds. Indiana Uni. Press.
+Gilbert Ryle, 1949. The Concept of Mind. Uni. of Chicago Press.
+Wilfrid Sellars, 1974, "Toward a Theory of the Categories" in Essays in Philosophy and Its History. Reidel.
+Barry Smith, 2003. "Ontology" in Blackwell Guide to the Philosophy of Computing and Information. Blackwell.
+
+External links
+
+ Aristotle's Categories at MIT.
+ 
+ "Ontological Categories and How to Use Them" – Amie Thomasson.
+ "Recent Advances in Metaphysics" – E. J. Lowe.
+ Theory and History of Ontology – Raul Corazzon.
+
+Concepts in metaphysics
+Concrete is a composite material composed of aggregate bonded together with a fluid cement that cures over time. Concrete is the second-most-used substance in the world after water, and is the most widely used building material. Its usage worldwide, ton for ton, is twice that of steel, wood, plastics, and aluminium combined.
+
+When aggregate is mixed with dry Portland cement and water, the mixture forms a fluid slurry that is easily poured and molded into shape. The cement reacts with the water through a process called concrete hydration that hardens it over several hours to form a hard matrix that binds the materials together into a durable stone-like material that has many uses. This time allows concrete to not only be cast in forms, but also to have a variety of tooled processes performed. The hydration process is exothermic, which means ambient temperature plays a significant role in how long it takes concrete to set. Often, additives (such as pozzolans or superplasticizers) are included in the mixture to improve the physical properties of the wet mix, delay or accelerate the curing time, or otherwise change the finished material. Most concrete is poured with reinforcing materials (such as steel rebar) embedded to provide tensile strength, yielding reinforced concrete.
+
+In the past, lime based cement binders, such as lime putty, were often used but sometimes with other hydraulic cements, (water resistant) such as a calcium aluminate cement or with Portland cement to form Portland cement concrete (named for its visual resemblance to Portland stone). Many other non-cementitious types of concrete exist with other methods of binding aggregate together, including asphalt concrete with a bitumen binder, which is frequently used for road surfaces, and polymer concretes that use polymers as a binder. Concrete is distinct from mortar. Whereas concrete is itself a building material, mortar is a bonding agent that typically holds bricks, tiles and other masonry units together. Grout is another material associated with concrete and cement. It does not contain coarse aggregates and is usually either pourable or thixotropic, and is used to fill gaps between masonry components or coarse aggregate which has already been put in place. Some methods of concrete manufacture and repair involve pumping grout into the gaps to make up a solid mass in situ.
+
+Etymology 
+The word concrete comes from the Latin word "concretus" (meaning compact or condensed), the perfect passive participle of "concrescere", from "con-" (together) and "crescere" (to grow).
+
+History
+
+Ancient times
+Mayan concrete at the ruins of Uxmal (850-925 A.D.) is referenced in Incidents of Travel in the Yucatán by John L. Stephens. "The roof is flat and had been covered with cement". "The floors were cement, in some places hard, but, by long exposure, broken, and now crumbling under the feet." "But throughout the wall was solid, and consisting of large stones imbedded in mortar, almost as hard as rock."
+
+Small-scale production of concrete-like materials was pioneered by the Nabatean traders who occupied and controlled a series of oases and developed a small empire in the regions of southern Syria and northern Jordan from the 4th century BC. They discovered the advantages of hydraulic lime, with some self-cementing properties, by 700 BC. They built kilns to supply mortar for the construction of rubble masonry houses, concrete floors, and underground waterproof cisterns. They kept the cisterns secret as these enabled the Nabataeans to thrive in the desert. Some of these structures survive to this day.
+
+Classical era
+
+In the Ancient Egyptian and later Roman eras, builders discovered that adding volcanic ash to lime allowed the mix to set underwater. They discovered the pozzolanic reaction.
+
+Concrete floors were found in the royal palace of Tiryns, Greece, which dates roughly to 1400-1200 BC. Lime mortars were used in Greece, such as in Crete and Cyprus, in 800 BC. The Assyrian Jerwan Aqueduct (688 BC) made use of waterproof concrete. Concrete was used for construction in many ancient structures.
+
+The Romans used concrete extensively from 300 BC to 476 AD. During the Roman Empire, Roman concrete (or opus caementicium) was made from quicklime, pozzolana and an aggregate of pumice. Its widespread use in many Roman structures, a key event in the history of architecture termed the Roman architectural revolution, freed Roman construction from the restrictions of stone and brick materials. It enabled revolutionary new designs in terms of both structural complexity and dimension. The Colosseum in Rome was built largely of concrete, and the Pantheon has the world's largest unreinforced concrete dome.
+
+Concrete, as the Romans knew it, was a new and revolutionary material. Laid in the shape of arches, vaults and domes, it quickly hardened into a rigid mass, free from many of the internal thrusts and strains that troubled the builders of similar structures in stone or brick.
+
+Modern tests show that opus caementicium had as much compressive strength as modern Portland-cement concrete (ca. ). However, due to the absence of reinforcement, its tensile strength was far lower than modern reinforced concrete, and its mode of application also differed:
+
+Modern structural concrete differs from Roman concrete in two important details. First, its mix consistency is fluid and homogeneous, allowing it to be poured into forms rather than requiring hand-layering together with the placement of aggregate, which, in Roman practice, often consisted of rubble. Second, integral reinforcing steel gives modern concrete assemblies great strength in tension, whereas Roman concrete could depend only upon the strength of the concrete bonding to resist tension.
+
+The long-term durability of Roman concrete structures has been found to be due to its use of pyroclastic (volcanic) rock and ash, whereby the crystallization of strätlingite (a specific and complex calcium aluminosilicate hydrate) and the coalescence of this and similar calcium–aluminium-silicate–hydrate cementing binders helped give the concrete a greater degree of fracture resistance even in seismically active environments. Roman concrete is significantly more resistant to erosion by seawater than modern concrete; it used pyroclastic materials which react with seawater to form Al-tobermorite crystals over time.
+
+The widespread use of concrete in many Roman structures ensured that many survive to the present day. The Baths of Caracalla in Rome are just one example. Many Roman aqueducts and bridges, such as the magnificent Pont du Gard in southern France, have masonry cladding on a concrete core, as does the dome of the Pantheon.
+
+Middle Ages
+After the Roman Empire, the use of burned lime and pozzolana was greatly reduced. Low kiln temperatures in the burning of lime, lack of pozzolana, and poor mixing all contributed to a decline in the quality of concrete and mortar. From the 11th century, the increased use of stone in church and castle construction led to an increased demand for mortar. Quality began to improve in the 12th century through better grinding and sieving. Medieval lime mortars and concretes were non-hydraulic and were used for binding masonry, "hearting" (binding rubble masonry cores) and foundations. Bartholomaeus Anglicus in his De proprietatibus rerum (1240) describes the making of mortar. In an English translation from 1397, it reads "lyme ... is a stone brent; by medlynge thereof with sonde and water sement is made". From the 14th century, the quality of mortar was again excellent, but only from the 17th century was pozzolana commonly added.
+
+The Canal du Midi was built using concrete in 1670.
+
+Industrial era
+
+Perhaps the greatest step forward in the modern use of concrete was Smeaton's Tower, built by British engineer John Smeaton in Devon, England, between 1756 and 1759. This third Eddystone Lighthouse pioneered the use of hydraulic lime in concrete, using pebbles and powdered brick as aggregate.
+
+A method for producing Portland cement was developed in England and patented by Joseph Aspdin in 1824. Aspdin chose the name for its similarity to Portland stone, which was quarried on the Isle of Portland in Dorset, England. His son William continued developments into the 1840s, earning him recognition for the development of "modern" Portland cement.
+
+Reinforced concrete was invented in 1849 by Joseph Monier. and the first reinforced concrete house was built by François Coignet in 1853.
+The first concrete reinforced bridge was designed and built by Joseph Monier in 1875.
+
+Prestressed concrete and post-tensioned concrete were pioneered by Eugène Freyssinet, a French  structural and civil engineer. Concrete components or structures are compressed by tendon cables during, or after, their fabrication in order to strengthen them against tensile forces developing when put in service. Freyssinet patented the technique on 2 October 1928.
+
+Composition
+Concrete is an artificial composite material, comprising a matrix of cementitious binder (typically Portland cement paste or asphalt) and a dispersed phase or "filler" of aggregate (typically a rocky material, loose stones, and sand). The binder "glues" the filler together to form a synthetic conglomerate. Many types of concrete are available, determined by the formulations of binders and the types of aggregate used to suit the application of the engineered material. These variables determine strength and density, as well as chemical and thermal resistance of the finished product.
+
+Construction aggregates consist of large chunks of material in a concrete mix, generally a coarse gravel or crushed rocks such as limestone, or granite, along with finer materials such as sand.
+
+Cement paste, most commonly made of Portland cement, is the most prevalent kind of concrete binder. For cementitious binders, water is mixed with the dry cement powder and aggregate, which produces a semi-liquid slurry (paste) that can be shaped, typically by pouring it into a form. The concrete solidifies and hardens through a chemical process called hydration. The water reacts with the cement, which bonds the other components together, creating a robust, stone-like material. Other cementitious materials, such as fly ash and slag cement, are sometimes added—either pre-blended with the cement or directly as a concrete component—and become a part of the binder for the aggregate. Fly ash and slag can enhance some properties of concrete such as fresh properties and durability. Alternatively, other materials can also be used as a concrete binder: the most prevalent substitute is asphalt, which is used as the binder in asphalt concrete.
+
+Admixtures are added to modify the cure rate or properties of the material. Mineral admixtures use recycled materials as concrete ingredients. Conspicuous materials include fly ash, a by-product of coal-fired power plants; ground granulated blast furnace slag, a by-product of steelmaking; and silica fume, a by-product of industrial electric arc furnaces.
+
+Structures employing Portland cement concrete usually include steel reinforcement because this type of concrete can be formulated with high compressive strength, but always has lower tensile strength. Therefore, it is usually reinforced with materials that are strong in tension, typically steel rebar.
+
+The mix design depends on the type of structure being built, how the concrete is mixed and delivered, and how it is placed to form the structure.
+
+Cement
+
+Portland cement is the most common type of cement in general usage. It is a basic ingredient of concrete, mortar, and many plasters. British masonry worker Joseph Aspdin patented Portland cement in 1824. It was named because of the similarity of its color to Portland limestone, quarried from the English Isle of Portland and used extensively in London architecture. It consists of a mixture of calcium silicates (alite, belite), aluminates and ferrites—compounds which combine calcium, silicon, aluminium and iron in forms which will react with water. Portland cement and similar materials are made by heating limestone (a source of calcium) with clay or shale (a source of silicon, aluminium and iron) and grinding this product (called clinker) with a source of sulfate (most commonly gypsum).
+
+In modern cement kilns, many advanced features are used to lower the fuel consumption per ton of clinker produced. Cement kilns are extremely large, complex, and inherently dusty industrial installations, and have emissions which must be controlled. Of the various ingredients used to produce a given quantity of concrete, the cement is the most energetically expensive. Even complex and efficient kilns require 3.3 to 3.6 gigajoules of energy to produce a ton of clinker and then grind it into cement. Many kilns can be fueled with difficult-to-dispose-of wastes, the most common being used tires. The extremely high temperatures and long periods of time at those temperatures allows cement kilns to efficiently and completely burn even difficult-to-use fuels.
+
+Water
+Combining water with a cementitious material forms a cement paste by the process of hydration. The cement paste glues the aggregate together, fills voids within it, and makes it flow more freely.
+
+As stated by Abrams' law, a lower water-to-cement ratio yields a stronger, more durable concrete, whereas more water gives a freer-flowing concrete with a higher slump. Impure water used to make concrete can cause problems when setting or in causing premature failure of the structure.
+
+Portland cement consists of five major compounds of calcium silicates and aluminates ranging from 5 to 50% in weight, which all undergo hydration to contribute to final material's strength. Thus, the hydration of cement involves many reactions, often occurring at the same time. As the reactions proceed, the products of the cement hydration process gradually bond together the individual sand and gravel particles and other components of the concrete to form a solid mass.
+
+Hydration of tricalcium silicate 
+ Cement chemist notation:  C3S + H → C-S-H + CH + heat
+ Standard notation:  Ca3SiO5 + H2O → CaO・SiO2・H2O (gel) + Ca(OH)2 + heat
+ Balanced:  2 Ca3SiO5 + 7 H2O → 3 CaO・2 SiO2・4 H2O (gel) + 3 Ca(OH)2 + heat
+  (approximately as the exact ratios of CaO, SiO2 and H2O in C-S-H can vary)
+
+Due to the nature of the chemical bonds created in these reactions and the final characteristics of the hardened cement paste formed, the process of cement hydration is considered irreversible.
+
+Aggregates
+
+Fine and coarse aggregates make up the bulk of a concrete mixture. Sand, natural gravel, and crushed stone are used mainly for this purpose. Recycled aggregates (from construction, demolition, and excavation waste) are increasingly used as partial replacements for natural aggregates, while a number of manufactured aggregates, including air-cooled blast furnace slag and bottom ash are also permitted.
+
+The size distribution of the aggregate determines how much binder is required. Aggregate with a very even size distribution has the biggest gaps whereas adding aggregate with smaller particles tends to fill these gaps. The binder must fill the gaps between the aggregate as well as paste the surfaces of the aggregate together, and is typically the most expensive component. Thus, variation in sizes of the aggregate reduces the cost of concrete. The aggregate is nearly always stronger than the binder, so its use does not negatively affect the strength of the concrete.
+
+Redistribution of aggregates after compaction often creates non-homogeneity due to the influence of vibration. This can lead to strength gradients.
+
+Decorative stones such as quartzite, small river stones or crushed glass are sometimes added to the surface of concrete for a decorative "exposed aggregate" finish, popular among landscape designers.
+
+Admixtures
+Admixtures are materials in the form of powder or fluids that are added to the concrete to give it certain characteristics not obtainable with plain concrete mixes. Admixtures are defined as additions "made as the concrete mix is being prepared". The most common admixtures are retarders and accelerators. In normal use, admixture dosages are less than 5% by mass of cement and are added to the concrete at the time of batching/mixing. (See  below.) The common types of admixtures are as follows:
+ Accelerators speed up the hydration (hardening) of the concrete. Typical materials used are calcium chloride, calcium nitrate and sodium nitrate. However, use of chlorides may cause corrosion in steel reinforcing and is prohibited in some countries, so that nitrates may be favored, even though they are less effective than the chloride salt. Accelerating admixtures are especially useful for modifying the properties of concrete in cold weather.
+ Air entraining agents add and entrain tiny air bubbles in the concrete, which reduces damage during freeze-thaw cycles, increasing durability. However, entrained air entails a tradeoff with strength, as each 1% of air may decrease compressive strength by 5%. If too much air becomes trapped in the concrete as a result of the mixing process, defoamers can be used to encourage the air bubble to agglomerate, rise to the surface of the wet concrete and then disperse.
+ Bonding agents are used to create a bond between old and new concrete (typically a type of polymer) with wide temperature tolerance and corrosion resistance.
+ Corrosion inhibitors are used to minimize the corrosion of steel and steel bars in concrete.
+ Crystalline admixtures are typically added during batching of the concrete to lower permeability. The reaction takes place when exposed to water and un-hydrated cement particles to form insoluble needle-shaped crystals, which fill capillary pores and micro-cracks in the concrete to block pathways for water and waterborne contaminates. Concrete with crystalline admixture can expect to self-seal as constant exposure to water will continuously initiate crystallization to ensure permanent waterproof protection.
+ Pigments can be used to change the color of concrete, for aesthetics.
+ Plasticizers increase the workability of plastic, or "fresh", concrete, allowing it to be placed more easily, with less consolidating effort. A typical plasticizer is lignosulfonate. Plasticizers can be used to reduce the water content of a concrete while maintaining workability and are sometimes called water-reducers due to this use. Such treatment improves its strength and durability characteristics.
+ Superplasticizers (also called high-range water-reducers) are a class of plasticizers that have fewer deleterious effects and can be used to increase workability more than is practical with traditional plasticizers. Superplasticizers are used to increase compressive strength. It increases the workability of the concrete and lowers the need for water content by 15–30%. 
+ Pumping aids improve pumpability, thicken the paste and reduce separation and bleeding.
+ Retarders slow the hydration of concrete and are used in large or difficult pours where partial setting is undesirable before completion of the pour. Typical polyol retarders are sugar, sucrose, sodium gluconate, glucose, citric acid, and tartaric acid.
+
+Mineral admixtures and blended cements
+
+Inorganic materials that have pozzolanic or latent hydraulic properties, these very fine-grained materials are added to the concrete mix to improve the properties of concrete (mineral admixtures), or as a replacement for Portland cement (blended cements). Products which incorporate limestone, fly ash, blast furnace slag, and other useful materials with pozzolanic properties into the mix, are being tested and used. These developments are ever growing in relevance to minimize the impacts caused by cement use, notorious for being one of the largest producers (at about 5 to 10%) of global greenhouse gas emissions. The use of alternative materials also is capable of lowering costs, improving concrete properties, and recycling wastes, the latest being relevant for circular economy aspects of the construction industry, whose demand is ever growing with greater impacts on raw material extraction, waste generation and landfill practices.
+ Fly ash: A by-product of coal-fired electric generating plants, it is used to partially replace Portland cement (by up to 60% by mass). The properties of fly ash depend on the type of coal burnt. In general, siliceous fly ash is pozzolanic, while calcareous fly ash has latent hydraulic properties.
+ Ground granulated blast furnace slag (GGBFS or GGBS): A by-product of steel production is used to partially replace Portland cement (by up to 80% by mass). It has latent hydraulic properties.
+ Silica fume: A by-product of the production of silicon and ferrosilicon alloys. Silica fume is similar to fly ash, but has a particle size 100 times smaller. This results in a higher surface-to-volume ratio and a much faster pozzolanic reaction. Silica fume is used to increase strength and durability of concrete, but generally requires the use of superplasticizers for workability.
+ High reactivity metakaolin (HRM): Metakaolin produces concrete with strength and durability similar to concrete made with silica fume. While silica fume is usually dark gray or black in color, high-reactivity metakaolin is usually bright white in color, making it the preferred choice for architectural concrete where appearance is important.
+ Carbon nanofibers can be added to concrete to enhance compressive strength and gain a higher Young's modulus, and also to improve the electrical properties required for strain monitoring, damage evaluation and self-health monitoring of concrete. Carbon fiber has many advantages in terms of mechanical and electrical properties (e.g., higher strength) and self-monitoring behavior due to the high tensile strength and high electrical conductivity.
+ Carbon products have been added to make concrete electrically conductive, for deicing purposes.
+ New research from Japan's University of Kitakyushu shows that a washed and dried recycled mix of used diapers can be an environmental solution to producing less landfill and using less sand in concrete production. A model home was built in Indonesia to test the strength and durability of the new diaper-cement composite.
+
+Production
+
+Concrete production is the process of mixing together the various ingredients—water, aggregate, cement, and any additives—to produce concrete. Concrete production is time-sensitive. Once the ingredients are mixed, workers must put the concrete in place before it hardens. In modern usage, most concrete production takes place in a large type of industrial facility called a concrete plant, or often a batch plant. The usual method of placement is casting in formwork, which holds the mix in shape until it has set enough to hold its shape unaided.
+
+In general usage, concrete plants come in two main types, ready mix plants and central mix plants. A ready-mix plant mixes all the ingredients except water, while a central mix plant mixes all the ingredients including water. A central-mix plant offers more accurate control of the concrete quality through better measurements of the amount of water added, but must be placed closer to the work site where the concrete will be used, since hydration begins at the plant.
+
+A concrete plant consists of large storage hoppers for various reactive ingredients like cement, storage for bulk ingredients like aggregate and water, mechanisms for the addition of various additives and amendments, machinery to accurately weigh, move, and mix some or all of those ingredients, and facilities to dispense the mixed concrete, often to a concrete mixer truck.
+
+Modern concrete is usually prepared as a viscous fluid, so that it may be poured into forms, which are containers erected in the field to give the concrete its desired shape. Concrete formwork can be prepared in several ways, such as slip forming and steel plate construction. Alternatively, concrete can be mixed into dryer, non-fluid forms and used in factory settings to manufacture precast concrete products.
+
+A wide variety of equipment is used for processing concrete, from hand tools to heavy industrial machinery. Whichever equipment builders use, however, the objective is to produce the desired building material; ingredients must be properly mixed, placed, shaped, and retained within time constraints. Any interruption in pouring the concrete can cause the initially placed material to begin to set before the next batch is added on top. This creates a horizontal plane of weakness called a cold joint between the two batches. Once the mix is where it should be, the curing process must be controlled to ensure that the concrete attains the desired attributes. During concrete preparation, various technical details may affect the quality and nature of the product.
+
+Design mix
+Design mix ratios are decided by an engineer after analyzing the properties of the specific ingredients being used. Instead of using a 'nominal mix' of 1 part cement, 2 parts sand, and 4 parts aggregate (the second example from above), a civil engineer will custom-design a concrete mix to exactly meet the requirements of the site and conditions, setting material ratios and often designing an admixture package to fine-tune the properties or increase the performance envelope of the mix. Design-mix concrete can have very broad specifications that cannot be met with more basic nominal mixes, but the involvement of the engineer often increases the cost of the concrete mix.
+
+Concrete Mixes are primarily divided into nominal mix, standard mix and design mix.
+
+Nominal mix ratios are given in volume of . Nominal mixes are a simple, fast way of getting a basic idea of the properties of the finished concrete without having to perform testing in advance.
+
+Various governing bodies (such as British Standards) define nominal mix ratios into a number of grades, usually ranging from lower compressive strength to higher compressive strength. The grades usually indicate the 28-day cube strength.
+
+Mixing
+
+Thorough mixing is essential to produce uniform, high-quality concrete.
+
+ has shown that the mixing of cement and water into a paste before combining these materials with aggregates can increase the compressive strength of the resulting concrete. The paste is generally mixed in a , shear-type mixer at a w/c (water to cement ratio) of 0.30 to 0.45 by mass. The cement paste premix may include admixtures such as accelerators or retarders, superplasticizers, pigments, or silica fume. The premixed paste is then blended with aggregates and any remaining batch water and final mixing is completed in conventional concrete mixing equipment.
+
+Sample analysis – Workability
+
+Workability is the ability of a fresh (plastic) concrete mix to fill the form/mold properly with the desired work (pouring, pumping, spreading, tamping, vibration) and without reducing the concrete's quality. Workability depends on water content, aggregate (shape and size distribution), cementitious content and age (level of hydration) and can be modified by adding chemical admixtures, like superplasticizer. Raising the water content or adding chemical admixtures increases concrete workability. Excessive water leads to increased bleeding or segregation of aggregates (when the cement and aggregates start to separate), with the resulting concrete having reduced quality. Changes in gradation can also affect workability of the concrete, although a wide range of gradation can be used for various applications. An undesirable gradation can mean using a large aggregate that is too large for the size of the formwork, or which has too few smaller aggregate grades to serve to fill the gaps between the larger grades, or using too little or too much sand for the same reason, or using too little water, or too much cement, or even using jagged crushed stone instead of smoother round aggregate such as pebbles. Any combination of these factors and others may result in a mix which is too harsh, i.e., which does not flow or spread out smoothly, is difficult to get into the formwork, and which is difficult to surface finish.
+
+Workability can be measured by the concrete slump test, a simple measure of the plasticity of a fresh batch of concrete following the ASTM C 143 or EN 12350-2 test standards. Slump is normally measured by filling an "Abrams cone" with a sample from a fresh batch of concrete. The cone is placed with the wide end down onto a level, non-absorptive surface. It is then filled in three layers of equal volume, with each layer being tamped with a steel rod to consolidate the layer. When the cone is carefully lifted off, the enclosed material slumps a certain amount, owing to gravity. A relatively dry sample slumps very little, having a slump value of one or two inches (25 or 50 mm) out of . A relatively wet concrete sample may slump as much as eight inches. Workability can also be measured by the flow table test.
+
+Slump can be increased by addition of chemical admixtures such as plasticizer or superplasticizer without changing the water-cement ratio. Some other admixtures, especially air-entraining admixture, can increase the slump of a mix.
+
+High-flow concrete, like self-consolidating concrete, is tested by other flow-measuring methods. One of these methods includes placing the cone on the narrow end and observing how the mix flows through the cone while it is gradually lifted.
+
+After mixing, concrete is a fluid and can be pumped to the location where needed.
+
+Curing
+
+Maintaining optimal conditions for cement hydration
+Concrete must be kept moist during curing in order to achieve optimal strength and durability. During curing hydration occurs, allowing calcium-silicate hydrate (C-S-H) to form. Over 90% of a mix's final strength is typically reached within four weeks, with the remaining 10% achieved over years or even decades. The conversion of calcium hydroxide in the concrete into calcium carbonate from absorption of CO2 over several decades further strengthens the concrete and makes it more resistant to damage. This carbonation reaction, however, lowers the pH of the cement pore solution and can corrode the reinforcement bars.
+
+Hydration and hardening of concrete during the first three days is critical. Abnormally fast drying and shrinkage due to factors such as evaporation from wind during placement may lead to increased tensile stresses at a time when it has not yet gained sufficient strength, resulting in greater shrinkage cracking. The early strength of the concrete can be increased if it is kept damp during the curing process. Minimizing stress prior to curing minimizes cracking. High-early-strength concrete is designed to hydrate faster, often by increased use of cement that increases shrinkage and cracking. The strength of concrete changes (increases) for up to three years. It depends on cross-section dimension of elements and conditions of structure exploitation. Addition of short-cut polymer fibers can improve (reduce) shrinkage-induced stresses during curing and increase early and ultimate compression strength.
+
+Properly curing concrete leads to increased strength and lower permeability and avoids cracking where the surface dries out prematurely. Care must also be taken to avoid freezing or overheating due to the exothermic setting of cement. Improper curing can cause scaling, reduced strength, poor abrasion resistance and cracking.
+
+Curing techniques avoiding water loss by evaporation
+During the curing period, concrete is ideally maintained at controlled temperature and humidity. To ensure full hydration during curing, concrete slabs are often sprayed with "curing compounds" that create a water-retaining film over the concrete. Typical films are made of wax or related hydrophobic compounds. After the concrete is sufficiently cured, the film is allowed to abrade from the concrete through normal use.
+
+Traditional conditions for curing involve spraying or ponding the concrete surface with water. The adjacent picture shows one of many ways to achieve this, ponding—submerging setting concrete in water and wrapping in plastic to prevent dehydration. Additional common curing methods include wet burlap and plastic sheeting covering the fresh concrete.
+
+For higher-strength applications, accelerated curing techniques may be applied to the concrete. A common technique involves heating the poured concrete with steam, which serves to both keep it damp and raise the temperature so that the hydration process proceeds more quickly and more thoroughly.
+
+Alternative types
+
+Asphalt
+
+Asphalt concrete (commonly called asphalt, blacktop, or pavement in North America, and tarmac, bitumen macadam, or rolled asphalt in the United Kingdom and the Republic of Ireland) is a composite material commonly used to surface roads, parking lots, airports, as well as the core of embankment dams. Asphalt mixtures have been used in pavement construction since the beginning of the twentieth century. It consists of mineral aggregate bound together with asphalt, laid in layers, and compacted. The process was refined and enhanced by Belgian inventor and U.S. immigrant Edward De Smedt.
+
+The terms asphalt (or asphaltic) concrete, bituminous asphalt concrete, and bituminous mixture are typically used only in engineering and construction documents, which define concrete as any composite material composed of mineral aggregate adhered with a binder. The abbreviation, AC, is sometimes used for asphalt concrete but can also denote asphalt content or asphalt cement, referring to the liquid asphalt portion of the composite material.
+
+Graphene enhanced concrete 
+
+Graphene enhanced concretes are standard designs of concrete mixes, except that during the cement-mixing or production process, a small amount of chemically engineered graphene  is added. These enhanced graphene concretes are designed around the concrete application.
+
+Microbial 
+Bacteria such as Bacillus pasteurii, Bacillus pseudofirmus, Bacillus cohnii, Sporosarcina pasteuri, and Arthrobacter crystallopoietes increase the compression strength of concrete through their biomass. However some forms of bacteria can also be concrete-destroying.  Bacillus sp. CT-5. can reduce corrosion of reinforcement in reinforced concrete by up to four times. Sporosarcina pasteurii reduces water and chloride permeability. B. pasteurii increases resistance to acid.  Bacillus pasteurii and B. sphaericuscan induce calcium carbonate precipitation in the surface of cracks, adding compression strength.
+
+Nanoconcrete 
+
+Nanoconcrete (also spelled "nano concrete"' or "nano-concrete") is a class of materials that contains Portland cement particles that are no greater than 100 μm and particles of silica no greater than 500 μm, which fill voids that would otherwise occur in normal concrete, thereby substantially increasing the material's strength. It is widely used in foot and highway bridges where high flexural and compressive strength are indicated.
+
+Pervious 
+
+Pervious concrete is a mix of specially graded coarse aggregate, cement, water, and little-to-no fine aggregates. This concrete is also known as "no-fines" or porous concrete. Mixing the ingredients in a carefully controlled process creates a paste that coats and bonds the aggregate particles. The hardened concrete contains interconnected air voids totaling approximately 15 to 25 percent. Water runs through the voids in the pavement to the soil underneath. Air entrainment admixtures are often used in freeze-thaw climates to minimize the possibility of frost damage. Pervious concrete also permits rainwater to filter through roads and parking lots, to recharge aquifers, instead of contributing to runoff and flooding.
+
+Polymer 
+
+Polymer concretes are mixtures of aggregate and any of various polymers and may be reinforced. The cement is costlier than lime-based cements, but polymer concretes nevertheless have advantages; they have significant tensile strength even without reinforcement, and they are largely impervious to water. Polymer concretes are frequently used for the repair and construction of other applications, such as drains.
+
+Volcanic 
+Volcanic concrete substitutes volcanic rock for the limestone that is burned to form clinker. It consumes a similar amount of energy, but does not directly emit carbon as a byproduct. Volcanic rock/ash are used as supplementary cementitious materials in concrete to improve the resistance to sulfate, chloride and alkali silica reaction due to pore refinement. Also, they are generally cost effective in comparison to other aggregates, good for semi and light weight concretes, and good for thermal and acoustic insulation.
+
+Pyroclastic materials, such as pumice, scoria, and ashes are formed from cooling magma during explosive volcanic eruptions. They are used as supplementary cementitious materials (SCM) or as aggregates for cements and concretes. They have been extensively used since ancient times to produce materials for building applications. For example, pumice and other volcanic glasses were added as a natural pozzolanic material for mortars and plasters during the construction of the Villa San Marco in the Roman period (89 BC – 79 AD), which remain one of the best-preserved otium villae of the Bay of Naples in Italy.
+
+Waste light
+
+Waste light is form of polymer modified concrete. The specific polymer admixture allows the replacement of all the traditional aggregates (gravel, sand, stone) by any mixture of solid waste materials in the grain size of 3–10 mm to form a low-compressive-strength (3–20 N/mm2) product for road and building construction. One cubic meter of waste light concrete contains 1.1–1.3 m3 of shredded waste and no other aggregates.
+
+Sulfur concrete 
+
+Sulfur concrete is a special concrete that uses sulfur as a binder and does not require cement or water.
+
+Properties
+
+Concrete has relatively high compressive strength, but much lower tensile strength. Therefore, it is usually reinforced with materials that are strong in tension (often steel). The elasticity of concrete is relatively constant at low stress levels but starts decreasing at higher stress levels as matrix cracking develops. Concrete has a very low coefficient of thermal expansion and shrinks as it matures. All concrete structures crack to some extent, due to shrinkage and tension. Concrete that is subjected to long-duration forces is prone to creep.
+
+Tests can be performed to ensure that the properties of concrete correspond to specifications for the application.
+
+The ingredients affect the strengths of the material. Concrete strength values are usually specified as the lower-bound compressive strength of either a cylindrical or cubic specimen as determined by standard test procedures.
+
+The strengths of concrete is dictated by its function. Very low-strength— or less—concrete may be used when the concrete must be lightweight. Lightweight concrete is often achieved by adding air, foams, or lightweight aggregates, with the side effect that the strength is reduced. For most routine uses,  concrete is often used.  concrete is readily commercially available as a more durable, although more expensive, option. Higher-strength concrete is often used for larger civil projects. Strengths above  are often used for specific building elements. For example, the lower floor columns of high-rise concrete buildings may use concrete of  or more, to keep the size of the columns small. Bridges may use long beams of high-strength concrete to lower the number of spans required. Occasionally, other structural needs may require high-strength concrete. If a structure must be very rigid, concrete of very high strength may be specified, even much stronger than is required to bear the service loads. Strengths as high as  have been used commercially for these reasons.
+
+Energy efficiency
+The cement produced for making concrete accounts for about 8% of worldwide  emissions per year (compared to, e.g., global aviation at 1.9%). The two largest sources of  are produced by the cement manufacturing process, arising from (1) the decarbonation reaction of limestone in the cement kiln (T ≈ 950 °C), and (2) from the combustion of fossil fuel to reach the sintering temperature (T ≈ 1450 °C) of cement clinker in the kiln. The energy required for extracting, crushing, and mixing the raw materials (construction aggregates used in the concrete production, and also limestone and clay feeding the cement kiln) is lower. Energy requirement for transportation of ready-mix concrete is also lower because it is produced nearby the construction site from local resources, typically manufactured within 100 kilometers of the job site. The overall embodied energy of concrete at roughly 1 to 1.5 megajoules per kilogram is therefore lower than for many structural and construction materials.
+
+Once in place, concrete offers a great energy efficiency over the lifetime of a building. Concrete walls leak air far less than those made of wood frames. Air leakage accounts for a large percentage of energy loss from a home. The thermal mass properties of concrete increase the efficiency of both residential and commercial buildings. By storing and releasing the energy needed for heating or cooling, concrete's thermal mass delivers year-round benefits by reducing temperature swings inside and minimizing heating and cooling costs. While insulation reduces energy loss through the building envelope, thermal mass uses walls to store and release energy. Modern concrete wall systems use both external insulation and thermal mass to create an energy-efficient building. Insulating concrete forms (ICFs) are hollow blocks or panels made of either insulating foam or rastra that are stacked to form the shape of the walls of a building and then filled with reinforced concrete to create the structure.
+
+Fire safety
+
+Concrete buildings are more resistant to fire than those constructed using steel frames, since concrete has lower heat conductivity than steel and can thus last longer under the same fire conditions. Concrete is sometimes used as a fire protection for steel frames, for the same effect as above. Concrete as a fire shield, for example Fondu fyre, can also be used in extreme environments like a missile launch pad.
+
+Options for non-combustible construction include floors, ceilings and roofs made of cast-in-place and hollow-core precast concrete. For walls, concrete masonry technology and Insulating Concrete Forms (ICFs) are additional options. ICFs are hollow blocks or panels made of fireproof insulating foam that are stacked to form the shape of the walls of a building and then filled with reinforced concrete to create the structure.
+
+Concrete also provides good resistance against externally applied forces such as high winds, hurricanes, and tornadoes owing to its lateral stiffness, which results in minimal horizontal movement. However, this stiffness can work against certain types of concrete structures, particularly where a relatively higher flexing structure is required to resist more extreme forces.
+
+Earthquake safety
+As discussed above, concrete is very strong in compression, but weak in tension. Larger earthquakes can generate very large shear loads on structures. These shear loads subject the structure to both tensile and compressional loads. Concrete structures without reinforcement, like other unreinforced masonry structures, can fail during severe earthquake shaking. Unreinforced masonry structures constitute one of the largest earthquake risks globally. These risks can be reduced through seismic retrofitting of at-risk buildings, (e.g. school buildings in Istanbul, Turkey).
+
+Construction with concrete
+
+Concrete is one of the most durable building materials. It provides superior fire resistance compared with wooden construction and gains strength over time. Structures made of concrete can have a long service life. Concrete is used more than any other artificial material in the world. As of 2006, about 7.5 billion cubic meters of concrete are made each year, more than one cubic meter for every person on Earth.
+
+Reinforced concrete 
+
+The use of reinforcement, in the form of iron was introduced in the 1850s by French industrialist François Coignet, and it was not until the 1880s that German civil engineer G. A. Wayss used steel as reinforcement. Concrete is a relatively brittle material that is strong under compression but less in tension. Plain, unreinforced concrete is unsuitable for many structures as it is relatively poor at withstanding stresses induced by vibrations, wind loading, and so on. Hence, to increase its overall strength, steel rods, wires, mesh or cables can be embedded in concrete before it is set. This reinforcement, often known as rebar, resists tensile forces.
+
+Reinforced concrete (RC) is a versatile composite and one of the most widely used materials in modern construction. It is made up of different constituent materials with very different properties that complement each other. In the case of reinforced concrete, the component materials are almost always concrete and steel. These two materials form a strong bond together and are able to resist a variety of applied forces, effectively acting as a single structural element.
+
+Reinforced concrete can be precast or cast-in-place (in situ) concrete, and is used in a wide range of applications such as; slab, wall, beam, column, foundation, and frame construction. Reinforcement is generally placed in areas of the concrete that are likely to be subject to tension, such as the lower portion of beams. Usually, there is a minimum of 50 mm cover, both above and below the steel reinforcement, to resist spalling and corrosion which can lead to structural instability. Other types of non-steel reinforcement, such as Fibre-reinforced concretes are used for specialized applications, predominately as a means of controlling cracking.
+
+Precast concrete 
+
+Precast concrete is concrete which is cast in one place for use elsewhere and is a mobile material. The largest part of precast production is carried out in the works of specialist suppliers, although in some instances, due to economic and geographical factors, scale of product or difficulty of access, the elements are cast on or adjacent to the construction site. Precasting offers considerable advantages because it is carried out in a controlled environment, protected from the elements, but the downside of this is the contribution to greenhouse gas emission from transportation to the construction site.
+
+Advantages to be achieved by employing precast concrete:
+ Preferred dimension schemes exist, with elements of tried and tested designs available from a catalogue.
+ Major savings in time result from manufacture of structural elements apart from the series of events which determine overall duration of the construction, known by planning engineers as the 'critical path'.
+ Availability of Laboratory facilities capable of the required control tests, many being certified for specific testing in accordance with National Standards.
+ Equipment with capability suited to specific types of production such as stressing beds with appropriate capacity, moulds and machinery dedicated to particular products.
+ High-quality finishes achieved direct from the mould eliminate the need for interior decoration and ensure low maintenance costs.
+
+Mass structures
+
+Due to cement's exothermic chemical reaction while setting up, large concrete structures such as dams, navigation locks, large mat foundations, and large breakwaters generate excessive heat during hydration and associated expansion. To mitigate these effects, post-cooling is commonly applied during construction. An early example at Hoover Dam used a network of pipes between vertical concrete placements to circulate cooling water during the curing process to avoid damaging overheating. Similar systems are still used; depending on volume of the pour, the concrete mix used, and ambient air temperature, the cooling process may last for many months after the concrete is placed. Various methods also are used to pre-cool the concrete mix in mass concrete structures.
+
+Another approach to mass concrete structures that minimizes cement's thermal by-product is the use of roller-compacted concrete, which uses a dry mix which has a much lower cooling requirement than conventional wet placement. It is deposited in thick layers as a semi-dry material then roller compacted into a dense, strong mass.
+
+Surface finishes
+
+Raw concrete surfaces tend to be porous and have a relatively uninteresting appearance. Many finishes can be applied to improve the appearance and preserve the surface against staining, water penetration, and freezing.
+
+Examples of improved appearance include stamped concrete where the wet concrete has a pattern impressed on the surface, to give a paved, cobbled or brick-like effect, and may be accompanied with coloration. Another popular effect for flooring and table tops is polished concrete where the concrete is polished optically flat with diamond abrasives and sealed with polymers or other sealants.
+
+Other finishes can be achieved with chiseling, or more conventional techniques such as painting or covering it with other materials.
+
+The proper treatment of the surface of concrete, and therefore its characteristics, is an important stage in the construction and renovation of architectural structures.
+
+Prestressed structures
+
+Prestressed concrete is a form of reinforced concrete that builds in compressive stresses during construction to oppose tensile stresses experienced in use. This can greatly reduce the weight of beams or slabs, by
+better distributing the stresses in the structure to make optimal use of the reinforcement. For example, a horizontal beam tends to sag. Prestressed reinforcement along the bottom of the beam counteracts this.
+In pre-tensioned concrete, the prestressing is achieved by using steel or polymer tendons or bars that are subjected to a tensile force prior to casting, or for post-tensioned concrete, after casting.
+
+There are two different systems being used:
+ Pretensioned concrete is almost always precast, and contains steel wires (tendons) that are held in tension while the concrete is placed and sets around them.
+ Post-tensioned concrete has ducts through it. After the concrete has gained strength, tendons are pulled through the ducts and stressed. The ducts are then filled with grout. Bridges built in this way have experienced considerable corrosion of the tendons, so external post-tensioning may now be used in which the tendons run along the outer surface of the concrete.
+
+More than  of highways in the United States are paved with this material. Reinforced concrete, prestressed concrete and precast concrete are the most widely used types of concrete functional extensions in modern days. For more information see Brutalist architecture.
+
+Placement
+Once mixed, concrete is typically transported to the place where it is intended to become a structural item. Various methods of transportation and placement are used depending on the distances involve, quantity needed, and other details of application. Large amounts are often transported by truck, poured free under gravity or through a tremie, or pumped through a pipe. Smaller amounts may be carried in a skip (a metal container which can be tilted or opened to release the contents, usually transported by crane or hoist), or wheelbarrow, or carried in toggle bags for manual placement underwater.
+
+Cold weather placement
+
+Extreme weather conditions (extreme heat or cold; windy conditions, and humidity variations) can significantly alter the quality of concrete. Many precautions are observed in cold weather placement. Low temperatures significantly slow the chemical reactions involved in hydration of cement, thus affecting the strength development. Preventing freezing is the most important precaution, as formation of ice crystals can cause damage to the crystalline structure of the hydrated cement paste. If the surface of the concrete pour is insulated from the outside temperatures, the heat of hydration will prevent freezing.
+
+The American Concrete Institute (ACI) definition of cold weather placement, ACI 306, is:
+ A period when for more than three successive days the average daily air temperature drops below 40 °F (~ 4.5 °C), and
+ Temperature stays below  for more than one-half of any 24-hour period.
+
+In Canada, where temperatures tend to be much lower during the cold season, the following criteria are used by CSA A23.1:
+ When the air temperature is ≤ 5 °C, and
+ When there is a probability that the temperature may fall below 5 °C within 24 hours of placing the concrete.
+
+The minimum strength before exposing concrete to extreme cold is . CSA A 23.1 specified a compressive strength of 7.0 MPa to be considered safe for exposure to freezing.
+
+Underwater placement 
+
+Concrete may be placed and cured underwater. Care must be taken in the placement method to prevent washing out the cement. Underwater placement methods include the tremie, pumping, skip placement, manual placement using toggle bags, and bagwork.
+
+ is an alternative method of forming a concrete mass underwater, where the forms are filled with coarse aggregate and the voids then completely filled with pumped grout.
+
+Roads
+Concrete roads are more fuel efficient to drive on, more reflective and last significantly longer than other paving surfaces, yet have a much smaller market share than other paving solutions. Modern-paving methods and design practices have changed the economics of concrete paving, so that a well-designed and placed concrete pavement will be less expensive on initial costs and significantly less expensive over the life cycle. Another major benefit is that pervious concrete can be used, which eliminates the need to place storm drains near the road, and reducing the need for slightly sloped roadway to help rainwater to run off. No longer requiring discarding rainwater through use of drains also means that less electricity is needed (more pumping is otherwise needed in the water-distribution system), and no rainwater gets polluted as it no longer mixes with polluted water. Rather, it is immediately absorbed by the ground.
+
+Environment, health and safety
+
+The manufacture and use of concrete produce a wide range of environmental, economic and social impacts.
+
+Concrete, cement and the environment
+A major component of concrete is cement, a fine powder used mainly to bind sand and coarser aggregates together in concrete. Although a variety of cement types exist, the most common is "Portland cement", which is produced by mixing clinker with smaller quantities of other additives such as gypsum and ground limestone. The production of clinker, the main constituent of cement, is responsible for the bulk of the sector's greenhouse gas emissions, including both energy intensity and process emissions.
+
+The cement industry is one of the three primary producers of carbon dioxide, a major greenhouse gas – the other two being energy production and transportation industries. On average, every tonne of cement produced releases one tonne of CO2 into the atmosphere. Pioneer cement manufacturers have claimed to reach lower carbon intensities, with 590 kg of CO2eq per tonne of cement produced. The emissions are due to combustion and calcination processes, which roughly account for 40% and 60% of the greenhouse gases, respectively. Considering that cement is only a fraction of the constituents of concrete, it is estimated that a tonne of concrete is responsible for emitting about 100–200 kg of CO2. Every year more than 10 billion tonnes of concrete are used worldwide. In the coming years, large quantities of concrete will continue to be used, and the mitigation of CO2 emissions from the sector will be even more critical.
+
+Concrete is used to create hard surfaces that contribute to surface runoff, which can cause heavy soil erosion, water pollution, and flooding, but conversely can be used to divert, dam, and control flooding. Concrete dust released by building demolition and natural disasters can be a major source of dangerous air pollution. Concrete is a contributor to the urban heat island effect, though less so than asphalt.
+
+Concrete and climate change mitigation
+Reducing the cement clinker content might have positive effects on the environmental life-cycle assessment of concrete. Some research work on reducing the cement clinker content in concrete has already been carried out. However, there exist different research strategies. Often replacement of some clinker for large amounts of slag or fly ash was investigated based on conventional concrete technology. This could lead to a waste of scarce raw materials such as slag and fly ash. The aim of other research activities is the efficient use of cement and reactive materials like slag and fly ash in concrete based on a modified mix design approach.
+
+An environmental investigation found that the embodied carbon of a precast concrete facade can be reduced by 50% when using the presented fiber reinforced high performance concrete in place of typical reinforced concrete cladding.
+
+Studies have been conducted about commercialization of low-carbon concretes. Life cycle assessment (LCA) of low-carbon concrete was investigated according to the ground granulated blast-furnace slag (GGBS) and fly ash (FA) replacement ratios. Global warming potential (GWP) of GGBS decreased by 1.1 kg CO2 eq/m3, while FA decreased by 17.3 kg CO2 eq/m3 when the mineral admixture replacement ratio was increased by 10%. This study also compared the compressive strength properties of binary blended low-carbon concrete according to the replacement ratios, and the applicable range of mixing proportions was derived.
+
+Researchers at University of Auckland are working on utilizing biochar in concrete applications to reduce carbon emissions during concrete production and to improve strength.
+
+Concrete and climate change adaptation
+High-performance building materials will be particularly important for enhancing resilience, including for flood defenses and critical-infrastructure protection. Risks to infrastructure and cities posed by extreme weather events are especially serious for those places exposed to flood and hurricane damage, but also where residents need protection from extreme summer temperatures. Traditional concrete can come under strain when exposed to humidity and higher concentrations of atmospheric CO2. While concrete is likely to remain important in applications where the environment is challenging, novel, smarter and more adaptable materials are also needed.
+
+Concrete – health and safety
+
+Grinding of concrete can produce hazardous dust. Exposure to cement dust can lead to issues such as silicosis, kidney disease, skin irritation and similar effects. The U.S. National Institute for Occupational Safety and Health in the United States recommends attaching local exhaust ventilation shrouds to electric concrete grinders to control the spread of this dust. In addition, the Occupational Safety and Health Administration (OSHA) has placed more stringent regulations on companies whose workers regularly come into contact with silica dust. An updated silica rule, which OSHA put into effect 23 September 2017 for construction companies, restricted the amount of breathable crystalline silica workers could legally come into contact with to 50 micro grams per cubic meter of air per 8-hour workday. That same rule went into effect 23 June 2018 for general industry, hydraulic fracturing and maritime. That deadline was extended to 23 June 2021 for engineering controls in the hydraulic fracturing industry. Companies which fail to meet the tightened safety regulations can face financial charges and extensive penalties. The presence of some substances in concrete, including useful and unwanted additives, can cause health concerns due to toxicity and radioactivity. Fresh concrete (before curing is complete) is highly alkaline and must be handled with proper protective equipment.
+
+Circular economy 
+Concrete is an excellent material with which to make long-lasting and energy-efficient buildings. However, even with good design, human needs change and potential waste will be generated.
+
+End-of-life: concrete degradation and waste 
+
+Concrete can be damaged by many processes, such as the expansion of corrosion products of the steel reinforcement bars, freezing of trapped water, fire or radiant heat, aggregate expansion, sea water effects, bacterial corrosion, leaching, erosion by fast-flowing water, physical damage and chemical damage (from carbonatation, chlorides, sulfates and distillate water). The micro fungi Aspergillus alternaria and Cladosporium were able to grow on samples of concrete used as a radioactive waste barrier in the Chernobyl reactor; leaching aluminium, iron, calcium, and silicon.
+
+Concrete may be considered waste according to the European Commission decision of 2014/955/EU for the List of Waste under the codes: 17 (construction and demolition wastes, including excavated soil from contaminated sites) 01 (concrete, bricks, tiles and ceramics), 01 (concrete), and 17.01.06* (mixtures of, separate fractions of concrete, bricks, tiles and ceramics containing hazardous substances), and 17.01.07 (mixtures of, separate fractions of concrete, bricks, tiles and ceramics other than those mentioned in 17.01.06).  It is estimated that in 2018 the European Union generated 371,910 thousand tons of mineral waste from construction and demolition, and close to 4% of this quantity is considered hazardous. Germany, France and the United Kingdom were the top three polluters with 86,412 thousand tons, 68,976 and 68,732 thousand tons of construction waste generation, respectively.
+
+Currently, there is not an End-of-Waste criteria for concrete materials in the EU. However, different sectors have been proposing alternatives for concrete waste and re purposing it as a secondary raw material in various applications, including concrete manufacturing itself.
+
+Reuse of concrete 
+Reuse of blocks in original form, or by cutting into smaller blocks, has even less environmental impact; however, only a limited market currently exists. Improved building designs that allow for slab reuse and building transformation without demolition could increase this use. Hollow core concrete slabs are easy to dismantle and the span is normally constant, making them good for reuse.
+
+Other cases of re-use are possible with pre-cast concrete pieces: through selective demolition, such pieces can be disassembled and collected for further use in other building sites. Studies show that back-building and remounting plans for building units (i.e., re-use of pre-fabricated concrete) is an alternative for a kind of construction which protects resources and saves energy. Especially long-living, durable, energy-intensive building materials, such as concrete, can be kept in the life-cycle longer through recycling. Prefabricated constructions are the prerequisites for constructions necessarily capable of being taken apart. In the case of optimal application in the building carcass, savings in costs are estimated in 26%, a lucrative complement to new building methods. However, this depends on several courses to be set. The viability of this alternative has to be studied as the logistics associated with transporting heavy pieces of concrete can impact the operation financially and also increase the carbon footprint of the project. Also, ever changing regulations on new buildings worldwide may require higher quality standards for construction elements and inhibit the use of old elements which may be classified as obsolete.
+
+Recycling of concrete
+
+Concrete recycling is an increasingly common method for disposing of concrete structures. Concrete debris were once routinely shipped to landfills for disposal, but recycling is increasing due to improved environmental awareness, governmental laws and economic benefits.
+
+Contrary to general belief, concrete recovery is achievable – concrete can be crushed and reused as aggregate in new projects.
+
+Recycling or recovering concrete reduces natural resource exploitation and associated transportation costs, and reduces waste landfill. However, it has little impact on reducing greenhouse gas emissions as most emissions occur when cement is made, and cement alone cannot be recycled. At present, most recovered concrete is used for road sub-base and civil engineering projects. From a sustainability viewpoint, these relatively low-grade uses currently provide the optimal outcome.
+
+The recycling process can be done in situ, with mobile plants, or in specific recycling units. The input material can be returned concrete which is fresh (wet) from ready-mix trucks, production waste at a pre-cast production facility, or waste from construction and demolition. The most significant source is demolition waste, preferably pre-sorted from selective demolition processes.
+
+By far the most common method for recycling dry and hardened concrete involves crushing. Mobile sorters and crushers are often installed on construction sites to allow on-site processing. In other situations, specific processing sites are established, which are usually able to produce higher quality aggregate. Screens are used to achieve desired particle size, and remove dirt, foreign particles and fine material from the coarse aggregate.
+
+Chloride and sulfates are undesired contaminants originated from soil and weathering and can provoke corrosion problems on aluminium and steel structures. The final product, Recycled Concrete Aggregate (RCA), presents interesting properties such as: angular shape, rougher surface, lower specific gravity (20%), higher water absorption, and pH greater than 11 – this elevated pH increases the risk of alkali reactions.
+
+The lower density of RCA usually Increases project efficiency and improve job cost – recycled concrete aggregates yield more volume by weight (up to 15%). The physical properties of coarse aggregates made from crushed demolition concrete make it the preferred material for applications such as road base and sub-base. This is because recycled aggregates often have better compaction properties and require less cement for sub-base uses. Furthermore, it is generally cheaper to obtain than virgin material.
+
+Applications of recycled concrete aggregate 
+The main commercial applications of the final recycled concrete aggregate are:
+ Aggregate base course (road base), or the untreated aggregates used as foundation for roadway pavement, is the underlying layer (under pavement surfacing) which forms a structural foundation for paving. To this date this has been the most popular application for RCA due to technical-economic aspects.
+ Aggregate for ready-mix concrete, by replacing from 10 to 45% of the natural aggregates in the concrete mix with a blend of cement, sand and water. Some concept buildings are showing the progress of this field. Because the RCA itself contains cement, the ratios of the mix have to be adjusted to achieve desired structural requirements such as workability, strength and water absorption.
+ Soil Stabilization, with the incorporation of recycled aggregate, lime, or fly ash into marginal quality subgrade material used to enhance the load bearing capacity of that subgrade.
+ Pipe bedding: serving as a stable bed or firm foundation in which to lay underground utilities. Some countries' regulations prohibit the use of RCA and other construction and demolition wastes in filtration and drainage beds due to potential contamination with chromium and pH-value impacts.
+ Landscape Materials: to promote green architecture. To date, recycled concrete aggregate has been used as boulder/stacked rock walls, underpass abutment structures, erosion structures, water features, retaining walls, and more.
+
+Cradle-to-cradle challenges 
+
+The applications developed for RCA so far are not exhaustive, and many more uses are to be developed as regulations, institutions and norms find ways to accommodate construction and demolition waste as secondary raw materials in a safe and economic way. However, considering the purpose of having a circularity of resources in the concrete life cycle, the only application of RCA that could be considered as recycling of concrete is the replacement of natural aggregates on concrete mixes. All the other applications would fall under the category of downcycling. It is estimated that even near complete recovery of concrete from construction and demolition waste will only supply about 20% of total aggregate needs in the developed world.
+
+The path towards circularity goes beyond concrete technology itself, depending on multilateral advances in the cement industry, research and development of alternative materials, building design and management, and demolition as well as conscious use of spaces in urban areas to reduce consumption.
+
+World records
+The world record for the largest concrete pour in a single project is the Three Gorges Dam in Hubei Province, China by the Three Gorges Corporation. The amount of concrete used in the construction of the dam is estimated at 16 million cubic meters over 17 years. The previous record was 12.3 million cubic meters held by Itaipu hydropower station in Brazil.
+
+The world record for concrete pumping was set on 7 August 2009 during the construction of the Parbati Hydroelectric Project, near the village of Suind, Himachal Pradesh, India, when the concrete mix was pumped through a vertical height of .
+
+The Polavaram dam works in Andhra Pradesh on 6 January 2019 entered the Guinness World Records by pouring 32,100 cubic metres of concrete in 24 hours. The world record for the largest continuously poured concrete raft was achieved in August 2007 in Abu Dhabi by contracting firm Al Habtoor-CCC Joint Venture and the concrete supplier is Unibeton Ready Mix. The pour (a part of the foundation for the Abu Dhabi's Landmark Tower) was 16,000 cubic meters of concrete poured within a two-day period. The previous record, 13,200 cubic meters poured in 54 hours despite a severe tropical storm requiring the site to be covered with tarpaulins to allow work to continue, was achieved in 1992 by joint Japanese and South Korean consortiums Hazama Corporation and the Samsung C&T Corporation for the construction of the Petronas Towers in Kuala Lumpur, Malaysia.
+
+The world record for largest continuously poured concrete floor was completed 8 November 1997, in Louisville, Kentucky by design-build firm EXXCEL Project Management. The monolithic placement consisted of  of concrete placed in 30 hours, finished to a flatness tolerance of FF 54.60 and a levelness tolerance of FL 43.83. This surpassed the previous record by 50% in total volume and 7.5% in total area.
+
+The record for the largest continuously placed underwater concrete pour was completed 18 October 2010, in New Orleans, Louisiana by contractor C. J. Mahan Construction Company, LLC of Grove City, Ohio. The placement consisted of 10,251 cubic yards of concrete placed in 58.5 hours using two concrete pumps and two dedicated concrete batch plants. Upon curing, this placement allows the  cofferdam to be dewatered approximately  below sea level to allow the construction of the Inner Harbor Navigation Canal Sill & Monolith Project to be completed in the dry.
+
+See also
+
+Further reading
+
+References
+
+External links 
+ 
+ Advantage and Disadvantage of Concrete
+ 
+ 
+ Release of ultrafine particles from three simulated building processes
+ Concrete: The Quest for Greener Alternatives
+
+ 
+Building materials
+Masonry
+Pavements
+Sculpture materials
+Composite materials
+Heterogeneous chemical mixtures
+Roofing materials
+Coitus interruptus, also known as withdrawal, pulling out or the pull-out method, is a method of birth control during penetrative sexual intercourse, whereby the penis is withdrawn from a vagina prior to ejaculation so that the ejaculate (semen) may be directed away from the vagina in an effort to avoid insemination.
+
+This method was used by an estimated 38 million couples worldwide in 1991. Coitus interruptus does not protect against sexually transmitted infections (STIs/STDs).
+
+History
+Perhaps the oldest description of the use of the withdrawal method to avoid pregnancy is the story of Onan in the Torah and the Bible.  This text is believed to have been written down over 2,500 years ago.  Societies in the ancient civilizations of Greece and Rome preferred small families and are known to have practiced a variety of birth control methods.  There are references that have led historians to believe withdrawal was sometimes used as birth control.  However, these societies viewed birth control as a woman's responsibility, and the only well-documented contraception methods were female-controlled devices (both possibly effective, such as pessaries, and ineffective, such as amulets).
+
+After the decline of the Roman Empire in the 5th century AD, contraceptive practices fell out of use in Europe; the use of contraceptive pessaries, for example, is not documented again until the 15th century. If withdrawal was used during the Roman Empire, knowledge of the practice may have been lost during its decline.
+
+From the 18th century until the development of modern methods, withdrawal was one of the most popular methods of birth-control in Europe, North America, and elsewhere.
+
+Effects 
+Like many methods of birth control, reliable effect is achieved only by correct and consistent use. Observed failure rates of withdrawal vary depending on the population being studied: American studies have found actual failure rates of 15–28% per year. One U.S. study, based on self-reported data from the 2006-2010 cycle of the National Survey of Family Growth, found significant differences in failure rate based on parity status. Women with 0 previous births had a 12-month failure rate of only 8.4%, which then increased to 20.4% for those with 1 prior birth and again to 27.7% for those with 2 or more.
+
+An analysis of Demographic and Health Surveys in 43 developing countries between 1990 and 2013 found a median 12-month failure rate across subregions of 13.4%, with a range of 7.8-17.1%. Individual countries within the subregions were even more varied. A large scale study of women in England and Scotland during 1968–1974 to determine the efficacy of various contraceptive methods found a failure rate of 6.7 per 100 woman-years of use. This was a “typical use” failure rate, including user failure to use the method correctly. In comparison, the combined oral contraceptive pill has an actual use failure rate of 2–8%, while intrauterine devices (IUDs) have an actual use failure rate of 0.1–0.8%.  Condoms have an actual use failure rate of 10–18%. However, some authors suggest that actual effectiveness of withdrawal could be similar to the effectiveness of condoms; this area needs further research. (See Comparison of birth control methods.)
+
+For couples that use coitus interruptus consistently and correctly at every act of intercourse, the failure rate is 4% per year. This rate is derived from an educated guess based on a modest chance of sperm in the pre-ejaculate. In comparison, the pill has a perfect-use failure rate of 0.3%, IUDs a rate of 0.1-0.6%, and internal condoms a rate of 2%.
+
+It has been suggested that the pre-ejaculate ("Cowper's fluid") emitted by the penis prior to ejaculation may contain spermatozoa (sperm cells), which would compromise the effectiveness of the method. However, several small studies have failed to find any viable sperm in the fluid. While no large conclusive studies have been done, it is believed by some that the cause of method (correct-use) failure is the pre-ejaculate fluid picking up sperm from a previous ejaculation. For this reason, it is recommended that the male partner urinate between ejaculations, to clear the urethra of sperm, and wash any ejaculate from objects that might come near the woman's vulva (e.g. hands and penis).
+
+However, recent research suggests that this might not be accurate. A contrary, yet non-generalizable study that found mixed evidence, including individual cases of a high sperm concentration, was published in March 2011. A noted limitation to these previous studies' findings is that pre-ejaculate samples were analyzed after the critical two-minute point.  That is, looking for motile sperm in small amounts of pre-ejaculate via microscope after two minutes – when the sample has most likely dried – makes examination and evaluation "extremely difficult".  Thus, in March 2011 a team of researchers assembled 27 male volunteers and analyzed their pre-ejaculate samples within two minutes after producing them.  The researchers found that 11 of the 27 men (41%) produced pre-ejaculatory samples that contained sperm, and 10 of these samples (37%) contained a "fair amount" of motile sperm (i.e. as few as 1 million to as many as 35 million).
+This study therefore recommends, in order to minimize unintended pregnancy and disease transmission, the use of condoms from the first moment of genital contact.
+As a point of reference, a study showed that, of couples who conceived within a year of trying, only 2.5% included a male partner with a total sperm count (per ejaculate) of 23 million sperm or less.
+However, across a wide range of observed values, total sperm count (as with other identified semen and sperm characteristics) has weak power to predict which couples are at risk of pregnancy. Regardless, this study introduced the concept that some men may consistently have sperm in their pre-ejaculate, due to a "leakage," while others may not.
+
+Similarly, another robust study performed in 2016 found motile sperm in the pre-ejaculate of 16.7% (7/42) healthy men. What more, this study attempted to exclude contamination of sperm from ejaculate by drying the pre-ejaculate specimens to reveal a fern-like pattern, characteristics of true pre-ejaculate. All pre-ejaculate specimens were examined within an hour of production and then dried; all pre-ejaculate specimens were found to be true pre-ejaculate.
+
+It is widely believed that urinating after an ejaculation will flush the urethra of remaining sperm. However, some of the subjects in the March 2011 study who produced sperm in their pre-ejaculate did urinate (sometimes more than once) before producing their sample. Therefore, some males can release the pre-ejaculate fluid containing sperm without a previous ejaculation.
+
+Advantages 
+The advantage of coitus interruptus is that it can be used by people who have objections to, or do not have access to, other forms of contraception. Some people prefer it so they can avoid possible adverse effects of hormonal contraceptives or so that they can have a full experience and be able to "feel" their partner. Other reasons for the popularity of this method are it has no direct monetary cost, requires no artificial devices, has no physical side effects, can be practiced without a prescription or medical consultation, and provides no barriers to stimulation.
+
+Disadvantages 
+Compared to the other common reversible methods of contraception such as IUDs, hormonal contraceptives, and male condoms, coitus interruptus is less effective at preventing pregnancy.  As a result, it is also less cost-effective than many more effective methods: although the method itself has no direct cost, users have a greater chance of incurring the risks and expenses of either child-birth or abortion.  Only models that assume all couples practice perfect use of the method find cost savings associated with the choice of withdrawal as a birth control method.
+
+The method is largely ineffective in the prevention of sexually transmitted infections (STIs/STDs), like HIV, since pre-ejaculate may carry viral particles or bacteria which may infect the partner if this fluid comes in contact with mucous membranes.  However, a reduction in the volume of bodily fluids exchanged during intercourse may reduce the likelihood of disease transmission compared to using no method due to the smaller number of pathogens present.
+
+Prevalence 
+Based on data from surveys conducted during the late 1990s, 3% of women of childbearing age worldwide rely on withdrawal as their primary method of contraception. Regional popularity of the method varies widely, from a low of 1% in Africa to 16% in Western Asia.
+
+In the United States, according to the National Survey of Family Growth (NSFG) in 2014, 8.1% of reproductive-aged women reported using withdrawal as a primary contraceptive method. This was a significant increase from 2012 when 4.8% of women reported the use of withdrawal as their most effective method. However, when withdrawal is used in addition to or in rotation with another contraceptive method, the percentage of women using withdrawal jumps from 5% for sole use and 11% for any withdrawal use in 2002, and for adolescents from 7.1% of sole withdrawal use to 14.6% of any withdrawal use in 2006–2008.
+
+When asked if withdrawal was used at least once in the past month by women, use of withdrawal increased from 13% as sole use to 33% ever use in the past month. These increases are even more pronounced for adolescents 15 to 19 years old and young women 20 to 24 years old Similarly, the NSFG reports that 9.8% of unmarried men who have had sexual intercourse in the last three months in 2002 used withdrawal, which then increased to 14.5% in 2006–2010, and then to 18.8% in 2011–2015. The use of withdrawal varied by the unmarried man's age and cohabiting status, but not by ethnicity or race. The use of withdrawal decreased significantly with increasing age groups, ranging from 26.2% among men aged 15–19 to 12% among men aged 35–44. The use of withdrawal was significantly higher for never-married men (23.0%) compared with formerly married (16.3%) and cohabiting (13.0%) men.
+
+For 1998, about 18% of married men in Turkey reported using withdrawal as a contraceptive method.
+
+See also 
+ Coitus reservatus 
+ Coitus saxonicus 
+ Masturbation
+
+References
+
+External links 
+ Contraception and abortion in Islam
+ Withdrawal
+
+Methods of birth control
+Contraception for males
+Latin words and phrases
+A condom is a sheath-shaped barrier device used during sexual intercourse to reduce the probability of pregnancy or a sexually transmitted infection (STI). There are both male and female condoms.
+
+The male condom is rolled onto an erect penis before intercourse and works by forming a physical barrier which blocks semen from entering the body of a sexual partner. Male condoms are typically made from latex and, less commonly, from polyurethane, polyisoprene, or lamb intestine. Male condoms have the advantages of ease of use, ease of access, and few side effects. Individuals with latex allergy should use condoms made from a material other than latex, such as polyurethane. Female condoms are typically made from polyurethane and may be used multiple times.
+
+With proper use—and use at every act of intercourse—women whose partners use male condoms experience a 2% per-year pregnancy rate. With typical use, the rate of pregnancy is 18% per-year. Their use greatly decreases the risk of gonorrhea, chlamydia, trichomoniasis, hepatitis B, and HIV/AIDS. To a lesser extent, they also protect against genital herpes, human papillomavirus (HPV), and syphilis.
+
+Condoms as a method of preventing STIs have been used since at least 1564. Rubber condoms became available in 1855, followed by latex condoms in the 1920s. It is on the World Health Organization's List of Essential Medicines. As of 2019, globally around 21% of those using birth control use the condom, making it the second-most common method after female sterilization (24%). Rates of condom use are highest in East and Southeast Asia, Europe and North America. About six to nine billion are sold a year.
+
+Medical uses
+
+Birth control 
+
+The effectiveness of condoms, as of most forms of contraception, can be assessed two ways. Perfect use or method effectiveness rates only include people who use condoms properly and consistently. Actual use, or typical use effectiveness rates are of all condom users, including those who use condoms incorrectly or do not use condoms at every act of intercourse. Rates are generally presented for the first year of use. Most commonly the Pearl Index is used to calculate effectiveness rates, but some studies use decrement tables.
+
+The typical use pregnancy rate among condom users varies depending on the population being studied, ranging from 10 to 18% per year. The perfect use pregnancy rate of condoms is 2% per year. Condoms may be combined with other forms of contraception (such as spermicide) for greater protection.
+
+Sexually transmitted infections 
+
+Condoms are widely recommended for the prevention of sexually transmitted infections (STIs). They have been shown to be effective in reducing infection rates in both men and women. While not perfect, the condom is effective at reducing the transmission of organisms that cause AIDS, genital herpes, cervical cancer, genital warts, syphilis, chlamydia, gonorrhea, and other diseases. Condoms are often recommended as an adjunct to more effective birth control methods (such as IUD) in situations where STD protection is also desired.
+For this reason, condoms are frequently used by those in the swinging (sexual practice) community.
+
+According to a 2000 report by the National Institutes of Health (NIH), consistent use of latex condoms reduces the risk of HIV transmission by approximately 85% relative to risk when unprotected, putting the seroconversion rate (infection rate) at 0.9 per 100 person-years with condom, down from 6.7 per 100 person-years. Analysis published in 2007 from the University of Texas Medical Branch and the World Health Organization found similar risk reductions of 80–95%.
+
+The 2000 NIH review concluded that condom use significantly reduces the risk of gonorrhea for men. A 2006 study reports that proper condom use decreases the risk of transmission of human papillomavirus (HPV) to women by approximately 70%. Another study in the same year found consistent condom use was effective at reducing transmission of herpes simplex virus-2, also known as genital herpes, in both men and women.
+
+Although a condom is effective in limiting exposure, some disease transmission may occur even with a condom. Infectious areas of the genitals, especially when symptoms are present, may not be covered by a condom, and as a result, some diseases like HPV and herpes may be transmitted by direct contact. The primary effectiveness issue with using condoms to prevent STDs, however, is inconsistent use.
+
+Condoms may also be useful in treating potentially precancerous cervical changes. Exposure to human papillomavirus, even in individuals already infected with the virus, appears to increase the risk of precancerous changes. The use of condoms helps promote regression of these changes. In addition, researchers in the UK suggest that a hormone in semen can aggravate existing cervical cancer, condom use during sex can prevent exposure to the hormone.
+
+Causes of failure 
+
+Condoms may slip off the penis after ejaculation, break due to improper application or physical damage (such as tears caused when opening the package), or break or slip due to latex degradation (typically from usage past the expiration date, improper storage, or exposure to oils). The rate of breakage is between 0.4% and 2.3%, while the rate of slippage is between 0.6% and 1.3%. Even if no breakage or slippage is observed, 1–3% of women will test positive for semen residue after intercourse with a condom. Failure rates are higher for anal sex, and until 2022, condoms were only approved by the FDA for vaginal sex. The One Male Condom received FDA approval for anal sex on February 23, 2022.
+
+"Double bagging", using two condoms at once, is often believed to cause a higher rate of failure due to the friction of rubber on rubber. This claim is not supported by research. The limited studies that have been done found that the simultaneous use of multiple condoms decreases the risk of condom breakage.
+
+Different modes of condom failure result in different levels of semen exposure. If a failure occurs during application, the damaged condom may be disposed of and a new condom applied before intercourse begins – such failures generally pose no risk to the user. One study found that semen exposure from a broken condom was about half that of unprotected intercourse; semen exposure from a slipped condom was about one-fifth that of unprotected intercourse.
+
+Standard condoms will fit almost any penis, with varying degrees of comfort or risk of slippage. Many condom manufacturers offer "snug" or "magnum" sizes. Some manufacturers also offer custom sized-to-fit condoms, with claims that they are more reliable and offer improved sensation/comfort. Some studies have associated larger penises and smaller condoms with increased breakage and decreased slippage rates (and vice versa), but other studies have been inconclusive.
+
+It is recommended for condoms manufacturers to avoid very thick or very thin condoms, because they are both considered less effective. Some authors encourage users to choose thinner condoms "for greater durability, sensation, and comfort", but others warn that "the thinner the condom, the smaller the force required to break it".
+
+Experienced condom users are significantly less likely to have a condom slip or break compared to first-time users, although users who experience one slippage or breakage are more likely to suffer a second such failure. An article in Population Reports suggests that education on condom use reduces behaviors that increase the risk of breakage and slippage. A Family Health International publication also offers the view that education can reduce the risk of breakage and slippage, but emphasizes that more research needs to be done to determine all of the causes of breakage and slippage.
+
+Among people who intend condoms to be their form of birth control, pregnancy may occur when the user has sex without a condom. The person may have run out of condoms, or be traveling and not have a condom with them, or dislike the feel of condoms and decide to "take a chance". This behavior is the primary cause of typical use failure (as opposed to method or perfect use failure).
+
+Another possible cause of condom failure is sabotage. One motive is to have a child against a partner's wishes or consent. Some commercial sex workers from Nigeria reported clients sabotaging condoms in retaliation for being coerced into condom use. Using a fine needle to make several pinholes at the tip of the condom is believed to significantly impact on their effectiveness. Cases of such condom sabotage have occurred.
+
+Side effects 
+The use of latex condoms by people with an allergy to latex can cause allergic symptoms, such as skin irritation. In people with severe latex allergies, using a latex condom can potentially be life-threatening. Repeated use of latex condoms can also cause the development of a latex allergy in some people. Irritation may also occur due to spermicides that may be present.
+
+Use 
+
+Male condoms are usually packaged inside a foil or plastic wrapper, in a rolled-up form, and are designed to be applied to the tip of the penis and then unrolled over the erect penis. It is important that some space be left in the tip of the condom so that semen has a place to collect; otherwise it may be forced out of the base of the device. Most condoms have a teat end for this purpose. After use, it is recommended the condom be wrapped in tissue or tied in a knot, then disposed of in a trash receptacle. Condoms are used to reduce the likelihood of pregnancy during intercourse and to reduce the likelihood of contracting sexually transmitted infections (STIs). Condoms are also used during fellatio to reduce the likelihood of contracting STIs.
+
+Some couples find that putting on a condom interrupts sex, although others incorporate condom application as part of their foreplay. Some men and women find the physical barrier of a condom dulls sensation. Advantages of dulled sensation can include prolonged erection and delayed ejaculation; disadvantages might include a loss of some sexual excitement. Advocates of condom use also cite their advantages of being inexpensive, easy to use, and having few side effects.
+
+Adult film industry 
+In 2012 proponents gathered 372,000 voter signatures through a citizens' initiative in Los Angeles County to put Measure B on the 2012 ballot. As a result, Measure B, a law requiring the use of condoms in the production of pornographic films, was passed. This requirement has received much criticism and is said by some to be counter-productive, merely forcing companies that make pornographic films to relocate to other places without this requirement. Producers claim that condom use depresses sales.
+
+Sex education 
+Condoms are often used in sex education programs, because they have the capability to reduce the chances of pregnancy and the spread of some sexually transmitted diseases when used correctly. A recent American Psychological Association (APA) press release supported the inclusion of information about condoms in sex education, saying "comprehensive sexuality education programs ... discuss the appropriate use of condoms", and "promote condom use for those who are sexually active."
+
+In the United States, teaching about condoms in public schools is opposed by some religious organizations. Planned Parenthood, which advocates family planning and sex education, argues that no studies have shown abstinence-only programs to result in delayed intercourse, and cites surveys showing that 76% of American parents want their children to receive comprehensive sexuality education including condom use.
+
+Infertility treatment 
+
+Common procedures in infertility treatment such as semen analysis and intrauterine insemination (IUI) require collection of semen samples. These are most commonly obtained through masturbation, but an alternative to masturbation is use of a special collection condom to collect semen during sexual intercourse.
+
+Collection condoms are made from silicone or polyurethane, as latex is somewhat harmful to sperm. Some religions prohibit masturbation entirely. Also, compared with samples obtained from masturbation, semen samples from collection condoms have higher total sperm counts, sperm motility, and percentage of sperm with normal morphology. For this reason, they are believed to give more accurate results when used for semen analysis, and to improve the chances of pregnancy when used in procedures such as intracervical or intrauterine insemination. Adherents of religions that prohibit contraception, such as Catholicism, may use collection condoms with holes pricked in them.
+
+For fertility treatments, a collection condom may be used to collect semen during sexual intercourse where the semen is provided by the woman's partner. Private sperm donors may also use a collection condom to obtain samples through masturbation or by sexual intercourse with a partner and will transfer the ejaculate from the collection condom to a specially designed container. The sperm is transported in such containers, in the case of a donor, to a recipient woman to be used for insemination, and in the case of a woman's partner, to a fertility clinic for processing and use. However, transportation may reduce the fecundity of the sperm. Collection condoms may also be used where semen is produced at a sperm bank or fertility clinic.
+
+Condom therapy is sometimes prescribed to infertile couples when the female has high levels of antisperm antibodies. The theory is that preventing exposure to her partner's semen will lower her level of antisperm antibodies, and thus increase her chances of pregnancy when condom therapy is discontinued. However, condom therapy has not been shown to increase subsequent pregnancy rates.
+
+Other uses 
+
+Condoms excel as multipurpose containers and barriers because they are waterproof, elastic, durable, and (for military and espionage uses) will not arouse suspicion if found.
+
+Ongoing military utilization began during World War II, and includes covering the muzzles of rifle barrels to prevent fouling, the waterproofing of firing assemblies in underwater demolitions, and storage of corrosive materials and garrotes by paramilitary agencies.
+
+Condoms have also been used to smuggle alcohol, cocaine, heroin, and other drugs across borders and into prisons by filling the condom with drugs, tying it in a knot and then either swallowing it or inserting it into the rectum. These methods are very dangerous and potentially lethal; if the condom breaks, the drugs inside become absorbed into the bloodstream and can cause an overdose.
+
+Medically, condoms can be used to cover endovaginal ultrasound probes, or in field chest needle decompressions they can be used to make a one-way valve.
+
+Condoms have also been used to protect scientific samples from the environment, and to waterproof microphones for underwater recording.
+
+Types 
+Most condoms have a reservoir tip or teat end, making it easier to accommodate the man's ejaculate. Condoms come in different sizes and shapes.
+
+They also come in a variety of surfaces intended to stimulate the user's partner. Condoms are usually supplied with a lubricant coating to facilitate penetration, while flavored condoms are principally used for oral sex. As mentioned above, most condoms are made of latex, but polyurethane and lambskin condoms also exist.
+
+Female condom 
+
+Male condoms have a tight ring to form a seal around the penis, while female condoms usually have a large stiff ring to prevent them from slipping into the body orifice. The Female Health Company produced a female condom that was initially made of polyurethane, but newer versions are made of nitrile rubber. Medtech Products produces a female condom made of latex.
+
+Materials
+
+Natural latex 
+
+Latex has outstanding elastic properties: Its tensile strength exceeds 30 MPa, and latex condoms may be stretched in excess of 800% before breaking. In 1990 the ISO set standards for condom production (ISO 4074, Natural latex rubber condoms), and the EU followed suit with its CEN standard (Directive 93/42/EEC concerning medical devices). Every latex condom is tested for holes with an electric current. If the condom passes, it is rolled and packaged. In addition, a portion of each batch of condoms is subject to water leak and air burst testing.
+
+While the advantages of latex have made it the most popular condom material, it does have some drawbacks. Latex condoms are damaged when used with oil-based substances as lubricants, such as petroleum jelly, cooking oil, baby oil, mineral oil, skin lotions, suntan lotions, cold creams, butter or margarine. Contact with oil makes latex condoms more likely to break or slip off due to loss of elasticity caused by the oils. Additionally, latex allergy precludes use of latex condoms and is one of the principal reasons for the use of other materials. In May 2009, the U.S. Food and Drug Administration (FDA) granted approval for the production of condoms composed of Vytex, latex that has been treated to remove 90% of the proteins responsible for allergic reactions. An allergen-free condom made of synthetic latex (polyisoprene) is also available.
+
+Synthetic 
+The most common non-latex condoms are made from polyurethane. Condoms may also be made from other synthetic materials, such as AT-10 resin, and most polyisoprene.
+
+Polyurethane condoms tend to be the same width and thickness as latex condoms, with most polyurethane condoms between 0.04 mm and 0.07 mm thick.
+
+Polyurethane can be considered better than latex in several ways: it conducts heat better than latex, is not as sensitive to temperature and ultraviolet light (and so has less rigid storage requirements and a longer shelf life), can be used with oil-based lubricants, is less allergenic than latex, and does not have an odor. Polyurethane condoms have gained FDA approval for sale in the United States as an effective method of contraception and HIV prevention, and under laboratory conditions have been shown to be just as effective as latex for these purposes.
+
+However, polyurethane condoms are less elastic than latex ones, and may be more likely to slip or break than latex, lose their shape or bunch up more than latex, and are more expensive.
+
+Polyisoprene is a synthetic version of natural rubber latex. While significantly more expensive, it has the advantages of latex (such as being softer and more elastic than polyurethane condoms) without the protein which is responsible for latex allergies. Unlike polyurethane condoms, they cannot be used with an oil-based lubricant.
+
+Lambskin 
+Condoms made from sheep intestines, labeled "lambskin", are also available. Although they are generally effective as a contraceptive by blocking sperm, it is presumed that they are less effective than latex in preventing the transmission of sexually transmitted infections because of pores in the material. This is based on the idea that intestines, by their nature, are porous, permeable membranes, and while sperm are too large to pass through the pores, viruses — such as HIV, herpes, and genital warts — are small enough to pass. However, there are to date no clinical data confirming or denying this theory.
+
+As a result of laboratory data on condom porosity, in 1989, the FDA began requiring lambskin condom manufacturers to indicate that the products were not to be used for the prevention of sexually transmitted infections. This was based on the presumption that lambskin condoms would be less effective than latex in preventing HIV transmission, rather than a conclusion that lambskin condoms lack efficacy in STI prevention altogether. An FDA publication in 1992 states that lambskin condoms "provide good birth control and a varying degree of protection against some, but not all, sexually transmitted diseases" and that the labelling requirement was decided upon because the FDA "cannot expect people to know which STDs they need to be protected against", and since "the reality is that you don't know what your partner has, we wanted natural-membrane condoms to have labels that don't allow the user to assume they're effective against the small viral STDs."
+
+Some believe that lambskin condoms provide a more "natural" sensation and lack the allergens inherent to latex. Still, because of their lesser protection against infection, other hypoallergenic materials such as polyurethane are recommended for latex-allergic users and partners. Lambskin condoms are also significantly more expensive than different types, and as slaughter by-products, they are also not vegetarian.
+
+Spermicide 
+Some latex condoms are lubricated at the manufacturer with a small amount of a nonoxynol-9, a spermicidal chemical. According to Consumer Reports, condoms lubricated with spermicide have no additional benefit in preventing pregnancy, have a shorter shelf life, and may cause urinary tract infections in women. In contrast, application of separately packaged spermicide is believed to increase the contraceptive efficacy of condoms.
+
+Nonoxynol-9 was once believed to offer additional protection against STDs (including HIV) but recent studies have shown that, with frequent use, nonoxynol-9 may increase the risk of HIV transmission. The World Health Organization says that spermicidally lubricated condoms should no longer be promoted. However, it recommends using a nonoxynol-9 lubricated condom over no condom at all. , nine condom manufacturers have stopped manufacturing condoms with nonoxynol-9 and Planned Parenthood has discontinued the distribution of condoms so lubricated.
+
+Ribbed and studded 
+
+Textured condoms include studded and ribbed condoms which can provide extra sensations to both partners. The studs or ribs can be located on the inside, outside, or both; alternatively, they are located in specific sections to provide directed stimulation to either the G-spot or frenulum. Many textured condoms which advertise "mutual pleasure" also are bulb-shaped at the top, to provide extra stimulation to the penis. Some women experience irritation during vaginal intercourse with studded condoms.
+
+Other 
+A Swiss company (Lamprecht A.G) produces extra small condoms aimed at the teenage market. Designed to be used by boys as young as fourteen, Ceylor 'Hotshot' condoms are aimed at reducing teenage pregnancies.
+
+The anti-rape condom is another variation designed to be worn by women. It is designed to cause pain to the attacker, hopefully allowing the victim a chance to escape.
+
+A collection condom is used to collect semen for fertility treatments or sperm analysis. These condoms are designed to maximize sperm life and may be coated on the inside with a sperm-friendly lubricant.
+
+Some condom-like devices are intended for entertainment only, such as glow-in-the dark condoms. These novelty condoms may not provide protection against pregnancy and STDs.
+
+In February 2022, the U.S. Food and Drug Administration (FDA) approved the first condoms specifically indicated to help reduce transmission of sexually transmitted infections (STIs) during anal intercourse.
+
+Prevalence 
+The prevalence of condom use varies greatly between countries. Most surveys of contraceptive use are among married women, or women in informal unions. Japan has the highest rate of condom usage in the world: in that country, condoms account for almost 80% of contraceptive use by married women. On average, in developed countries, condoms are the most popular method of birth control: 28% of married contraceptive users rely on condoms. In the average less-developed country, condoms are less common: only 6–8% of married contraceptive users choose condoms.
+
+History
+
+Before the 19th century 
+Whether condoms were used in ancient civilizations is debated by archaeologists and historians. In ancient Egypt, Greece, and Rome, pregnancy prevention was generally seen as a woman's responsibility, and the only well documented contraception methods were female-controlled devices. In Asia before the 15th century, some use of glans condoms (devices covering only the head of the penis) is recorded. Condoms seem to have been used for contraception, and to have been known only by members of the upper classes. In China, glans condoms may have been made of oiled silk paper, or of lamb intestines. In Japan, condoms called Kabuto-gata (甲形) were made of tortoise shell or animal horn.
+
+In 16th-century Italy, anatomist and physician Gabriele Falloppio wrote a treatise on syphilis. The earliest documented strain of syphilis, first appearing in Europe in a 1490s outbreak, caused severe symptoms and often death within a few months of contracting the disease. Falloppio's treatise is the earliest uncontested description of condom use: it describes linen sheaths soaked in a chemical solution and allowed to dry before use. The cloths he described were sized to cover the glans of the penis, and were held on with a ribbon. Falloppio claimed that an experimental trial of the linen sheath demonstrated protection against syphilis.
+
+After this, the use of penis coverings to protect from disease is described in a wide variety of literature throughout Europe. The first indication that these devices were used for birth control, rather than disease prevention, is the 1605 theological publication De iustitia et iure (On justice and law) by Catholic theologian Leonardus Lessius, who condemned them as immoral. In 1666, the English Birth Rate Commission attributed a recent downward fertility rate to use of "condons", the first documented use of that word or any similar spelling. Other early spellings include "condam" and "quondam", from which the Italian derivation guantone has been suggested, from guanto, "a glove".
+
+In addition to linen, condoms during the Renaissance were made out of intestines and bladder. In the late 16th century, Dutch traders introduced condoms made from "fine leather" to Japan. Unlike the horn condoms used previously, these leather condoms covered the entire penis.
+
+Casanova in the 18th century was one of the first reported using "assurance caps" to prevent impregnating his mistresses.
+
+From at least the 18th century, condom use was opposed in some legal, religious, and medical circles for essentially the same reasons that are given today: condoms reduce the likelihood of pregnancy, which some thought immoral or undesirable for the nation; they do not provide full protection against sexually transmitted infections, while belief in their protective powers was thought to encourage sexual promiscuity; and, they are not used consistently due to inconvenience, expense, or loss of sensation.
+
+Despite some opposition, the condom market grew rapidly. In the 18th century, condoms were available in a variety of qualities and sizes, made from either linen treated with chemicals, or "skin" (bladder or intestine softened by treatment with sulfur and lye). They were sold at pubs, barbershops, chemist shops, open-air markets, and at the theater throughout Europe and Russia. They later spread to America, although in every place there were generally used only by the middle and upper classes, due to both expense and lack of sex education.
+
+1800 through 1920s 
+
+The early 19th century saw contraceptives promoted to the poorer classes for the first time. Writers on contraception tended to prefer other birth control methods to the condom. By the late 19th century, many feminists expressed distrust of the condom as a contraceptive, as its use was controlled and decided upon by men alone. They advocated instead for methods controlled by women, such as diaphragms and spermicidal douches. Other writers cited both the expense of condoms and their unreliability (they were often riddled with holes and often fell off or tore). Still, they discussed condoms as a good option for some and the only contraceptive that protects from disease.
+
+Many countries passed laws impeding the manufacture and promotion of contraceptives. In spite of these restrictions, condoms were promoted by traveling lecturers and in newspaper advertisements, using euphemisms in places where such ads were illegal. Instructions on how to make condoms at home were distributed in the United States and Europe. Despite social and legal opposition, at the end of the 19th century the condom was the Western world's most popular birth control method.
+
+Beginning in the second half of the 19th century, American rates of sexually transmitted diseases skyrocketed. Causes cited by historians include the effects of the American Civil War and the ignorance of prevention methods promoted by the Comstock laws. To fight the growing epidemic, sex education classes were introduced to public schools for the first time, teaching about venereal diseases and how they were transmitted. They generally taught abstinence was the only way to avoid sexually transmitted diseases. Condoms were not promoted for disease prevention because the medical community and moral watchdogs considered STDs to be punishment for sexual misbehavior. The stigma against people with  these diseases was so significant that many hospitals refused to treat people with syphilis.
+
+The German military was the first to promote condom use among its soldiers in the later 19th century. Early 20th century experiments by the American military concluded that providing condoms to soldiers significantly lowered rates of sexually transmitted diseases. During World War I, the United States and (at the beginning of the war only) Britain were the only countries with soldiers in Europe who did not provide condoms and promote their use.
+
+In the decades after World War I, there remained social and legal obstacles to condom use throughout the U.S. and Europe. Founder of psychoanalysis Sigmund Freud opposed all methods of birth control because their failure rates were too high. Freud was especially opposed to the condom because he thought it cut down on sexual pleasure. Some feminists continued to oppose male-controlled contraceptives such as condoms. In 1920 the Church of England's Lambeth Conference condemned all "unnatural means of conception avoidance". The Bishop of London, Arthur Winnington-Ingram, complained of the huge number of condoms discarded in alleyways and parks, especially after weekends and holidays.
+
+However, European militaries continued to provide condoms to their members for disease protection, even in countries where they were illegal for the general population. Through the 1920s, catchy names and slick packaging became an increasingly important marketing technique for many consumer items, including condoms and cigarettes. Quality testing became more common, involving filling each condom with air followed by one of several methods intended to detect loss of pressure. Worldwide, condom sales doubled in the 1920s.
+
+Rubber and manufacturing advances 
+In 1839, Charles Goodyear discovered a way of processing natural rubber, which is too stiff when cold and too soft when warm, in such a way as to make it elastic. This proved to have advantages for the manufacture of condoms; unlike the sheep's gut condoms, they could stretch and did not tear quickly when used. The rubber vulcanization process was patented by Goodyear in 1844. The first rubber condom was produced in 1855. The earliest rubber condoms had a seam and were as thick as a bicycle inner tube. Besides this type, small rubber condoms covering only the glans were often used in England and the United States. There was more risk of losing them and if the rubber ring was too tight, it would constrict the penis. This type of condom was the original "capote" (French for condom), perhaps because of its resemblance to a woman's bonnet worn at that time, also called a capote.
+
+For many decades, rubber condoms were manufactured by wrapping strips of raw rubber around penis-shaped molds, then dipping the wrapped molds in a chemical solution to cure the rubber. In 1912, Polish-born inventor Julius Fromm developed a new, improved manufacturing technique for condoms: dipping glass molds into a raw rubber solution. Called cement dipping, this method required adding gasoline or benzene to the rubber to make it liquid. 
+Around 1920 patent lawyer and vice-president of the United States Rubber Company Ernest Hopkinson invented a new technique of converting latex into rubber without a coagulant (demulsifier), which featured using water as a solvent and warm air to dry the solution, as well as optionally preserving liquid latex with ammonia. Condoms made this way, commonly called "latex" ones, required less labor to produce than cement-dipped rubber condoms, which had to be smoothed by rubbing and trimming. The use of water to suspend the rubber instead of gasoline and benzene eliminated the fire hazard previously associated with all condom factories. Latex condoms also performed better for the consumer: they were stronger and thinner than rubber condoms, and had a shelf life of five years (compared to three months for rubber).
+
+Until the twenties, all condoms were individually hand-dipped by semi-skilled workers. Throughout the decade of the 1920s, advances in the automation of the condom assembly line were made. The first fully automated line was patented in 1930. Major condom manufacturers bought or leased conveyor systems, and small manufacturers were driven out of business. The skin condom, now significantly more expensive than the latex variety, became restricted to a niche high-end market.
+
+1930 to present 
+
+In 1930 the Anglican Church's Lambeth Conference sanctioned the use of birth control by married couples. In 1931 the Federal Council of Churches in the U.S. issued a similar statement. The Roman Catholic Church responded by issuing the encyclical Casti connubii affirming its opposition to all contraceptives, a stance it has never reversed. In the 1930s, legal restrictions on condoms began to be relaxed. But during this period Fascist Italy and Nazi Germany increased restrictions on condoms (limited sales as disease preventatives were still allowed). During the Depression, condom lines by Schmid gained in popularity. Schmid still used the cement-dipping method of manufacture which had two advantages over the latex variety. Firstly, cement-dipped condoms could be safely used with oil-based lubricants. Secondly, while less comfortable, these older-style rubber condoms could be reused and so were more economical, a valued feature in hard times. More attention was brought to quality issues in the 1930s, and the U.S. Food and Drug Administration began to regulate the quality of condoms sold in the United States.
+
+Throughout World War II, condoms were not only distributed to male U.S. military members, but also heavily promoted with films, posters, and lectures. European and Asian militaries on both sides of the conflict also provided condoms to their troops throughout the war, even Germany which outlawed all civilian use of condoms in 1941. In part because condoms were readily available, soldiers found a number of non-sexual uses for the devices, many of which continue to this day. After the war, condom sales continued to grow. From 1955 to 1965, 42% of Americans of reproductive age relied on condoms for birth control. In Britain from 1950 to 1960, 60% of married couples used condoms. The birth control pill became the world's most popular method of birth control in the years after its 1960 début, but condoms remained a strong second. The U.S. Agency for International Development pushed condom use in developing countries to help solve the "world population crises": by 1970 hundreds of millions of condoms were being used each year in India alone.(This number has grown in recent decades: in 2004, the government of India purchased 1.9 billion condoms for distribution at family planning clinics.)
+
+In the 1960s and 1970s quality regulations tightened, and more legal barriers to condom use were removed. In Ireland, legal condom sales were allowed for the first time in 1978. Advertising, however was one area that continued to have legal restrictions. In the late 1950s, the American National Association of Broadcasters banned condom advertisements from national television; this policy remained in place until 1979.
+
+After it was discovered in the early 1980s that AIDS can be a sexually transmitted infection, the use of condoms was encouraged to prevent transmission of HIV. Despite opposition by some political, religious, and other figures, national condom promotion campaigns occurred in the U.S. and Europe. These campaigns increased condom use significantly.
+
+Due to increased demand and greater social acceptance, condoms began to be sold in a wider variety of retail outlets, including in supermarkets and in discount department stores such as Walmart. Condom sales increased every year until 1994, when media attention to the AIDS pandemic began to decline. The phenomenon of decreasing use of condoms as disease preventatives has been called prevention fatigue or condom fatigue. Observers have cited condom fatigue in both Europe and North America. As one response, manufacturers have changed the tone of their advertisements from scary to humorous.
+
+New developments continued to occur in the condom market, with the first polyurethane condom—branded Avanti and produced by the manufacturer of Durex—introduced in the 1990s. Worldwide condom use is expected to continue to grow: one study predicted that developing nations would need 18.6 billion condoms by 2015. , condoms are available inside prisons in Canada, most of the European Union, Australia, Brazil, Indonesia, South Africa, and the US states of Vermont (on September 17, 2013, the Californian Senate approved a bill for condom distribution inside the state's prisons, but the bill was not yet law at the time of approval).
+
+The global condom market was estimated at US$9.2 billion in 2020.
+
+Etymology and other terms 
+The term condom first appears in the early 18th century: early forms include condum (1706 and 1717), condon (1708) and cundum (1744). The word's etymology is unknown. In popular tradition, the invention and naming of the condom came to be attributed to an associate of England's King Charles II, one "Dr. Condom" or "Earl of Condom". There is however no evidence of the existence of such a person, and condoms had been used for over one hundred years before King Charles II acceded to the throne in 1660.
+
+A variety of unproven Latin etymologies have been proposed, including  (receptacle),  (house), and  (scabbard or case). It has also been speculated to be from the Italian word guantone, derived from guanto, meaning glove. William E. Kruck wrote an article in 1981 concluding that, "As for the word 'condom', I need state only that its origin remains completely unknown, and there ends this search for an etymology." Modern dictionaries may also list the etymology as "unknown".
+
+Other terms are also commonly used to describe condoms. In North America condoms are also commonly known as prophylactics, or rubbers. In Britain they may be called French letters or rubber johnnies. Additionally, condoms may be referred to using the manufacturer's name.
+
+Society and culture 
+
+Some moral and scientific criticism of condoms exists despite the many benefits of condoms agreed on by scientific consensus and sexual health experts.
+
+Condom usage is typically recommended for new couples who have yet to develop full trust in their partner with regard to STDs. Established couples on the other hand have few concerns about STDs, and can use other methods of birth control such as the pill, which does not act as a barrier to intimate sexual contact. Note that the polar debate with regard to condom usage is attenuated by the target group the argument is directed. Notably the age category and stable partner question are factors, as well as the distinction between heterosexual and homosexuals, who have different kinds of sex and have different risk consequences and factors.
+
+Among the prime objections to condom usage is the blocking of erotic sensation, or the intimacy that barrier-free sex provides. As the condom is held tightly to the skin of the penis, it diminishes the delivery of stimulation through rubbing and friction. Condom proponents claim this has the benefit of making sex last longer, by diminishing sensation and delaying male ejaculation. Those who promote condom-free heterosexual sex (slang: "bareback") claim that the condom puts a barrier between partners, diminishing what is normally a highly sensual, intimate, and spiritual connection between partners.
+
+Religious 
+
+The United Church of Christ (UCC), a Reformed denomination of the Congregationalist tradition, promotes the distribution of condoms in churches and faith-based educational settings. Michael Shuenemeyer, a UCC minister, has stated that "The practice of safer sex is a matter of life and death. People of faith make condoms available because we have chosen life so that we and our children may live."
+
+On the other hand, the Roman Catholic Church opposes all kinds of sexual acts outside of marriage, as well as any sexual act in which the chance of successful conception has been reduced by direct and intentional acts (for example, surgery to prevent conception) or foreign objects (for example, condoms).
+
+The use of condoms to prevent STI transmission is not specifically addressed by Catholic doctrine, and is currently a topic of debate among theologians and high-ranking Catholic authorities. A few, such as Belgian Cardinal Godfried Danneels, believe the Catholic Church should actively support condoms used to prevent disease, especially serious diseases such as AIDS. However, the majority view—including all statements from the Vatican—is that condom-promotion programs encourage promiscuity, thereby actually increasing STI transmission. This view was most recently reiterated in 2009 by Pope Benedict XVI.
+
+The Roman Catholic Church is the largest organized body of any world religion. The church has hundreds of programs dedicated to fighting the AIDS epidemic in Africa, but its opposition to condom use in these programs has been highly controversial.
+
+In a November 2011 interview, Pope Benedict XVI discussed for the first time the use of condoms to prevent STI transmission. He said that the use of a condom can be justified in a few individual cases if the purpose is to reduce the risk of an HIV infection. He gave as an example male prostitutes. There was some confusion at first whether the statement applied only to homosexual prostitutes and thus not to heterosexual intercourse at all. However, Federico Lombardi, spokesman for the Vatican, clarified that it applied to heterosexual and transsexual prostitutes, whether male or female, as well. He did, however, also clarify that the Vatican's principles on sexuality and contraception had not been changed.
+
+Scientific and environmental 
+More generally, some scientific researchers have expressed objective concern over certain ingredients sometimes added to condoms, notably talc and nitrosamines. Dry dusting powders are applied to latex condoms before packaging to prevent the condom from sticking to itself when rolled up. Previously, talc was used by most manufacturers, but cornstarch is currently the most popular dusting powder. Although rare during normal use, talc is known to be potentially irritant to mucous membranes (such as in the vagina). Cornstarch is generally believed to be safe; however, some researchers have raised concerns over its use as well.
+
+Nitrosamines, which are potentially carcinogenic in humans, are believed to be present in a substance used to improve elasticity in latex condoms. A 2001 review stated that humans regularly receive 1,000 to 10,000 times greater nitrosamine exposure from food and tobacco than from condom use and concluded that the risk of cancer from condom use is very low. However, a 2004 study in Germany detected nitrosamines in 29 out of 32 condom brands tested, and concluded that exposure from condoms might exceed the exposure from food by 1.5- to 3-fold.
+
+In addition, the large-scale use of disposable condoms has resulted in concerns over their environmental impact via littering and in landfills, where they can eventually wind up in wildlife environments if not incinerated or otherwise permanently disposed of first. Polyurethane condoms in particular, given they are a form of plastic, are not biodegradable, and latex condoms take a very long time to break down. Experts, such as AVERT, recommend condoms be disposed of in a garbage receptacle, as flushing them down the toilet (which some people do) may cause plumbing blockages and other problems. Furthermore, the plastic and foil wrappers condoms are packaged in are also not biodegradable. However, the benefits condoms offer are widely considered to offset their small landfill mass. Frequent condom or wrapper disposal in public areas such as a parks have been seen as a persistent litter problem.
+
+While biodegradable, latex condoms damage the environment when disposed of improperly. According to the Ocean Conservancy, condoms, along with certain other types of trash, cover the coral reefs and smother sea grass and other bottom dwellers. The United States Environmental Protection Agency also has expressed concerns that many animals might mistake the litter for food.
+
+Cultural barriers to use 
+In much of the Western world, the introduction of the pill in the 1960s was associated with a decline in condom use. In Japan, oral contraceptives were not approved for use until September 1999, and even then access was more restricted than in other industrialized nations. Perhaps because of this restricted access to hormonal contraception, Japan has the highest rate of condom usage in the world: in 2008, 80% of contraceptive users relied on condoms.
+
+Cultural attitudes toward gender roles, contraception, and sexual activity vary greatly around the world, and range from extremely conservative to extremely liberal. But in places where condoms are misunderstood, mischaracterised, demonised, or looked upon with overall cultural disapproval, the prevalence of condom use is directly affected. In less-developed countries and among less-educated populations, misperceptions about how disease transmission and conception work negatively affect the use of condoms; additionally, in cultures with more traditional gender roles, women may feel uncomfortable demanding that their partners use condoms.
+
+As an example, Latino immigrants in the United States often face cultural barriers to condom use. A study on female HIV prevention published in the Journal of Sex Health Research asserts that Latino women often lack the attitudes needed to negotiate safe sex due to traditional gender-role norms in the Latino community, and may be afraid to bring up the subject of condom use with their partners. Women who participated in the study often reported that because of the general machismo subtly encouraged in Latino culture, their male partners would be angry or possibly violent at the woman's suggestion that they use condoms. A similar phenomenon has been noted in a survey of low-income American black women; the women in this study also reported a fear of violence at the suggestion to their male partners that condoms be used.
+
+A telephone survey conducted by Rand Corporation and Oregon State University, and published in the Journal of Acquired Immune Deficiency Syndromes showed that belief in AIDS conspiracy theories among United States black men is linked to rates of condom use. As conspiracy beliefs about AIDS grow in a given sector of these black men, consistent condom use drops in that same sector. Female use of condoms was not similarly affected.
+
+In the African continent, condom promotion in some areas has been impeded by anti-condom campaigns by some Muslim and Catholic clerics. Among the Maasai in Tanzania, condom use is hampered by an aversion to "wasting" sperm, which is given sociocultural importance beyond reproduction. Sperm is believed to be an "elixir" to women and to have beneficial health effects. Maasai women believe that, after conceiving a child, they must have sexual intercourse repeatedly so that the additional sperm aids the child's development. Frequent condom use is also considered by some Maasai to cause impotence. Some women in Africa believe that condoms are "for prostitutes" and that respectable women should not use them. A few clerics even promote the lie that condoms are deliberately laced with HIV. In the United States, possession of many condoms has been used by police to accuse women of engaging in prostitution. The Presidential Advisory Council on HIV/AIDS has condemned this practice and there are efforts to end it.
+
+Middle-Eastern couples who have not had children, because of the strong desire and social pressure to establish fertility as soon as possible within marriage, rarely use condoms.
+
+In 2017, India restricted TV advertisements for condoms to between the hours of 10 pm to 6 am. Family planning advocates were against this, saying it was liable to "undo decades of progress on sexual and reproductive health".
+
+Major manufacturers 
+
+One analyst described the size of the condom market as something that "boggles the mind". Numerous small manufacturers, nonprofit groups, and government-run manufacturing plants exist around the world. Within the condom market, there are several major contributors, among them both for-profit businesses and philanthropic organizations. Most large manufacturers have ties to the business that reach back to the end of the 19th century.
+
+Economics 
+In the United States condoms usually cost less than US$1.00.
+
+Research 
+
+A spray-on condom made of latex is intended to be easier to apply and more successful in preventing the transmission of diseases. , the spray-on condom was not going to market because the drying time could not be reduced below two to three minutes.
+
+The Invisible Condom, developed at Université Laval in Quebec, Canada, is a gel that hardens upon increased temperature after insertion into the vagina or rectum. In the lab, it has been shown to effectively block HIV and herpes simplex virus. The barrier breaks down and liquefies after several hours. , the invisible condom is in the clinical trial phase, and has not yet been approved for use.
+
+Also developed in 2005 is a condom treated with an erectogenic compound. The drug-treated condom is intended to help the wearer maintain his erection, which should also help reduce slippage. If approved, the condom would be marketed under the Durex brand. , it was still in clinical trials. In 2009, Ansell Healthcare, the makers of Lifestyle condoms, introduced the X2 condom lubricated with "Excite Gel" which contains the amino acid L-arginine and is intended to improve the strength of the erectile response.
+
+In March 2013, philanthropist Bill Gates offered US$100,000 grants through his foundation for a condom design that "significantly preserves or enhances pleasure" to encourage more males to adopt the use of condoms for safer sex. The grant information stated: "The primary drawback from the male perspective is that condoms decrease pleasure as compared to no condom, creating a trade-off that many men find unacceptable, particularly given that the decisions about use must be made just prior to intercourse. Is it possible to develop a product without this stigma, or better, one that is felt to enhance pleasure?" In November of the same year, 11 research teams were selected to receive the grant money.
+
+References
+
+External links 
+
+ "Sheathing Cupid's Arrow: the Oldest Artificial Contraceptive May Be Ripe for a Makeover", The Economist, February 2014.
+
+16th-century introductions
+ 
+HIV/AIDS
+Prevention of HIV/AIDS
+Penis
+Sexual health
+World Health Organization essential medicines
+Wikipedia medicine articles ready to translate
+Contraception for males
+A country code is a short alphanumeric identification code for countries and dependent areas. Its primary use is in data processing and communications. Several identification systems have been developed.
+
+The term country code frequently refers to ISO 3166-1 alpha-2, as well as the telephone country code, which is embodied in the E.164 recommendation by the International Telecommunication Union (ITU).
+
+ISO 3166-1
+The standard ISO 3166-1 defines short identification codes for most countries and dependent areas:
+ISO 3166-1 alpha-2: two-letter code
+ISO 3166-1 alpha-3: three-letter code
+ISO 3166-1 numeric: three-digit code
+
+The two-letter codes are used as the basis for other codes and applications, for example,
+for ISO 4217 currency codes
+with deviations, for country code top-level domain names (ccTLDs) on the Internet: list of Internet TLDs.
+Other applications are defined in ISO 3166-1 alpha-2.
+
+ITU country codes
+In telecommunication, a country code, or international subscriber dialing (ISD) code, is a telephone number prefix used in international direct dialing (IDD) and for destination routing of telephone calls to a country other than the caller's. A country or region with an autonomous telephone administration must apply for membership in the International Telecommunication Union (ITU) to participate in the international public switched telephone network (PSTN). County codes are defined by the ITU-T section of the ITU in standards E.123 and E.164.
+
+Country codes constitute the international telephone numbering plan, and are dialed only when calling a telephone number in another country. They are dialed before the national telephone number. International calls require at least one additional prefix to be dialing before the country code, to connect the call to international circuits, the international call prefix. When printing telephone numbers this is indicated by a plus-sign (+) in front of a complete international telephone number, per recommendation E164 by the ITU.
+
+Other country codes
+European Union:
+Before the 2004 EU enlargement the EU used the UN Road Traffic Conventions license plate codes. Since then, it has used the ISO 3166-1 alpha-2 code, but with two modifications:
+EL for Greece (instead of GR)
+(formerly) UK for United Kingdom (instead of GB)
+The Nomenclature des unités territoriales statistiques (Nomenclature of territorial units for statistics, NUTS) of the European Union, mostly focusing on subdivisions of the EU member states
+FIFA (Fédération Internationale de Football Association) assigns a three-letter code (dubbed FIFA Trigramme) to each of its member and non-member countries: List of FIFA country codes
+Federal Information Processing Standard (FIPS) 10-4 defined two-letter codes used by the U.S. government and in the CIA World Factbook: list of FIPS country codes. On September 2, 2008, FIPS 10-4 was one of ten standards withdrawn by NIST as a Federal Information Processing Standard.
+ The Bureau of Transportation Statistics, part of the United States Department of Transportation (US DOT), maintains its own list of codes, so-called World Area Codes (WAC), for state and country codes.
+ GOST 7.67: country codes in Cyrillic from the GOST standards committee
+From the International Civil Aviation Organization (ICAO):
+The national prefixes used in aircraft registration numbers
+Location prefixes in four-character ICAO airport codes
+International Olympic Committee (IOC) three-letter codes used in sporting events: list of IOC country codes
+From the International Telecommunication Union (ITU):
+the E.212 mobile country codes (MCC), for mobile/wireless phone addresses,
+the first few characters of call signs of radio stations (maritime, aeronautical, amateur radio, broadcasting, and so on) define the country: the ITU prefix,
+ITU letter codes for member-countries,
+ITU prefix - amateur and experimental stations - The International Telecommunication Union (ITU) assigns national telecommunication prefixes for amateur and experimental radio use, so that operators can be identified by their country of origin. These prefixes are legally administered by the national entity to which prefix ranges are assigned.
+Three-digit codes used to identify countries in maritime mobile radio transmissions, known as maritime identification digits
+License plates for automobiles:
+Under the 1949 and 1968 United Nations Road Traffic Conventions (distinguishing signs of vehicles in international traffic): List of international license plate codes.
+Diplomatic license plates in the United States, assigned by the U.S. State Department.
+North Atlantic Treaty Organization (NATO) used two-letter codes of its own: list of NATO country codes. They were largely borrowed from the FIPS 10-4 codes mentioned below. In 2003 the eighth edition of the Standardisation Agreement (STANAG) adopted the ISO 3166 three-letter codes with one exception (the code for Macedonia). With the ninth edition, NATO is transitioning to four- and six-letter codes based on ISO 3166 with a few exceptions and additions
+United Nations Development Programme (UNDP) also has its own list of trigram country codes
+ World Intellectual Property Organization (WIPO): WIPO ST.3 gives two-letter codes to countries and regional intellectual property organizations
+World Meteorological Organization (WMO) maintains a list of country codes, used in reporting meteorological observations
+ UIC (the International Union of Railways): UIC Country Codes
+
+The developers of ISO 3166 intended that in time it would replace other coding systems.
+
+Other codings
+Country identities may be encoded in the following coding systems:
+The initial digits of International Standard Book Numbers (ISBN) are group identifiers for countries, areas, or language regions.
+The first three digits of GS1 Company Prefixes used to identify products, for example, in barcodes, designate (national) numbering agencies.
+
+Lists of country codes by country
+A -
+B -
+C -
+D–E -
+F -
+G -
+H–I -
+J–K -
+L -
+M -
+N -
+O–Q -
+R -
+S -
+T -
+U–Z
+
+See also
+List of ISO 3166 country codes
+ISO 639 language codes
+Language code
+Numbering scheme
+
+References
+
+External links
+Comparison of various systems
+Another comparison: 
+A comparison with ISO, IFS and others with notes
+United Nations Region Codes
+
+ 
+Geocodes
+Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived characteristics (synapomorphies) that are not present in more distant groups and ancestors. However, from an empirical perspective, common ancestors are inferences based on a cladistic hypothesis of relationships of taxa whose character states can be observed. Theoretically, a last common ancestor and all its descendants constitute a (minimal) clade. Importantly, all descendants stay in their overarching ancestral clade. For example, if the terms worms or fishes were used within a strict cladistic framework, these terms would include humans. Many of these terms are normally used paraphyletically, outside of cladistics, e.g. as a 'grade', which  are fruitless to precisely delineate, especially when including extinct species. Radiation results in the generation of new subclades by bifurcation, but in practice sexual hybridization may blur very closely related groupings.
+
+As a hypothesis, a clade can be rejected only if some groupings were explicitly excluded. It may then be found that the excluded group did actually descend from the last common ancestor of the group, and thus emerged within the group. ("Evolved from" is misleading, because in cladistics all descendants stay in the ancestral group). Upon finding that the group is paraphyletic this way, either such excluded groups should be granted to the clade, or the group should be abolished.
+
+Branches down to the divergence to the next significant (e.g. extant) sister are considered stem-groupings of the clade, but in principle each level stands on its own, to be assigned a unique name. For a fully bifurcated tree, adding a group to a tree also adds an additional (named) clade, and a new level on that branch. Specifically, also extinct groups are always put on a side-branch, not distinguishing whether an actual ancestor of other groupings was found.
+
+The techniques and nomenclature of cladistics have been applied to disciplines other than biology.  (See phylogenetic nomenclature.)
+
+Cladistics findings are posing a difficulty for taxonomy, where the rank and (genus-)naming of established groupings may turn out to be inconsistent.
+
+Cladistics is now the most commonly used method to classify organisms.
+
+History 
+
+The original methods used in cladistic analysis and the school of taxonomy derived from the work of the German entomologist Willi Hennig, who referred to it as phylogenetic systematics (also the title of his 1966 book); the terms "cladistics" and "clade" were popularized by other researchers. Cladistics in the original sense refers to a particular set of methods used in phylogenetic analysis, although it is now sometimes used to refer to the whole field.
+
+What is now called the cladistic method appeared as early as 1901 with a work by Peter Chalmers Mitchell for birds and subsequently by Robert John Tillyard (for insects) in 1921, and W. Zimmermann (for plants) in 1943.  The term "clade" was introduced in 1958 by Julian Huxley after having been coined by Lucien Cuénot in 1940, "cladogenesis" in 1958, "cladistic" by Arthur Cain and Harrison in 1960, "cladist" (for an adherent of Hennig's school) by Ernst Mayr in 1965, and "cladistics" in 1966. Hennig referred to his own approach as "phylogenetic systematics". From the time of his original formulation until the end of the 1970s, cladistics competed as an analytical and philosophical approach to systematics with phenetics and so-called evolutionary taxonomy. Phenetics was championed at this time by the numerical taxonomists Peter Sneath and Robert Sokal, and evolutionary taxonomy by Ernst Mayr.
+
+Originally conceived, if only in essence, by Willi Hennig in a book published in 1950, cladistics did not flourish until its translation into English in 1966 (Lewin 1997). Today, cladistics is the most popular method for inferring phylogenetic trees from morphological data.
+
+In the 1990s, the development of effective polymerase chain reaction techniques allowed the application of cladistic methods to biochemical and molecular genetic traits of organisms, vastly expanding the amount of data available for phylogenetics. At the same time, cladistics rapidly became popular in evolutionary biology, because computers made it possible to process large quantities of data about organisms and their characteristics.
+
+Methodology 
+
+The cladistic method interprets each shared character state transformation as a potential piece of evidence for grouping. Synapomorphies (shared, derived character states) are viewed as evidence of grouping, while symplesiomorphies (shared ancestral character states) are not.  The outcome of a cladistic analysis is a cladogram – a tree-shaped diagram (dendrogram) that is interpreted to represent the best hypothesis of phylogenetic relationships. Although traditionally such cladograms were generated largely on the basis of morphological characters and originally calculated by hand, genetic sequencing data and computational phylogenetics are now commonly used in phylogenetic analyses, and the parsimony criterion has been abandoned by many phylogeneticists in favor of more "sophisticated" but less parsimonious evolutionary models of character state transformation. Cladists contend that these models are unjustified because there is no evidence that they recover more "true" or "correct" results from actual empirical data sets 
+
+Every cladogram is based on a particular dataset analyzed with a particular method. Datasets are tables consisting of molecular, morphological, ethological and/or other characters and a list of operational taxonomic units (OTUs), which may be genes, individuals, populations, species, or larger taxa that are presumed to be monophyletic and therefore to form, all together, one large clade; phylogenetic analysis infers the branching pattern within that clade. Different datasets and different methods, not to mention violations of the mentioned assumptions, often result in different cladograms. Only scientific investigation can show which is more likely to be correct.
+
+Until recently, for example, cladograms like the following have generally been accepted as accurate representations of the ancestral relations among turtles, lizards, crocodilians, and birds:
+
+If this phylogenetic hypothesis is correct, then the last common ancestor of turtles and birds, at the branch near the  lived earlier than the last common ancestor of lizards and birds, near the . Most molecular evidence, however, produces cladograms more like this:
+
+If this is accurate, then the last common ancestor of turtles and birds lived later than the last common ancestor of lizards and birds. Since the cladograms show two mutually exclusive hypotheses to describe the evolutionary history, at most one of them is correct.
+
+The cladogram to the right represents the current universally accepted hypothesis that all primates, including strepsirrhines like the lemurs and lorises, had a common ancestor all of whose descendants are or were primates, and so form a clade; the name Primates is therefore recognized for this clade. Within the primates, all anthropoids (monkeys, apes, and humans) are hypothesized to have had a common ancestor all of whose descendants are or were anthropoids, so they form the clade called Anthropoidea. The "prosimians", on the other hand, form a paraphyletic taxon. The name Prosimii is not used in phylogenetic nomenclature, which names only clades; the "prosimians" are instead divided between the clades Strepsirhini and Haplorhini, where the latter contains Tarsiiformes and Anthropoidea.
+
+Lemurs and tarsiers may have looked closely related to humans, in the sense of being close on the evolutionary tree to humans. However, from the perspective of a tarsier, humans and lemurs would have looked close, in the exact same sense. Cladistics forces a neutral perspective, treating all branches (extant or extinct) in the same manner. It also forces one to try to make statements, and honestly take into account findings, about the exact historic relationships between the groups.
+
+Terminology for character states 
+
+The following terms, coined by Hennig, are used to identify shared or distinct character states among groups:
+  A plesiomorphy ("close form") or ancestral state is a character state that a taxon has retained from its ancestors. When two or more taxa that are not nested within each other share a plesiomorphy, it is a symplesiomorphy (from syn-, "together"). Symplesiomorphies do not mean that the taxa that exhibit that character state are necessarily closely related. For example, Reptilia is traditionally characterized by (among other things) being cold-blooded (i.e., not maintaining a constant high body temperature), whereas birds are warm-blooded. Since cold-bloodedness is a plesiomorphy, inherited from the common ancestor of traditional reptiles and birds, and thus a symplesiomorphy of turtles, snakes and crocodiles (among others), it does not mean that turtles, snakes and crocodiles form a clade that excludes the birds.
+  An apomorphy ("separate form") or derived state is an innovation. It can thus be used to diagnose a clade – or even to help define a clade name in phylogenetic nomenclature. Features that are derived in individual taxa (a single species or a group that is represented by a single terminal in a given phylogenetic analysis) are called autapomorphies (from auto-, "self"). Autapomorphies express nothing about relationships among groups; clades are identified (or defined) by synapomorphies (from syn-, "together"). For example, the possession of digits that are homologous with those of Homo sapiens is a synapomorphy within the vertebrates. The tetrapods can be singled out as consisting of the first vertebrate with such digits homologous to those of Homo sapiens together with all descendants of this vertebrate (an apomorphy-based phylogenetic definition). Importantly, snakes and other tetrapods that do not have digits are nonetheless tetrapods: other characters, such as amniotic eggs and diapsid skulls, indicate that they descended from ancestors that possessed digits which are homologous with ours.
+ A character state is homoplastic or "an instance of homoplasy" if it is shared by two or more organisms but is absent from their common ancestor or from a later ancestor in the lineage leading to one of the organisms. It is therefore inferred to have evolved by convergence or reversal. Both mammals and birds are able to maintain a high constant body temperature (i.e., they are warm-blooded). However, the accepted cladogram explaining their significant features indicates that their common ancestor is in a group lacking this character state, so the state must have evolved independently in the two clades. Warm-bloodedness is separately a synapomorphy of mammals (or a larger clade) and of birds (or a larger clade), but it is not a synapomorphy of any group including both these clades. Hennig's Auxiliary Principle states that shared character states should be considered evidence of grouping unless they are contradicted by the weight of other evidence; thus, homoplasy of some feature among members of a group may only be inferred after a phylogenetic hypothesis for that group has been established.
+
+The terms plesiomorphy and apomorphy are relative; their application depends on the position of a group within a tree. For example, when trying to decide whether the tetrapods form a clade, an important question is whether having four limbs is a synapomorphy of the earliest taxa to be included within Tetrapoda: did all the earliest members of the Tetrapoda inherit four limbs from a common ancestor, whereas all other vertebrates did not, or at least not homologously? By contrast, for a group within the tetrapods, such as birds, having four limbs is a plesiomorphy. Using these two terms allows a greater precision in the discussion of homology, in particular allowing clear expression of the hierarchical relationships among different homologous features.
+
+It can be difficult to decide whether a character state is in fact the same and thus can be classified as a synapomorphy, which may identify a monophyletic group, or whether it only appears to be the same and is thus a homoplasy, which cannot identify such a group. There is a danger of circular reasoning: assumptions about the shape of a phylogenetic tree are used to justify decisions about character states, which are then used as evidence for the shape of the tree. Phylogenetics uses various forms of parsimony to decide such questions; the conclusions reached often depend on the dataset and the methods. Such is the nature of empirical science, and for this reason, most cladists refer to their cladograms as hypotheses of relationship. Cladograms that are supported by a large number and variety of different kinds of characters are viewed as more robust than those based on more limited evidence.
+
+Terminology for taxa 
+Mono-, para- and polyphyletic taxa can be understood based on the shape of the tree (as done above), as well as based on their character states. These are compared in the table below.
+
+Criticism 
+
+Cladistics, either generally or in specific applications, has been criticized from its beginnings. Decisions as to whether particular character states are homologous, a precondition of their being synapomorphies, have been challenged as involving circular reasoning and subjective judgements. Of course, the potential unreliability of evidence is a problem for any systematic method, or for that matter, for any empirical scientific endeavor at all.
+
+Transformed cladistics arose in the late 1970s  in an attempt to resolve some of these problems by removing a priori assumptions about phylogeny from cladistic analysis, but it has remained unpopular.
+
+Issues
+
+Ancestors 
+The cladistic method does not identify fossil species as actual ancestors of a clade. Instead, fossil taxa are identified as belonging to separate extinct branches. While a fossil species could be the actual ancestor of a clade, there is no way to know that.  Therefore, a more conservative hypothesis is that the fossil taxon is related to other fossil and extant taxa, as implied by the pattern of shared apomorphic features.
+
+Extinction status 
+An otherwise extinct group with any extant descendants, is not considered (literally) extinct, and for instance does not have a date of extinction.
+
+Hybridization, interbreeding 
+
+Anything having to do with biology and sex is complicated and messy, and cladistics is no exception. Many species reproduce sexually, and are capable of interbreeding for millions of years. Worse, during such a period, many branches may have radiated, and it may take hundreds of millions of years for them to have whittled down to just two. Only then one can theoretically assign proper last common ancestors of groupings which do not inadvertently include earlier branches. The process of true cladistic bifurcation can thus take a much more extended time than one is usually aware of. In practice, for recent radiations, cladistically guided findings only give a coarse impression of the complexity. A more detailed account will give details about fractions of introgressions between groupings, and even geographic variations thereof. This has been used as an argument for the use of paraphyletic  groupings, but typically other reasons are quoted.
+
+Horizontal gene transfer 
+
+Horizontal gene transfer is the mobility of genetic info between different organisms that can have immediate or delayed effects for the reciprocal host. There are several processes in nature which can cause horizontal gene transfer. This does typically not directly interfere with ancestry of the organism, but can complicate the determination of that ancestry. On another level, one can map the horizontal gene transfer processes, by determining the phylogeny of the individual genes using cladistics.
+
+Naming stability 
+
+If there is unclarity in mutual relationships, there are a lot of possible trees. Assigning names to each possible clade may not be prudent. Furthermore, established names are discarded in cladistics, or alternatively carry connotations which may no longer hold, such as when additional groups are found to have emerged in them. Naming changes are the direct result of changes in the recognition of mutual relationships, which often is still in flux, especially for extinct species. Hanging on to older naming and/or connotations is counter-productive, as they typically do not reflect actual mutual relationships precisely at all. E.g.  Archaea, Asgard archaea, protists, slime molds, worms, invertebrata, fishes, reptilia, monkeys, Ardipithecus, Australopithecus, Homo erectus all contain Homo sapiens cladistically, in their sensu lato meaning. For originally extinct stem groups, sensu lato generally means generously keeping previously included groups, which then may come to include even living species. A pruned sensu stricto meaning is often adopted instead, but the group would need to be restricted to a single branche on the stem. Other branches then get their own name and level. This is commensurate to the fact that more senior stem branches are in fact closer related to the resulting group than the more basal stem branches; that those stem branches only may have lived for a short time does not affect that assessment in cladistics.
+
+In disciplines other than biology 
+The comparisons used to acquire data on which cladograms can be based are not limited to the field of biology. Any group of individuals or classes that are hypothesized to have a common ancestor, and to which a set of common characteristics may or may not apply, can be compared pairwise. Cladograms can be used to depict the hypothetical descent relationships within groups of items in many different academic realms. The only requirement is that the items have characteristics that can be identified and measured.
+
+Anthropology and archaeology: Cladistic methods have been used to reconstruct the development of cultures or artifacts using groups of cultural traits or artifact features.
+
+Comparative mythology and folktale use cladistic methods to reconstruct the protoversion of many myths. Mythological phylogenies constructed with mythemes clearly support low horizontal transmissions (borrowings), historical (sometimes Palaeolithic) diffusions and punctuated evolution. They also are a powerful way to test hypotheses about cross-cultural relationships among folktales.
+
+Literature: Cladistic methods have been used in the classification of the surviving manuscripts of the Canterbury Tales, and the manuscripts of the Sanskrit Charaka Samhita.
+
+Historical linguistics: Cladistic methods have been used to reconstruct the phylogeny of languages using linguistic features. This is similar to the traditional comparative method of historical linguistics, but is more explicit in its use of parsimony and allows much faster analysis of large datasets (computational phylogenetics).
+
+Textual criticism or stemmatics: Cladistic methods have been used to reconstruct the phylogeny of manuscripts of the same work (and reconstruct the lost original) using distinctive copying errors as apomorphies. This differs from traditional historical-comparative linguistics in enabling the editor to evaluate and place in genetic relationship large groups of manuscripts with large numbers of variants that would be impossible to handle manually. It also enables parsimony analysis of contaminated traditions of transmission that would be impossible to evaluate manually in a reasonable period of time.
+
+Astrophysics infers the history of relationships between galaxies to create branching diagram hypotheses of galaxy diversification.
+
+See also 
+
+ Bioinformatics
+ Biomathematics
+ Coalescent theory
+ Common descent
+ Glossary of scientific naming
+ Language family
+ Patrocladogram
+ Phylogenetic network
+ Scientific classification
+ Stratocladistics
+ Subclade
+ Systematics
+ Three-taxon analysis
+ Tree model
+ Tree structure
+
+Notes and references
+
+Bibliography 
+
+ 
+ 
+ 
+ 
+ 
+ 
+  Available free online at Gallica (No direct URL). This is the paper credited by  for the first use of the term 'clade'.
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+  responding to .
+  Translated from manuscript in German eventually published in 1982 (Phylogenetische Systematik, Verlag Paul Parey, Berlin).
+ 
+ 
+ 
+ d'Huy, Julien (2012b), "Le motif de Pygmalion : origine afrasienne et diffusion en Afrique". Sahara, 23: 49-59 .
+ d'Huy, Julien (2013a), "Polyphemus (Aa. Th. 1137)." "A phylogenetic reconstruction of a prehistoric tale". Nouvelle Mythologie Comparée / New Comparative Mythology 1, 
+ 
+ d'Huy, Julien (2013c) "Les mythes évolueraient par ponctuations". Mythologie française, 252, 2013c: 8-12. 
+ d'Huy, Julien (2013d) "A Cosmic Hunt in the Berber sky : a phylogenetic reconstruction of Palaeolithic mythology". Les Cahiers de l'AARS, 15, 2013d: 93-106. 
+ 
+ 
+ 
+ 
+ 
+ 
+  Reissued 1997 in paperback. Includes a reprint of Mayr's 1974 anti-cladistics paper at pp. 433–476, "Cladistic analysis or cladistic classification." This is the paper to which  is a response.
+ 
+ 
+ 
+ .
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ Tehrani, Jamshid J., 2013, "The Phylogeny of Little Red Riding Hood", PLOS ONE, 13 November.
+
+External links 
+
+ 
+ OneZoom: Tree of Life – all living species as intuitive and zoomable fractal explorer (responsive design)
+ Willi Hennig Society
+ Cladistics (scholarly journal of the Willi Hennig Society)
+ 
+ 
+ 
+ 
+ 
+
+Phylogenetics
+Evolutionary biology
+Zoology
+Philosophy of biology
+A calendar is a system of organizing days. This is done by giving names to periods of time, typically days, weeks, months and years. A date is the designation of a single and specific day within such a system. A calendar is also a physical record (often paper) of such a system. A calendar can also mean a list of planned events, such as a court calendar, or a partly or fully chronological list of documents, such as a calendar of wills.
+
+Periods in a calendar (such as years and months) are usually, though not necessarily, synchronized with the cycle of the sun or the moon. The most common type of pre-modern calendar was the lunisolar calendar, a lunar calendar that occasionally adds one intercalary month to remain synchronized with the solar year over the long term.
+
+Etymology
+The term calendar is taken from , the term for the first day of the month in the Roman calendar, related to the verb  'to call out', referring to the "calling" of the new moon when it was first seen. Latin  meant 'account book, register' (as accounts were settled and debts were collected on the calends of each month). The Latin term was adopted in Old French as  and from there in Middle English as  by the 13th century (the spelling calendar is early modern).
+
+History 
+
+The course of the sun and the moon are the most salient regularly recurring natural events useful for timekeeping, and in pre-modern societies around the world lunation and the year were most commonly used as time units. Nevertheless, the Roman calendar contained remnants of a very ancient pre-Etruscan 10-month solar year. 
+
+The first recorded physical calendars, dependent on the development of writing in the Ancient Near East, are the Bronze Age Egyptian and Sumerian calendars.
+
+During the Vedic period India developed a sophisticated timekeeping methodology and calendars for Vedic rituals. According to Yukio Ohashi, the Vedanga calendar in ancient India was based on astronomical studies during the Vedic Period and was not derived from other cultures.
+
+A large number of calendar systems in the Ancient Near East were based on the Babylonian calendar dating from the Iron Age, among them the calendar system of the Persian Empire, which in turn gave rise to the Zoroastrian calendar and the Hebrew calendar. 
+
+A great number of Hellenic calendars were developed in Classical Greece, and during the Hellenistic period they gave rise to the ancient Roman calendar and to various Hindu calendars. 
+
+Calendars in antiquity were lunisolar, depending on the introduction of intercalary months to align the solar and the lunar years. This was mostly based on observation, but there may have been early attempts to model the pattern of intercalation algorithmically, as evidenced in the fragmentary 2nd-century Coligny calendar.
+
+The Roman calendar was reformed by Julius Caesar in 46 BC. His "Julian" calendar was no longer dependent on the observation of the new moon, but followed an algorithm of introducing a leap day every four years. This created a dissociation of the calendar month from lunation. The Gregorian calendar, introduced in 1582, corrected most of the remaining difference between the Julian calendar and the solar year.
+
+The Islamic calendar is based on the prohibition of intercalation (nasi') by Muhammad, in Islamic tradition dated to a sermon given on 9 Dhu al-Hijjah AH 10 (Julian date: 6 March 632). This resulted in an observation-based lunar calendar that shifts relative to the seasons of the solar year.
+
+There have been several modern proposals for reform of the modern calendar, such as the World Calendar, the International Fixed Calendar, the Holocene calendar, and the Hanke-Henry Permanent Calendar. Such ideas are mooted from time to time, but have failed to gain traction because of the loss of continuity and the massive upheaval that implementing them would involve, as well as their effect on cycles of religious activity.
+
+Systems 
+
+A full calendar system has a different calendar date for every day. Thus the week cycle is by itself not a full calendar system; neither is a system to name the days within a year without a system for identifying the years.
+
+The simplest calendar system just counts time periods from a reference date. This applies for the Julian day or Unix Time. Virtually the only possible variation is using a different reference date, in particular, one less distant in the past to make the numbers smaller. Computations in these systems are just a matter of addition and subtraction.
+
+Other calendars have one (or multiple) larger units of time.
+
+Calendars that contain one level of cycles:
+ week and weekday – this system (without year, the week number keeps on increasing) is not very common
+ year and ordinal date within the year, e.g., the ISO 8601 ordinal date system
+
+Calendars with two levels of cycles:
+ year, month, and day – most systems, including the Gregorian calendar (and its very similar predecessor, the Julian calendar), the Islamic calendar, the Solar Hijri calendar and the Hebrew calendar
+ year, week, and weekday – e.g., the ISO week date
+
+Cycles can be synchronized with periodic phenomena:
+
+ Lunar calendars are synchronized to the motion of the Moon (lunar phases); an example is the Islamic calendar.
+ Solar calendars are based on perceived seasonal changes synchronized to the apparent motion of the Sun; an example is the Persian calendar.
+ Lunisolar calendars are based on a combination of both solar and lunar reckonings; examples include the traditional calendar of China, the Hindu calendar in India and Nepal, and the Hebrew calendar.
+ The week cycle is an example of one that is not synchronized to any external phenomenon (although it may have been derived from lunar phases, beginning anew every month).
+
+Very commonly a calendar includes more than one type of cycle or has both cyclic and non-cyclic elements.
+
+Most calendars incorporate more complex cycles.   For example, the vast majority of them track years, months, weeks and days.   The seven-day week is practically universal, though its use varies. It has run uninterrupted for millennia.
+
+Solar
+
+Solar calendars assign a date to each solar day. A day may consist of the period between sunrise and sunset, with a following period of night, or it may be a period between successive events such as two sunsets. The length of the interval between two such successive events may be allowed to vary slightly during the year, or it may be averaged into a mean solar day. Other types of calendar may also use a solar day.
+
+Lunar
+
+Not all calendars use the solar year as a unit. A lunar calendar is one in which days are numbered within each lunar phase cycle.  Because the length of the lunar month is not an even fraction of the length of the tropical year, a purely lunar calendar quickly drifts against the seasons, which do not vary much near the equator.  It does, however, stay constant with respect to other phenomena, notably tides. An example is the Islamic calendar.
+Alexander Marshack, in a controversial reading, believed that marks on a bone baton () represented a lunar calendar. Other marked bones may also represent lunar calendars. Similarly, Michael Rappenglueck believes that marks on a 15,000-year-old cave painting represent a lunar calendar.
+
+Lunisolar
+A lunisolar calendar is a lunar calendar that compensates by adding an extra month as needed to realign the months with the seasons. Prominent examples of lunisolar calendar are Hindu calendar and Buddhist calendar that are popular in South Asia and Southeast Asia. Another example is the Hebrew calendar, which uses a 19-year cycle.
+
+Subdivisions
+
+Nearly all calendar systems group consecutive days into "months" and also into "years". In a solar calendar a year approximates Earth's tropical year (that is, the time it takes for a complete cycle of seasons), traditionally used to facilitate the planning of agricultural activities. In a lunar calendar, the month approximates the cycle of the moon phase. Consecutive days may be grouped into other periods such as the week.
+
+Because the number of days in the tropical year is not a whole number, a solar calendar must have a different number of days in different years. This may be handled, for example, by adding an extra day in leap years. The same applies to months in a lunar calendar and also the number of months in a year in a lunisolar calendar. This is generally known as intercalation. Even if a calendar is solar, but not lunar, the year cannot be divided entirely into months that never vary in length.
+
+Cultures may define other units of time, such as the week, for the purpose of scheduling regular activities that do not easily coincide with months or years. Many cultures use different baselines for their calendars' starting years. Historically, several countries have based their calendars on regnal years, a calendar based on the reign of their current sovereign. For example, the year 2006 in Japan is year 18 Heisei, with Heisei being the era name of Emperor Akihito.
+
+Other types
+
+Arithmetical and astronomical
+
+An astronomical calendar is based on ongoing observation; examples are the religious Islamic calendar and the old religious Jewish calendar in the time of the Second Temple. Such a calendar is also referred to as an observation-based calendar. The advantage of such a calendar is that it is perfectly and perpetually accurate. The disadvantage is that working out when a particular date would occur is difficult.
+
+An arithmetic calendar is one that is based on a strict set of rules; an example is the current Jewish calendar. Such a calendar is also referred to as a rule-based calendar. The advantage of such a calendar is the ease of calculating when a particular date occurs. The disadvantage is imperfect accuracy. Furthermore, even if the calendar is very accurate, its accuracy diminishes slowly over time, owing to changes in Earth's rotation. This limits the lifetime of an accurate arithmetic calendar to a few thousand years. After then, the rules would need to be modified from observations made since the invention of the calendar.
+
+Complete and incomplete
+
+Calendars may be either complete or incomplete. Complete calendars provide a way of naming each consecutive day, while incomplete calendars do not. The early Roman calendar, which had no way of designating the days of the winter months other than to lump them together as "winter", is an example of an incomplete calendar, while the Gregorian calendar is an example of a complete calendar.
+
+Usage
+
+The primary practical use of a calendar is to identify days: to be informed about or to agree on a future event and to record an event that has happened. Days may be significant for agricultural, civil, religious, or social reasons. For example, a calendar provides a way to determine when to start planting or harvesting, which days are religious or civil holidays, which days mark the beginning and end of business accounting periods, and which days have legal significance, such as the day taxes are due or a contract expires. Also, a calendar may, by identifying a day, provide other useful information about the day such as its season.
+
+Calendars are also used as part of a complete timekeeping system: date and time of day together specify a moment in time.  In the modern world, timekeepers can show time, date, and weekday. Some may also show the lunar phase.
+
+Gregorian
+The Gregorian calendar is the de facto international standard and is used almost everywhere in the world for civil purposes. The widely used  solar aspect is a cycle of leap days in a 400-year cycle designed to keep the duration of the year aligned with the solar year. There is a lunar aspect which approximates the position of the moon during the year, and is used in the  calculation of the date of Easter.  Each Gregorian year has either 365 or 366 days (the leap day being inserted as 29 February), amounting to an average Gregorian year of 365.2425 days (compared to a solar year of 365.2422 days).
+
+The calendar was introduced in 1582 as a refinement to the Julian calendar, which had been in use throughout the European Middle Ages, amounting to a 0.002% correction in the length of the year. During the Early Modern period, its adoption was mostly limited to Roman Catholic nations, but by the 19th century it had become widely adopted for the sake of convenience in international trade. The last European country to adopt it was Greece, in 1923.
+
+The calendar epoch used by the Gregorian calendar is inherited from the medieval convention established by Dionysius Exiguus and associated with the Julian calendar. The year number is variously given as AD (for Anno Domini) or CE (for Common Era or Christian Era).
+
+Religious
+
+The most important use of pre-modern calendars is keeping track of the liturgical year and the observation of religious feast days.
+
+While the Gregorian calendar is itself historically motivated to the calculation of the Easter date, it is now in worldwide secular use as the de facto standard. Alongside the use of the Gregorian calendar for secular matters, there remain several calendars in use for religious purposes.
+
+Western Christian liturgical calendars are based on the cycle of the Roman Rite of the Catholic Church and generally include the liturgical seasons of Advent, Christmas, Ordinary Time (Time after Epiphany), Lent, Easter, and Ordinary Time (Time after Pentecost). Some Christian calendars do not include Ordinary Time and every day falls into a denominated season.
+
+Eastern Christians, including the Orthodox Church, use the Julian calendar.
+
+The Islamic calendar or Hijri calendar is a lunar calendar consisting of 12 lunar months in a year of 354 or 355 days. It is used to date events in most of the Muslim countries (concurrently with the Gregorian calendar) and used by Muslims everywhere to determine the proper day on which to celebrate Islamic holy days and festivals. Its epoch is the Hijra (corresponding to AD 622)
+With an annual drift of 11 or 12 days, the seasonal relation is repeated approximately every 33 Islamic years.
+
+Various Hindu calendars remain in use in the Indian subcontinent, including the Nepali calendars, Bengali calendar, Malayalam calendar, Tamil calendar, Vikrama Samvat used in Northern India, and Shalivahana calendar in the Deccan states.
+
+The Buddhist calendar and the traditional lunisolar calendars of Cambodia, Laos, Myanmar, Sri Lanka and Thailand are also based on an older version of the Hindu calendar.
+
+Most of the Hindu calendars are inherited from a system first enunciated in Vedanga Jyotisha of Lagadha, standardized in the Sūrya Siddhānta and subsequently reformed by astronomers such as Āryabhaṭa (AD 499), Varāhamihira (6th century) and Bhāskara II (12th century).
+
+The Hebrew calendar is used by Jews worldwide for religious and cultural affairs, also influences civil matters in Israel (such as national holidays) and can be used business dealings (such as for the dating of cheques).
+
+Followers of the Baháʼí Faith use the Baháʼí calendar. The Baháʼí Calendar, also known as the Badi Calendar was first established by the Bab in the Kitab-i-Asma. The Baháʼí Calendar is also purely a solar calendar and comprises 19 months each having nineteen days.
+
+National
+The Chinese, Hebrew, Hindu, and Julian calendars are widely used for religious and social purposes.
+
+The Iranian (Persian) calendar is used in Iran and some parts of Afghanistan. The Assyrian calendar is in use by the members of the Assyrian community in the Middle East (mainly Iraq, Syria, Turkey, and Iran) and the diaspora. The first year of the calendar is exactly 4750 years prior to the start of the Gregorian calendar. The Ethiopian calendar or Ethiopic calendar is the principal calendar used in Ethiopia and Eritrea, with the Oromo calendar also in use in some areas. In neighboring Somalia, the Somali calendar co-exists alongside the Gregorian and Islamic calendars. In Thailand, where the Thai solar calendar is used, the months and days have adopted the western standard, although the years are still based on the traditional Buddhist calendar.
+
+Fiscal
+
+A fiscal calendar generally means the accounting year of a government or a business. It is used for budgeting, keeping accounts, and taxation. It is a set of 12 months that may start at any date in a year. The US government's fiscal year starts on 1 October and ends on 30 September. The government of India's fiscal year starts on 1 April and ends on 31 March. Small traditional businesses in India start the fiscal year on Diwali festival and end the day before the next year's Diwali festival.
+
+In accounting (and particularly accounting software), a fiscal calendar (such as a 4/4/5 calendar) fixes each month at a specific number of weeks to facilitate comparisons from month to month and year to year. January always has exactly 4 weeks (Sunday through Saturday), February has 4 weeks, March has 5 weeks, etc. Note that this calendar will normally need to add a 53rd week to every 5th or 6th year, which might be added to December or might not be, depending on how the organization uses those dates. There exists an international standard way to do this (the ISO week). The ISO week starts on a Monday and ends on a Sunday. Week 1 is always the week that contains 4 January in the Gregorian calendar.
+
+Formats
+
+The term calendar applies not only to a given scheme of timekeeping but also to a specific record or device displaying such a scheme, for example, an appointment book in the form of a pocket calendar (or personal organizer), desktop calendar, a wall calendar, etc.
+
+In a paper calendar, one or two sheets can show a single day, a week, a month, or a year. If a sheet is for a single day, it easily shows the date and the weekday. If a sheet is for multiple days it shows a conversion table to convert from weekday to date and back. With a special pointing device, or by crossing out past days, it may indicate the current date and weekday. This is the most common usage of the word.
+
+In the US Sunday is considered the first day of the week and so appears on the far left and Saturday the last day of the week appearing on the far right. In Britain, the weekend may appear at the end of the week so the first day is Monday and the last day is Sunday. The US calendar display is also used in Britain.
+
+It is common to display the Gregorian calendar in separate monthly grids of seven columns (from Monday to Sunday, or Sunday to Saturday depending on which day is considered to start the week – this varies according to country) and five to six rows (or rarely, four rows when the month of February contains 28 days in common years beginning on the first day of the week), with the day of the month numbered in each cell, beginning with 1.   The sixth row is sometimes eliminated by marking 23/30 and 24/31 together as necessary.
+
+When working with weeks rather than months, a continuous format is sometimes more convenient, where no blank cells are inserted to ensure that the first day of a new month begins on a fresh row.
+
+Software
+
+Calendaring software provides users with an electronic version of a calendar, and may additionally provide an appointment book, address book, or contact list.
+Calendaring is a standard feature of many PDAs, EDAs, and smartphones. The software may be a local package designed for individual use (e.g., Lightning extension for Mozilla Thunderbird, Microsoft Outlook without Exchange Server, or Windows Calendar) or maybe a networked package that allows for the sharing of information between users (e.g., Mozilla Sunbird, Windows Live Calendar, Google Calendar, or Microsoft Outlook with Exchange Server).
+
+See also 
+
+ General Roman Calendar
+ List of calendars
+ Advent calendar
+ Calendar reform
+ Calendrical calculation
+ Docket (court)
+ History of calendars
+ Horology
+ List of international common standards
+ List of unofficial observances by date
+ Real-time clock (RTC), which underlies the Calendar software on modern computers.
+ Unit of time
+
+References
+
+Citations
+
+Sources
+
+Further reading
+
+External links
+
+ 
+ 
+ 
+Calendar converter, including all major civil, religious and technical calendars.
+
+ 
+Units of time
+Physical cosmology is a branch of cosmology concerned with the study of cosmological models.  A cosmological model, or simply cosmology, provides a description of the largest-scale structures and dynamics of the universe and allows study of fundamental questions about its origin, structure, evolution, and ultimate fate.  Cosmology as a science originated with the Copernican principle, which implies that celestial bodies obey identical physical laws to those on Earth, and Newtonian mechanics, which first allowed those physical laws to be understood.
+
+Physical cosmology, as it is now understood, began with the development in 1915 of Albert Einstein's general theory of relativity, followed by major observational discoveries in the 1920s: first, Edwin Hubble discovered that the universe contains a huge number of external galaxies beyond the Milky Way; then, work by Vesto Slipher and others showed that the universe is expanding. These advances made it possible to speculate about the origin of the universe, and allowed the establishment of the Big Bang theory, by Georges Lemaître, as the leading cosmological model. A few researchers still advocate a handful of alternative cosmologies; however, most cosmologists agree that the Big Bang theory best explains the observations.
+
+Dramatic advances in observational cosmology since the 1990s, including the cosmic microwave background, distant supernovae and galaxy redshift surveys, have led to the development of a standard model of cosmology. This model requires the universe to contain large amounts of dark matter and dark energy whose nature is currently not well understood, but the model gives detailed predictions that are in excellent agreement with many diverse observations.
+
+Cosmology draws heavily on the work of many disparate areas of research in theoretical and applied physics. Areas relevant to cosmology include particle physics experiments and theory, theoretical and observational astrophysics, general relativity, quantum mechanics, and plasma physics.
+
+Subject history 
+
+Modern cosmology developed along tandem tracks of theory and observation. In 1916, Albert Einstein published his theory of general relativity, which provided a unified description of gravity as a geometric property of space and time. At the time, Einstein believed in a static universe, but found that his original formulation of the theory did not permit it. This is because masses distributed throughout the universe gravitationally attract, and move toward each other over time. However, he realized that his equations permitted the introduction of a constant term which could counteract the attractive force of gravity on the cosmic scale. Einstein published his first paper on relativistic cosmology in 1917, in which he added this cosmological constant to his field equations in order to force them to model a static universe. The Einstein model describes a static universe; space is finite and unbounded (analogous to the surface of a sphere, which has a finite area but no edges). However, this so-called Einstein model is unstable to small perturbations—it will eventually start to expand or contract. It was later realized that Einstein's model was just one of a larger set of possibilities, all of which were consistent with general relativity and the cosmological principle. The cosmological solutions of general relativity were found by Alexander Friedmann in the early 1920s. His equations describe the Friedmann–Lemaître–Robertson–Walker universe, which may expand or contract, and whose geometry may be open, flat, or closed.
+
+In the 1910s, Vesto Slipher (and later Carl Wilhelm Wirtz) interpreted the red shift of spiral nebulae as a Doppler shift that indicated they were receding from Earth. However, it is difficult to determine the distance to astronomical objects. One way is to compare the physical size of an object to its angular size, but a physical size must be assumed to do this. Another method is to measure the brightness of an object and assume an intrinsic luminosity, from which the distance may be determined using the inverse-square law. Due to the difficulty of using these methods, they did not realize that the nebulae were actually galaxies outside our own Milky Way, nor did they speculate about the cosmological implications. In 1927, the Belgian Roman Catholic priest Georges Lemaître independently derived the Friedmann–Lemaître–Robertson–Walker equations and proposed, on the basis of the recession of spiral nebulae, that the universe began with the "explosion" of a "primeval atom"—which was later called the Big Bang. In 1929, Edwin Hubble provided an observational basis for Lemaître's theory. Hubble showed that the spiral nebulae were galaxies by determining their distances using measurements of the brightness of Cepheid variable stars. He discovered a relationship between the redshift of a galaxy and its distance. He interpreted this as evidence that the galaxies are receding from Earth in every direction at speeds proportional to their distance. This fact is now known as Hubble's law, though the numerical factor Hubble found relating recessional velocity and distance was off by a factor of ten, due to not knowing about the types of Cepheid variables.
+
+Given the cosmological principle, Hubble's law suggested that the universe was expanding. Two primary explanations were proposed for the expansion. One was Lemaître's Big Bang theory, advocated and developed by George Gamow. The other explanation was Fred Hoyle's steady state model in which new matter is created as the galaxies move away from each other. In this model, the universe is roughly the same at any point in time.
+
+For a number of years, support for these theories was evenly divided. However, the observational evidence began to support the idea that the universe evolved from a hot dense state. The discovery of the cosmic microwave background in 1965 lent strong support to the Big Bang model, and since the precise measurements of the cosmic microwave background by the Cosmic Background Explorer in the early 1990s, few cosmologists have seriously proposed other theories of the origin and evolution of the cosmos. One consequence of this is that in standard general relativity, the universe began with a singularity, as demonstrated by Roger Penrose and Stephen Hawking in the 1960s.
+
+An alternative view to extend the Big Bang model, suggesting the universe had no beginning or singularity and the age of the universe is infinite, has been presented.
+
+In September 2023, astrophysicists questioned the overall current view of the universe, in the form of the Standard Model of Cosmology, based on the latest James Webb Space Telescope studies.
+
+Energy of the cosmos
+The lightest chemical elements, primarily hydrogen and helium, were created during the Big Bang through the process of nucleosynthesis. In a sequence of stellar nucleosynthesis reactions, smaller atomic nuclei are then combined into larger atomic nuclei, ultimately forming stable iron group elements such as iron and nickel, which have the highest nuclear binding energies. The net process results in a later energy release, meaning subsequent to the Big Bang. Such reactions of nuclear particles can lead to sudden energy releases from cataclysmic variable stars such as novae. Gravitational collapse of matter into black holes also powers the most energetic processes, generally seen in the nuclear regions of galaxies, forming quasars and active galaxies.
+
+Cosmologists cannot explain all cosmic phenomena exactly, such as those related to the accelerating expansion of the universe, using conventional forms of energy. Instead, cosmologists propose a new form of energy called dark energy that permeates all space. One hypothesis is that dark energy is just the vacuum energy, a component of empty space that is associated with the virtual particles that exist due to the uncertainty principle.
+
+There is no clear way to define the total energy in the universe using the most widely accepted theory of gravity, general relativity. Therefore, it remains controversial whether the total energy is conserved in an expanding universe. For instance, each photon that travels through intergalactic space loses energy due to the redshift effect. This energy is not transferred to any other system, so seems to be permanently lost. On the other hand, some cosmologists insist that energy is conserved in some sense; this follows the law of conservation of energy.
+
+Different forms of energy may dominate the cosmos—relativistic particles which are referred to as radiation, or non-relativistic particles referred to as matter. Relativistic particles are particles whose rest mass is zero or negligible compared to their kinetic energy, and so move at the speed of light or very close to it; non-relativistic particles have much higher rest mass than their energy and so move much slower than the speed of light.
+
+As the universe expands, both matter and radiation become diluted. However, the energy densities of radiation and matter dilute at different rates. As a particular volume expands, mass-energy density is changed only by the increase in volume, but the energy density of radiation is changed both by the increase in volume and by the increase in the wavelength of the photons that make it up. Thus the energy of radiation becomes a smaller part of the universe's total energy than that of matter as it expands. The very early universe is said to have been 'radiation dominated' and radiation controlled the deceleration of expansion. Later, as the average energy per photon becomes roughly 10 eV and lower, matter dictates the rate of deceleration and the universe is said to be 'matter dominated'. The intermediate case is not treated well analytically. As the expansion of the universe continues, matter dilutes even further and the cosmological constant becomes dominant, leading to an acceleration in the universe's expansion.
+
+History of the universe
+
+The history of the universe is a central issue in cosmology. The history of the universe is divided into different periods called epochs, according to the dominant forces and processes in each period. The standard cosmological model is known as the Lambda-CDM model.
+
+Equations of motion
+
+Within the standard cosmological model, the equations of motion governing the universe as a whole are derived from general relativity with a small, positive cosmological constant. The solution is an expanding universe; due to this expansion, the radiation and matter in the universe cool down and become diluted. At first, the expansion is slowed down by gravitation attracting the radiation and matter in the universe. However, as these become diluted, the cosmological constant becomes more dominant and the expansion of the universe starts to accelerate rather than decelerate. In our universe this happened billions of years ago.
+
+Particle physics in cosmology
+
+During the earliest moments of the universe, the average energy density was very high, making knowledge of particle physics critical to understanding this environment. Hence, scattering processes and decay of unstable elementary particles are important for cosmological models of this period.
+
+As a rule of thumb, a scattering or a decay process is cosmologically important in a certain epoch if the time scale describing that process is smaller than, or comparable to, the time scale of the expansion of the universe. The time scale that describes the expansion of the universe is  with  being the Hubble parameter, which varies with time. The expansion timescale  is roughly equal to the age of the universe at each point in time.
+
+Timeline of the Big Bang
+
+Observations suggest that the universe began around 13.8 billion years ago. Since then, the evolution of the universe has passed through three phases. The very early universe, which is still poorly understood, was the split second in which the universe was so hot that particles had energies higher than those currently accessible in particle accelerators on Earth. Therefore, while the basic features of this epoch have been worked out in the Big Bang theory, the details are largely based on educated guesses.
+Following this, in the early universe, the evolution of the universe proceeded according to known high energy physics. This is when the first protons, electrons and neutrons formed, then nuclei and finally atoms. With the formation of neutral hydrogen, the cosmic microwave background was emitted. Finally, the epoch of structure formation began, when matter started to aggregate into the first stars and quasars, and ultimately galaxies, clusters of galaxies and superclusters formed. The future of the universe is not yet firmly known, but according to the ΛCDM model it will continue expanding forever.
+
+Areas of study
+Below, some of the most active areas of inquiry in cosmology are described, in roughly chronological order. This does not include all of the Big Bang cosmology, which is presented in Timeline of the Big Bang.
+
+Very early universe
+The early, hot universe appears to be well explained by the Big Bang from roughly 10−33 seconds onwards, but there are several problems. One is that there is no compelling reason, using current particle physics, for the universe to be flat, homogeneous, and isotropic (see the cosmological principle). Moreover, grand unified theories of particle physics suggest that there should be magnetic monopoles in the universe, which have not been found. These problems are resolved by a brief period of cosmic inflation, which drives the universe to flatness, smooths out anisotropies and inhomogeneities to the observed level, and exponentially dilutes the monopoles. The physical model behind cosmic inflation is extremely simple, but it has not yet been confirmed by particle physics, and there are difficult problems reconciling inflation and quantum field theory. Some cosmologists think that string theory and brane cosmology will provide an alternative to inflation.
+
+Another major problem in cosmology is what caused the universe to contain far more matter than antimatter. Cosmologists can observationally deduce that the universe is not split into regions of matter and antimatter. If it were, there would be X-rays and gamma rays produced as a result of annihilation, but this is not observed. Therefore, some process in the early universe must have created a small excess of matter over antimatter, and this (currently not understood) process is called baryogenesis. Three required conditions for baryogenesis were derived by Andrei Sakharov in 1967, and requires a violation of the particle physics symmetry, called CP-symmetry, between matter and antimatter. However, particle accelerators measure too small a violation of CP-symmetry to account for the baryon asymmetry. Cosmologists and particle physicists look for additional violations of the CP-symmetry in the early universe that might account for the baryon asymmetry.
+
+Both the problems of baryogenesis and cosmic inflation are very closely related to particle physics, and their resolution might come from high energy theory and experiment, rather than through observations of the universe.
+
+Big Bang Theory
+
+Big Bang nucleosynthesis is the theory of the formation of the elements in the early universe. It finished when the universe was about three minutes old and its temperature dropped below that at which nuclear fusion could occur. Big Bang nucleosynthesis had a brief period during which it could operate, so only the very lightest elements were produced. Starting from hydrogen ions (protons), it principally produced deuterium, helium-4, and lithium. Other elements were produced in only trace abundances. The basic theory of nucleosynthesis was developed in 1948 by George Gamow, Ralph Asher Alpher, and Robert Herman. It was used for many years as a probe of physics at the time of the Big Bang, as the theory of Big Bang nucleosynthesis connects the abundances of primordial light elements with the features of the early universe. Specifically, it can be used to test the equivalence principle, to probe dark matter, and test neutrino physics. Some cosmologists have proposed that Big Bang nucleosynthesis suggests there is a fourth "sterile" species of neutrino.
+
+Standard model of Big Bang cosmology
+The ΛCDM (Lambda cold dark matter) or Lambda-CDM model is a parametrization of the Big Bang cosmological model in which the universe contains a cosmological constant, denoted by Lambda (Greek Λ), associated with dark energy, and cold dark matter (abbreviated CDM). It is frequently referred to as the standard model of Big Bang cosmology.
+
+Cosmic microwave background
+
+The cosmic microwave background is radiation left over from decoupling after the epoch of recombination when neutral atoms first formed. At this point, radiation produced in the Big Bang stopped Thomson scattering from charged ions. The radiation, first observed in 1965 by Arno Penzias and Robert Woodrow Wilson, has a perfect thermal black-body spectrum. It has a temperature of 2.7 kelvins today and is isotropic to one part in 105. Cosmological perturbation theory, which describes the evolution of slight inhomogeneities in the early universe, has allowed cosmologists to precisely calculate the angular power spectrum of the radiation, and it has been measured by the recent satellite experiments (COBE and WMAP) and many ground and balloon-based experiments (such as Degree Angular Scale Interferometer, Cosmic Background Imager, and Boomerang). One of the goals of these efforts is to measure the basic parameters of the Lambda-CDM model with increasing accuracy, as well as to test the predictions of the Big Bang model and look for new physics. The results of measurements made by WMAP, for example, have placed limits on the neutrino masses.
+
+Newer experiments, such as QUIET and the Atacama Cosmology Telescope, are trying to measure the polarization of the cosmic microwave background. These measurements are expected to provide further confirmation of the theory as well as information about cosmic inflation, and the so-called secondary anisotropies, such as the Sunyaev-Zel'dovich effect and Sachs-Wolfe effect, which are caused by interaction between galaxies and clusters with the cosmic microwave background.
+
+On 17 March 2014, astronomers of the BICEP2 Collaboration announced the apparent detection of B-mode polarization of the CMB, considered to be evidence of primordial gravitational waves that are predicted by the theory of inflation to occur during the earliest phase of the Big Bang. However, later that year the Planck collaboration provided a more accurate measurement of cosmic dust, concluding that the B-mode signal from dust is the same strength as that reported from BICEP2. On 30 January 2015, a joint analysis of BICEP2 and Planck data was published and the European Space Agency announced that the signal can be entirely attributed to interstellar dust in the Milky Way.
+
+Formation and evolution of large-scale structure
+
+Understanding the formation and evolution of the largest and earliest structures (i.e., quasars, galaxies, clusters and superclusters) is one of the largest efforts in cosmology. Cosmologists study a model of hierarchical structure formation in which structures form from the bottom up, with smaller objects forming first, while the largest objects, such as superclusters, are still assembling. One way to study structure in the universe is to survey the visible galaxies, in order to construct a three-dimensional picture of the galaxies in the universe and measure the matter power spectrum. This is the approach of the Sloan Digital Sky Survey and the 2dF Galaxy Redshift Survey.
+
+Another tool for understanding structure formation is simulations, which cosmologists use to study the gravitational aggregation of matter in the universe, as it clusters into filaments, superclusters and voids. Most simulations contain only non-baryonic cold dark matter, which should suffice to understand the universe on the largest scales, as there is much more dark matter in the universe than visible, baryonic matter. More advanced simulations are starting to include baryons and study the formation of individual galaxies. Cosmologists study these simulations to see if they agree with the galaxy surveys, and to understand any discrepancy.
+
+Other, complementary observations to measure the distribution of matter in the distant universe and to probe reionization include:
+ The Lyman-alpha forest, which allows cosmologists to measure the distribution of neutral atomic hydrogen gas in the early universe, by measuring the absorption of light from distant quasars by the gas.
+ The 21-centimeter absorption line of neutral atomic hydrogen also provides a sensitive test of cosmology.
+ Weak lensing, the distortion of a distant image by gravitational lensing due to dark matter.
+
+These will help cosmologists settle the question of when and how structure formed in the universe.
+
+Dark matter
+
+Evidence from Big Bang nucleosynthesis, the cosmic microwave background, structure formation, and galaxy rotation curves suggests that about 23% of the mass of the universe consists of non-baryonic dark matter, whereas only 4% consists of visible, baryonic matter. The gravitational effects of dark matter are well understood, as it behaves like a cold, non-radiative fluid that forms haloes around galaxies. Dark matter has never been detected in the laboratory, and the particle physics nature of dark matter remains completely unknown. Without observational constraints, there are a number of candidates, such as a stable supersymmetric particle, a weakly interacting massive particle, a gravitationally-interacting massive particle, an axion, and a massive compact halo object. Alternatives to the dark matter hypothesis include a modification of gravity at small accelerations (MOND) or an effect from brane cosmology. TeVeS is a version of MOND that can explain gravitational lensing.
+
+Dark energy
+
+If the universe is flat, there must be an additional component making up 73% (in addition to the 23% dark matter and 4% baryons) of the energy density of the universe. This is called dark energy. In order not to interfere with Big Bang nucleosynthesis and the cosmic microwave background, it must not cluster in haloes like baryons and dark matter. There is strong observational evidence for dark energy, as the total energy density of the universe is known through constraints on the flatness of the universe, but the amount of clustering matter is tightly measured, and is much less than this. The case for dark energy was strengthened in 1999, when measurements demonstrated that the expansion of the universe has begun to gradually accelerate.
+
+Apart from its density and its clustering properties, nothing is known about dark energy. Quantum field theory predicts a cosmological constant (CC) much like dark energy, but 120 orders of magnitude larger than that observed. Steven Weinberg and a number of string theorists (see string landscape) have invoked the 'weak anthropic principle': i.e. the reason that physicists observe a universe with such a small cosmological constant is that no physicists (or any life) could exist in a universe with a larger cosmological constant. Many cosmologists find this an unsatisfying explanation: perhaps because while the weak anthropic principle is self-evident (given that living observers exist, there must be at least one universe with a cosmological constant which allows for life to exist) it does not attempt to explain the context of that universe. For example, the weak anthropic principle alone does not distinguish between:
+ Only one universe will ever exist and there is some underlying principle that constrains the CC to the value we observe.
+ Only one universe will ever exist and although there is no underlying principle fixing the CC, we got lucky.
+ Lots of universes exist (simultaneously or serially) with a range of CC values, and of course ours is one of the life-supporting ones.
+
+Other possible explanations for dark energy include quintessence or a modification of gravity on the largest scales. The effect on cosmology of the dark energy that these models describe is given by the dark energy's equation of state, which varies depending upon the theory. The nature of dark energy is one of the most challenging problems in cosmology.
+
+A better understanding of dark energy is likely to solve the problem of the ultimate fate of the universe. In the current cosmological epoch, the accelerated expansion due to dark energy is preventing structures larger than superclusters from forming. It is not known whether the acceleration will continue indefinitely, perhaps even increasing until a big rip, or whether it will eventually reverse, lead to a Big Freeze, or follow some other scenario.
+
+Gravitational waves
+Gravitational waves  are ripples in the curvature of spacetime that propagate as waves at the speed of light, generated in certain gravitational interactions that propagate outward from their source. Gravitational-wave astronomy is an emerging branch of observational astronomy which aims to use gravitational waves to collect observational data about sources of detectable gravitational waves such as binary star systems composed of white dwarfs, neutron stars, and black holes; and events such as supernovae, and the formation of the early universe shortly after the Big Bang.
+
+In 2016, the LIGO Scientific Collaboration and Virgo Collaboration teams announced that they had made the first observation of gravitational waves, originating from a pair of merging black holes using the Advanced LIGO detectors. On 15 June 2016, a second detection of gravitational waves from coalescing black holes was announced. Besides LIGO, many other gravitational-wave observatories (detectors) are under construction.
+
+Other areas of inquiry
+Cosmologists also study:
+ Whether primordial black holes were formed in our universe, and what happened to them.
+ Detection of cosmic rays with energies above the GZK cutoff, and whether it signals a failure of special relativity at high energies.
+ The equivalence principle, whether or not Einstein's general theory of relativity is the correct theory of gravitation, and if the fundamental laws of physics are the same everywhere in the universe.
+
+See also
+
+ Accretion
+ Hubble's law
+ Illustris project
+ List of cosmologists
+ Physical ontology
+ Quantum cosmology
+ String cosmology
+ Universal Rotation Curve
+
+References
+
+Further reading
+
+Popular
+
+Textbooks
+  Introductory cosmology and general relativity without the full tensor apparatus, deferred until the last part of the book.
+  Modern introduction to cosmology covering the homogeneous and inhomogeneous universe as well as inflation and the CMB.
+  An introductory text, released slightly before the WMAP results.
+ 
+ 
+  For undergraduates; mathematically gentle with a strong historical focus.
+  An introductory astronomy text.
+  The classic reference for researchers.
+  Cosmology without general relativity.
+  An introduction to cosmology with a thorough discussion of inflation.
+ 
+  Discusses the formation of large-scale structures in detail.
+  An introduction including more on general relativity and quantum field theory than most.
+  Strong historical focus.
+  The classic work on large-scale structure and correlation functions.
+ 
+  A standard reference for the mathematical formalism.
+
+External links
+
+From groups
+ Cambridge Cosmology – from Cambridge University (public home page)
+ Cosmology 101 – from the NASA WMAP group
+ Center for Cosmological Physics. University of Chicago, Chicago.
+ Origins, Nova Online – Provided by PBS.
+
+From individuals
+ Gale, George, "Cosmology: Methodological Debates in the 1930s and 1940s", The Stanford Encyclopedia of Philosophy, Edward N. Zalta (ed.)
+ Madore, Barry F., "Level 5 : A Knowledgebase for Extragalactic Astronomy and Cosmology". Caltech and Carnegie. Pasadena, California.
+ Tyler, Pat, and Phil Newman "Beyond Einstein". Laboratory for High Energy Astrophysics (LHEA) NASA Goddard Space Flight Center.
+ Wright, Ned. "Cosmology tutorial and FAQ". Division of Astronomy & Astrophysics, UCLA.
+ 
+ 
+
+ 
+Philosophy of physics
+Philosophy of time
+Astronomical sub-disciplines
+Astrophysics
+In physical cosmology, cosmic inflation, cosmological inflation, or just inflation, is a theory of exponential expansion of space in the early universe. The inflationary epoch is believed to have lasted from  seconds to between  and  seconds  after the Big Bang. Following the inflationary period, the universe continued to expand, but at a slower rate. The acceleration of this expansion due to dark energy began after the universe was already over 7.7 billion years old (5.4 billion years ago).
+
+Inflation theory was developed in the late 1970s and early 80s, with notable contributions by several theoretical physicists, including Alexei Starobinsky  at Landau Institute for Theoretical Physics, Alan Guth at Cornell University, and Andrei Linde at Lebedev Physical Institute. Alexei Starobinsky, Alan Guth, and Andrei Linde won the 2014 Kavli Prize "for pioneering the theory of cosmic inflation". It was developed further in the early 1980s. It explains the origin of the large-scale structure of the cosmos. Quantum fluctuations in the microscopic inflationary region, magnified to cosmic size, become the seeds for the growth of structure in the Universe (see galaxy formation and evolution and structure formation). Many physicists also believe that inflation explains why the universe appears to be the same in all directions (isotropic), why the cosmic microwave background radiation is distributed evenly, why the universe is flat, and why no magnetic monopoles have been observed.
+
+The detailed particle physics mechanism responsible for inflation is unknown. The basic inflationary paradigm is accepted by most physicists, as a number of inflation model predictions have been confirmed by observation; however, a substantial minority of scientists dissent from this position. The hypothetical field thought to be responsible for inflation is called the inflaton.
+
+In 2002 three of the original architects of the theory were recognized for their major contributions; physicists Alan Guth of M.I.T., Andrei Linde of Stanford, and Paul Steinhardt of Princeton shared the prestigious Dirac Prize "for development of the concept of inflation in cosmology". In 2012 Guth and Linde were awarded the Breakthrough Prize in Fundamental Physics for their invention and development of inflationary cosmology.
+
+Overview 
+
+Around 1930, Edwin Hubble discovered that light from remote galaxies was redshifted; the more remote, the more shifted. This implies that the galaxies are receding from the Earth, with more distant galaxies receding more rapidly, such that galaxies also recede from each other. This expansion of the universe was previously predicted by Alexander Friedmann and Georges Lemaître from the theory of general relativity. It can be understood as a consequence of an initial impulse, which sent the contents of the universe flying apart at such a rate that their mutual gravitational attraction has not reversed their separation.
+
+Inflation may provide this initial impulse. According to the Friedmann equations that describe the dynamics of an expanding universe, a fluid with sufficiently negative pressure exerts gravitational repulsion in the cosmological context. A field in a positive-energy false vacuum state could represent such a fluid, and the resulting repulsion would set the universe into exponential expansion. This inflation phase was originally proposed by Alan Guth in 1979 because the exponential expansion could dilute exotic relics, such as magnetic monopoles, that were predicted by grand unified theories at the time. This would explain why such relics were not seen. It was quickly realized that such accelerated expansion would resolve the horizon problem and the flatness problem. These problems arise from the notion that to look like it does today, the Universe must have started from very finely tuned, or "special", initial conditions at the Big Bang.
+
+Theory 
+
+An expanding universe generally has a cosmological horizon, which, by analogy with the more familiar horizon caused by the curvature of Earth's surface, marks the boundary of the part of the Universe that an observer can see. Light (or other radiation) emitted by objects beyond the cosmological horizon in an accelerating universe never reaches the observer, because the space in between the observer and the object is expanding too rapidly.
+
+The observable universe is one causal patch of a much larger unobservable universe; other parts of the Universe cannot communicate with Earth yet. These parts of the Universe are outside our current cosmological horizon. In the standard hot big bang model, without inflation, the cosmological horizon moves out, bringing new regions into view. Yet as a local observer sees such a region for the first time, it looks no different from any other region of space the local observer has already seen: its background radiation is at nearly the same temperature as the background radiation of other regions, and its space-time curvature is evolving lock-step with the others. This presents a mystery: how did these new regions know what temperature and curvature they were supposed to have? They couldn't have learned it by getting signals, because they were not previously in communication with our past light cone.
+
+Inflation answers this question by postulating that all the regions come from an earlier era with a big vacuum energy, or cosmological constant. A space with a cosmological constant is qualitatively different: instead of moving outward, the cosmological horizon stays put. For any one observer, the distance to the cosmological horizon is constant. With exponentially expanding space, two nearby observers are separated very quickly; so much so, that the distance between them quickly exceeds the limits of communications. The spatial slices are expanding very fast to cover huge volumes. Things are constantly moving beyond the cosmological horizon, which is a fixed distance away, and everything becomes homogeneous.
+
+As the inflationary field slowly relaxes to the vacuum, the cosmological constant goes to zero and space begins to expand normally. The new regions that come into view during the normal expansion phase are exactly the same regions that were pushed out of the horizon during inflation, and so they are at nearly the same temperature and curvature, because they come from the same originally small patch of space.
+
+The theory of inflation thus explains why the temperatures and curvatures of different regions are so nearly equal. It also predicts that the total curvature of a space-slice at constant global time is zero. This prediction implies that the total ordinary matter, dark matter and residual vacuum energy in the Universe have to add up to the critical density, and the evidence supports this. More strikingly, inflation allows physicists to calculate the minute differences in temperature of different regions from quantum fluctuations during the inflationary era, and many of these quantitative predictions have been confirmed.
+
+Space expands
+In a space that expands exponentially (or nearly exponentially) with time, any pair of free-floating objects that are initially at rest will move apart from each other at an accelerating rate, at least as long as they are not bound together by any force.  From the point of view of one such object, the spacetime is something like an inside-out Schwarzschild black hole—each object is surrounded by a spherical event horizon.  Once the other object has fallen through this horizon it can never return, and even light signals it sends will never reach the first object (at least so long as the space continues to expand exponentially).
+
+In the approximation that the expansion is exactly exponential, the horizon is static and remains a fixed physical distance away.  This patch of an inflating universe can be described by the following metric:
+
+This exponentially expanding spacetime is called a de Sitter space, and to sustain it there must be a cosmological constant, a vacuum energy density that is constant  in space and time and proportional to Λ in the above metric. For the case of exactly exponential expansion, the vacuum energy has a negative pressure p equal in magnitude to its energy density ρ; the equation of state is p=−ρ.
+
+Inflation is typically not an exactly exponential expansion, but rather quasi- or near-exponential.  In such a universe the horizon will slowly grow with time as the vacuum energy density gradually decreases.
+
+Few inhomogeneities remain
+Because the accelerating expansion of space stretches out any initial variations in density or temperature to very large length scales, an essential feature of inflation is that it smooths out inhomogeneities and anisotropies, and reduces the curvature of space. This pushes the Universe into a very simple state in which it is completely dominated by the inflaton field and the only significant inhomogeneities are tiny quantum fluctuations. Inflation also dilutes exotic heavy particles, such as the magnetic monopoles predicted by many extensions to the Standard Model of particle physics. If the Universe was only hot enough to form such particles before a period of inflation, they would not be observed in nature, as they would be so rare that it is quite likely that there are none in the observable universe. Together, these effects are called the inflationary "no-hair theorem" by analogy with the no hair theorem for black holes.
+
+The "no-hair" theorem works essentially because the cosmological horizon is no different from a black-hole horizon, except for not testable disagreements about what is on the other side. The interpretation of the no-hair theorem is that the Universe (observable and unobservable) expands by an enormous factor during inflation. In an expanding universe, energy densities generally fall, or get diluted, as the volume of the Universe increases. For example, the density of ordinary "cold" matter (dust) goes down as the inverse of the volume: when linear dimensions double, the energy density goes down by a factor of eight; the radiation energy density goes down even more rapidly as the Universe expands since the wavelength of each photon is stretched (redshifted), in addition to the photons being dispersed by the expansion. When linear dimensions are doubled, the energy density in radiation falls by a factor of sixteen (see the solution of the energy density continuity equation for an ultra-relativistic fluid). During inflation, the energy density in the inflaton field is roughly constant. However, the energy density in everything else, including inhomogeneities, curvature, anisotropies, exotic particles, and standard-model particles is falling, and through sufficient inflation these all become negligible. This leaves the Universe flat and symmetric, and (apart from the homogeneous inflaton field) mostly empty, at the moment inflation ends and reheating begins.
+
+Duration
+A key requirement is that inflation must continue long enough to produce the present observable universe from a single, small inflationary Hubble volume. This is necessary to ensure that the Universe appears flat, homogeneous and isotropic at the largest observable scales. This requirement is generally thought to be satisfied if the Universe expanded by a factor of at least  during inflation.
+
+Reheating
+Inflation is a period of supercooled expansion, when the temperature drops by a factor of 100,000 or so. (The exact drop is model-dependent, but in the first models it was typically from  K down to  K.) This relatively low temperature is maintained during the inflationary phase. When inflation ends the temperature returns to the pre-inflationary temperature; this is called reheating or thermalization because the large potential energy of the inflaton field decays into particles and fills the Universe with Standard Model particles, including electromagnetic radiation, starting the radiation dominated phase of the Universe. Because the nature of the inflaton field is not known, this process is still poorly understood, although it is believed to take place through a parametric resonance.
+
+Motivations
+Inflation resolves several problems in Big Bang cosmology that were discovered in the 1970s. Inflation was first proposed by Alan Guth in 1979 while investigating the problem of why no magnetic monopoles are seen today; he found that a positive-energy false vacuum would, according to general relativity, generate an exponential expansion of space. It was very quickly realised that such an expansion would resolve many other long-standing problems. These problems arise from the observation that to look like it does today, the Universe would have to have started from very finely tuned, or "special" initial conditions at the Big Bang. Inflation attempts to resolve these problems by providing a dynamical mechanism that drives the Universe to this special state, thus making a universe like ours much more likely in the context of the Big Bang theory.
+
+Horizon problem
+
+The horizon problem is the problem of determining why the Universe appears statistically homogeneous and isotropic in accordance with the cosmological principle. For example, molecules in a canister of gas are distributed homogeneously and isotropically because they are in thermal equilibrium: gas throughout the canister has had enough time to interact to dissipate inhomogeneities and anisotropies. The situation is quite different in the big bang model without inflation, because gravitational expansion does not give the early universe enough time to equilibrate. In a big bang with only the matter and radiation known in the Standard Model, two widely separated regions of the observable universe cannot have equilibrated because they move apart from each other faster than the speed of light and thus have never come into causal contact. In the early Universe, it was not possible to send a light signal between the two regions. Because they have had no interaction, it is difficult to explain why they have the same temperature (are thermally equilibrated). Historically, proposed solutions included the Phoenix universe of Georges Lemaître, the related oscillatory universe of Richard Chase Tolman, and the Mixmaster universe of Charles Misner. Lemaître and Tolman proposed that a universe undergoing a number of cycles of contraction and expansion could come into thermal equilibrium. Their models failed, however, because of the buildup of entropy over several cycles. Misner made the (ultimately incorrect) conjecture that the Mixmaster mechanism, which made the Universe more chaotic, could lead to statistical homogeneity and isotropy.
+
+Flatness problem
+
+The flatness problem is sometimes called one of the Dicke coincidences (along with the cosmological constant problem).
+It became known in the 1960s that the density of matter in the Universe was comparable to the critical density necessary for a flat universe (that is, a universe whose large scale geometry is the usual Euclidean geometry, rather than a non-Euclidean hyperbolic or spherical geometry).
+
+Therefore, regardless of the shape of the universe the contribution of spatial curvature to the expansion of the Universe could not be much greater than the contribution of matter. But as the Universe expands, the curvature redshifts away more slowly than matter and radiation. Extrapolated into the past, this presents a fine-tuning problem because the contribution of curvature to the Universe must be exponentially small (sixteen orders of magnitude less than the density of radiation at Big Bang nucleosynthesis, for example). This problem is exacerbated by recent observations of the cosmic microwave background that have demonstrated that the Universe is flat to within a few percent.
+
+Magnetic-monopole problem
+The magnetic monopole problem, sometimes called "the exotic-relics problem", says that if the early universe were very hot, a large number of very heavy, stable magnetic monopoles would have been produced.
+
+Stable magnetic monopoles are a problem for Grand Unified Theories, which propose that at high temperatures (such as in the early universe) the electromagnetic force, strong, and weak nuclear forces are not actually fundamental forces but arise due to spontaneous symmetry breaking from a single gauge theory.
+These theories predict a number of heavy, stable particles that have not been observed in nature. The most notorious is the magnetic monopole, a kind of stable, heavy "charge" of magnetic field.
+
+Monopoles are predicted to be copiously produced following Grand Unified Theories at high temperature,
+and they should have persisted to the present day, to such an extent that they would become the primary constituent of the Universe.
+Not only is that not the case, but all searches for them have failed, placing stringent limits on the density of relic magnetic monopoles in the Universe.
+
+A period of inflation that occurs below the temperature where magnetic monopoles can be produced would offer a possible resolution of this problem: Monopoles would be separated from each other as the Universe around them expands, potentially lowering their observed density by many orders of magnitude. Though, as cosmologist Martin Rees has written,
+ "Skeptics about exotic physics might not be hugely impressed by a theoretical argument to explain the absence of particles that are themselves only hypothetical. Preventive medicine can readily seem 100 percent effective against a disease that doesn't exist!"
+
+History
+
+Precursors
+In the early days of General Relativity, Albert Einstein introduced the cosmological constant to allow a static solution, which was a three-dimensional sphere with a uniform density of matter. Later, Willem de Sitter found a highly symmetric inflating universe, which described a universe with a cosmological constant that is otherwise empty.
+It was discovered that Einstein's universe is unstable, and that small fluctuations cause it to collapse or turn into a de Sitter universe.
+
+In the early 1970s, Zeldovich noticed the flatness and horizon problems of Big Bang cosmology; before his work, cosmology was presumed to be symmetrical on purely philosophical grounds. In the Soviet Union, this and other considerations led Belinski and Khalatnikov to analyze the chaotic BKL singularity in General Relativity. Misner's Mixmaster universe attempted to use this chaotic behavior to solve the cosmological problems, with limited success.
+
+False vacuum
+
+In the late 1970s, Sidney Coleman applied the instanton techniques developed by Alexander Polyakov and collaborators to study the fate of the false vacuum in quantum field theory. Like a metastable phase in statistical mechanics—water below the freezing temperature or above the boiling point—a quantum field would need to nucleate a large enough bubble of the new vacuum, the new phase, in order to make a transition. Coleman found the most likely decay pathway for vacuum decay and calculated the inverse lifetime per unit volume. He eventually noted that gravitational effects would be significant, but he did not calculate these effects and did not apply the results to cosmology.
+
+The universe could have been spontaneously created from nothing (no space, time, nor matter) by quantum fluctuations of metastable false vacuum causing an expanding bubble of true vacuum.
+
+Starobinsky inflation
+
+In the Soviet Union, Alexei Starobinsky noted that quantum corrections to general relativity should be important for the early universe. These generically lead to curvature-squared corrections to the Einstein–Hilbert action and a form of f(R) modified gravity. The solution to Einstein's equations in the presence of curvature squared terms, when the curvatures are large, leads to an effective cosmological constant. Therefore, he proposed that the early universe went through an inflationary de Sitter era.
+This resolved the cosmology problems and led to specific predictions for the corrections to the microwave background radiation, corrections that were then calculated in detail. Starobinsky used the action 
+
+which corresponds to the potential
+
+in the Einstein frame. This results in the observables:
+
+Monopole problem
+In 1978, Zeldovich noted the magnetic monopole problem, which was an unambiguous quantitative version of the horizon problem, this time in a subfield of particle physics, which led to several speculative attempts to resolve it. In 1980 Alan Guth realized that false vacuum decay in the early universe would solve the problem, leading him to propose a scalar-driven inflation. Starobinsky's and Guth's scenarios both predicted an initial de Sitter phase, differing only in mechanistic details.
+
+Early inflationary models
+
+Guth proposed inflation in January 1981 to explain the nonexistence of magnetic monopoles;
+it was Guth who coined the term "inflation". At the same time, Starobinsky argued that quantum corrections to gravity would replace the supposed initial singularity of the Universe with an exponentially expanding de Sitter phase.
+In October 1980, Demosthenes Kazanas suggested that exponential expansion could eliminate the particle horizon and perhaps solve the horizon problem,
+while Sato suggested that an exponential expansion could eliminate domain walls (another kind of exotic relic). In 1981 Einhorn and Sato published a model similar to Guth's and showed that it would resolve the puzzle of the magnetic monopole abundance in Grand Unified Theories. Like Guth, they concluded that such a model not only required fine tuning of the cosmological constant, but also would likely lead to a much too granular universe, i.e., to large density variations resulting from bubble wall collisions.
+
+Guth proposed that as the early universe cooled, it was trapped in a false vacuum with a high energy density, which is much like a cosmological constant. As the very early universe cooled it was trapped in a metastable state (it was supercooled), which it could only decay out of through the process of bubble nucleation via quantum tunneling. Bubbles of true vacuum spontaneously form in the sea of false vacuum and rapidly begin expanding at the speed of light. Guth recognized that this model was problematic because the model did not reheat properly: when the bubbles nucleated, they did not generate any radiation. Radiation could only be generated in collisions between bubble walls. But if inflation lasted long enough to solve the initial conditions problems, collisions between bubbles became exceedingly rare. In any one causal patch it is likely that only one bubble would nucleate.
+
+Slow-roll inflation
+The bubble collision problem was solved by Linde and independently by Andreas Albrecht and Paul Steinhardt in a model named new inflation or slow-roll inflation (Guth's model then became known as old inflation). In this model, instead of tunneling out of a false vacuum state, inflation occurred by a scalar field rolling down a potential energy hill. When the field rolls very slowly compared to the expansion of the Universe, inflation occurs. However, when the hill becomes steeper, inflation ends and reheating can occur.
+
+Effects of asymmetries
+
+Eventually, it was shown that new inflation does not produce a perfectly symmetric universe, but that quantum fluctuations in the inflaton are created. These fluctuations form the primordial seeds for all structure created in the later universe. These fluctuations were first calculated by Viatcheslav Mukhanov and G. V. Chibisov in analyzing Starobinsky's similar model. In the context of inflation, they were worked out independently of the work of Mukhanov and Chibisov at the three-week 1982 Nuffield Workshop on the Very Early Universe at Cambridge University. The fluctuations were calculated by four groups working separately over the course of the workshop: Stephen Hawking; Starobinsky; Guth and So-Young Pi; and Bardeen, Steinhardt and Turner.
+
+Observational status
+Inflation is a mechanism for realizing the cosmological principle, which is the basis of the standard model of physical cosmology: it accounts for the homogeneity and isotropy of the observable universe. In addition, it accounts for the observed flatness and absence of magnetic monopoles. Since Guth's early work, each of these observations has received further confirmation, most impressively by the detailed observations of the cosmic microwave background made by the Planck spacecraft. This analysis shows that the Universe is flat to within  percent, and that it is homogeneous and isotropic to one part in 100,000.
+
+Inflation predicts that the structures visible in the Universe today formed through the gravitational collapse of perturbations that were formed as quantum mechanical fluctuations in the inflationary epoch. The detailed form of the spectrum of perturbations, called a nearly-scale-invariant Gaussian random field is very specific and has only two free parameters. One is the amplitude of the spectrum and the spectral index, which measures the slight deviation from scale invariance predicted by inflation (perfect scale invariance corresponds to the idealized de Sitter universe).
+The other free parameter is the tensor to scalar ratio. The simplest inflation models, those without fine-tuning, predict a tensor to scalar ratio near 0.1 .
+
+Inflation predicts that the observed perturbations should be in thermal equilibrium with each other (these are called adiabatic or isentropic perturbations). This structure for the perturbations has been confirmed by the Planck spacecraft, WMAP spacecraft and other cosmic microwave background (CMB) experiments, and galaxy surveys, especially the ongoing Sloan Digital Sky Survey. These experiments have shown that the one part in 100,000 inhomogeneities observed have exactly the form predicted by theory. There is evidence for a slight deviation from scale invariance. The spectral index,  is one for a scale-invariant Harrison–Zel'dovich spectrum. The simplest inflation models predict that  is between 0.92 and 0.98 . This is the range that is possible without fine-tuning of the parameters related to energy. From Planck data it can be inferred that =0.968 ± 0.006, and a tensor to scalar ratio that is less than 0.11 . These are considered an important confirmation of the theory of inflation.
+
+Various inflation theories have been proposed that make radically different predictions, but they generally have much more fine-tuning than should be necessary. As a physical model, however, inflation is most valuable in that it robustly predicts the initial conditions of the Universe based on only two adjustable parameters: the spectral index (that can only change in a small range) and the amplitude of the perturbations. Except in contrived models, this is true regardless of how inflation is realized in particle physics.
+
+Occasionally, effects are observed that appear to contradict the simplest models of inflation. The first-year WMAP data suggested that the spectrum might not be nearly scale-invariant, but might instead have a slight curvature. However, the third-year data revealed that the effect was a statistical anomaly. Another effect remarked upon since the first cosmic microwave background satellite, the Cosmic Background Explorer is that the amplitude of the quadrupole moment of the CMB is unexpectedly low and the other low multipoles appear to be preferentially aligned with the ecliptic plane. Some have claimed that this is a signature of non-Gaussianity and thus contradicts the simplest models of inflation. Others have suggested that the effect may be due to other new physics, foreground contamination, or even publication bias.
+
+An experimental program is underway to further test inflation with more precise CMB measurements. In particular, high precision measurements of the so-called "B-modes" of the polarization of the background radiation could provide evidence of the gravitational radiation produced by inflation, and could also show whether the energy scale of inflation predicted by the simplest models (~ GeV) is correct. In March 2014, the BICEP2 team announced B-mode CMB polarization confirming inflation had been demonstrated. The team announced the tensor-to-scalar power ratio  was between 0.15 and 0.27 (rejecting the null hypothesis;  is expected to be 0 in the absence of inflation). However, on 19 June 2014, lowered confidence in confirming the findings was reported; on 19 September 2014, a further reduction in confidence was reported and, on 30 January 2015, even less confidence yet was reported. By 2018, additional data suggested, with 95% confidence, that  is 0.06 or lower: consistent with the null hypothesis, but still also consistent with many remaining models of inflation.
+
+Other potentially corroborating measurements are expected from the Planck spacecraft, although it is unclear if the signal will be visible, or if contamination from foreground sources will interfere. Other forthcoming measurements, such as those of 21 centimeter radiation (radiation emitted and absorbed from neutral hydrogen before the first stars formed), may measure the power spectrum with even greater resolution than the CMB and galaxy surveys, although it is not known if these measurements will be possible or if interference with radio sources on Earth and in the galaxy will be too great.
+
+Theoretical status
+
+In Guth's early proposal, it was thought that the inflaton was the Higgs field, the field that explains the mass of the elementary particles. It is now believed by some that the inflaton cannot be the Higgs field
+although the recent discovery of the Higgs boson has increased the number of works considering the Higgs field as inflaton.
+One problem of this identification is the current tension with experimental data at the electroweak scale, which is currently under study at the Large Hadron Collider (LHC). Other models of inflation relied on the properties of Grand Unified Theories. Since the simplest models of grand unification have failed, it is now thought by many physicists that inflation will be included in a supersymmetric theory such as string theory or a supersymmetric grand unified theory. At present, while inflation is understood principally by its detailed predictions of the initial conditions for the hot early universe, the particle physics is largely ad hoc modelling. As such, although predictions of inflation have been consistent with the results of observational tests, many open questions remain.
+
+Fine-tuning problem
+One of the most severe challenges for inflation arises from the need for fine tuning. In new inflation, the slow-roll conditions must be satisfied for inflation to occur. The slow-roll conditions say that the inflaton potential must be flat (compared to the large vacuum energy) and that the inflaton particles must have a small mass. New inflation requires the Universe to have a scalar field with an especially flat potential and special initial conditions. However, explanations for these fine-tunings have been proposed. For example, classically scale invariant field theories, where scale invariance is broken by quantum effects, provide an explanation of the flatness of inflationary potentials, as long as the theory can be studied through perturbation theory.
+
+Linde proposed a theory known as chaotic inflation in which he suggested that the conditions for inflation were actually satisfied quite generically. Inflation will occur in virtually any universe that begins in a chaotic, high energy state that has a scalar field with unbounded potential energy. However, in his model the inflaton field necessarily takes values larger than one Planck unit: for this reason, these are often called large field models and the competing new inflation models are called small field models. In this situation, the predictions of effective field theory are thought to be invalid, as renormalization should cause large corrections that could prevent inflation.
+This problem has not yet been resolved and some cosmologists argue that the small field models, in which inflation can occur at a much lower energy scale, are better models. While inflation depends on quantum field theory (and the semiclassical approximation to quantum gravity) in an important way, it has not been completely reconciled with these theories.
+
+Brandenberger commented on fine-tuning in another situation. The amplitude of the primordial inhomogeneities produced in inflation is directly tied to the energy scale of inflation. This scale is suggested to be around  GeV or  times the Planck energy. The natural scale is naïvely the Planck scale so this small value could be seen as another form of fine-tuning (called a hierarchy problem): the energy density given by the scalar potential is down by  compared to the Planck density. This is not usually considered to be a critical problem, however, because the scale of inflation corresponds naturally to the scale of gauge unification.
+
+Eternal inflation
+
+In many models, the inflationary phase of the Universe's expansion lasts forever in at least some regions of the Universe. This occurs because inflating regions expand very rapidly, reproducing themselves. Unless the rate of decay to the non-inflating phase is sufficiently fast, new inflating regions are produced more rapidly than non-inflating regions. In such models, most of the volume of the Universe is continuously inflating at any given time.
+
+All models of eternal inflation produce an infinite, hypothetical multiverse, typically a fractal. The multiverse theory has created significant dissension in the scientific community about the viability of the inflationary model.
+
+Paul Steinhardt, one of the original architects of the inflationary model, introduced the first example of eternal inflation in 1983. He showed that the inflation could proceed forever by producing bubbles of non-inflating space filled with hot matter and radiation surrounded by empty space that continues to inflate. The bubbles could not grow fast enough to keep up with the inflation. Later that same year, Alexander Vilenkin showed that eternal inflation is generic.
+
+Although new inflation is classically rolling down the potential, quantum fluctuations can sometimes lift it to previous levels. These regions in which the inflaton fluctuates upwards expand much faster than regions in which the inflaton has a lower potential energy, and tend to dominate in terms of physical volume. It has been shown that any inflationary theory with an unbounded potential is eternal. There are well-known theorems that this steady state cannot continue forever into the past. Inflationary spacetime, which is similar to de Sitter space, is incomplete without a contracting region. However, unlike de Sitter space, fluctuations in a contracting inflationary space collapse to form a gravitational singularity, a point where densities become infinite. Therefore, it is necessary to have a theory for the Universe's initial conditions.
+
+In eternal inflation, regions with inflation have an exponentially growing volume, while regions that are not inflating don't. This suggests that the volume of the inflating part of the Universe in the global picture is always unimaginably larger than the part that has stopped inflating, even though inflation eventually ends as seen by any single pre-inflationary observer. Scientists disagree about how to assign a probability distribution to this hypothetical anthropic landscape. If the probability of different regions is counted by volume, one should expect that inflation will never end or applying boundary conditions that a local observer exists to observe it, that inflation will end as late as possible.
+
+Some physicists believe this paradox can be resolved by weighting observers by their pre-inflationary volume. Others believe that there is no resolution to the paradox and that the multiverse is a critical flaw in the inflationary paradigm. Paul Steinhardt, who first introduced the eternal inflationary model, later became one of its most vocal critics for this reason.
+
+Initial conditions
+Some physicists have tried to avoid the initial conditions problem by proposing models for an eternally inflating universe with no origin. These models propose that while the Universe, on the largest scales, expands exponentially it was, is and always will be, spatially infinite and has existed, and will exist, forever.
+
+Other proposals attempt to describe the ex nihilo creation of the Universe based on quantum cosmology and the following inflation. Vilenkin put forth one such scenario. Hartle and Hawking offered the no-boundary proposal for the initial creation of the Universe in which inflation comes about naturally.
+
+Guth described the inflationary universe as the "ultimate free lunch": new universes, similar to our own, are continually produced in a vast inflating background. Gravitational interactions, in this case, circumvent (but do not violate) the first law of thermodynamics (energy conservation) and the second law of thermodynamics (entropy and the arrow of time problem). However, while there is consensus that this solves the initial conditions problem, some have disputed this, as it is much more likely that the Universe came about by a quantum fluctuation. Don Page was an outspoken critic of inflation because of this anomaly. He stressed that the thermodynamic arrow of time necessitates low entropy initial conditions, which would be highly unlikely. According to them, rather than solving this problem, the inflation theory aggravates it – the reheating at the end of the inflation era increases entropy, making it necessary for the initial state of the Universe to be even more orderly than in other Big Bang theories with no inflation phase.
+
+Hawking and Page later found ambiguous results when they attempted to compute the probability of inflation in the Hartle-Hawking initial state. Other authors have argued that, since inflation is eternal, the probability doesn't matter as long as it is not precisely zero: once it starts, inflation perpetuates itself and quickly dominates the Universe. However, Albrecht and Lorenzo Sorbo argued that the probability of an inflationary cosmos, consistent with today's observations, emerging by a random fluctuation from some pre-existent state is much higher than that of a non-inflationary cosmos. This is because the "seed" amount of non-gravitational energy required for the inflationary cosmos is so much less than that for a non-inflationary alternative, which outweighs any entropic considerations.
+
+Another problem that has occasionally been mentioned is the trans-Planckian problem or trans-Planckian effects. Since the energy scale of inflation and the Planck scale are relatively close, some of the quantum fluctuations that have made up the structure in our universe were smaller than the Planck length before inflation. Therefore, there ought to be corrections from Planck-scale physics, in particular the unknown quantum theory of gravity. Some disagreement remains about the magnitude of this effect: about whether it is just on the threshold of detectability or completely undetectable.
+
+Hybrid inflation
+Another kind of inflation, called hybrid inflation, is an extension of new inflation. It introduces additional scalar fields, so that while one of the scalar fields is responsible for normal slow roll inflation, another triggers the end of inflation: when inflation has continued for sufficiently long, it becomes favorable to the second field to decay into a much lower energy state.
+
+In hybrid inflation, one scalar field is responsible for most of the energy density (thus determining the rate of expansion), while another is responsible for the slow roll (thus determining the period of inflation and its termination). Thus fluctuations in the former inflaton would not affect inflation termination, while fluctuations in the latter would not affect the rate of expansion. Therefore, hybrid inflation is not eternal. When the second (slow-rolling) inflaton reaches the bottom of its potential, it changes the location of the minimum of the first inflaton's potential, which leads to a fast roll of the inflaton down its potential, leading to termination of inflation.
+
+Relation to dark energy
+Dark energy is broadly similar to inflation and is thought to be causing the expansion of the present-day universe to accelerate. However, the energy scale of dark energy is much lower,  GeV, roughly 27 orders of magnitude less than the scale of inflation.
+
+Inflation and string cosmology
+The discovery of flux compactifications opened the way for reconciling inflation and string theory. Brane inflation suggests that inflation arises from the motion of D-branes in the compactified geometry, usually towards a stack of anti-D-branes. This theory, governed by the Dirac-Born-Infeld action, is different from ordinary inflation. The dynamics are not completely understood. It appears that special conditions are necessary since inflation occurs in tunneling between two vacua in the string landscape. The process of tunneling between two vacua is a form of old inflation, but new inflation must then occur by some other mechanism.
+
+Inflation and loop quantum gravity
+When investigating the effects the theory of loop quantum gravity would have on cosmology, a loop quantum cosmology model has evolved that provides a possible mechanism for cosmological inflation. Loop quantum gravity assumes a quantized spacetime. If the energy density is larger than can be held by the quantized spacetime, it is thought to bounce back.
+
+Alternatives and adjuncts
+Other models have been advanced that are claimed to explain some or all of the observations addressed by inflation.
+
+Big bounce 
+The big bounce hypothesis attempts to replace the cosmic singularity with a cosmic contraction and bounce, thereby explaining the initial conditions that led to the big bang.
+The flatness and horizon problems are naturally solved in the Einstein-Cartan-Sciama-Kibble theory of gravity, without needing an exotic form of matter or free parameters.
+This theory extends general relativity by removing a constraint of the symmetry of the affine connection and regarding its antisymmetric part, the torsion tensor, as a dynamical variable. The minimal coupling between torsion and Dirac spinors generates a spin-spin interaction that is significant in fermionic matter at extremely high densities. Such an interaction averts the unphysical Big Bang singularity, replacing it with a cusp-like bounce at a finite minimum scale factor, before which the Universe was contracting. The rapid expansion immediately after the Big Bounce explains why the present Universe at largest scales appears spatially flat, homogeneous and isotropic. As the density of the Universe decreases, the effects of torsion weaken and the Universe smoothly enters the radiation-dominated era.
+
+Ekpyrotic and cyclic models 
+
+The ekpyrotic and cyclic models are also considered adjuncts to inflation. These models solve the horizon problem through an expanding epoch well before the Big Bang, and then generate the required spectrum of primordial density perturbations during a contracting phase leading to a Big Crunch. The Universe passes through the Big Crunch and emerges in a hot Big Bang phase. In this sense they are reminiscent of Richard Chace Tolman's oscillatory universe; in Tolman's model, however, the total age of the Universe is necessarily finite, while in these models this is not necessarily so. Whether the correct spectrum of density fluctuations can be produced, and whether the Universe can successfully navigate the Big Bang/Big Crunch transition, remains a topic of controversy and current research. Ekpyrotic models avoid the magnetic monopole problem as long as the temperature at the Big Crunch/Big Bang transition remains below the Grand Unified Scale, as this is the temperature required to produce magnetic monopoles in the first place. As things stand, there is no evidence of any 'slowing down' of the expansion, but this is not surprising as each cycle is expected to last on the order of a trillion years.
+
+String gas cosmology 
+String theory requires that, in addition to the three observable spatial dimensions, additional dimensions exist that are curled up or compactified (see also Kaluza–Klein theory). Extra dimensions appear as a frequent component of supergravity models and other approaches to quantum gravity. This raised the contingent question of why four space-time dimensions became large and the rest became unobservably small. An attempt to address this question, called string gas cosmology, was proposed by Robert Brandenberger and Cumrun Vafa. This model focuses on the dynamics of the early universe considered as a hot gas of strings. Brandenberger and Vafa show that a dimension of spacetime can only expand if the strings that wind around it can efficiently annihilate each other. Each string is a one-dimensional object, and the largest number of dimensions in which two strings will generically intersect (and, presumably, annihilate) is three. Therefore, the most likely number of non-compact (large) spatial dimensions is three. Current work on this model centers on whether it can succeed in stabilizing the size of the compactified dimensions and produce the correct spectrum of primordial density perturbations. The original model did not "solve the entropy and flatness problems of standard cosmology", although Brandenburger and coauthors later argued that these problems can be eliminated by implementing string gas cosmology in the context of a bouncing-universe scenario.
+
+Varying c 
+
+Cosmological models employing a variable speed of light have been proposed to resolve the horizon problem of and provide an alternative to cosmic inflation. In the VSL models, the fundamental constant c, denoting the speed of light in vacuum, is greater in the early universe than its present value, effectively increasing the particle horizon at the time of decoupling sufficiently to account for the observed isotropy of the CMB.
+
+Criticisms
+Since its introduction by Alan Guth in 1980, the inflationary paradigm has become widely accepted. Nevertheless, many physicists, mathematicians, and philosophers of science have voiced criticisms, claiming untestable predictions and a lack of serious empirical support. In 1999, John Earman and Jesús Mosterín published a thorough critical review of inflationary cosmology, concluding,
+ "we do not think that there are, as yet, good grounds for admitting any of the models of inflation into the standard core of cosmology."
+
+As pointed out by Roger Penrose from 1986 on, in order to work, inflation requires extremely specific initial conditions of its own, so that the problem (or pseudo-problem) of initial conditions is not solved:
+ "There is something fundamentally misconceived about trying to explain the uniformity of the early universe as resulting from a thermalization process. ... For, if the thermalization is actually doing anything ... then it represents a definite increasing of the entropy. Thus, the universe would have been even more special before the thermalization than after."
+
+The problem of specific or "fine-tuned" initial conditions would not have been solved; it would have gotten worse. At a conference in 2015, Penrose said that
+ "inflation isn't falsifiable, it's falsified. ... BICEP did a wonderful service by bringing all the Inflation-ists out of their shell, and giving them a black eye."
+
+A recurrent criticism of inflation is that the invoked inflaton field does not correspond to any known physical field, and that its potential energy curve seems to be an ad hoc contrivance to accommodate almost any data obtainable. Paul Steinhardt, one of the founding fathers of inflationary cosmology, has recently become one of its sharpest critics. He calls 'bad inflation' a period of accelerated expansion whose outcome conflicts with observations, and 'good inflation' one compatible with them:
+ "Not only is bad inflation more likely than good inflation, but no inflation is more likely than either ... Roger Penrose considered all the possible configurations of the inflaton and gravitational fields. Some of these configurations lead to inflation ... Other configurations lead to a uniform, flat universe directly – without inflation. Obtaining a flat universe is unlikely overall. Penrose's shocking conclusion, though, was that obtaining a flat universe without inflation is much more likely than with inflation – by a factor of 10 to the googol power!"
+Together with Anna Ijjas and Abraham Loeb, he wrote articles claiming that the inflationary paradigm is in trouble in view of the data from the Planck satellite.
+
+Counter-arguments were presented by Alan Guth, David Kaiser, and Yasunori Nomura
+and by Andrei Linde,
+saying that
+ "cosmic inflation is on a stronger footing than ever before".
+
+See also
+
+Notes
+
+References
+
+Sources
+
+External links
+
+ Was Cosmic Inflation The 'Bang' Of The Big Bang?, by Alan Guth, 1997
+ 
+ update 2004 by Andrew Liddle
+ 
+ 
+ The Growth of Inflation Symmetry, December 2004
+ Guth's logbook showing the original idea
+ WMAP Bolsters Case for Cosmic Inflation, March 2006
+ NASA March 2006 WMAP press release 
+ Max Tegmark's Our Mathematical Universe (2014), "Chapter 5: Inflation"
+
+ 
+Physical cosmology
+Concepts in astronomy
+Astronomical events
+1980 in science
+The candela ( or ; symbol: cd) is the unit of luminous intensity in the International System of Units (SI). It measures luminous power per unit solid angle emitted by a light source in a particular direction. Luminous intensity is analogous to radiant intensity, but instead of simply adding up the contributions of every wavelength of light in the source's spectrum, the contribution of each wavelength is weighted by the luminous efficiency function, the model of the sensitivity of the human eye to different wavelengths, standardized by the CIE and ISO. A common wax candle emits light with a luminous intensity of roughly one candela. If emission in some directions is blocked by an opaque barrier, the emission would still be approximately one candela in the directions that are not obscured.
+
+The word candela is Latin for candle. The old name "candle" is still sometimes used, as in foot-candle and the modern definition of candlepower.
+
+Definition
+The 26th General Conference on Weights and Measures (CGPM) redefined the candela in 2018. The new definition, which took effect on 20 May 2019, is:
+
+The candela [...] is defined by taking the fixed numerical value of the luminous efficacy of monochromatic radiation of frequency , Kcd, to be 683 when expressed in the unit lm W−1, which is equal to , or , where the kilogram, metre and second are defined in terms of h, c and ΔνCs.
+
+Explanation
+
+The frequency chosen is in the visible spectrum near green, corresponding to a wavelength of about 555 nanometres. The human eye, when adapted for bright conditions, is most sensitive near this frequency. Under these conditions, photopic vision dominates the visual perception of our eyes over the scotopic vision. At other frequencies, more radiant intensity is required to achieve the same luminous intensity, according to the frequency response of the human eye. The luminous intensity for light of a particular wavelength λ is given by
+
+where  is the luminous intensity,  is the radiant intensity and  is the photopic luminous efficiency function. If more than one wavelength is present (as is usually the case), one must integrate over the spectrum of wavelengths to get the total luminous intensity.
+
+Examples
+A common candle emits light with roughly 1 cd luminous intensity. 
+A 25 W compact fluorescent light bulb puts out around 1700 lumens; if that light is radiated equally in all directions (i.e. over 4 steradians), it will have an intensity of 
+Focused into a 20° beam (0.095 steradians), the same light bulb would have an intensity of around 18,000 cd within the beam.
+
+History
+Prior to 1948, various standards for luminous intensity were in use in a number of countries. These were typically based on the brightness of the flame from a "standard candle" of defined composition, or the brightness of an incandescent filament of specific design. One of the best-known of these was the English standard of candlepower. One candlepower was the light produced by a pure spermaceti candle weighing one sixth of a pound and burning at a rate of 120 grains per hour. Germany, Austria and Scandinavia used the Hefnerkerze, a unit based on the output of a Hefner lamp.
+
+A better standard for luminous intensity was needed. In 1884, Jules Violle had proposed a standard based on the light emitted by 1 cm2 of platinum at its melting point (or freezing point). The resulting unit of intensity, called the "violle", was roughly equal to 60 English candlepower. Platinum was convenient for this purpose because it had a high enough melting point, was not prone to oxidation, and could be obtained in pure form. Violle showed that the intensity emitted by pure platinum was strictly dependent on its temperature, and so platinum at its melting point should have a consistent luminous intensity. 
+
+In practice, realizing a standard based on Violle's proposal turned out to be more difficult than expected. Impurities on the surface of the platinum could directly affect its emissivity, and in addition impurities could affect the luminous intensity by altering the melting point. Over the following half century various scientists tried to make a practical intensity standard based on incandescent platinum. The successful approach was to suspend a hollow shell of thorium dioxide with a small hole in it in a bath of molten platinum. The shell (cavity) serves as a black body, producing black-body radiation that depends on the temperature and is not sensitive to details of how the device is constructed.
+
+In 1937, the Commission Internationale de l'Éclairage (International Commission on Illumination) and the CIPM proposed a "new candle" based on this concept, with value chosen to make it similar to the earlier unit candlepower. The decision was promulgated by the CIPM in 1946:
+The value of the new candle is such that the brightness of the full radiator at the temperature of solidification of platinum is 60 new candles per square centimetre.
+
+It was then ratified in 1948 by the 9th CGPM which adopted a new name for this unit, the candela. In 1967 the 13th CGPM removed the term "new candle" and gave an amended version of the candela definition, specifying the atmospheric pressure applied to the freezing platinum:
+The candela is the luminous intensity, in the perpendicular direction, of a surface of  square metre of a black body at the temperature of freezing platinum under a pressure of  newtons per square metre.
+
+In 1979, because of the difficulties in realizing a Planck radiator at high temperatures and the new possibilities offered by radiometry, the 16th CGPM adopted a new definition of the candela:
+
+The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency  and that has a radiant intensity in that direction of  watt per steradian.
+
+The definition describes how to produce a light source that (by definition) emits one candela, but does not specify the luminous efficiency function for weighting radiation at other frequencies.  Such a source could then be used to calibrate instruments designed to measure luminous intensity with reference to a specified luminous efficiency function. An appendix to the SI Brochure makes it clear that the luminous efficiency function is not uniquely specified, but must be selected to fully define the candela.
+
+The arbitrary (1/683) term was chosen so that the new definition would precisely match the old definition. Although the candela is now defined in terms of the second (an SI base unit) and the watt (a derived SI unit), the candela remains a base unit of the SI system, by definition.
+
+The 26th CGPM approved the modern definition of the candela in 2018 as part of the 2019 redefinition of SI base units, which redefined the SI base units in terms of fundamental physical constants.
+
+SI photometric light units
+
+Relationships between luminous intensity, luminous flux, and illuminance
+If a source emits a known luminous intensity  (in candelas) in a well-defined cone, the total luminous flux  in lumens is given by
+
+where  is the radiation angle of the lamp—the full vertex angle of the emission cone. For example, a lamp that emits 590 cd with a radiation angle of 40° emits about 224 lumens. See MR16 for emission angles of some common lamps.
+
+If the source emits light uniformly in all directions, the flux can be found by multiplying the intensity by 4: a uniform 1 candela source emits 12.6 lumens.
+
+For the purpose of measuring illumination, the candela is not a practical unit, as it only applies to idealized point light sources, each approximated by a source small compared to the distance from which its luminous radiation is measured, also assuming that it is done so in the absence of other light sources. What gets directly measured by a light meter is incident light on a sensor of finite area, i.e. illuminance in lm/m2 (lux). However, if designing illumination from many point light sources, like light bulbs, of known approximate omnidirectionally uniform intensities, the contributions to illuminance from incoherent light being additive, it is mathematically estimated as follows. If  is the position of the ith source of uniform intensity , and  is the unit vector normal to the illuminated elemental opaque area  being measured, and provided that all light sources lie in the same half-space divided by the plane of this area,
+
+In the case of a single point light source of intensity Iv, at a distance r and normally incident, this reduces to
+
+SI multiples
+Like other SI units, the candela can also be modified by adding a metric prefix that multiplies it by a power of 10, for example millicandela (mcd) for 10−3 candela.
+
+References
+
+SI base units
+Units of luminous intensity
+Condensed matter physics is the field of physics that deals with the macroscopic and microscopic physical properties of matter, especially the solid and liquid phases which arise from electromagnetic forces between atoms. More generally, the subject deals with condensed phases of matter: systems of many constituents with strong interactions among them. More exotic condensed phases include the superconducting phase exhibited by certain materials at extremely low cryogenic temperature, the ferromagnetic and antiferromagnetic phases of spins on crystal lattices of atoms, and the Bose–Einstein condensate found in ultracold atomic systems. Condensed matter physicists seek to understand the behavior of these phases by experiments to measure various material properties, and by applying the physical laws of quantum mechanics, electromagnetism, statistical mechanics, and other physics theories to develop mathematical models.
+
+The diversity of systems and phenomena available for study makes condensed matter physics the most active field of contemporary physics: one third of all American physicists self-identify as condensed matter physicists, and the Division of Condensed Matter Physics is the largest division at the American Physical Society.  The field overlaps with chemistry, materials science, engineering and nanotechnology, and relates closely to atomic physics and biophysics. The theoretical physics of condensed matter shares important concepts and methods with that of particle physics and nuclear physics.
+
+A variety of topics in physics such as crystallography, metallurgy, elasticity, magnetism, etc., were treated as distinct areas until the 1940s, when they were grouped together as solid-state physics. Around the 1960s, the study of physical properties of liquids was added to this list, forming the basis for the more comprehensive specialty of condensed matter physics. The Bell Telephone Laboratories was one of the first institutes to conduct a research program in condensed matter physics. According to founding director of the Max Planck Institute for Solid State Research, physics professor Manuel Cardona, it was Albert Einstein who created the modern field of condensed matter physics starting with his seminal 1905 article on the photoelectric effect and photoluminescence which opened the fields of photoelectron spectroscopy and photoluminescence spectroscopy, and later his 1907 article on the specific heat of solids which introduced, for the first time, the effect of lattice vibrations on the thermodynamic properties of crystals, in particular the specific heat. Deputy Director of the Yale Quantum Institute A. Douglas Stone makes a similar priority case for Einstein in his work on the synthetic history of quantum mechanics.
+
+Etymology
+According to physicist Philip Warren Anderson, the use of the term "condensed matter" to designate a field of study was coined by him and Volker Heine, when they changed the name of their group at the Cavendish Laboratories, Cambridge from Solid state theory to Theory of Condensed Matter in 1967, as they felt it better included their interest in liquids, nuclear matter, and so on. Although Anderson and Heine helped popularize the name "condensed matter", it had been used in Europe for some years, most prominently in the Springer-Verlag journal Physics of Condensed Matter, launched in 1963. The name "condensed matter physics" emphasized the commonality of scientific problems encountered by physicists working on solids, liquids, plasmas, and other complex matter, whereas "solid state physics" was often associated with restricted industrial applications of metals and semiconductors. In the 1960s and 70s, some physicists felt the more comprehensive name better fit the funding environment and Cold War politics of the time.
+
+References to "condensed" states can be traced to earlier sources. For example, in the introduction to his 1947 book Kinetic Theory of Liquids, Yakov Frenkel proposed that "The kinetic theory of liquids must accordingly be developed as a generalization and extension of the kinetic theory of solid bodies. As a matter of fact, it would be more correct to unify them under the title of 'condensed bodies'".
+
+History
+
+Classical physics
+
+One of the first studies of condensed states of matter was by English chemist Humphry Davy, in the first decades of the nineteenth century. Davy observed that of the forty chemical elements known at the time, twenty-six had metallic properties such as lustre, ductility and high electrical and thermal conductivity. This indicated that the atoms in John Dalton's atomic theory were not indivisible as Dalton claimed, but had inner structure. Davy further claimed that elements that were then believed to be gases, such as nitrogen and hydrogen could be liquefied under the right conditions and would then behave as metals.
+
+In 1823, Michael Faraday, then an assistant in Davy's lab, successfully liquefied chlorine and went on to liquefy all known gaseous elements, except for nitrogen, hydrogen, and oxygen. Shortly after, in 1869, Irish chemist Thomas Andrews studied the phase transition from a liquid to a gas and coined the term critical point to describe the condition where a gas and a liquid were indistinguishable as phases, and Dutch physicist Johannes van der Waals supplied the theoretical framework which allowed the prediction of critical behavior based on measurements at much higher temperatures. By 1908, James Dewar and Heike Kamerlingh Onnes were successfully able to liquefy hydrogen and then newly discovered helium, respectively.
+
+Paul Drude in 1900 proposed the first theoretical model for a classical electron moving through a metallic solid. Drude's model described properties of metals in terms of a gas of free electrons, and was the first microscopic model to explain empirical observations such as the Wiedemann–Franz law. However, despite the success of Drude's free electron model, it had one notable problem: it was unable to correctly explain the electronic contribution to the specific heat and magnetic properties of metals, and the temperature dependence of resistivity at low temperatures.
+
+In 1911, three years after helium was first liquefied, Onnes working at University of Leiden discovered superconductivity in mercury, when he observed the electrical resistivity of mercury to vanish at temperatures below a certain value. The phenomenon completely surprised the best theoretical physicists of the time, and it remained unexplained for several decades. Albert Einstein, in 1922, said regarding contemporary theories of superconductivity that "with our far-reaching ignorance of the quantum mechanics of composite systems we are very far from being able to compose a theory out of these vague ideas."
+
+Advent of quantum mechanics
+Drude's classical model was augmented by Wolfgang Pauli, Arnold Sommerfeld, Felix Bloch and other physicists.  Pauli realized that the free electrons in metal must obey the Fermi–Dirac statistics.  Using this idea, he developed the theory of paramagnetism in 1926.  Shortly after, Sommerfeld incorporated the Fermi–Dirac statistics into the free electron model and made it better to explain the heat capacity.  Two years later, Bloch used quantum mechanics to describe the motion of an electron in a periodic lattice. The mathematics of crystal structures developed by Auguste Bravais, Yevgraf Fyodorov and others was used to classify crystals by their symmetry group, and tables of crystal structures were the basis for the series International Tables of Crystallography, first published in 1935. Band structure calculations was first used in 1930 to predict the properties of new materials, and in 1947 John Bardeen, Walter Brattain and William Shockley developed the first semiconductor-based transistor, heralding a revolution in electronics.
+
+In 1879, Edwin Herbert Hall working at the Johns Hopkins University discovered a voltage developed across conductors transverse to an electric current in the conductor and magnetic field perpendicular to the current. This phenomenon arising due to the nature of charge carriers in the conductor came to be termed the Hall effect, but it was not properly explained at the time, since the electron was not experimentally discovered until 18 years later. After the advent of quantum mechanics, Lev Landau in 1930 developed the theory of Landau quantization and laid the foundation for the theoretical explanation for the quantum Hall effect discovered half a century later.
+
+Magnetism as a property of matter has been known in China since 4000 BC. However, the first modern studies of magnetism only started with the development of electrodynamics by Faraday, Maxwell and others in the nineteenth century, which included classifying materials as ferromagnetic, paramagnetic and diamagnetic based on their response to magnetization. Pierre Curie studied the dependence of magnetization on temperature and discovered the Curie point phase transition in ferromagnetic materials. In 1906, Pierre Weiss introduced the concept of magnetic domains to explain the main properties of ferromagnets. The first attempt at a microscopic description of magnetism was by Wilhelm Lenz and Ernst Ising through the Ising model that described magnetic materials as consisting of a periodic lattice of spins that collectively acquired magnetization. The Ising model was solved exactly to show that spontaneous magnetization cannot occur in one dimension but is possible in higher-dimensional lattices. Further research such as by Bloch on spin waves and Néel on antiferromagnetism led to developing new magnetic materials with applications to magnetic storage devices.
+
+Modern many-body physics
+
+The Sommerfeld model and spin models for ferromagnetism illustrated the successful application of quantum mechanics to condensed matter problems in the 1930s. However, there still were several unsolved problems, most notably the description of superconductivity and the Kondo effect. After World War II, several ideas from quantum field theory were applied to condensed matter problems. These included recognition of collective excitation modes of solids and the important notion of a quasiparticle. Russian physicist Lev Landau used the idea for the Fermi liquid theory wherein low energy properties of interacting fermion systems were given in terms of what are now termed Landau-quasiparticles. Landau also developed a mean-field theory for continuous phase transitions, which described ordered phases as spontaneous breakdown of symmetry. The theory also introduced the notion of an order parameter to distinguish between ordered phases. Eventually in 1956, John Bardeen, Leon Cooper and John Schrieffer developed the so-called BCS theory of superconductivity, based on the discovery that arbitrarily small attraction between two electrons of opposite spin mediated by phonons in the lattice can give rise to a bound state called a Cooper pair.
+
+The study of phase transitions and the critical behavior of observables, termed critical phenomena, was a major field of interest in the 1960s. Leo Kadanoff, Benjamin Widom and Michael Fisher developed the ideas of critical exponents and widom scaling. These ideas were unified by Kenneth G. Wilson in 1972, under the formalism of the renormalization group in the context of quantum field theory.
+
+The quantum Hall effect was discovered by Klaus von Klitzing, Dorda and Pepper in 1980 when they observed the Hall conductance to be integer multiples of a fundamental constant .(see figure) The effect was observed to be independent of parameters such as system size and impurities.  In 1981, theorist Robert Laughlin proposed a theory explaining the unanticipated precision of the integral plateau.  It also implied that the Hall conductance is proportional to a topological invariant, called Chern number, whose relevance for the band structure of solids was formulated by David J. Thouless and collaborators. Shortly after, in 1982, Horst Störmer and Daniel Tsui observed the fractional quantum Hall effect where the conductance was now a rational multiple of the constant . Laughlin, in 1983, realized that this was a consequence of quasiparticle interaction in the Hall states and formulated a variational method solution, named the Laughlin wavefunction. The study of topological properties of the fractional Hall effect remains an active field of research. Decades later, the aforementioned topological band theory advanced by David J. Thouless and collaborators was further expanded leading to the discovery of topological insulators. 
+
+In 1986, Karl Müller and Johannes Bednorz discovered the first high temperature superconductor, a material which was superconducting at temperatures as high as 50 kelvins.  It was realized that the high temperature superconductors are examples of strongly correlated materials where the electron–electron interactions play an important role. A satisfactory theoretical description of high-temperature superconductors is still not known and the field of strongly correlated materials continues to be an active research topic.
+
+In 2009, David Field and researchers at Aarhus University discovered spontaneous electric fields when creating prosaic films of various gases. This has more recently expanded to form the research area of spontelectrics.
+
+In 2012, several groups released preprints which suggest that samarium hexaboride has the properties of a topological insulator in accord with the earlier theoretical predictions. Since samarium hexaboride is an established Kondo insulator, i.e. a strongly correlated electron material, it is expected that the existence of a topological Dirac surface state in this material would lead to a topological insulator with strong electronic correlations.
+
+Theoretical
+Theoretical condensed matter physics involves the use of theoretical models to understand properties of states of matter. These include models to study the electronic properties of solids, such as the Drude model, the band structure and the density functional theory. Theoretical models have also been developed to study the physics of phase transitions, such as the Ginzburg–Landau theory, critical exponents and the use of mathematical methods of quantum field theory and the renormalization group. Modern theoretical studies involve the use of numerical computation of electronic structure and mathematical tools to understand phenomena such as high-temperature superconductivity, topological phases, and gauge symmetries.
+
+Emergence
+
+Theoretical understanding of condensed matter physics is closely related to the notion of emergence, wherein complex assemblies of particles behave in ways dramatically different from their individual constituents. For example, a range of phenomena related to high temperature superconductivity are understood poorly, although the microscopic physics of individual electrons and lattices is well known. Similarly, models of condensed matter systems have been studied where collective excitations behave like photons and electrons, thereby describing electromagnetism as an emergent phenomenon. Emergent properties can also occur at the interface between materials: one example is the lanthanum aluminate-strontium titanate interface, where two band-insulators are joined to create conductivity and superconductivity.
+
+Electronic theory of solids
+
+The metallic state has historically been an important building block for studying properties of solids. The first theoretical description of metals was given by Paul Drude in 1900 with the Drude model, which explained electrical and thermal properties by describing a metal as an ideal gas of then-newly discovered electrons.  He was able to derive the empirical Wiedemann-Franz law and get results in close agreement with the experiments.  This classical model was then improved by Arnold Sommerfeld who incorporated the Fermi–Dirac statistics of electrons and was able to explain the anomalous behavior of the specific heat of metals in the Wiedemann–Franz law.  In 1912, The structure of crystalline solids was studied by Max von Laue and Paul Knipping, when they observed the X-ray diffraction pattern of crystals, and concluded that crystals get their structure from periodic lattices of atoms.  In 1928, Swiss physicist Felix Bloch provided a wave function solution to the Schrödinger equation with a periodic potential, known as Bloch's theorem.
+
+Calculating electronic properties of metals by solving the many-body wavefunction is often computationally hard, and hence, approximation methods are needed to obtain meaningful predictions. The Thomas–Fermi theory, developed in the 1920s, was used to estimate system energy and electronic density by treating the local electron density as a variational parameter. Later in the 1930s, Douglas Hartree, Vladimir Fock and John Slater developed the so-called Hartree–Fock wavefunction as an improvement over the Thomas–Fermi model. The Hartree–Fock method accounted for exchange statistics of single particle electron wavefunctions.  In general, it is very difficult to solve the Hartree–Fock equation.  Only the free electron gas case can be solved exactly. Finally in 1964–65, Walter Kohn, Pierre Hohenberg and Lu Jeu Sham proposed the density functional theory (DFT) which gave realistic descriptions for bulk and surface properties of metals. The density functional theory has been widely used since the 1970s for band structure calculations of variety of solids.
+
+Symmetry breaking
+
+Some states of matter exhibit symmetry breaking, where the relevant laws of physics possess some form of symmetry that is broken. A common example is crystalline solids, which break continuous translational symmetry. Other examples include magnetized ferromagnets, which break rotational symmetry, and more exotic states such as the ground state of a BCS superconductor, that breaks U(1) phase rotational symmetry.
+
+Goldstone's theorem in quantum field theory states that in a system with broken continuous symmetry, there may exist excitations with arbitrarily low energy, called the Goldstone bosons. For example, in crystalline solids, these correspond to phonons, which are quantized versions of lattice vibrations.
+
+Phase transition
+
+Phase transition refers to the change of phase of a system, which is brought about by change in an external parameter such as temperature, pressure, or molar composition. In a single-component system, a classical phase transition occurs at a temperature (at a specific pressure) where there is an abrupt change in the  order of the system   For example, when ice melts and becomes water, the ordered hexagonal crystal structure of ice is modified to a hydrogen bonded, mobile arrangement of water molecules.
+
+In quantum phase transitions,  the temperature is set to absolute zero, and the non-thermal control parameter, such as pressure or magnetic field,  causes the phase transitions when order is destroyed by quantum fluctuations originating from the Heisenberg uncertainty principle. Here, the different quantum phases of the system refer to distinct ground states of the Hamiltonian matrix.  Understanding the behavior of quantum phase transition is important in the difficult tasks of explaining the properties of rare-earth magnetic insulators, high-temperature superconductors, and other substances.
+
+Two classes of phase transitions occur: first-order transitions and second-order or continuous transitions. For the latter, the two phases involved do not co-exist at the transition temperature, also called the critical point.  Near the critical point, systems undergo critical behavior, wherein several of their properties such as correlation length, specific heat, and magnetic susceptibility diverge exponentially.  These critical phenomena present serious challenges to physicists because normal macroscopic laws are no longer valid in the region, and novel ideas and methods must be invented to find the new laws that can describe the system.
+
+The simplest theory that can describe continuous phase transitions is the Ginzburg–Landau theory, which works in the so-called mean-field approximation.  However, it can only roughly explain continuous phase transition for ferroelectrics and type I superconductors which involves long range microscopic interactions.  For other types of systems that involves short range interactions near the critical point, a better theory is needed.
+
+Near the critical point, the fluctuations happen over broad range of size scales while the feature of the whole system is scale invariant.  Renormalization group methods successively average out the shortest wavelength fluctuations in stages while retaining their effects into the next stage.  Thus, the changes of a physical system as viewed at different size scales can be investigated systematically.  The methods, together with powerful computer simulation, contribute greatly to the explanation of the critical phenomena associated with continuous phase transition.
+
+Experimental
+Experimental condensed matter physics involves the use of experimental probes to try to discover new properties of materials. Such probes include effects of electric and magnetic fields, measuring response functions, transport properties and thermometry. Commonly used experimental methods include spectroscopy, with probes such as X-rays, infrared light and inelastic neutron scattering; study of thermal response, such as specific heat and measuring transport via thermal and heat conduction.
+
+Scattering
+
+Several condensed matter experiments involve scattering of an experimental probe, such as X-ray, optical photons, neutrons, etc., on constituents of a material. The choice of scattering probe depends on the observation energy scale of interest. Visible light has energy on the scale of 1 electron volt (eV) and is used as a scattering probe to measure variations in material properties such as dielectric constant and refractive index. X-rays have energies of the order of 10 keV and hence are able to probe atomic length scales, and are used to measure variations in electron charge density and crystal structure.
+
+Neutrons can also probe atomic length scales and are used to study scattering off nuclei and electron spins and magnetization (as neutrons have spin but no charge). Coulomb and Mott scattering measurements can be made by using electron beams as scattering probes.  Similarly, positron annihilation can be used as an indirect measurement of local electron density. Laser spectroscopy is an excellent tool for studying the microscopic properties of a medium, for example, to study forbidden transitions in media with nonlinear optical spectroscopy.
+
+External magnetic fields
+In experimental condensed matter physics, external magnetic fields act as thermodynamic variables that control the state, phase transitions and properties of material systems.  Nuclear magnetic resonance (NMR) is a method by which external magnetic fields are used to find resonance modes of individual nuclei, thus giving information about the atomic, molecular, and bond structure of their environment. NMR experiments can be made in magnetic fields with strengths up to 60 tesla.  Higher magnetic fields can improve the quality of NMR measurement data. Quantum oscillations is another experimental method where high magnetic fields are used to study material properties such as the geometry of the Fermi surface.  High magnetic fields will be useful in experimentally testing of the various theoretical predictions such as the quantized magnetoelectric effect, image magnetic monopole, and the half-integer quantum Hall effect.
+
+Nuclear spectroscopy
+The local structure, the structure of the nearest neighbour atoms, of condensed matter can be investigated with methods of nuclear spectroscopy, which are very sensitive to small changes. Using specific and radioactive nuclei, the nucleus becomes the probe that interacts with its surrounding electric and magnetic fields (hyperfine interactions). The methods are suitable to study defects, diffusion, phase change, magnetism. Common methods are e.g. NMR, Mössbauer spectroscopy, or perturbed angular correlation (PAC). Especially PAC is ideal for the study of phase changes at extreme temperature above 2000 °C due to no temperature dependence of the method.
+
+Cold atomic gases
+
+Ultracold atom trapping in optical lattices is an experimental tool commonly used in condensed matter physics, and in atomic, molecular, and optical physics. The method involves using optical lasers to form an interference pattern, which acts as a lattice, in which ions or atoms can be placed at very low temperatures. Cold atoms in optical lattices are used as quantum simulators, that is, they act as controllable systems that can model behavior of more complicated systems, such as frustrated magnets. In particular, they are used to engineer one-, two- and three-dimensional lattices for a Hubbard model with pre-specified parameters, and to study phase transitions for antiferromagnetic and spin liquid ordering.
+
+In 1995, a gas of rubidium atoms cooled down to a temperature of 170 nK was used to experimentally realize the Bose–Einstein condensate, a novel state of matter originally predicted by S. N. Bose and Albert Einstein, wherein a large number of atoms occupy one quantum state.
+
+Applications
+
+Research in condensed matter physics has given rise to several device applications, such as the development of the semiconductor transistor, laser technology, and several phenomena studied in the context of nanotechnology. Methods such as scanning-tunneling microscopy can be used to control processes at the nanometer scale, and have given rise to the study of nanofabrication. Such molecular machines were developed for example by Nobel laurate in chemistry Ben Feringa, Jean-Pierre Sauvage and Fraser Stoddart. Feringa and his team developed multiple molecular machines such as molecular car, molecular windmill and many more.
+
+In quantum computation, information is represented by quantum bits, or qubits. The qubits may decohere quickly before useful computation is completed. This serious problem must be solved before quantum computing may be realized. To solve this problem, several promising approaches are proposed in condensed matter physics, including Josephson junction qubits, spintronic qubits using the spin orientation of magnetic materials, or the topological non-Abelian anyons from fractional quantum Hall effect states.
+
+Condensed matter physics also has important uses for biomedicine, for example, the experimental method of magnetic resonance imaging, which is widely used in medical diagnosis.
+
+See also
+
+Notes
+
+References
+
+Further reading 
+ Anderson, Philip W. (2018-03-09). Basic Notions Of Condensed Matter Physics. CRC Press. .
+Girvin, Steven M.; Yang, Kun (2019-02-28). Modern Condensed Matter Physics. Cambridge University Press. .
+Coleman, Piers (2015).  Introduction to Many-Body Physics, Cambridge University Press, .
+P. M. Chaikin and T. C. Lubensky (2000). Principles of Condensed Matter Physics, Cambridge University Press; 1st edition, 
+ Alexander Altland and Ben Simons (2006). Condensed Matter Field Theory, Cambridge University Press, .
+ Michael P. Marder (2010). Condensed Matter Physics, second edition, John Wiley and Sons, .
+Lillian Hoddeson, Ernest Braun, Jürgen Teichmann and Spencer Weart, eds. (1992). Out of the Crystal Maze: Chapters from the History of Solid State Physics, Oxford University Press, .
+
+External links 
+ 
+
+ 
+Materials science
+Cultural anthropology is a branch of anthropology focused on the study of cultural variation among humans. It is in contrast to social anthropology, which perceives cultural variation as a subset of a posited anthropological constant. The term sociocultural anthropology includes both cultural and social anthropology traditions.
+
+Anthropologists have pointed out that through culture, people can adapt to their environment in non-genetic ways, so people living in different environments will often have different cultures. Much of anthropological theory has originated in an appreciation of and interest in the tension between the local (particular cultures) and the global (a universal human nature, or the web of connections between people in distinct places/circumstances).
+
+Cultural anthropology has a rich methodology, including participant observation (often called fieldwork because it requires the anthropologist spending an extended period of time at the research location), interviews, and surveys.
+
+History
+
+The rise of cultural anthropology took place within the context of the late 19th century, when questions regarding which cultures were "primitive" and which were "civilized" occupied the mind of not only Freud, but many others. Colonialism and its processes increasingly brought European thinkers into direct or indirect contact with "primitive others". The relative status of various humans, some of whom had modern advanced technologies that included engines and telegraphs, while others lacked anything but face-to-face communication techniques and still lived a Paleolithic lifestyle, was of interest to the first generation of cultural anthropologists.
+
+Theoretical foundations
+
+The concept of culture
+One of the earliest articulations of the anthropological meaning of the term "culture" came from Sir Edward Tylor who writes on the first page of his 1871 book: "Culture, or civilization, taken in its broad, ethnographic sense, is that complex whole which includes knowledge, belief, art, morals, law, custom, and any other capabilities and habits acquired by man as a member of society." The term "civilization" later gave way to definitions given by V. Gordon Childe, with culture forming an umbrella term and civilization becoming a particular kind of culture.
+
+According to Kay Milton, former director of anthropology research at Queens University Belfast, culture can be general or specific. This means culture can be something applied to all human beings or it can be specific to a certain group of people such as African American culture or Irish American culture. Specific cultures are structured systems which means they are organized very specifically and adding or taking away any element from that system may disrupt it.
+
+The critique of evolutionism
+Anthropology is concerned with the lives of people in different parts of the world, particularly in relation to the discourse of beliefs and practices. In addressing this question, ethnologists in the 19th century divided into two schools of thought. Some, like Grafton Elliot Smith, argued that different groups must have learned from one another somehow, however indirectly; in other words, they argued that cultural traits spread from one place to another, or "diffused".
+
+Other ethnologists argued that different groups had the capability of creating similar beliefs and practices independently. Some of those who advocated "independent invention", like Lewis Henry Morgan, additionally supposed that similarities meant that different groups had passed through the same stages of cultural evolution (See also classical social evolutionism). Morgan, in particular, acknowledged that certain forms of society and culture could not possibly have arisen before others. For example, industrial farming could not have been invented before simple farming, and metallurgy could not have developed without previous non-smelting processes involving metals (such as simple ground collection or mining). Morgan, like other 19th century social evolutionists, believed there was a more or less orderly progression from the primitive to the civilized.
+
+20th-century anthropologists largely reject the notion that all human societies must pass through the same stages in the same order, on the grounds that such a notion does not fit the empirical facts. Some 20th-century ethnologists, like Julian Steward, have instead argued that such similarities reflected similar adaptations to similar environments. Although 19th-century ethnologists saw "diffusion" and "independent invention" as mutually exclusive and competing theories, most ethnographers quickly reached a consensus that both processes occur, and that both can plausibly account for cross-cultural similarities. But these ethnographers also pointed out the superficiality of many such similarities. They noted that even traits that spread through diffusion often were given different meanings and function from one society to another. Analyses of large human concentrations in big cities, in multidisciplinary studies by Ronald Daus, show how new methods may be applied to the understanding of man living in a global world and how it was caused by the action of extra-European nations,  so highlighting the role of Ethics in modern anthropology.
+
+Accordingly, most of these anthropologists showed less interest in comparing cultures, generalizing about human nature, or discovering universal laws of cultural development, than in understanding particular cultures in those cultures' own terms. Such ethnographers and their students promoted the idea of "cultural relativism", the view that one can only understand another person's beliefs and behaviors in the context of the culture in which they live or lived.
+
+Others, such as Claude Lévi-Strauss (who was influenced both by American cultural anthropology and by French Durkheimian sociology), have argued that apparently similar patterns of development reflect fundamental similarities in the structure of human thought (see structuralism). By the mid-20th century, the number of examples of people skipping stages, such as going from hunter-gatherers to post-industrial service occupations in one generation, were so numerous that 19th-century evolutionism was effectively disproved.
+
+Cultural relativism
+
+Cultural relativism is a principle that was established as axiomatic in anthropological research by Franz Boas and later popularized by his students.  Boas first articulated the idea in 1887: "...civilization is not something absolute, but ... is relative, and ... our ideas and conceptions are true only so far as our civilization goes." Although Boas did not coin the term, it became common among anthropologists after Boas' death in 1942, to express their synthesis of a number of ideas Boas had developed. Boas believed that the sweep of cultures, to be found in connection with any sub-species, is so vast and pervasive that there cannot be a relationship between culture and race. Cultural relativism involves specific epistemological and methodological claims.  Whether or not these claims require a specific ethical stance is a matter of debate. This principle should not be confused with moral relativism.
+
+Cultural relativism was in part a response to Western ethnocentrism. Ethnocentrism may take obvious forms, in which one consciously believes that one's people's arts are the most beautiful, values the most virtuous, and beliefs the most truthful. Boas, originally trained in physics and geography, and heavily influenced by the thought of Kant, Herder, and von Humboldt, argued that one's culture may mediate and thus limit one's perceptions in less obvious ways. This understanding of culture confronts anthropologists with two problems: first, how to escape the unconscious bonds of one's own culture, which inevitably bias our perceptions of and reactions to the world, and second, how to make sense of an unfamiliar culture.  The principle of cultural relativism thus forced anthropologists to develop innovative methods and heuristic strategies.
+
+Boas and his students realized that if they were to conduct scientific research in other cultures, they would need to employ methods that would help them escape the limits of their own ethnocentrism.  One such method is that of ethnography: basically, they advocated living with people of another culture for an extended period of time, so that they could learn the local language and be enculturated, at least partially, into that culture. In this context, cultural relativism is of fundamental methodological importance, because it calls attention to the importance of the local context in understanding the meaning of particular human beliefs and activities.  Thus, in 1948 Virginia Heyer wrote, "Cultural relativity, to phrase it in starkest abstraction, states the relativity of the part to the whole.  The part gains its cultural significance by its place in the whole, and cannot retain its integrity in a different situation."
+
+Theoretical approaches
+
+ Actor–network theory
+ Cultural materialism
+ Culture theory
+ Feminist anthropology
+ Functionalism
+ Symbolic and interpretive anthropology
+ Political economy in anthropology
+ Practice theory
+ Structuralism
+ Post-structuralism
+ Systems theory in anthropology
+
+Comparison with social anthropology
+The rubric cultural anthropology is generally applied to ethnographic works that are holistic in approach, are oriented to the ways in which culture affects individual experience, or aim to provide a rounded view of the knowledge, customs, and institutions of a people. Social anthropology is a term applied to ethnographic works that attempt to isolate a particular system of social relations such as those that comprise domestic life, economy, law, politics, or religion, give analytical priority to the organizational bases of social life, and attend to cultural phenomena as somewhat secondary to the main issues of social scientific inquiry.
+
+Parallel with the rise of cultural anthropology in the United States, social anthropology developed as an academic discipline in Britain and in France.
+
+Foundational thinkers
+
+Lewis Henry Morgan
+Lewis Henry Morgan (1818–1881), a lawyer from Rochester, New York, became an advocate for and ethnological scholar of the Iroquois. His comparative analyses of religion, government, material culture, and especially kinship patterns proved to be influential contributions to the field of anthropology. Like other scholars of his day (such as Edward Tylor), Morgan argued that human societies could be classified into categories of cultural evolution on a scale of progression that ranged from savagery, to barbarism, to civilization. Generally, Morgan used technology (such as bowmaking or pottery) as an indicator of position on this scale.
+
+Franz Boas, founder of the modern discipline 
+
+ 
+
+Franz Boas (1858–1942) established academic anthropology in the United States in opposition to Morgan's evolutionary perspective. His approach was empirical, skeptical of overgeneralizations, and eschewed attempts to establish universal laws. For example, Boas studied immigrant children to demonstrate that biological race was not immutable, and that human conduct and behavior resulted from nurture, rather than nature.
+
+Influenced by the German tradition, Boas argued that the world was full of distinct cultures, rather than societies whose evolution could be measured by how much or how little "civilization" they had. He believed that each culture has to be studied in its particularity, and argued that cross-cultural generalizations, like those made in the natural sciences, were not possible.
+
+In doing so, he fought discrimination against immigrants, blacks, and indigenous peoples of the Americas. Many American anthropologists adopted his agenda for social reform, and theories of race continue to be popular subjects for anthropologists today. The so-called "Four Field Approach" has its origins in Boasian Anthropology, dividing the discipline in the four crucial and interrelated fields of sociocultural, biological, linguistic, and archaic anthropology (e.g. archaeology). Anthropology in the United States continues to be deeply influenced by the Boasian tradition, especially its emphasis on culture.
+
+Kroeber, Mead, and Benedict
+Boas used his positions at Columbia University and the American Museum of Natural History (AMNH) to train and develop multiple generations of students. His first generation of students included Alfred Kroeber, Robert Lowie, Edward Sapir, and Ruth Benedict, who each produced richly detailed studies of indigenous North American cultures. They provided a wealth of details used to attack the theory of a single evolutionary process. Kroeber and Sapir's focus on Native American languages helped establish linguistics as a truly general science and free it from its historical focus on Indo-European languages.
+
+The publication of Alfred Kroeber's textbook Anthropology (1923) marked a turning point in American anthropology. After three decades of amassing material, Boasians felt a growing urge to generalize. This was most obvious in the 'Culture and Personality' studies carried out by younger Boasians such as Margaret Mead and Ruth Benedict. Influenced by psychoanalytic psychologists including Sigmund Freud and Carl Jung, these authors sought to understand the way that individual personalities were shaped by the wider cultural and social forces in which they grew up.
+
+Though such works as Mead's Coming of Age in Samoa (1928) and Benedict's The Chrysanthemum and the Sword (1946) remain popular with the American public, Mead and Benedict never had the impact on the discipline of anthropology that some expected. Boas had planned for Ruth Benedict to succeed him as chair of Columbia's anthropology department, but she was sidelined in favor of Ralph Linton, and Mead was limited to her offices at the AMNH.
+
+Wolf, Sahlins, Mintz, and political economy
+
+In the 1950s and mid-1960s anthropology tended increasingly to model itself after the natural sciences. Some anthropologists, such as Lloyd Fallers and Clifford Geertz, focused on processes of modernization by which newly independent states could develop. Others, such as Julian Steward and Leslie White, focused on how societies evolve and fit their ecological niche—an approach popularized by Marvin Harris.
+
+Economic anthropology as influenced by Karl Polanyi and practiced by Marshall Sahlins and George Dalton challenged standard neoclassical economics to take account of cultural and social factors, and employed Marxian analysis into anthropological study. In England, British Social Anthropology's paradigm began to fragment as Max Gluckman and Peter Worsley experimented with Marxism and authors such as Rodney Needham and Edmund Leach incorporated Lévi-Strauss's structuralism into their work. Structuralism also influenced a number of developments in the 1960s and 1970s, including cognitive anthropology and componential analysis.
+
+In keeping with the times, much of anthropology became politicized through the Algerian War of Independence and opposition to the Vietnam War; Marxism became an increasingly popular theoretical approach in the discipline. By the 1970s the authors of volumes such as Reinventing Anthropology worried about anthropology's relevance.
+
+Since the 1980s issues of power, such as those examined in Eric Wolf's Europe and the People Without History, have been central to the discipline. In the 1980s books like Anthropology and the Colonial Encounter pondered anthropology's ties to colonial inequality, while the immense popularity of theorists such as Antonio Gramsci and Michel Foucault moved issues of power and hegemony into the spotlight. Gender and sexuality became popular topics, as did the relationship between history and anthropology, influenced by Marshall Sahlins, who drew on Lévi-Strauss and Fernand Braudel to examine the relationship between symbolic meaning, sociocultural structure, and individual agency in the processes of historical transformation. Jean and John Comaroff produced a whole generation of anthropologists at the University of Chicago that focused on these themes. Also influential in these issues were Nietzsche, Heidegger, the critical theory of the Frankfurt School, Derrida and Lacan.
+
+Geertz, Schneider, and interpretive anthropology
+
+Many anthropologists reacted against the renewed emphasis on materialism and scientific modelling derived from Marx by emphasizing the importance of the concept of culture. Authors such as David Schneider, Clifford Geertz, and Marshall Sahlins developed a more fleshed-out concept of culture as a web of meaning or signification, which proved very popular within and beyond the discipline. Geertz was to state:
+
+Geertz's interpretive method involved what he called "thick description". The cultural symbols of rituals, political and economic action, and of kinship, are "read" by the anthropologist as if they are a document in a foreign language. The interpretation of those symbols must be re-framed for their anthropological audience, i.e. transformed from the "experience-near" but foreign concepts of the other culture, into the "experience-distant" theoretical concepts of the anthropologist. These interpretations must then be reflected back to its originators, and its adequacy as a translation fine-tuned in a repeated way, a process called the hermeneutic circle. Geertz applied his method in a number of areas, creating programs of study that were very productive. His analysis of "religion as a cultural system" was particularly influential outside of anthropology. David Schnieder's cultural analysis of American kinship has proven equally influential.  Schneider demonstrated that the American folk-cultural emphasis on "blood connections" had an undue influence on anthropological kinship theories, and that kinship is not a biological characteristic but a cultural relationship established on very different terms in different societies.
+
+Prominent British symbolic anthropologists include Victor Turner and Mary Douglas.
+
+The post-modern turn
+In the late 1980s and 1990s authors such as James Clifford pondered ethnographic authority, in particular how and why anthropological knowledge was possible and authoritative. They were reflecting trends in research and discourse initiated by feminists in the academy, although they excused themselves from commenting specifically on those pioneering critics. Nevertheless, key aspects of feminist theory and methods became de rigueur as part of the 'post-modern moment' in anthropology: Ethnographies became more interpretative and reflexive, explicitly addressing the author's methodology; cultural, gendered, and racial positioning; and their influence on the ethnographic analysis. This was part of a more general trend of postmodernism that was popular contemporaneously. Currently anthropologists pay attention to a wide variety of issues pertaining to the contemporary world, including globalization, medicine and biotechnology, indigenous rights, virtual communities, and the anthropology of industrialized societies.
+
+Socio-cultural anthropology subfields
+
+ Anthropology of art
+ Cognitive anthropology
+ Anthropology of development
+ Disability anthropology
+ Ecological anthropology
+ Economic anthropology
+ Feminist anthropology and anthropology of gender and sexuality
+ Ethnohistory and historical anthropology
+ Kinship and family
+ Legal anthropology
+ Multimodal anthropology
+ Media anthropology
+ Medical anthropology
+ Political anthropology
+ Political economy in anthropology
+ Psychological anthropology
+ Public anthropology
+ Anthropology of religion
+ Cyborg anthropology
+ Transpersonal anthropology
+ Urban anthropology
+ Visual anthropology
+
+Methods
+Modern cultural anthropology has its origins in, and developed in reaction to, 19th century ethnology, which involves the organized comparison of human societies. Scholars like E.B. Tylor and J.G. Frazer in England worked mostly with materials collected by others—usually missionaries, traders, explorers, or colonial officials—earning them the moniker of "arm-chair anthropologists".
+
+Participant observation
+
+Participant observation is one of the principal research methods of cultural anthropology. It relies on the assumption that the best way to understand a group of people is to interact with them closely over a long period of time. The method originated in the field research of social anthropologists, especially Bronislaw Malinowski in Britain, the students of Franz Boas in the United States, and in the later urban research of the Chicago School of Sociology. Historically, the group of people being studied was a small, non-Western society. However, today it may be a specific corporation, a church group, a sports team, or a small town. There are no restrictions as to what the subject of participant observation can be, as long as the group of people is studied intimately by the observing anthropologist over a long period of time. This allows the anthropologist to develop trusting relationships with the subjects of study and receive an inside perspective on the culture, which helps him or her to give a richer description when writing about the culture later. Observable details (like daily time allotment) and more hidden details (like taboo behavior) are more easily observed and interpreted over a longer period of time, and researchers can discover discrepancies between what participants say—and often believe—should happen (the formal system) and what actually does happen, or between different aspects of the formal system; in contrast, a one-time survey of people's answers to a set of questions might be quite consistent, but is less likely to show conflicts between different aspects of the social system or between conscious representations and behavior.
+
+Interactions between an ethnographer and a cultural informant must go both ways. Just as an ethnographer may be naive or curious about a culture, the members of that culture may be curious about the ethnographer. To establish connections that will eventually lead to a better understanding of the cultural context of a situation, an anthropologist must be open to becoming part of the group, and willing to develop meaningful relationships with its members. One way to do this is to find a small area of common experience between an anthropologist and their subjects, and then to expand from this common ground into the larger area of difference. Once a single connection has been established, it becomes easier to integrate into the community, and more likely that accurate and complete information is being shared with the anthropologist.
+
+Before participant observation can begin, an anthropologist must choose both a location and a focus of study. This focus may change once the anthropologist is actively observing the chosen group of people, but having an idea of what one wants to study before beginning fieldwork allows an anthropologist to spend time researching background information on their topic. It can also be helpful to know what previous research has been conducted in one's chosen location or on similar topics, and if the participant observation takes place in a location where the spoken language is not one the anthropologist is familiar with, they will usually also learn that language. This allows the anthropologist to become better established in the community. The lack of need for a translator makes communication more direct, and allows the anthropologist to give a richer, more contextualized representation of what they witness. In addition, participant observation often requires permits from governments and research institutions in the area of study, and always needs some form of funding.
+
+The majority of participant observation is based on conversation. This can take the form of casual, friendly dialogue, or can also be a series of more structured interviews. A combination of the two is often used, sometimes along with photography, mapping, artifact collection, and various other methods. In some cases, ethnographers also turn to structured observation, in which an anthropologist's observations are directed by a specific set of questions they are trying to answer. In the case of structured observation, an observer might be required to record the order of a series of events, or describe a certain part of the surrounding environment. While the anthropologist still makes an effort to become integrated into the group they are studying, and still participates in the events as they observe, structured observation is more directed and specific than participant observation in general. This helps to standardize the method of study when ethnographic data is being compared across several groups or is needed to fulfill a specific purpose, such as research for a governmental policy decision.
+
+One common criticism of participant observation is its lack of objectivity. Because each anthropologist has their own background and set of experiences, each individual is likely to interpret the same culture in a different way. Who the ethnographer is has a lot to do with what they will eventually write about a culture, because each researcher is influenced by their own perspective. This is considered a problem especially when anthropologists write in the ethnographic present, a present tense which makes a culture seem stuck in time, and ignores the fact that it may have interacted with other cultures or gradually evolved since the anthropologist made observations. To avoid this, past ethnographers have advocated for strict training, or for anthropologists working in teams. However, these approaches have not generally been successful, and modern ethnographers often choose to include their personal experiences and possible biases in their writing instead.
+
+Participant observation has also raised ethical questions, since an anthropologist is in control of what they report about a culture. In terms of representation, an anthropologist has greater power than their subjects of study, and this has drawn criticism of participant observation in general. Additionally, anthropologists have struggled with the effect their presence has on a culture. Simply by being present, a researcher causes changes in a culture, and anthropologists continue to question whether or not it is appropriate to influence the cultures they study, or possible to avoid having influence.
+
+Ethnography
+
+In the 20th century, most cultural and social anthropologists turned to the crafting of ethnographies. An ethnography is a piece of writing about a people, at a particular place and time. Typically, the anthropologist lives among people in another society for a period of time, simultaneously participating in and observing the social and cultural life of the group.
+
+Numerous other ethnographic techniques have resulted in ethnographic writing or details being preserved, as cultural anthropologists also curate materials, spend long hours in libraries, churches and schools poring over records, investigate graveyards, and decipher ancient scripts. A typical ethnography will also include information about physical geography, climate and habitat. It is meant to be a holistic piece of writing about the people in question, and today often includes the longest possible timeline of past events that the ethnographer can obtain through primary and secondary research.
+
+Bronisław Malinowski developed the ethnographic method, and Franz Boas taught it in the United States. Boas' students such as Alfred L. Kroeber, Ruth Benedict and Margaret Mead drew on his conception of culture and cultural relativism to develop cultural anthropology in the United States. Simultaneously, Malinowski and A.R. Radcliffe Brown's students were developing social anthropology in the United Kingdom. Whereas cultural anthropology focused on symbols and values, social anthropology focused on social groups and institutions. Today socio-cultural anthropologists attend to all these elements.
+
+In the early 20th century, socio-cultural anthropology developed in different forms in Europe and in the United States. European "social anthropologists" focused on observed social behaviors and on "social structure", that is, on relationships among social roles (for example, husband and wife, or parent and child) and social institutions (for example, religion, economy, and politics).
+
+American "cultural anthropologists" focused on the ways people expressed their view of themselves and their world, especially in symbolic forms, such as art and myths. These two approaches frequently converged and generally complemented one another. For example, kinship and leadership function both as symbolic systems and as social institutions. Today almost all socio-cultural anthropologists refer to the work of both sets of predecessors, and have an equal interest in what people do and in what people say.
+
+Cross-cultural comparison
+One means by which anthropologists combat ethnocentrism is to engage in the process of cross-cultural comparison. It is important to test so-called "human universals" against the ethnographic record. Monogamy, for example, is frequently touted as a universal human trait, yet comparative study shows that it is not.
+The Human Relations Area Files, Inc. (HRAF) is a research agency based at Yale University. Since 1949, its mission has been to encourage and facilitate worldwide comparative studies of human culture, society, and behavior in the past and present. The name came from the Institute of Human Relations, an interdisciplinary program/building at Yale at the time. The Institute of Human Relations had sponsored HRAF's precursor, the Cross-Cultural Survey (see George Peter Murdock), as part of an effort to develop an integrated science of human behavior and culture. The two eHRAF databases on the Web are expanded and updated annually. eHRAF World Cultures includes materials on cultures, past and present, and covers nearly 400 cultures.  The second database, eHRAF Archaeology, covers major archaeological traditions and many more sub-traditions and sites around the world.
+
+Comparison across cultures includies the industrialized (or de-industrialized) West. Cultures in the more traditional standard cross-cultural sample of small scale societies are:
+
+Multi-sited ethnography
+Ethnography dominates socio-cultural anthropology. Nevertheless, many contemporary socio-cultural anthropologists have rejected earlier models of ethnography as treating local cultures as bounded and isolated. These anthropologists continue to concern themselves with the distinct ways people in different locales experience and understand their lives, but they often argue that one cannot understand these particular ways of life solely from a local perspective; they instead combine a focus on the local with an effort to grasp larger political, economic, and cultural frameworks that impact local lived realities. Notable proponents of this approach include Arjun Appadurai, James Clifford, George Marcus, Sidney Mintz, Michael Taussig, Eric Wolf and Ronald Daus.
+
+A growing trend in anthropological research and analysis is the use of multi-sited ethnography, discussed in George Marcus' article, "Ethnography In/Of the World System: the Emergence of Multi-Sited Ethnography". Looking at culture as embedded in macro-constructions of a global social order, multi-sited ethnography uses traditional methodology in various locations both spatially and temporally. Through this methodology, greater insight can be gained when examining the impact of world-systems on local and global communities.
+
+Also emerging in multi-sited ethnography are greater interdisciplinary approaches to fieldwork, bringing in methods from cultural studies, media studies, science and technology studies, and others. In multi-sited ethnography, research tracks a subject across spatial and temporal boundaries. For example, a multi-sited ethnography may follow a "thing", such as a particular commodity, as it is transported through the networks of global capitalism.
+
+Multi-sited ethnography may also follow ethnic groups in diaspora, stories or rumours that appear in multiple locations and in multiple time periods, metaphors that appear in multiple ethnographic locations, or the biographies of individual people or groups as they move through space and time. It may also follow conflicts that transcend boundaries. An example of multi-sited ethnography is Nancy Scheper-Hughes' work on the international black market for the trade of human organs. In this research, she follows organs as they are transferred through various legal and illegal networks of capitalism, as well as the rumours and urban legends that circulate in impoverished communities about child kidnapping and organ theft.
+
+Sociocultural anthropologists have increasingly turned their investigative eye on to "Western" culture. For example, Philippe Bourgois won the Margaret Mead Award in 1997 for In Search of Respect, a study of the entrepreneurs in a Harlem crack-den. Also growing more popular are ethnographies of professional communities, such as laboratory researchers, Wall Street investors, law firms, or information technology (IT) computer employees.
+
+Topics
+
+Kinship and family
+
+Kinship refers to the anthropological study of the ways in which humans form and maintain relationships with one another and how those relationships operate within and define social organization.
+
+Research in kinship studies often crosses over into different anthropological subfields including medical, feminist, and public anthropology. This is likely due to its fundamental concepts, as articulated by linguistic anthropologist Patrick McConvell: Throughout history, kinship studies have primarily focused on the topics of marriage, descent, and procreation. Anthropologists have written extensively on the variations within marriage across cultures and its legitimacy as a human institution. There are stark differences between communities in terms of marital practice and value, leaving much room for anthropological fieldwork. For instance, the Nuer of Sudan and the Brahmans of Nepal practice polygyny, where one man has several marriages to two or more women. The Nyar of India and Nyimba of Tibet and Nepal practice polyandry, where one woman is often married to two or more men. The marital practice found in most cultures, however, is monogamy, where one woman is married to one man. Anthropologists also study different marital taboos across cultures, most commonly the incest taboo of marriage within sibling and parent-child relationships. It has been found that all cultures have an incest taboo to some degree, but the taboo shifts between cultures when the marriage extends beyond the nuclear family unit.
+
+There are similar foundational differences where the act of procreation is concerned. Although anthropologists have found that biology is acknowledged in every cultural relationship to procreation, there are differences in the ways in which cultures assess the constructs of parenthood. For example, in the Nuyoo municipality of Oaxaca, Mexico, it is believed that a child can have partible maternity and partible paternity. In this case, a child would have multiple biological mothers in the case that it is born of one woman and then breastfed by another. A child would have multiple biological fathers in the case that the mother had sex with multiple men, following the commonplace belief in Nuyoo culture that pregnancy must be preceded by sex with multiple men in order have the necessary accumulation of semen.
+
+Late twentieth-century shifts in interest
+In the twenty-first century, Western ideas of kinship have evolved beyond the traditional assumptions of the nuclear family, raising anthropological questions of consanguinity, lineage, and normative marital expectation. The shift can be traced back to the 1960s, with the reassessment of kinship's basic principles offered by Edmund Leach, Rodney Neeham, David Schneider, and others. Instead of relying on narrow ideas of Western normalcy, kinship studies increasingly catered to "more ethnographic voices, human agency, intersecting power structures, and historical contex". The study of kinship evolved to accommodate for the fact that it cannot be separated from its institutional roots and must pay respect to the society in which it lives, including that society's contradictions, hierarchies, and individual experiences of those within it. This shift was progressed further by the emergence of second-wave feminism in the early 1970s, which introduced ideas of marital oppression, sexual autonomy, and domestic subordination. Other themes that emerged during this time included the frequent comparisons between Eastern and Western kinship systems and the increasing amount of attention paid to anthropologists' own societies, a swift turn from the focus that had traditionally been paid to largely "foreign", non-Western communities.
+
+Kinship studies began to gain mainstream recognition in the late 1990s with the surging popularity of feminist anthropology, particularly with its work related to biological anthropology and the intersectional critique of gender relations. At this time, there was the arrival of "Third World feminism", a movement that argued kinship studies could not examine the gender relations of developing countries in isolation, and must pay respect to racial and economic nuance as well. This critique became relevant, for instance, in the anthropological study of Jamaica: race and class were seen as the primary obstacles to Jamaican liberation from economic imperialism, and gender as an identity was largely ignored. Third World feminism aimed to combat this in the early twenty-first century by promoting these categories as coexisting factors. In Jamaica, marriage as an institution is often substituted for a series of partners, as poor women cannot rely on regular financial contributions in a climate of economic instability. In addition, there is a common practice of Jamaican women artificially lightening their skin tones in order to secure economic survival. These anthropological findings, according to Third World feminism, cannot see gender, racial, or class differences as separate entities, and instead must acknowledge that they interact together to produce unique individual experiences.
+
+Rise of reproductive anthropology
+Kinship studies have also experienced a rise in the interest of reproductive anthropology with the advancement of assisted reproductive technologies (ARTs), including in vitro fertilization (IVF). These advancements have led to new dimensions of anthropological research, as they challenge the Western standard of biogenetically based kinship, relatedness, and parenthood. According to anthropologists Maria C. Inhorn and Daphna Birenbaum-Carmeli, "ARTs have pluralized notions of relatedness and led to a more dynamic notion of "kinning" namely, kinship as a process, as something under construction, rather than a natural given". With this technology, questions of kinship have emerged over the difference between biological and genetic relatedness, as gestational surrogates can provide a biological environment for the embryo while the genetic ties remain with a third party. If genetic, surrogate, and adoptive maternities are involved, anthropologists have acknowledged that there can be the possibility for three "biological" mothers to a single child. With ARTs, there are also anthropological questions concerning the intersections between wealth and fertility: ARTs are generally only available to those in the highest income bracket, meaning the infertile poor are inherently devalued in the system. There have also been issues of reproductive tourism and bodily commodification, as individuals seek economic security through hormonal stimulation and egg harvesting, which are potentially harmful procedures. With IVF, specifically, there have been many questions of embryotic value and the status of life, particularly as it relates to the manufacturing of stem cells, testing, and research.
+
+Current issues in kinship studies, such as adoption, have revealed and challenged the Western cultural disposition towards the genetic, "blood" tie. Western biases against single parent homes have also been explored through similar anthropological research, uncovering that a household with a single parent experiences "greater levels of scrutiny and [is] routinely seen as the 'other' of the nuclear, patriarchal family". The power dynamics in reproduction, when explored through a comparative analysis of "conventional" and "unconventional" families, have been used to dissect the Western assumptions of child bearing and child rearing in contemporary kinship studies.
+
+Critiques of kinship studies 
+Kinship, as an anthropological field of inquiry, has been heavily criticized across the discipline. One critique is that, as its inception, the framework of kinship studies was far too structured and formulaic, relying on dense language and stringent rules. Another critique, explored at length by American anthropologist David Schneider, argues that kinship has been limited by its inherent Western ethnocentrism. Schneider proposes that kinship is not a field that can be applied cross-culturally, as the theory itself relies on European assumptions of normalcy. He states in the widely circulated 1984 book A critique of the study of kinship that "[K]inship has been defined by European social scientists, and European social scientists use their own folk culture as the source of many, if not all of their ways of formulating and understanding the world about them". However, this critique has been challenged by the argument that it is linguistics, not cultural divergence, that has allowed for a European bias, and that the bias can be lifted by centering the methodology on fundamental human concepts. Polish anthropologist Anna Wierzbicka argues that "mother" and "father" are examples of such fundamental human concepts, and can only be Westernized when conflated with English concepts such as "parent" and "sibling".
+
+A more recent critique of kinship studies is its solipsistic focus on privileged, Western human relations and its promotion of normative ideals of human exceptionalism. In Critical Kinship Studies, social psychologists Elizabeth Peel and Damien Riggs argue for a move beyond this human-centered framework, opting instead to explore kinship through a "posthumanist" vantage point where anthropologists focus on the intersecting relationships of human animals, non-human animals, technologies and practices.
+
+Institutional anthropology
+The role of anthropology in institutions has expanded significantly since the end of the 20th century. Much of this development can be attributed to the rise in anthropologists working outside of academia and the increasing importance of globalization in both institutions and the field of anthropology. Anthropologists can be employed by institutions such as for-profit business, nonprofit organizations, and governments. For instance, cultural anthropologists are commonly employed by the United States federal government.
+
+The two types of institutions defined in the field of anthropology are total institutions and social institutions. Total institutions are places that comprehensively coordinate the actions of people within them, and examples of total institutions include prisons, convents, and hospitals. Social institutions, on the other hand, are constructs that regulate individuals' day-to-day lives, such as kinship, religion, and economics. Anthropology of institutions may analyze labor unions, businesses ranging from small enterprises to corporations, government, medical organizations, education, prisons, and financial institutions. Nongovernmental organizations have garnered particular interest in the field of institutional anthropology because they are capable of fulfilling roles previously ignored by governments, or previously realized by families or local groups, in an attempt to mitigate social problems.
+
+The types and methods of scholarship performed in the anthropology of institutions can take a number of forms. Institutional anthropologists may study the relationship between organizations or between an organization and other parts of society. Institutional anthropology may also focus on the inner workings of an institution, such as the relationships, hierarchies and cultures formed, and the ways that these elements are transmitted and maintained, transformed, or abandoned over time. Additionally, some anthropology of institutions examines the specific design of institutions and their corresponding strength. More specifically, anthropologists may analyze specific events within an institution, perform semiotic investigations, or analyze the mechanisms by which knowledge and culture are organized and dispersed.
+
+In all manifestations of institutional anthropology, participant observation is critical to understanding the intricacies of the way an institution works and the consequences of actions taken by individuals within it. Simultaneously, anthropology of institutions extends beyond examination of the commonplace involvement of individuals in institutions to discover how and why the organizational principles evolved in the manner that they did.
+
+Common considerations taken by anthropologists in studying institutions include the physical location at which a researcher places themselves, as important interactions often take place in private, and the fact that the members of an institution are often being examined in their workplace and may not have much idle time to discuss the details of their everyday endeavors. The ability of individuals to present the workings of an institution in a particular light or frame must additionally be taken into account when using interviews and document analysis to understand an institution, as the involvement of an anthropologist may be met with distrust when information being released to the public is not directly controlled by the institution and could potentially be damaging.
+
+See also
+
+References
+
+External links
+
+ Official website of Human Relations Area Files (HRAF) based at Yale University
+ A Basic Guide to Cross-Cultural Research from HRAF
+Conversion of units is the conversion between different units of measurement for the same quantity, typically through multiplicative conversion factors which change the measured quantity value without changing its effects. Unit conversion is often easier within the metric or the SI than in others, due to the regular 10-base in all units and the prefixes that increase or decrease by 3 powers of 10 at a time.
+
+Overview 
+The process of conversion depends on the specific situation and the intended purpose. This may be governed by regulation, contract, technical specifications or other published standards. Engineering judgment may include such factors as:
+ The precision and accuracy of measurement and the associated uncertainty of measurement.
+ The statistical confidence interval or tolerance interval of the initial measurement.
+ The number of significant figures of the measurement.
+ The intended use of the measurement including the engineering tolerances.
+ Historical definitions of the units and their derivatives used in old measurements; e.g., international foot vs. US survey foot.
+
+Some conversions from one system of units to another need to be exact, without increasing or decreasing the precision of the first measurement. This is sometimes called soft conversion. It does not involve changing the physical configuration of the item being measured.
+
+By contrast, a hard conversion or an adaptive conversion may not be exactly equivalent. It changes the measurement to convenient and workable numbers and units in the new system. It sometimes involves a slightly different configuration, or size substitution, of the item. Nominal values are sometimes allowed and used.
+
+Factor-label method 
+
+The factor-label method, also known as the unit-factor method or the unity bracket method, is a widely used technique for unit conversions using the rules of algebra.
+
+The factor-label method is the sequential application of conversion factors expressed as fractions and arranged so that any dimensional unit appearing in both the numerator and denominator of any of the fractions can be cancelled out until only the desired set of dimensional units is obtained. For example, 10 miles per hour can be converted to metres per second by using a sequence of conversion factors as shown below:
+
+Each conversion factor is chosen based on the relationship between one of the original units and one of the desired units (or some intermediary unit), before being re-arranged to create a factor that cancels out the original unit. For example, as "mile" is the numerator in the original fraction and , "mile" will need to be the denominator in the conversion factor. Dividing both sides of the equation by 1 mile yields , which when simplified results in the dimensionless . Because of the identity property of multiplication, multiplying any quantity (physical or not) by the dimensionless 1 does not change that quantity. Once this and the conversion factor for seconds per hour have been multiplied by the original fraction to cancel out the units mile and hour, 10 miles per hour converts to 4.4704 metres per second.
+
+As a more complex example, the concentration of nitrogen oxides (NOx) in the flue gas from an industrial furnace can be converted to a mass flow rate expressed in grams per hour (g/h) of NOx by using the following information as shown below:
+
+ NOx concentration = 10 parts per million by volume = 10 ppmv = 10 volumes/106 volumes
+ NOx molar mass = 46 kg/kmol = 46 g/mol
+ Flow rate of flue gas = 20 cubic metres per minute = 20 m3/min
+ The flue gas exits the furnace at 0 °C temperature and 101.325 kPa absolute pressure.
+ The molar volume of a gas at 0 °C temperature and 101.325 kPa is 22.414 m3/kmol.
+
+After canceling out any dimensional units that appear both in the numerators and denominators of the fractions in the above equation, the NOx concentration of 10 ppmv converts to mass flow rate of 24.63 grams per hour.
+
+Checking equations that involve dimensions 
+The factor-label method can also be used on any mathematical equation to check whether or not the dimensional units on the left hand side of the equation are the same as the dimensional units on the right hand side of the equation. Having the same units on both sides of an equation does not ensure that the equation is correct, but having different units on the two sides (when expressed in terms of base units) of an equation implies that the equation is wrong.
+
+For example, check the universal gas law equation of , when:
+ the pressure P is in pascals (Pa)
+ the volume V is in cubic metres (m3)
+ the amount of substance n is in moles (mol)
+ the universal gas constant R is 8.3145 Pa⋅m3/(mol⋅K)
+ the temperature T is in kelvins (K)
+
+As can be seen, when the dimensional units appearing in the numerator and denominator of the equation's right hand side are cancelled out, both sides of the equation have the same dimensional units. Dimensional analysis can be used as a tool to construct equations that relate non-associated physico-chemical properties. The equations may reveal hitherto unknown or overlooked properties of matter, in the form of left-over dimensions – dimensional adjusters – that can then be assigned physical significance. It is important to point out that such 'mathematical manipulation' is neither without prior precedent, nor without considerable scientific significance. Indeed, the Planck constant, a fundamental physical constant, was 'discovered' as a purely mathematical abstraction or representation that built on the Rayleigh–Jeans law for preventing the ultraviolet catastrophe. It was assigned and ascended to its quantum physical significance either in tandem or post mathematical dimensional adjustment – not earlier.
+
+Limitations 
+The factor-label method can convert only unit quantities for which the units are in a linear relationship intersecting at 0. (Ratio scale in Stevens's typology) Most units fit this paradigm. An example for which it cannot be used is the conversion between degrees Celsius and kelvins (or degrees Fahrenheit). Between degrees Celsius and kelvins, there is a constant difference rather than a constant ratio, while between degrees Celsius and degrees Fahrenheit there is neither a constant difference nor a constant ratio. There is, however, an affine transform (, rather than a linear transform ) between them.
+
+For example, the freezing point of water is 0 °C and 32 °F, and a 5 °C change is the same as a 9 °F change. Thus, to convert from units of Fahrenheit to units of Celsius, one subtracts 32 °F (the offset from the point of reference), divides by 9 °F and multiplies by 5 °C (scales by the ratio of units), and adds 0 °C (the offset from the point of reference). Reversing this yields the formula for obtaining a quantity in units of Celsius from units of Fahrenheit; one could have started with the equivalence between 100 °C and 212 °F, though this would yield the same formula at the end.
+
+Hence, to convert the numerical quantity value of a temperature T[F] in degrees Fahrenheit to a numerical quantity value T[C] in degrees Celsius, this formula may be used:
+
+T[C] = (T[F] − 32) × 5/9.
+
+To convert T[C] in degrees Celsius to T[F] in degrees Fahrenheit, this formula may be used:
+
+T[F] = (T[C] × 9/5) + 32.
+
+Example
+Starting with:
+
+replace the original unit  with its meaning in terms of the desired unit , e.g. if , then:
+
+Now  and  are both numerical values, so just calculate their product.
+
+Or, which is just mathematically the same thing, multiply Z by unity, the product is still Z:
+
+For example, you have an expression for a physical value Z involving the unit feet per second () and you want it in terms of the unit miles per hour ():
+
+Or as an example using the metric system, you have a value of fuel economy in the unit litres per 100 kilometres and you want it in terms of the unit microlitres per metre:
+
+Calculation involving non-SI Units 
+In the cases where non-SI units are used, the numerical calculation of a formula can be done by first working out the pre-factor, and then plug in the numerical values of the given/known quantities.
+
+For example, in the study of Bose–Einstein condensate, atomic mass  is usually given in daltons, instead of kilograms, and chemical potential  is often given in the Boltzmann constant times nanokelvin. The condensate's healing length is given by:
+
+For a 23Na condensate with chemical potential of (the Boltzmann constant times) 128 nK, the calculation of healing length (in micrometres) can be done in two steps:
+
+Calculate the pre-factor 
+Assume that  this gives
+
+which is our pre-factor.
+
+Calculate the numbers 
+Now, make use of the fact that . With , .
+
+This method is especially useful for programming and/or making a worksheet, where input quantities are taking multiple different values; For example, with the pre-factor calculated above, it is very easy to see that the healing length of 174Yb with chemical potential 20.3 nK is .
+
+Software tools 
+There are many conversion tools. They are found in the function libraries of applications such as spreadsheets databases, in calculators, and in macro packages and plugins for many other applications such as the mathematical, scientific and technical applications.
+
+There are many standalone applications that offer the thousands of the various units with conversions. For example, the free software movement offers a command line utility GNU units for Linux and Windows. The Unified Code for Units of Measure is also a popular option.
+
+See also 
+
+Accuracy and precision
+Conversion of units of temperature
+Dimensional analysis
+English units
+False precision
+Imperial units
+International System of Units
+Mesures usuelles
+Metric prefix (e.g. "kilo-" prefix)
+Metric system
+Natural units
+Orders of Magnitude
+Rounding
+Significant figures
+United States customary units
+Unit of length
+Units of measurement
+
+Notes and references 
+
+Notes
+
+External links 
+
+ 
+NIST Guide to SI Units Many conversion factors listed.
+The Unified Code for Units of Measure
+Units, Symbols, and Conversions XML Dictionary
+
+"Instruction sur les poids et mesures républicaines:déduites de la grandeur de la terre,uniformes pour toute la République,et sur les calculs relatifs à leur division décimale"
+
+Unicalc Live web calculator doing units conversion by dimensional analysis
+Math Skills Review
+U.S. EPA tutorial
+A Discussion of Units
+Short Guide to Unit Conversions
+Canceling Units Lesson
+Chapter 11: Behavior of Gases Chemistry: Concepts and Applications, Denton independent school District
+Air Dispersion Modeling Conversions and Formulas
+www.gnu.org/software/units  free program, very practical
+
+ 
+Metrication
+Conversion of units of measurement
+A city is a human settlement of a notable size. It can be defined as a permanent and densely settled place with administratively defined boundaries whose members work primarily on non-agricultural tasks. Cities generally have extensive systems for housing, transportation, sanitation, utilities, land use, production of goods, and communication. Their density facilitates interaction between people, government organizations, and businesses, sometimes benefiting different parties in the process, such as improving the efficiency of goods and service distribution.
+
+Historically, city dwellers have been a small proportion of humanity overall, but following two centuries of unprecedented and rapid urbanization, more than half of the world population now lives in cities, which has had profound consequences for global sustainability. Present-day cities usually form the core of larger metropolitan areas and urban areas—creating numerous commuters traveling toward city centres for employment, entertainment, and education. However, in a world of intensifying globalization, all cities are to varying degrees also connected globally beyond these regions. This increased influence means that cities also have significant influences on global issues, such as sustainable development, climate change, and global health. Because of these major influences on global issues, the international community has prioritized investment in sustainable cities through Sustainable Development Goal 11. Due to the efficiency of transportation and the smaller land consumption, dense cities hold the potential to have a smaller ecological footprint per inhabitant than more sparsely populated areas. Therefore, compact cities are often referred to as a crucial element in fighting climate change. However, this concentration can also have significant negative consequences, such as forming urban heat islands, concentrating pollution, and stressing water supplies and other resources.
+
+Other important traits of cities besides population include the capital status and relative continued occupation of the city. For example, country capitals such as Athens,Beijing, Jakarta, Kuala Lumpur, London, Manila, Mexico City, Moscow, Nairobi, New Delhi, Paris, Rome, Seoul, Singapore, Tokyo, and Washington, D.C. reflect the identity and apex of their respective nations. Some historic capitals, such as Kyoto, Yogyakarta, and Xi'an, maintain their reflection of cultural identity even without modern capital status. Religious holy sites offer another example of capital status within a religion; examples include Jerusalem, Mecca, Varanasi, Ayodhya, Haridwar, and Prayagraj.
+
+Meaning 
+
+A city can be distinguished from other human settlements by its relatively great size, but also by its functions and its special symbolic status, which may be conferred by a central authority. The term can also refer either to the physical streets and buildings of the city or to the collection of people who dwell there and can be used in a general sense to mean urban rather than rural territory.
+
+National censuses use a variety of definitions – invoking factors such as population, population density, number of dwellings, economic function, and infrastructure – to classify populations as urban. Typical working definitions for small-city populations start at around 100,000 people. Common population definitions for an urban area (city or town) range between 1,500 and 50,000 people, with most U.S. states using a minimum between 1,500 and 5,000 inhabitants. Some jurisdictions set no such minima. In the United Kingdom, city status is awarded by the Crown and then remains permanent. (Historically, the qualifying factor was the presence of a cathedral, resulting in some very small cities such as Wells, with a population of 12,000 , and St Davids, with a population of 1,841 .) According to the "functional definition", a city is not distinguished by size alone, but also by the role it plays within a larger political context. Cities serve as administrative, commercial, religious, and cultural hubs for their larger surrounding areas.
+
+The presence of a literate elite is often associated with cities because of the cultural diversities present in a city. A typical city has professional administrators, regulations, and some form of taxation (food and other necessities or means to trade for them) to support the government workers. (This arrangement contrasts with the more typically horizontal relationships in a tribe or village accomplishing common goals through informal agreements between neighbors, or the leadership of a chief.) The governments may be based on heredity, religion, military power, work systems such as canal-building, food distribution, land-ownership, agriculture, commerce, manufacturing, finance, or a combination of these. Societies that live in cities are often called civilizations.
+
+The degree of urbanization is a modern metric to help define what comprises a city: "a population of at least 50,000 inhabitants in contiguous dense grid cells (>1,500 inhabitants per square kilometer)". This metric was "devised over years by the European Commission, OECD, World Bank and others, and endorsed in March [2021] by the United Nations ... largely for the purpose of international statistical comparison".
+
+Etymology 
+The word city and the related civilization come from the Latin root civitas, originally meaning 'citizenship' or 'community member' and eventually coming to correspond with urbs, meaning 'city' in a more physical sense. The Roman civitas was closely linked with the Greek polis—another common root appearing in English words such as metropolis.
+
+In toponymic terminology, names of individual cities and towns are called astionyms (from Ancient Greek ἄστυ 'city or town' and ὄνομα 'name').
+
+Geography
+
+Urban geography deals both with cities in their larger context and with their internal structure. Cities are estimated to cover about 3% of the land surface of the Earth.
+
+Site 
+
+Town siting has varied through history according to natural, technological, economic, and military contexts. Access to water has long been a major factor in city placement and growth, and despite exceptions enabled by the advent of rail transport in the nineteenth century, through the present most of the world's urban population lives near the coast or on a river.
+
+Urban areas as a rule cannot produce their own food and therefore must develop some relationship with a hinterland that sustains them. Only in special cases such as mining towns which play a vital role in long-distance trade, are cities disconnected from the countryside which feeds them. Thus, centrality within a productive region influences siting, as economic forces would, in theory, favor the creation of marketplaces in optimal mutually reachable locations.
+
+Center 
+
+The vast majority of cities have a central area containing buildings with special economic, political, and religious significance. Archaeologists refer to this area by the Greek term temenos or if fortified as a citadel. These spaces historically reflect and amplify the city's centrality and importance to its wider sphere of influence. Today cities have a city center or downtown, sometimes coincident with a central business district.
+
+Public space 
+Cities typically have public spaces where anyone can go. These include privately owned spaces open to the public as well as forms of public land such as public domain and the commons. Western philosophy since the time of the Greek agora has considered physical public space as the substrate of the symbolic public sphere. Public art adorns (or disfigures) public spaces. Parks and other natural sites within cities provide residents with relief from the hardness and regularity of typical built environments. Urban green spaces are another component of public space that provides the benefit of mitigating the urban heat island effect, especially in cities that are in warmer climates. These spaces prevent carbon imbalances, extreme habitat losses, electricity and water consumption, and human health risks.
+
+Internal structure 
+
+The urban structure generally follows one or more basic patterns: geomorphic, radial, concentric, rectilinear, and curvilinear. The physical environment generally constrains the form in which a city is built. If located on a mountainside, urban structures may rely on terraces and winding roads. It may be adapted to its means of subsistence (e.g. agriculture or fishing). And it may be set up for optimal defense given the surrounding landscape. Beyond these "geomorphic" features, cities can develop internal patterns, due to natural growth or to city planning.
+
+In a radial structure, main roads converge on a central point. This form could evolve from successive growth over a long time, with concentric traces of town walls and citadels marking older city boundaries. In more recent history, such forms were supplemented by ring roads moving traffic around the outskirts of a town. Dutch cities such as Amsterdam and Haarlem are structured as a central square surrounded by concentric canals marking every expansion. In cities such as Moscow, this pattern is still clearly visible.
+
+A system of rectilinear city streets and land plots, known as the grid plan, has been used for millennia in Asia, Europe, and the Americas.  The Indus Valley civilization built Mohenjo-Daro, Harappa, and other cities on a grid pattern, using ancient principles described by Kautilya, and aligned with the compass points. The ancient Greek city of Priene exemplifies a grid plan with specialized districts used across the Hellenistic Mediterranean.
+
+Urban areas 
+The urban-type settlement extends far beyond the traditional boundaries of the city proper in a form of development sometimes described critically as urban sprawl. Decentralization and dispersal of city functions (commercial, industrial, residential, cultural, political) has transformed the very meaning of the term and has challenged geographers seeking to classify territories according to an urban-rural binary.
+
+Metropolitan areas include suburbs and exurbs organized around the needs of commuters, and sometimes edge cities characterized by a degree of economic and political independence. (In the US these are grouped into metropolitan statistical areas for purposes of demography and marketing.) Some cities are now part of a continuous urban landscape called urban agglomeration, conurbation, or megalopolis (exemplified by the BosWash corridor of the Northeastern United States.)
+
+History
+
+The emergence of cities from proto-urban settlements, such as Çatalhöyük, is a non-linear development that demonstrates the varied experiences of early urbanization. 
+
+The cities of Jericho, Aleppo, Faiyum, Yerevan, Athens, Matera, Damascus, and Argos are among those laying claim to the longest continual inhabitation.
+
+Cities, characterized by population density, symbolic function, and urban planning, have existed for thousands of years. In the conventional view, civilization and the city were both followed by the development of agriculture, which enabled the production of surplus food and thus a social division of labor (with concomitant social stratification) and trade. Early cities often featured granaries, sometimes within a temple. A minority viewpoint considers that cities may have arisen without agriculture, due to alternative means of subsistence (fishing), to use as communal seasonal shelters, to their value as bases for defensive and offensive military organization, or to their inherent economic function. Cities played a crucial role in the establishment of political power over an area, and ancient leaders such as Alexander the Great founded and created them with zeal.
+
+Ancient times 
+
+Jericho and Çatalhöyük, dated to the eighth millennium BC, are among the earliest proto-cities known to archaeologists. However, the Mesopotamian city of Uruk from the mid-fourth millennium BC (ancient Iraq) is considered by most archaeologists to be the first true city, innovating many characteristics for cities to follow, with its name attributed to the Uruk period.
+
+In the fourth and third millennium BC, complex civilizations flourished in the river valleys of Mesopotamia, India, China, and Egypt. Excavations in these areas have found the ruins of cities geared variously towards trade, politics, or religion. Some had large, dense populations, but others carried out urban activities in the realms of politics or religion without having large associated populations.
+
+Among the early Old World cities, Mohenjo-Daro of the Indus Valley civilization in present-day Pakistan, existing from about 2600 BC, was one of the largest, with a population of 50,000 or more and a sophisticated sanitation system. China's planned cities were constructed according to sacred principles to act as celestial microcosms.
+
+The Ancient Egyptian cities known physically by archaeologists are not extensive. They include (known by their Arab names) El Lahun, a workers' town associated with the pyramid of Senusret II, and the religious city Amarna built by Akhenaten and abandoned. These sites appear planned in a highly regimented and stratified fashion, with a minimalistic grid of rooms for the workers and increasingly more elaborate housing available for higher classes.
+
+In Mesopotamia, the civilization of Sumer, followed by Assyria and Babylon, gave rise to numerous cities, governed by kings and fostered multiple languages written in cuneiform. The Phoenician trading empire, flourishing around the turn of the first millennium BC, encompassed numerous cities extending from Tyre, Cydon, and Byblos to Carthage and Cádiz.
+
+In the following centuries, independent city-states of Greece, especially Athens, developed the polis, an association of male landowning citizens who collectively constituted the city. The agora, meaning "gathering place" or "assembly", was the center of the athletic, artistic, spiritual, and political life of the polis. Rome was the first city that surpassed one million inhabitants. Under the authority of its empire, Rome transformed and founded many cities (), and with them brought its principles of urban architecture, design, and society.
+
+In the ancient Americas, early urban traditions developed in the Andes and Mesoamerica. In the Andes, the first urban centers developed in the Norte Chico civilization, Chavin and Moche cultures, followed by major cities in the Huari, Chimu, and Inca cultures. The Norte Chico civilization included as many as 30 major population centers in what is now the Norte Chico region of north-central coastal Peru. It is the oldest known civilization in the Americas, flourishing between the 30th and 18th centuries BC. Mesoamerica saw the rise of early urbanism in several cultural regions, beginning with the Olmec and spreading to the Preclassic Maya, the Zapotec of Oaxaca, and Teotihuacan in central Mexico. Later cultures such as the Aztec, Andean civilizations, Mayan, Mississippians, and Pueblo peoples drew on these earlier urban traditions. Many of their ancient cities continue to be inhabited, including major metropolitan cities such as Mexico City, in the same location as Tenochtitlan; while ancient continuously inhabited Pueblos are near modern urban areas in New Mexico, such as Acoma Pueblo near the Albuquerque metropolitan area and Taos Pueblo near Taos; while others like Lima are located nearby ancient Peruvian sites such as Pachacamac.
+
+Jenné-Jeno, located in present-day Mali and dating to the third century BC, lacked monumental architecture and a distinctive elite social class—but nevertheless had specialized production and relations with a hinterland. Pre-Arabic trade contacts probably existed between Jenné-Jeno and North Africa. Other early urban centers in sub-Saharan Africa, dated to around 500 AD, include Awdaghust, Kumbi-Saleh the ancient capital of Ghana, and Maranda a center located on a trade route between Egypt and Gao.
+
+Middle Ages
+
+In the remnants of the Roman Empire, cities of late antiquity gained independence but soon lost population and importance. The locus of power in the West shifted to Constantinople and to the ascendant Islamic civilization with its major cities Baghdad, Cairo, and Córdoba. From the 9th through the end of the 12th century, Constantinople, the capital of the Eastern Roman Empire, was the largest and wealthiest city in Europe, with a population approaching 1 million. The Ottoman Empire gradually gained control over many cities in the Mediterranean area, including Constantinople in 1453.
+
+In the Holy Roman Empire, beginning in the 12th century, free imperial cities such as Nuremberg, Strasbourg, Frankfurt, Basel, Zurich, and Nijmegen became a privileged elite among towns having won self-governance from their local lord or having been granted self-governance by the emperor and being placed under his immediate protection. By 1480, these cities, as far as still part of the empire, became part of the Imperial Estates governing the empire with the emperor through the Imperial Diet.
+
+By the 13th and 14th centuries, some cities become powerful states, taking surrounding areas under their control or establishing extensive maritime empires. In Italy, medieval communes developed into city-states including the Republic of Venice and the Republic of Genoa. In Northern Europe, cities including Lübeck and Bruges formed the Hanseatic League for collective defense and commerce. Their power was later challenged and eclipsed by the Dutch commercial cities of Ghent, Ypres, and Amsterdam. Similar phenomena existed elsewhere, as in the case of Sakai, which enjoyed considerable autonomy in late medieval Japan.
+
+In the first millennium AD, the Khmer capital of Angkor in Cambodia grew into the most extensive preindustrial settlement in the world by area, covering over 1,000 km2 and possibly supporting up to one million people.
+
+Early modern
+In the West, nation-states became the dominant unit of political organization following the Peace of Westphalia in the seventeenth century. Western Europe's larger capitals (London and Paris) benefited from the growth of commerce following the emergence of an Atlantic trade. However, most towns remained small.
+
+During the Spanish colonization of the Americas, the old Roman city concept was extensively used. Cities were founded in the middle of the newly conquered territories and were bound to several laws regarding administration, finances, and urbanism.
+
+Industrial age
+
+The growth of the modern industry from the late 18th century onward led to massive urbanization and the rise of new great cities, first in Europe and then in other regions, as new opportunities brought huge numbers of migrants from rural communities into urban areas. England led the way as London became the capital of a world empire and cities across the country grew in locations strategic for manufacturing. In the United States from 1860 to 1910, the introduction of railroads reduced transportation costs, and large manufacturing centers began to emerge, fueling migration from rural to city areas.
+
+Some industrialized cities were confronted with health challenges associated with overcrowding, occupational hazards of industry, contaminated water and air, poor sanitation, and communicable diseases such as typhoid and cholera. Factories and slums emerged as regular features of the urban landscape.
+
+Post-industrial age
+In the second half of the 20th century, deindustrialization (or "economic restructuring") in the West led to poverty, homelessness, and urban decay in formerly prosperous cities. America's "Steel Belt" became a "Rust Belt" and cities such as Detroit, Michigan, and Gary, Indiana began to shrink, contrary to the global trend of massive urban expansion. Such cities have shifted with varying success into the service economy and public-private partnerships, with concomitant gentrification, uneven revitalization efforts, and selective cultural development. Under the Great Leap Forward and subsequent five-year plans continuing today, China has undergone concomitant urbanization and industrialization and become the world's leading manufacturer.
+
+Amidst these economic changes, high technology and instantaneous telecommunication enable select cities to become centers of the knowledge economy. A new smart city paradigm, supported by institutions such as the RAND Corporation and IBM, is bringing computerized surveillance, data analysis, and governance to bear on cities and city dwellers. Some companies are building brand-new master-planned cities from scratch on greenfield sites.
+
+Urbanization 
+
+Urbanization is the process of migration from rural to urban areas, driven by various political, economic, and cultural factors. Until the 18th century, an equilibrium existed between the rural agricultural population and towns featuring markets and small-scale manufacturing. With the agricultural and industrial revolutions urban population began its unprecedented growth, both through migration and demographic expansion. In England, the proportion of the population living in cities jumped from 17% in 1801 to 72% in 1891. In 1900, 15% of the world's population lived in cities. The cultural appeal of cities also plays a role in attracting residents.
+
+Urbanization rapidly spread across Europe and the Americas and since the 1950s has taken hold in Asia and Africa as well. The Population Division of the United Nations Department of Economic and Social Affairs reported in 2014 that for the first time, more than half of the world population lives in cities.
+
+Latin America is the most urban continent, with four-fifths of its population living in cities, including one-fifth of the population said to live in shantytowns (favelas, poblaciones callampas, etc.). Batam, Indonesia, Mogadishu, Somalia, Xiamen, China, and Niamey, Niger, are considered among the world's fastest-growing cities, with annual growth rates of 5–8%. In general, the more developed countries of the "Global North" remain more urbanized than the less developed countries of the "Global South"—but the difference continues to shrink because urbanization is happening faster in the latter group. Asia is home to by far the greatest absolute number of city-dwellers: over two billion and counting. The UN predicts an additional 2.5 billion city dwellers (and 300 million fewer country dwellers) worldwide by 2050, with 90% of urban population expansion occurring in Asia and Africa.
+
+Megacities, cities with populations in the multi-millions, have proliferated into the dozens, arising especially in Asia, Africa, and Latin America. Economic globalization fuels the growth of these cities, as new torrents of foreign capital arrange for rapid industrialization, as well as the relocation of major businesses from Europe and North America, attracting immigrants from near and far. A deep gulf divides the rich and poor in these cities, with usually contain a super-wealthy elite living in gated communities and large masses of people living in substandard housing with inadequate infrastructure and otherwise poor conditions.
+
+Cities around the world have expanded physically as they grow in population, with increases in their surface extent, with the creation of high-rise buildings for residential and commercial use, and with development underground.
+
+Urbanization can create rapid demand for water resources management, as formerly good sources of freshwater become overused and polluted, and the volume of sewage begins to exceed manageable levels.
+
+Government 
+
+The local government of cities takes different forms including prominently the municipality (especially in England, in the United States, India, and other British colonies; legally, the municipal corporation; municipio in Spain and Portugal, and, along with municipalidad, in most former parts of the Spanish and Portuguese empires) and the commune (in France and Chile; or comune in Italy).
+
+The chief official of the city has the title of mayor. Whatever their true degree of political authority, the mayor typically acts as the figurehead or personification of their city.
+
+Legal conflicts and issues arise more frequently in cities than elsewhere due to the bare fact of their greater density. Modern city governments thoroughly regulate everyday life in many dimensions, including public and personal health, transport, burial, resource use and extraction, recreation, and the nature and use of buildings. Technologies, techniques, and laws governing these areas—developed in cities—have become ubiquitous in many areas.
+Municipal officials may be appointed from a higher level of government or elected locally.
+
+Municipal services 
+
+Cities typically provide municipal services such as education, through school systems; policing, through police departments; and firefighting, through fire departments; as well as the city's basic infrastructure. These are provided more or less routinely, in a more or less equal fashion. Responsibility for administration usually falls on the city government, but some services may be operated by a higher level of government, while others may be privately run. Armies may assume responsibility for policing cities in states of domestic turmoil such as America's King assassination riots of 1968.
+
+Finance 
+The traditional basis for municipal finance is local property tax levied on real estate within the city. Local government can also collect revenue for services, or by leasing land that it owns. However, financing municipal services, as well as urban renewal and other development projects, is a perennial problem, which cities address through appeals to higher governments, arrangements with the private sector, and techniques such as privatization (selling services into the private sector), corporatization (formation of quasi-private municipally-owned corporations), and financialization (packaging city assets into tradeable financial public contracts and other related rights). This situation has become acute in deindustrialized cities and in cases where businesses and wealthier citizens have moved outside of city limits and therefore beyond the reach of taxation. Cities in search of ready cash increasingly resort to the municipal bond, essentially a loan with interest and a repayment date. City governments have also begun to use tax increment financing, in which a development project is financed by loans based on future tax revenues which it is expected to yield. Under these circumstances, creditors and consequently city governments place a high importance on city credit ratings.
+
+Governance 
+
+Governance includes government but refers to a wider domain of social control functions implemented by many actors including non-governmental organizations. The impact of globalization and the role of multinational corporations in local governments worldwide, has led to a shift in perspective on urban governance, away from the "urban regime theory" in which a coalition of local interests functionally govern, toward a theory of outside economic control, widely associated in academics with the philosophy of neoliberalism. In the neoliberal model of governance, public utilities are privatized, the industry is deregulated, and corporations gain the status of governing actors—as indicated by the power they wield in public-private partnerships and over business improvement districts, and in the expectation of self-regulation through corporate social responsibility. The biggest investors and real estate developers act as the city's de facto urban planners.
+
+The related concept of good governance places more emphasis on the state, with the purpose of assessing urban governments for their suitability for development assistance. The concepts of governance and good governance are especially invoked in emergent megacities, where international organizations consider existing governments inadequate for their large populations.
+
+Urban planning 
+
+Urban planning, the application of forethought to city design, involves optimizing land use, transportation, utilities, and other basic systems, in order to achieve certain objectives. Urban planners and scholars have proposed overlapping theories as ideals for how plans should be formed. Planning tools, beyond the original design of the city itself, include public capital investment in infrastructure and land-use controls such as zoning. The continuous process of comprehensive planning involves identifying general objectives as well as collecting data to evaluate progress and inform future decisions.
+
+Government is legally the final authority on planning but in practice, the process involves both public and private elements. The legal principle of eminent domain is used by the government to divest citizens of their property in cases where its use is required for a project. Planning often involves tradeoffs—decisions in which some stand to gain and some to lose—and thus is closely connected to the prevailing political situation.
+
+The history of urban planning dates to some of the earliest known cities, especially in the Indus Valley and Mesoamerican civilizations, which built their cities on grids and apparently zoned different areas for different purposes. The effects of planning, ubiquitous in today's world, can be seen most clearly in the layout of planned communities, fully designed prior to construction, often with consideration for interlocking physical, economic, and cultural systems.
+
+Society
+
+Social structure 
+Urban society is typically stratified. Spatially, cities are formally or informally segregated along ethnic, economic, and racial lines. People living relatively close together may live, work, and play in separate areas, and associate with different people, forming ethnic or lifestyle enclaves or, in areas of concentrated poverty, ghettoes. While in the US and elsewhere poverty became associated with the inner city, in France it has become associated with the banlieues, areas of urban development that surround the city proper. Meanwhile, across Europe and North America, the racially white majority is empirically the most segregated group. Suburbs in the West, and, increasingly, gated communities and other forms of "privatopia" around the world, allow local elites to self-segregate into secure and exclusive neighborhoods.
+
+Landless urban workers, contrasted with peasants and known as the proletariat, form a growing stratum of society in the age of urbanization. In Marxist doctrine, the proletariat will inevitably revolt against the bourgeoisie as their ranks swell with disenfranchised and disaffected people lacking all stake in the status quo. The global urban proletariat of today, however, generally lacks the status of factory workers which in the nineteenth century provided access to the means of production.
+
+Economics 
+
+Historically, cities rely on rural areas for intensive farming to yield surplus crops, in exchange for which they provide money, political administration, manufactured goods, and culture. Urban economics tends to analyze larger agglomerations, stretching beyond city limits, in order to reach a more complete understanding of the local labor market.
+
+As hubs of trade, cities have long been home to retail commerce and consumption through the interface of shopping. In the 20th century, department stores using new techniques of advertising, public relations, decoration, and design, transformed urban shopping areas into fantasy worlds encouraging self-expression and escape through consumerism.
+
+In general, the density of cities expedites commerce and facilitates knowledge spillovers, helping people and firms exchange information and generate new ideas. A thicker labor market allows for better skill matching between firms and individuals. Population density enables also sharing of common infrastructure and production facilities; however, in very dense cities, increased crowding and waiting times may lead to some negative effects.
+
+Although manufacturing fueled the growth of cities, many now rely on a tertiary or service economy. The services in question range from tourism, hospitality, entertainment, and housekeeping to grey-collar work in law, financial consulting, and administration.
+
+According to a scientific model of cities by Professor Geoffrey West, with the doubling of a city's size, salaries per capita will generally increase by 15%.
+
+Culture and communications 
+
+Cities are typically hubs for education and the arts, supporting universities, museums, temples, and other cultural institutions. They feature impressive displays of architecture ranging from small to enormous and ornate to brutal; skyscrapers, providing thousands of offices or homes within a small footprint, and visible from miles away, have become iconic urban features. Cultural elites tend to live in cities, bound together by shared cultural capital, and themselves play some role in governance. By virtue of their status as centers of culture and literacy, cities can be described as the locus of civilization, human history, and social change.
+
+Density makes for effective mass communication and transmission of news, through heralds, printed proclamations, newspapers, and digital media. These communication networks, though still using cities as hubs, penetrate extensively into all populated areas. In the age of rapid communication and transportation, commentators have described urban culture as nearly ubiquitous or as no longer meaningful.
+
+Today, a city's promotion of its cultural activities dovetails with place branding and city marketing, public diplomacy techniques used to inform development strategy; attract businesses, investors, residents, and tourists; and to create shared identity and sense of place within the metropolitan area. Physical inscriptions, plaques, and monuments on display physically transmit a historical context for urban places. Some cities, such as Jerusalem, Mecca, and Rome have indelible religious status and for hundreds of years have attracted pilgrims. Patriotic tourists visit Agra to see the Taj Mahal, or New York City to visit the World Trade Center. Elvis lovers visit Memphis to pay their respects at Graceland. Place brands (which include place satisfaction and place loyalty) have great economic value (comparable to the value of commodity brands) because of their influence on the decision-making process of people thinking about doing business in—"purchasing" (the brand of)—a city.
+
+Bread and circuses among other forms of cultural appeal, attract and entertain the masses. Sports also play a major role in city branding and local identity formation. Cities go to considerable lengths in competing to host the Olympic Games, which bring global attention and tourism. Paris, a city known for its cultural history, is the site of the next Olympics in the summer of 2024.
+
+Warfare 
+
+Cities play a crucial strategic role in warfare due to their economic, demographic, symbolic, and political centrality. For the same reasons, they are targets in asymmetric warfare. Many cities throughout history were founded under military auspices, a great many have incorporated fortifications, and military principles continue to influence urban design. Indeed, war may have served as the social rationale and economic basis for the very earliest cities.
+
+Powers engaged in geopolitical conflict have established fortified settlements as part of military strategies, as in the case of garrison towns, America's Strategic Hamlet Program during the Vietnam War, and Israeli settlements in Palestine. While occupying the Philippines, the US Army ordered local people to concentrate in cities and towns, in order to isolate committed insurgents and battle freely against them in the countryside.
+
+During World War II, national governments on occasion declared certain cities open, effectively surrendering them to an advancing enemy in order to avoid damage and bloodshed. Urban warfare proved decisive, however, in the Battle of Stalingrad, where Soviet forces repulsed German occupiers, with extreme casualties and destruction. In an era of low-intensity conflict and rapid urbanization, cities have become sites of long-term conflict waged both by foreign occupiers and by local governments against insurgency. Such warfare, known as counterinsurgency, involves techniques of surveillance and psychological warfare as well as close combat, and functionally extends modern urban crime prevention, which already uses concepts such as defensible space.
+
+Although capture is the more common objective, warfare has in some cases spelled complete destruction for a city. Mesopotamian tablets and ruins attest to such destruction, as does the Latin motto Carthago delenda est. Since the atomic bombings of Hiroshima and Nagasaki and throughout the Cold War, nuclear strategists continued to contemplate the use of "counter-value" targeting: crippling an enemy by annihilating its valuable cities, rather than aiming primarily at its military forces.
+
+Climate change
+
+Infrastructure 
+
+Urban infrastructure involves various physical networks and spaces necessary for transportation, water use, energy, recreation, and public functions. Infrastructure carries a high initial cost in fixed capital but lower marginal costs and thus positive economies of scale. Because of the higher barriers to entry, these networks have been classified as natural monopolies, meaning that economic logic favors control of each network by a single organization, public or private.
+
+Infrastructure in general plays a vital role in a city's capacity for economic activity and expansion, underpinning the very survival of the city's inhabitants, as well as technological, commercial, industrial, and social activities. Structurally, many infrastructure systems take the form of networks with redundant links and multiple pathways, so that the system as a whole continue to operate even if parts of it fail. The particulars of a city's infrastructure systems have historical path dependence because new development must build from what exists already.
+
+Megaprojects such as the construction of airports, power plants, and railways require large upfront investments and thus tend to require funding from the national government or the private sector. Privatization may also extend to all levels of infrastructure construction and maintenance.
+
+Urban infrastructure ideally serves all residents equally but in practice may prove uneven—with, in some cities, clear first-class and second-class alternatives.
+
+Utilities 
+
+Public utilities (literally, useful things with general availability) include basic and essential infrastructure networks, chiefly concerned with the supply of water, electricity, and telecommunications capability to the populace.
+
+Sanitation, necessary for good health in crowded conditions, requires water supply and waste management as well as individual hygiene. Urban water systems include principally a water supply network and a network (sewerage system) for sewage and stormwater. Historically, either local governments or private companies have administered urban water supply, with a tendency toward government water supply in the 20th century and a tendency toward private operation at the turn of the twenty-first. The market for private water services is dominated by two French companies, Veolia Water (formerly Vivendi) and Engie (formerly Suez), said to hold 70% of all water contracts worldwide.
+
+Modern urban life relies heavily on the energy transmitted through electricity for the operation of electric machines (from household appliances to industrial machines to now-ubiquitous electronic systems used in communications, business, and government) and for traffic lights, street lights, and indoor lighting. Cities rely to a lesser extent on hydrocarbon fuels such as gasoline and natural gas for transportation, heating, and cooking. Telecommunications infrastructure such as telephone lines and coaxial cables also traverse cities, forming dense networks for mass and point-to-point communications.
+
+Transportation 
+
+Because cities rely on specialization and an economic system based on wage labor, their inhabitants must have the ability to regularly travel between home, work, commerce, and entertainment. City dwellers travel by foot or by wheel on roads and walkways, or use special rapid transit systems based on underground, overground, and elevated rail. Cities also rely on long-distance transportation (truck, rail, and airplane) for economic connections with other cities and rural areas.
+
+City streets historically were the domain of horses and their riders and pedestrians, who only sometimes had sidewalks and special walking areas reserved for them. In the West, bicycles or (velocipedes), efficient human-powered machines for short- and medium-distance travel, enjoyed a period of popularity at the beginning of the twentieth century before the rise of automobiles. Soon after, they gained a more lasting foothold in Asian and African cities under European influence. In Western cities, industrializing, expanding, and electrifying public transit systems, and especially streetcars enabled urban expansion as new residential neighborhoods sprung up along transit lines and workers rode to and from work downtown.
+
+Since the mid-20th century, cities have relied heavily on motor vehicle transportation, with major implications for their layout, environment, and aesthetics. (This transformation occurred most dramatically in the US—where corporate and governmental policies favored automobile transport systems—and to a lesser extent in Europe.) The rise of personal cars accompanied the expansion of urban economic areas into much larger metropolises, subsequently creating ubiquitous traffic issues with the accompanying construction of new highways, wider streets, and alternative walkways for pedestrians. However, severe traffic jams still occur regularly in cities around the world, as private car ownership and urbanization continue to increase, overwhelming existing urban street networks.
+
+The urban bus system, the world's most common form of public transport, uses a network of scheduled routes to move people through the city, alongside cars, on the roads. The economic function itself also became more decentralized as concentration became impractical and employers relocated to more car-friendly locations (including edge cities). Some cities have introduced bus rapid transit systems which include exclusive bus lanes and other methods for prioritizing bus traffic over private cars. Many big American cities still operate conventional public transit by rail, as exemplified by the ever-popular New York City Subway system. Rapid transit is widely used in Europe and has increased in Latin America and Asia.
+
+Walking and cycling ("non-motorized transport") enjoy increasing favor (more pedestrian zones and bike lanes) in American and Asian urban transportation planning, under the influence of such trends as the Healthy Cities movement, the drive for sustainable development, and the idea of a carfree city. Techniques such as road space rationing and road use charges have been introduced to limit urban car traffic.
+
+Housing 
+
+The housing of residents presents one of the major challenges every city must face. Adequate housing entails not only physical shelters but also the physical systems necessary to sustain life and economic activity.
+
+Homeownership represents status and a modicum of economic security, compared to renting which may consume much of the income of low-wage urban workers. Homelessness, or lack of housing, is a challenge currently faced by millions of people in countries rich and poor. Because cities generally have higher population densities than rural areas, city dwellers are more likely to reside in apartments and less likely to live in a single-family home.
+
+Ecology
+
+Urban ecosystems, influenced as they are by the density of human buildings and activities, differ considerably from those of their rural surroundings. Anthropogenic buildings and waste, as well as cultivation in gardens, create physical and chemical environments which have no equivalents in the wilderness, in some cases enabling exceptional biodiversity. They provide homes not only for immigrant humans but also for immigrant plants, bringing about interactions between species that never previously encountered each other. They introduce frequent disturbances (construction, walking) to plant and animal habitats, creating opportunities for recolonization and thus favoring young ecosystems with r-selected species dominant. On the whole, urban ecosystems are less complex and productive than others, due to the diminished absolute amount of biological interactions.
+
+Typical urban fauna includes insects (especially ants), rodents (mice, rats), and birds, as well as cats and dogs (domesticated and feral). Large predators are scarce. However, in North America, large predators such as coyotes and white-tailed deer roam in urban wildlife 
+
+Cities generate considerable ecological footprints, locally and at longer distances, due to concentrated populations and technological activities. From one perspective, cities are not ecologically sustainable due to their resource needs. From another, proper management may be able to ameliorate a city's ill effects. Air pollution arises from various forms of combustion, including fireplaces, wood or coal-burning stoves, other heating systems, and internal combustion engines. Industrialized cities, and today third-world megacities, are notorious for veils of smog (industrial haze) that envelop them, posing a chronic threat to the health of their millions of inhabitants. Urban soil contains higher concentrations of heavy metals (especially lead, copper, and nickel) and has lower pH than soil in the comparable wilderness.
+
+Modern cities are known for creating their own microclimates, due to concrete, asphalt, and other artificial surfaces, which heat up in sunlight and channel rainwater into underground ducts. The temperature in New York City exceeds nearby rural temperatures by an average of 2–3 °C and at times 5–10 °C differences have been recorded. This effect varies nonlinearly with population changes (independently of the city's physical size). Aerial particulates increase rainfall by 5–10%. Thus, urban areas experience unique climates, with earlier flowering and later leaf dropping than in nearby countries.
+
+Poor and working-class people face disproportionate exposure to environmental risks (known as environmental racism when intersecting also with racial segregation). For example, within the urban microclimate, less-vegetated poor neighborhoods bear more of the heat (but have fewer means of coping with it).
+
+One of the main methods of improving the urban ecology is including in the cities more urban green spaces: parks, gardens, lawns, and trees. These areas improve the health and well-being of the human, animal, and plant populations of the cities. Well-maintained urban trees can provide many social, ecological, and physical benefits to the residents of the city.
+
+A study published in Nature's Scientific Reports journal in 2019 found that people who spent at least two hours per week in nature were 23 percent more likely to be satisfied with their life and were 59 percent more likely to be in good health than those who had zero exposure. The study used data from almost 20,000 people in the UK. Benefits increased for up to 300 minutes of exposure. The benefits are applied to men and women of all ages, as well as across different ethnicities, socioeconomic statuses, and even those with long-term illnesses and disabilities. People who did not get at least two hours – even if they surpassed an hour per week – did not get the benefits. The study is the latest addition to a compelling body of evidence for the health benefits of nature. Many doctors already give nature prescriptions to their patients. The study didn't count time spent in a person's own yard or garden as time in nature, but the majority of nature visits in the study took place within two miles of home. "Even visiting local urban green spaces seems to be a good thing," Dr. White said in a press release. "Two hours a week is hopefully a realistic target for many people, especially given that it can be spread over an entire week to get the benefit."
+
+World city system 
+As the world becomes more closely linked through economics, politics, technology, and culture (a process called globalization), cities have come to play a leading role in transnational affairs, exceeding the limitations of international relations conducted by national governments. This phenomenon, resurgent today, can be traced back to the Silk Road, Phoenicia, and the Greek city-states, through the Hanseatic League and other alliances of cities. Today the information economy based on high-speed internet infrastructure enables instantaneous telecommunication around the world, effectively eliminating the distance between cities for the purposes of the international markets and other high-level elements of the world economy, as well as personal communications and mass media.
+
+Global city 
+
+A global city, also known as a world city, is a prominent centre of trade, banking, finance, innovation, and markets. Saskia Sassen used the term "global city" in her 1991 work, The Global City: New York, London, Tokyo to refer to a city's power, status, and cosmopolitanism, rather than to its size. Following this view of cities, it is possible to rank the world's cities hierarchically. Global cities form the capstone of the global hierarchy, exerting command and control through their economic and political influence. Global cities may have reached their status due to early transition to post-industrialism or through inertia which has enabled them to maintain their dominance from the industrial era. This type of ranking exemplifies an emerging discourse in which cities, considered variations on the same ideal type, must compete with each other globally to achieve prosperity.
+
+Critics of the notion point to the different realms of power and interchange. The term "global city" is heavily influenced by economic factors and, thus, may not account for places that are otherwise significant. Paul James, for example argues that the term is "reductive and skewed" in its focus on financial systems.
+
+Multinational corporations and banks make their headquarters in global cities and conduct much of their business within this context. American firms dominate the international markets for law and engineering and maintain branches in the biggest foreign global cities.
+
+Large cities have a great divide between populations of both ends of the financial spectrum. Regulations on immigration promote the exploitation of low- and high-skilled immigrant workers from poor areas. During employment, migrant workers may be subject to unfair working conditions, including working overtime, low wages, and lack of safety in workplaces.
+
+Transnational activity 
+Cities increasingly participate in world political activities independently of their enclosing nation-states. Early examples of this phenomenon are the sister city relationship and the promotion of multi-level governance within the European Union as a technique for European integration. Cities including Hamburg, Prague, Amsterdam, The Hague, and City of London maintain their own embassies to the European Union at Brussels.
+
+New urban dwellers are increasingly transmigrants, keeping one foot each (through telecommunications if not travel) in their old and their new homes.
+
+Global governance 
+Cities participate in global governance by various means including membership in global networks which transmit norms and regulations. At the general, global level, United Cities and Local Governments (UCLG) is a significant umbrella organization for cities; regionally and nationally, Eurocities, Asian Network of Major Cities 21, the Federation of Canadian Municipalities the National League of Cities, and the United States Conference of Mayors play similar roles. UCLG took responsibility for creating Agenda 21 for culture, a program for cultural policies promoting sustainable development, and has organized various conferences and reports for its furtherance.
+
+Networks have become especially prevalent in the arena of environmentalism and specifically climate change following the adoption of Agenda 21. Environmental city networks include the C40 Cities Climate Leadership Group, the United Nations Global Compact Cities Programme, the Carbon Neutral Cities Alliance (CNCA), the Covenant of Mayors and the Compact of Mayors, ICLEI – Local Governments for Sustainability, and the Transition Towns network.
+
+Cities with world political status as meeting places for advocacy groups, non-governmental organizations, lobbyists, educational institutions, intelligence agencies, military contractors, information technology firms, and other groups with a stake in world policymaking. They are consequently also sites for symbolic protest. South Africa has one of the highest rate of protests in the world. Pretoria, a city in South Africa had a rally where 5 thousand people took part in order to advocate for increasing wages to afford living costs.
+
+United Nations System 
+
+The United Nations System has been involved in a series of events and declarations dealing with the development of cities during this period of rapid urbanization.
+ The Habitat I conference in 1976 adopted the "Vancouver Declaration on Human Settlements" which identifies urban management as a fundamental aspect of development and establishes various principles for maintaining urban habitats.
+ Citing the Vancouver Declaration, the UN General Assembly in December 1977 authorized the United Nations Commission Human Settlements and the HABITAT Centre for Human Settlements, intended to coordinate UN activities related to housing and settlements.
+ The 1992 Earth Summit in Rio de Janeiro resulted in a set of international agreements including Agenda 21 which establishes principles and plans for sustainable development.
+ The Habitat II conference in 1996 called for cities to play a leading role in this program, which subsequently advanced the Millennium Development Goals and Sustainable Development Goals.
+ In January 2002 the UN Commission on Human Settlements became an umbrella agency called the United Nations Human Settlements Programme or UN-Habitat, a member of the United Nations Development Group.
+ The Habitat III conference of 2016 focused on implementing these goals under the banner of a "New Urban Agenda". The four mechanisms envisioned for effecting the New Urban Agenda are (1) national policies promoting integrated sustainable development, (2) stronger urban governance, (3) long-term integrated urban and territorial planning, and (4) effective financing frameworks. Just before this conference, the European Union concurrently approved an "Urban Agenda for the European Union" known as the Pact of Amsterdam.
+
+UN-Habitat coordinates the U.N. urban agenda, working with the UN Environmental Programme, the UN Development Programme, the Office of the High Commissioner for Human Rights, the World Health Organization, and the World Bank.
+
+The World Bank, a U.N. specialized agency, has been a primary force in promoting the Habitat conferences, and since the first Habitat conference has used their declarations as a framework for issuing loans for urban infrastructure. The bank's structural adjustment programs contributed to urbanization in the Third World by creating incentives to move to cities. The World Bank and UN-Habitat in 1999 jointly established the Cities Alliance (based at the World Bank headquarters in Washington, D.C.) to guide policymaking, knowledge sharing, and grant distribution around the issue of urban poverty. (UN-Habitat plays an advisory role in evaluating the quality of a locality's governance.) The Bank's policies have tended to focus on bolstering real estate markets through credit and technical assistance.
+
+The United Nations Educational, Scientific and Cultural Organization, UNESCO has increasingly focused on cities as key sites for influencing cultural governance. It has developed various city networks including the International Coalition of Cities against Racism and the Creative Cities Network. UNESCO's capacity to select World Heritage Sites gives the organization significant influence over cultural capital, tourism, and historic preservation funding.
+
+Representation in culture 
+
+Cities figure prominently in traditional Western culture, appearing in the Bible in both evil and holy forms, symbolized by Babylon and Jerusalem. Cain and Nimrod are the first city builders in the Book of Genesis. In Sumerian mythology Gilgamesh built the walls of Uruk.
+
+Cities can be perceived in terms of extremes or opposites: at once liberating and oppressive, wealthy and poor, organized and chaotic. The name anti-urbanism refers to various types of ideological opposition to cities, whether because of their culture or their political relationship with the country. Such opposition may result from identification of cities with oppression and the ruling elite. This and other political ideologies strongly influence narratives and themes in discourse about cities. In turn, cities symbolize their home societies.
+
+Writers, painters, and filmmakers have produced innumerable works of art concerning the urban experience. Classical and medieval literature includes a genre of descriptiones which treat of city features and history. Modern authors such as Charles Dickens and James Joyce are famous for evocative descriptions of their home cities. Fritz Lang conceived the idea for his influential 1927 film Metropolis while visiting Times Square and marveling at the nighttime neon lighting. Other early cinematic representations of cities in the twentieth century generally depicted them as technologically efficient spaces with smoothly functioning systems of automobile transport. By the 1960s, however, traffic congestion began to appear in such films as The Fast Lady (1962) and Playtime (1967).
+
+Literature, film, and other forms of popular culture have supplied visions of future cities both utopian and dystopian. The prospect of expanding, communicating, and increasingly interdependent world cities has given rise to images such as Nylonkong (New York, London, Hong Kong) and visions of a single world-encompassing ecumenopolis.
+
+See also
+ Lists of cities
+ List of adjectivals and demonyms for cities
+ Lost city
+ Metropolis
+ Compact city
+ Megacity
+ Settlement hierarchy
+ Urbanization
+
+Notes
+
+References
+
+Bibliography
+
+ Abrahamson, Mark (2004). Global Cities. Oxford University Press. 
+ Ashworth, G.J. War and the City. London & New York: Routledge, 1991. .
+ 
+ Bridge, Gary, and Sophie Watson, eds. (2000). A Companion to the City. Malden, MA: Blackwell, 2000/2003. 
+ Brighenti, Andrea Mubi, ed. (2013). Urban Interstices: The Aesthetics and the Politics of the In-between. Farnham: Ashgate Publishing. .
+ Carter, Harold (1995). The Study of Urban Geography. 4th ed. London: Arnold. 
+ Clark, Peter (ed.) (2013). The Oxford Handbook of Cities in World History. Oxford University Press. 
+ Curtis, Simon (2016). Global Cities and Global Order. Oxford University Press. 
+ Ellul, Jacques (1970). The Meaning of the City. Translated by Dennis Pardee. Grand Rapids, Michigan: Eerdmans, 1970. ; French original (written earlier, published later as): Sans feu ni lieu : Signification biblique de la Grande Ville; Paris: Gallimard, 1975. Republished 2003 with 
+ Gupta, Joyetta, Karin Pfeffer, Hebe Verrest, & Mirjam Ros-Tonen, eds. (2015). Geographies of Urban Governance: Advanced Theories, Methods and Practices. Springer, 2015. .
+ Hahn, Harlan, & Charles Levine (1980). Urban Politics: Past, Present, & Future. New York & London: Longman.
+ Hanson, Royce (ed.). Perspectives on Urban Infrastructure. Committee on National Urban Policy, Commission on Behavioral and Social Sciences and Education, National Research Council. Washington: National Academy Press, 1984.
+ Herrschel, Tassilo & Peter Newman (2017). Cities as International Actors: Urban and Regional Governance Beyond the Nation State. Palgrave Macmillan (Springer Nature). 
+ 
+ Grava, Sigurd (2003). Urban Transportation Systems: Choices for Communities. McGraw Hill, e-book. 
+ 
+ Kaplan, David H.; James O. Wheeler; Steven R. Holloway; & Thomas W. Hodler, cartographer (2004). Urban Geography. John Wiley & Sons, Inc. 
+ Kavaratzis, Mihalis, Gary Warnaby, & Gregory J. Ashworth, eds. (2015). Rethinking Place Branding: Comprehensive Brand Development for Cities and Regions. Springer. .
+ Kraas, Frauke, Surinder Aggarwal, Martin Coy, & Günter Mertins, eds. (2014). Megacities: Our Global Urban Future. United Nations "International Year of Planet Earth" book series. Springer. .
+ Latham, Alan, Derek McCormack, Kim McNamara, & Donald McNeil (2009). Key Concepts in Urban Geography. London: SAGE. .
+ Leach, William (1993). Land of Desire: Merchants, Power, and the Rise of a New American Culture. New York: Vintage Books (Random House), 1994. .
+ Levy, John M. (2017). Contemporary Urban Planning. 11th ed. New York: Routledge (Taylor & Francis).
+ Magnusson, Warren. Politics of Urbanism: Seeing like a city. London & New York: Routledge, 2011. .
+ Marshall, John U. (1989). The Structure of Urban Systems. University of Toronto Press. .
+ Marzluff, John M., Eric Schulenberger, Wilfried Endlicher, Marina Alberti, Gordon Bradley, Clre Ryan, Craig ZumBrunne, & Ute Simon (2008). Urban Ecology: An International Perspective on the Interaction Between Humans and Nature. New York: Springer Science+Business Media. .
+ McQuillan, Eugene. The Law of Municipal Corporations, 3rd ed. 1987 revised volume by Charles R.P. Keating, Esq. Wilmette, Illinois: Callaghan & Company.
+ Moholy-Nagy, Sibyl (1968). Matrix of Man: An Illustrated History of Urban Environment. New York: Frederick A Praeger. 
+ Mumford, Lewis  (1961). The City in History: Its Origins, Its Transformations, and Its Prospects. New York: Harcourt, Brace & World.
+ 
+ 
+ Paddison, Ronan, ed. (2001). Handbook of Urban Studies. London; Thousand Oaks, California; and New Delhi: Sage Publications. .
+ 
+ 
+ Rybczynski, W., City Life: Urban Expectations in a New World, (1995)
+ Smith, Michael E. (2002) The Earliest Cities. In Urban Life: Readings in Urban Anthropology, edited by George Gmelch and Walter Zenner, pp. 3–19. 4th ed. Waveland Press, Prospect Heights, IL.
+ Southall, Aidan (1998). The City in Time and Space. Cambridge University Press. 
+ Wellman, Kath & Marcus Spiller, eds. (2012). Urban Infrastructure: Finance and Management. Chichester, UK: Wiley-Blackwell. .
+
+Further reading
+
+ Berger, Alan S., The City: Urban Communities and Their Problems, Dubuque, Iowa : William C. Brown, 1978.
+ Chandler, T. Four Thousand Years of Urban Growth: An Historical Census. Lewiston, NY: Edwin Mellen Press, 1987.
+ Geddes, Patrick, City Development (1904)
+ 
+ Kemp, Roger L.  Managing America's Cities: A Handbook for Local Government Productivity, McFarland and Company, Inc., Publisher, Jefferson, North Carolina and London, 2007.  ().
+ Kemp, Roger L. How American Governments Work: A Handbook of City, County, Regional, State, and Federal Operations, McFarland and Company, Inc., Publisher, Jefferson, North Carolina and London. ().
+ Kemp, Roger L.  "City and Gown Relations: A Handbook of Best Practices", McFarland and Company, Inc., Publisher, Jefferson, North Carolina, US, and London, (2013).  ().
+ Monti, Daniel J. Jr., The American City: A Social and Cultural History. Oxford, England and Malden, Massachusetts: Blackwell Publishers, 1999. 391 pp. .
+ Reader, John (2005) Cities. Vintage, New York.
+ Robson, W.A., and Regan, D.E., ed., Great Cities of the World, (3d ed., 2 vol., 1972)
+ Smethurst, Paul (2015). The Bicycle – Towards a Global History. Palgrave Macmillan. .
+ Smith, L. Monica (2020) Cities: The First 6,000 Years. Penguin Books. 
+ Thernstrom, S., and Sennett, R., ed., Nineteenth-Century Cities (1969)
+ Toynbee, Arnold J. (ed), Cities of Destiny, New York: McGraw-Hill, 1967. Pan historical/geographical essays, many images. Starts with "Athens", ends with "The Coming World City-Ecumenopolis".
+ Weber, Max, The City, 1921. (tr. 1958)
+
+External links
+
+ World Urbanization Prospects, Website of the United Nations Population Division (archived 10 July 2017)
+  Urban population (% of total) – World Bank website based on UN data.
+ Degree of urbanization (percentage of urban population in total population) by continent in 2016 – Statista, based on Population Reference Bureau data.
+ 
+ 
+
+ 
+Cities
+Populated places by type
+Types of populated places
+Urban geography
+Chervil (; Anthriscus cerefolium), sometimes called French parsley or garden chervil (to distinguish it from similar plants also called chervil), is a delicate annual herb related to parsley. It was formerly called myrhis due to its volatile oil with an aroma similar to the resinous substance myrrh. It is commonly used to season mild-flavoured dishes and is a constituent of the French herb mixture .
+
+Name
+
+The name chervil is from Anglo-Norman, from Latin  or , meaning "leaves of joy"; the Latin is formed, as from an Ancient Greek word  ().
+
+Biology
+
+A member of the Apiaceae, chervil is native to the Caucasus but was spread by the Romans through most of Europe, where it is now naturalised. It is also grown frequently in the United States, where it sometimes escapes cultivation. Such escape can be recognized, however, as garden chervil is distinguished from all other Anthriscus species growing in North America (i.e., A. caucalis and A. sylvestris) by its having lanceolate-linear bracteoles and a fruit with a relatively long beak.
+
+The plants grow to , with tripinnate leaves that may be curly. The small white flowers form small umbels,  across. The fruit is about 1 cm long, oblong-ovoid with a slender, ridged beak.
+
+Uses and impact
+
+Culinary arts
+Chervil is used, particularly in France, to season poultry, seafood, young spring vegetables (such as carrots), soups, and sauces. More delicate than parsley, it has a faint taste of liquorice or aniseed.
+
+Chervil is one of the four traditional French , along with tarragon, chives, and parsley, which are essential to French cooking. Unlike the more pungent, robust herbs such as thyme and rosemary, which can take prolonged cooking, the  are added at the last minute, to salads, omelettes, and soups.
+
+Chemistry
+Essential oil obtained via water distillation of wild Turkish Anthriscus cerefolium was analyzed by gas chromatography - mass spectrometry identifying 4 compounds: methyl chavicol (83.10%), 1-allyl-2,4-dimethoxybenzene (15.15%), undecane (1.75%) and β-pinene (<0.01%).
+
+Horticulture
+According to some, slugs are attracted to chervil and the plant is sometimes used to bait them.
+
+Health
+
+Chervil has had various uses in folk medicine. It was claimed to be useful as a digestive aid, for lowering high blood pressure, and, infused with vinegar, for curing hiccups. Besides its digestive properties, it is used as a mild stimulant.
+
+Chervil has also been implicated in "strimmer dermatitis", another name for phytophotodermatitis, due to spray from weed trimmers and similar forms of contact. Other plants in the family Apiaceae can have similar effects.
+
+Cultivation
+Transplanting chervil can be difficult, due to the long taproot. It prefers a cool and moist location; otherwise, it rapidly goes to seed (also known as bolting). It is usually grown as a cool-season crop, like lettuce, and should be planted in early spring and late fall or in a winter greenhouse. Regular harvesting of leaves also helps to prevent bolting. If plants bolt despite precautions, the plant can be periodically re-sown throughout the growing season, thus producing fresh plants as older plants bolt and go out of production.
+
+Chervil grows to a height of , and a width of .
+
+References
+
+Further reading
+ 
+
+Apioideae
+Edible Apiaceae
+Herbs
+Medicinal plants of Asia
+Medicinal plants of Europe
+Root vegetables
+Chives, scientific name Allium schoenoprasum, is a species of flowering plant in the family Amaryllidaceae that produces edible leaves and flowers. Their close relatives include the  common onions, garlic, shallot, leek, scallion, and Chinese onion.
+
+A perennial plant, it is widespread in nature across much of Europe, Asia, and North America.
+
+A. schoenoprasum is the only species of Allium native to both the New and the Old Worlds.
+
+Chives are a commonly used herb and can be found in grocery stores or grown in home gardens. In culinary use, the green stalks (scapes) and the unopened, immature flower buds are diced and used as an ingredient for omelettes, fish, potatoes, soups, and many other dishes. The edible flowers can be used in salads. Chives have insect-repelling properties that can be used in gardens to control pests.
+
+The plant provides a great deal of nectar for pollinators. It was rated in the top 10 for most nectar production (nectar per unit cover per year) in a UK plants survey conducted by the AgriLand project which is supported by the UK Insect Pollinators Initiative.
+
+Description 
+Chives are a bulb-forming herbaceous perennial plant, growing to  tall. The bulbs are slender, conical,  long and  broad, and grow in dense clusters from the roots. The scapes (or stems) are hollow and tubular, up to  long and  across, with a soft texture, although, prior to the emergence of a flower, they may appear stiffer than usual. The grass-like leaves, which are shorter than the scapes, are also hollow and tubular, or terete, (round in cross-section) which distinguishes it at a glance from garlic chives (Allium tuberosum). 
+
+The flowers are pale purple, and star-shaped with six petals,  wide, and produced in a dense inflorescence of 10-30 together; before opening, the inflorescence is surrounded by a papery bract. The seeds are produced in a small, three-valved capsule, maturing in summer. The herb flowers from April to May in the southern parts of its habitat zones and in June in the northern parts.
+
+Chives are the only species of Allium native to both the New and the Old Worlds. Sometimes, the plants found in North America are classified as A. schoenoprasum var. sibiricum, although this is disputed. Differences between specimens are significant.  One example was found in northern Maine growing solitary, instead of in clumps, also exhibiting dingy grey flowers.
+
+Although chives are repulsive to insects in general, due to their sulfur compounds, their flowers attract bees, and they are at times kept to increase desired insect life.
+
+Taxonomy
+It was formally described by the Swedish botanist Carl Linnaeus in his seminal publication Species Plantarum in 1753.
+
+The name of the species derives from the Greek σχοίνος, skhoínos (sedge or rush) and πράσον, práson (leek). Its English name, chives, derives from the French word cive, from cepa, the Latin word for onion. In the Middle Ages, it was known as 'rush leek'.
+
+Some subspecies have been proposed, but are not accepted by Plants of the World Online, , which sinks them into the species:
+Allium schoenoprasum subsp. gredense (Rivas Goday) Rivas Mart., Fern.Gonz. & Sánchez Mata
+Allium schoenoprasum subsp. latiorifolium (Pau) Rivas Mart., Fern.Gonz. & Sánchez Mata
+Varieties have also been proposed, including A. schoenoprasum var. sibiricum. The Flora of North America notes that the species is very variable, and considers recognition of varieties as "unsound".
+
+Distribution and habitat
+Chives are native to temperate areas of Europe, Asia and North America.
+
+Range
+
+It is found in Asia within the Caucasus (in Armenia, Azerbaijan and Georgia), also in China, Iran, Iraq, Japan (within the islands of Hokkaido and Honshu), Kazakhstan, Kyrgyzstan, Mongolia, Pakistan, Russian Federation (within the krais of Kamchatka, Khabarovsk, and Primorye) Siberia and Turkey.
+
+In middle Europe, it is found within Austria, the Czech Republic, Germany, the Netherlands, Poland and Switzerland. In northern Europe, in Denmark, Finland, Norway, Sweden and the United Kingdom. In southeastern Europe, within Bulgaria,  Greece, Italy and Romania. It is also found in southwestern Europe, in France, Portugal and Spain.
+
+In North America, it is found in Canada (within the provinces and territories of Alberta, British Columbia, Manitoba, Northwest Territories, Nova Scotia, New Brunswick, Newfoundland, Nunavut, Ontario, Prince Edward Island, Quebec, Saskatchewan and Yukon), and the United States (within the states of Alaska, Colorado, Connecticut, Idaho, Maine, Maryland, Massachusetts, Michigan, Minnesota, Montana, New Hampshire, New Jersey, New York, Ohio, Oregon, Pennsylvania, Rhode Island, Vermont, Washington, West Virginia, Wisconsin and Wyoming).
+
+Uses
+
+Culinary arts 
+Chives are grown for their scapes and leaves, which are used for culinary purposes as a flavoring herb, and provide a somewhat milder onion-like flavor than those of other Allium species.
+
+Chives have a wide variety of culinary uses, such as in traditional dishes in France, Sweden, and elsewhere. In his 1806 book Attempt at a Flora (Försök til en flora), Anders Jahan Retzius describes how chives are used with pancakes, soups, fish, and sandwiches. They are also an ingredient of the gräddfil sauce with the traditional herring dish served at Swedish midsummer celebrations. The flowers may also be used to garnish dishes. 
+
+In Poland and Germany, chives are served with quark. Chives are one of the fines herbes of French cuisine, the others being tarragon, chervil and parsley. Chives can be found fresh at most markets year-round, making them readily available; they can also be dry-frozen without much impairment to the taste, giving home growers the opportunity to store large quantities harvested from their own gardens.
+
+Uses in plant cultivation 
+Retzius also describes how farmers would plant chives between the rocks making up the borders of their flowerbeds, to keep the plants free from pests (such as Japanese beetles). The growing plant repels unwanted insect life, and the juice of the leaves can be used for the same purpose, as well as fighting fungal infections, mildew, and scab.
+
+Cultivation 
+Chives are cultivated both for their culinary uses and for their ornamental value; the violet flowers are often used in ornamental dry bouquets. The flowers are also edible and are used in salads, or used to make blossom vinegars.
+
+Chives thrive in well-drained soil, rich in organic matter, with a pH of 6-7 and full sun. They can be grown from seed and mature in summer, or early the following spring. Typically, chives need to be germinated at a temperature of 15 to 20 °C (60-70 °F) and kept moist. They can also be planted under a cloche or germinated indoors in cooler climates, then planted out later. After at least four weeks, the young shoots should be ready to be planted out. They are also easily propagated by division.
+
+In cold regions, chives die back to the underground bulbs in winter, with the new leaves appearing in early spring. Chives starting to look old can be cut back to about 2–5 cm. When harvesting, the needed number of stalks should be cut to the base. During the growing season, the plant continually regrows leaves, allowing for a continuous harvest.
+
+Chives are susceptible to damage by leek moth larvae, which bore into the leaves or bulbs of the plant.
+
+History and cultural importance 
+Chives have been cultivated in Europe since the Middle Ages (from the fifth until the 15th centuries), although their usage dates back 5,000 years. They were sometimes referred to as "rush leeks".
+
+It was mentioned in 80 A.D. by Marcus Valerius Martialis in his "Epigrams".
+
+The Romans believed chives could relieve the pain from sunburn or a sore throat. They believed eating chives could increase blood pressure and act as a diuretic.
+
+Romani have used chives in fortune telling. Bunches of dried chives hung around a house were believed to ward off disease and evil.
+
+In the 19th century, Dutch farmers fed cattle on the herb to give a different taste to their milk.
+
+References
+
+External links 
+
+ 
+ Nutritional Information
+ 
+ Mrs. Grieve's "A Modern Herbal" @ Botanical.com
+ 
+
+Allium
+Flora of Asia
+Flora of Europe
+Flora of Northern America
+Garden plants
+Herbs
+Medicinal plants of Asia
+Medicinal plants of Europe
+Medicinal plants of North America
+Plants described in 1753
+Christopher J. Morris (born 15 June 1962) is an English comedian, radio presenter, actor, and filmmaker. Known for his deadpan, dark humour, surrealism, and controversial subject matter, he has been praised by the British Film Institute for his "uncompromising, moralistic drive".
+
+In the early 1990s, Morris teamed up with his radio producer Armando Iannucci to create On the Hour, a satire of news programmes. This was expanded into a television spin off, The Day Today, which launched the career of comedian Steve Coogan and has since been hailed as one of the most important satirical shows of the 1990s. Morris further developed the satirical news format with Brass Eye, which lampooned celebrities whilst focusing on themes such as crime and drugs. For many, the apotheosis of Morris' career was a Brass Eye special, which dealt with the moral panic surrounding paedophilia. It quickly became one of the most complained-about programmes in British television history, leading the Daily Mail to describe him as "the most loathed man on TV".
+
+Meanwhile, Morris' postmodern sketch comedy and ambient music radio show Blue Jam, which had seen controversy similar to Brass Eye, helped him to gain a cult following. Blue Jam was adapted into the TV series Jam, which some hailed as "the most radical and original television programme broadcast in years", and he went on to win the BAFTA Award for Best Short Film after expanding a Blue Jam sketch into My Wrongs 8245–8249 & 117, which starred Paddy Considine. This was followed by Nathan Barley, a sitcom written in collaboration with a then little-known Charlie Brooker that satirised hipsters, which had low ratings but found success upon its DVD release. Morris followed this by joining the cast of the sitcom The IT Crowd, his first project in which he did not have writing or producing input.
+
+In 2010, Morris directed his first feature-length film, Four Lions, which satirised Islamic terrorism through a group of inept British Muslims. Reception of the film was largely positive, earning Morris his second BAFTA Film Award, this time for Outstanding Debut. Since 2012, he has directed four episodes of Iannucci's political comedy Veep and appeared onscreen in The Double and Stewart Lee's Comedy Vehicle. His second feature-length film, The Day Shall Come, was released in 2019.
+
+Early life
+Christopher J Morris was born on 15 June 1962 in Colchester, Essex, the son of Rosemary Parrington and Paul Michael Morris. His father was a GP. Morris has a large red birthmark almost completely covering the left side of his face and neck, which he disguises with makeup when acting. He grew up in a Victorian farmhouse in the village of Buckden, Cambridgeshire, which he described as "very dull". He has two younger brothers, including theatre director Tom Morris. From an early age, he was a prankster and had a passion for radio. From the age of 10, he was educated at the independent Jesuit boarding school Stonyhurst College in Stonyhurst, Lancashire. He went to study zoology at the University of Bristol, where he gained a 2:1.
+
+Career
+
+Radio
+On graduating, Morris pursued a career as a musician in various bands, for which he played the bass guitar. He then went to work for Radio West, a local radio station in Bristol. He then took up a news traineeship with BBC Radio Cambridgeshire, where he took advantage of access to editing and recording equipment to create elaborate spoofs and parodies. He also spent time in early 1987 hosting a 2–4pm afternoon show and finally ended up presenting Saturday morning show I.T.
+
+In July 1987, he moved on to BBC Radio Bristol to present his own show No Known Cure, broadcast on Saturday and Sunday mornings. The show was surreal and satirical, with odd interviews conducted with unsuspecting members of the public. He was fired from Bristol in 1990 after "talking over the news bulletins and making silly noises". In 1988 he also joined, from its launch, Greater London Radio (GLR). He presented The Chris Morris Show on GLR until 1993, when one show got suspended after a sketch was broadcast involving a child "outing" celebrities.
+
+In 1991, Morris joined Armando Iannucci's spoof news project On the Hour. Broadcast on BBC Radio 4, it saw him work alongside Iannucci, Steve Coogan, Stewart Lee, Richard Herring and Rebecca Front. In 1992, Morris hosted Danny Baker's Radio 5 Morning Edition show for a week whilst Baker was on holiday. In 1994, Morris began a weekly evening show, the Chris Morris Music Show, on BBC Radio 1 alongside Peter Baynham and 'man with a mobile phone' Paul Garner. In the shows, Morris perfected the spoof interview style that would become a central component of his Brass Eye programme. In the same year, Morris teamed up with Peter Cook (as Sir Arthur Streeb-Greebling), in a series of improvised conversations for BBC Radio 3 entitled Why Bother?.
+
+Move into television and film
+
+In 1994, a BBC Two television series based on On the Hour was broadcast under the name The Day Today. The Day Today made a star of Morris, and marked the television debut of Steve Coogan's Alan Partridge character. The programme ended on a high after just one series, with Morris winning the 1994 British Comedy Award for Best Newcomer for his lead role as the Paxmanesque news anchor.
+
+In 1996, Morris appeared on the daytime programme The Time, The Place, posing as an academic, Thurston Lowe, in a discussion entitled "Are British Men Lousy Lovers?", but was found out when a producer alerted the show's host, John Stapleton.
+
+In 1997, the black humour which had featured in On the Hour and The Day Today became more prominent in Brass Eye, another spoof of current affairs television documentary, shown on Channel 4. All three series satirised and exaggerated issues expected of news shows. The second episode of Brass Eye, for example, satirised drugs and the political rhetoric surrounding them. To help convey the satire, Morris invented a fictional drug by the name of "cake". In the episode, British celebrities and politicians describe the supposed symptoms in detail; David Amess mentioned the fictional drug at Parliament. In 2001, Morris' satirized the moral panic regarding pedophilia in the most controversial episode of Brass Eye, "Paedogeddon". Channel 4 apologised for the episode after receiving criticism from tabloids and around 3,000 complaints from viewers, which, at the time, was the most for an episode of British television. 
+
+From 1997 to 1999, Morris created Blue Jam for BBC Radio 1, a surreal taboo-breaking radio show set to an ambient soundtrack. In 2000, this was followed by Jam, a television reworking. Morris released a 'remix' version of this, entitled Jaaaaam.
+
+In 2002, Morris ventured into film, directing the short My Wrongs#8245–8249 & 117, adapted from a Blue Jam monologue about a man led astray by a sinister talking dog. It was the first film project of Warp Films, a branch of Warp Records. In 2002 it won the BAFTA for best short film. In 2005 Morris worked on a sitcom entitled Nathan Barley, based on the character created by Charlie Brooker for his website TVGoHome (Morris had contributed to TVGoHome on occasion, under the pseudonym 'Sid Peach'). Co-written by Brooker and Morris, the series was broadcast on Channel 4 in early 2005.
+
+The IT Crowd and Comedy Vehicle
+Morris appeared in The IT Crowd, a Channel 4 sitcom which focuses on the information technology department of the fictional company Reynholm Industries. The series was written and directed by Graham Linehan (with whom Morris collaborated on The Day Today, Brass Eye and Jam) and produced by Ash Atalla. Morris played Denholm Reynholm, the eccentric managing director of the company. This marked the first time Morris had acted in a substantial role in a project which he has not developed himself. Morris' character appeared to leave the series during episode two of the second series. His character made a brief return in the first episode of the third series.
+
+In November 2007, Morris wrote an article for The Observer in response to Ronan Bennett's article published six days earlier in The Guardian. Bennett's article, "Shame on us", accused the novelist Martin Amis of racism. Morris' response, "The absurd world of Martin Amis", was also highly critical of Amis; although he did not accede to Bennett's accusation of racism, Morris likened Amis to the Muslim cleric Abu Hamza (who was jailed for inciting racial hatred in 2006), suggesting that both men employ "mock erudition, vitriol and decontextualised quotes from the Qu'ran" to incite hatred.
+
+Morris served as script editor for the 2009 series Stewart Lee's Comedy Vehicle, working with former colleagues Stewart Lee, Kevin Eldon and Armando Iannucci. He maintained this role for the second (2011) and third series (2014), also appearing as a mock interviewer dubbed the "hostile interrogator" in the third and fourth series.
+
+Four Lions, Veep, and other appearances
+
+Morris completed his debut feature film Four Lions in late 2009, a satire based on a group of Islamist terrorists in Sheffield.
+It premiered at the Sundance Film Festival in January 2010 and was short-listed for the festival's World Cinema Narrative prize. The film (working title Boilerhouse) was picked up by Film Four. Morris told The Sunday Times that the film sought to do for Islamic terrorism what Dad's Army, the classic BBC comedy, did for the Nazis by showing them as "scary but also ridiculous".
+
+In 2012, Morris directed the seventh and penultimate episode of the first season of Veep, an Armando Iannucci-devised American version of The Thick of It. In 2013, he returned to direct two episodes for the second season of Veep, and a further episode for season three in 2014.
+
+In 2013, Morris appeared briefly in Richard Ayoade's The Double, a black comedy film based on the Fyodor Dostoyevsky novella of the same name. Morris had previously worked with Ayoade on Nathan Barley and The IT Crowd.
+
+In February 2014, Morris made a surprise appearance at the beginning of a Stewart Lee live show, introducing the comedian with fictional anecdotes about their work together. The following month, Morris appeared in the third series of Stewart Lee's Comedy Vehicle as a "hostile interrogator", a role previously occupied by Armando Iannucci.
+
+In December 2014, it was announced that a short radio collaboration with Noel Fielding and Richard Ayoade would be broadcast on BBC Radio 6. According to Fielding, the work had been in progress since around 2006. However, in January 2015 it was decided, 'in consultation with [Morris]', that the project was not yet complete, and so the intended broadcast did not go ahead.
+
+The Day Shall Come
+A statement released by Film4 in February 2016 made reference to funding what would be Morris' second feature film. In November 2017 it was reported that Morris had shot the movie, starring Anna Kendrick, in the Dominican Republic but the title was not made public. It was later reported in January 2018 that Jim Gaffigan and Rupert Friend had joined the cast of the still-untitled film, and that the plot would revolve around an FBI hostage situation gone wrong. The completed film, titled The Day Shall Come, had its world premiere at South by Southwest on 11 March 2019.
+
+Music
+Morris often co-writes and performs incidental music for his television shows, notably with Jam and the 'extended remix' version, Jaaaaam. In the early 1990s Morris contributed a Pixies parody track entitled "Motherbanger" to a flexi-disc given away with an edition of Select music magazine. Morris supplied sketches for British band Saint Etienne's 1993 single "You're in a Bad Way" (the sketch 'Spongbake' appears at the end of the 4th track on the CD single).
+
+In 2000, he collaborated by mail with Amon Tobin to create the track "Bad Sex", which was released as a B-side on the Tobin single "Slowly".
+British band Stereolab's song "Nothing to Do with Me" from their 2001 album Sound-Dust featured various lines from Chris Morris sketches as lyrics.
+
+Style 
+Ramsey Ess of Vulture described Morris' comedy style as "crass" and "shocking", but noted an "underlying morality" and integrity, as well as the humor being Morris' priority.
+
+Recognition
+In 2003, Morris was listed in The Observer as one of the 50 funniest acts in British comedy. In 2005, Channel 4 aired a show called The Comedian's Comedian in which foremost writers and performers of comedy ranked their 50 favourite acts. Morris was at number eleven. Morris won the BAFTA for outstanding debut with his film Four Lions. Adeel Akhtar and Nigel Lindsay collected the award in his absence. Lindsay stated that Morris had sent him a text message before they collected the award reading, 'Doused in petrol, Zippo at the ready'. In June 2012 Morris was placed at number 16 in the Top 100 People in UK Comedy.
+
+In 2010, a biography, Disgusting Bliss: The Brass Eye of Chris Morris, was published. Written by Lucian Randall, the book depicted Morris as "brilliant but uncompromising", and a "frantic-minded perfectionist".
+
+In November 2014, a three-hour retrospective of Morris' radio career was broadcast on BBC Radio 4 Extra under the title 'Raw Meat Radio', presented by Mary Anne Hobbs and featuring interviews with Armando Iannucci, Peter Baynham, Paul Garner, and others.
+
+Awards
+Morris won the Best TV Comedy Newcomer award from the British Comedy Awards in 1994 for his performance in The Day Today. He has won two BAFTA awards: the BAFTA Award for Best Short Film in 2002 for My Wrongs #8245–8249 & 117, and the BAFTA Award for Outstanding Debut by a British director, writer or producer in 2011 for Four Lions.
+
+Personal life
+Morris and his wife, actress-turned-literary agent Jo Unwin, live in the Brixton district of London. The pair met in 1984 at the Edinburgh Festival, when he was playing bass guitar for the Cambridge Footlights Revue and she was in a comedy troupe called the Millies. They have two sons, Charles and Frederick, both of whom were born in Lambeth in south London. 
+
+Giving very few interviews and avoiding all social media, Morris has been described as a recluse.
+
+Works
+
+Film
+
+Television
+
+Other
+ Various works at BBC Radio Cambridgeshire (1986–1987) (presenter)
+ No Known Cure (July 1987 – March 1990, BBC Radio Bristol) (presenter)
+ Chris Morris (1988–1993, BBC GLR) (presenter)
+ Morning Edition (July 1990, BBC Radio 5) (guest presenter)
+ The Chris Morris Christmas Show (25 December 1990, BBC Radio 1)
+ On the Hour (1991–1992, BBC Radio 4) (co-writer, performer)
+ It's Only TV (September 1992, LWT) (unbroadcast pilot)
+ Why Bother? (1994, BBC Radio 3) (performer, editor)
+ The Chris Morris Music Show (1994, BBC Radio 1) (presenter)
+ Blue Jam (1997–1999, BBC Radio 1) (writer, director, performer, editor)
+ Second Class Male/Time To Go (1999, newspaper column for The Observer)
+ The Smokehammer (2002, website)
+ Absolute Atrocity Special (2002, newspaper pullout for The Observer)
+
+References
+
+External links
+ 
+ 
+ 
+
+1962 births
+Living people
+Alumni of the University of Bristol
+English male comedians
+English radio DJs
+English radio writers
+English satirists
+English screenwriters
+English male screenwriters
+People educated at Stonyhurst College
+People from Colchester
+People from Buckden, Cambridgeshire
+English film directors
+Outstanding Debut by a British Writer, Director or Producer BAFTA Award winners
+Comedians from Essex
+Colorado (, other variants) is a state in the Mountain West sub-region of the Western United States. It encompasses most of the Southern Rocky Mountains, as well as the northeastern portion of the Colorado Plateau and the western edge of the Great Plains. Colorado is the eighth most extensive and 21st most populous U.S. state. The United States Census Bureau estimated the population of Colorado at 5,839,926 as of July 1, 2022, a 1.15% increase since the 2020 United States census.
+
+The region has been inhabited by Native Americans and their ancestors for at least 13,500 years and possibly much longer. The eastern edge of the Rocky Mountains was a major migration route for early peoples who spread throughout the Americas. In 1848, much of the region was annexed to the United States with the Treaty of Guadalupe Hidalgo. The Pike's Peak Gold Rush of 1858–1862 created an influx of settlers. On February 28, 1861, U.S. President James Buchanan signed an act creating the Territory of Colorado, and on August 1, 1876, President Ulysses S. Grant signed Proclamation 230 admitting Colorado to the Union as the 38th state. The Spanish adjective "colorado" means "colored red" or "ruddy". Colorado is nicknamed the "Centennial State" because it became a state one century (and four weeks) after the signing of the United States Declaration of Independence.
+
+Colorado is bordered by Wyoming to the north, Nebraska to the northeast, Kansas to the east, Oklahoma to the southeast, New Mexico to the south, Utah to the west, and touches Arizona to the southwest at the Four Corners. Colorado is noted for its landscape of mountains, forests, high plains, mesas, canyons, plateaus, rivers, and desert lands. Colorado is one of the Mountain States and is often considered to be part of the southwestern United States. The high plains of Colorado may be considered a part of the midwestern United States.
+
+Denver is the capital, the most populous city, and the center of the Front Range Urban Corridor. Colorado Springs is the second most populous city. Residents of the state are known as Coloradans, although the antiquated "Coloradoan" is occasionally used. Major parts of the economy include government and defense, mining, agriculture, tourism, and increasingly other kinds of manufacturing. With increasing temperatures and decreasing water availability, Colorado's agriculture, forestry, and tourism economies are expected to be heavily affected by climate change.
+
+History
+
+The region that is today the State of Colorado has been inhabited by Native Americans and their Paleoamerican ancestors for at least 13,500 years and possibly more than 37,000 years. The eastern edge of the Rocky Mountains was a major migration route that was important to the spread of early peoples throughout the Americas. The Lindenmeier site in Larimer County contains artifacts dating from approximately 8720 BCE. The Ancient Pueblo peoples lived in the valleys and mesas of the Colorado Plateau. The Ute Nation inhabited the mountain valleys of the Southern Rocky Mountains and the Western Rocky Mountains, even as far east as the Front Range of the present day. The Apache and the Comanche also inhabited the Eastern and Southeastern parts of the state. In the 17th century, the Arapaho and Cheyenne moved west from the Great Lakes region to hunt across the High Plains of Colorado and Wyoming.
+
+The Spanish Empire claimed Colorado as part of its New Mexico province before U.S. involvement in the region. The U.S. acquired a territorial claim to the eastern Rocky Mountains with the Louisiana Purchase from France in 1803. This U.S. claim conflicted with the claim by Spain to the upper Arkansas River Basin as the exclusive trading zone of its colony of Santa Fe de Nuevo México. In 1806, Zebulon Pike led a U.S. Army reconnaissance expedition into the disputed region. Colonel Pike and his troops were arrested by Spanish cavalrymen in the San Luis Valley the following February, taken to Chihuahua, and expelled from Mexico the following July.
+
+The U.S. relinquished its claim to all land south and west of the Arkansas River and south of 42nd parallel north and west of the 100th meridian west as part of its purchase of Florida from Spain with the Adams-Onís Treaty of 1819. The treaty took effect on February 22, 1821. Having settled its border with Spain, the U.S. admitted the southeastern portion of the Territory of Missouri to the Union as the state of Missouri on August 10, 1821. The remainder of Missouri Territory, including what would become northeastern Colorado, became an unorganized territory and remained so for 33 years over the question of slavery. After 11 years of war, Spain finally recognized the independence of Mexico with the Treaty of Córdoba signed on August 24, 1821. Mexico eventually ratified the Adams–Onís Treaty in 1831. The Texian Revolt of 1835–36 fomented a dispute between the U.S. and Mexico which eventually erupted into the Mexican–American War in 1846. Mexico surrendered its northern territory to the U.S. with the Treaty of Guadalupe Hidalgo after the war in 1848; this included much of the western and southern areas of the current state of Colorado.
+
+Most American settlers traveling overland west to the Oregon Country, the new goldfields of California, or the new Mormon settlements of the State of Deseret in the Salt Lake Valley, avoided the rugged Southern Rocky Mountains, and instead followed the North Platte River and Sweetwater River to South Pass (Wyoming), the lowest crossing of the Continental Divide between the Southern Rocky Mountains and the Central Rocky Mountains. In 1849, the Mormons of the Salt Lake Valley organized the extralegal State of Deseret, claiming the entire Great Basin and all lands drained by the rivers Green, Grand, and Colorado. The federal government of the U.S. flatly refused to recognize the new Mormon government, because it was theocratic and sanctioned plural marriage. Instead, the Compromise of 1850 divided the Mexican Cession and the northwestern claims of Texas into a new state and two new territories, the state of California, the Territory of New Mexico, and the Territory of Utah. On April 9, 1851, Mexican American settlers from the area of Taos settled the village of San Luis, then in the New Mexico Territory, later to become Colorado's first permanent Euro-American settlement.
+
+In 1854, Senator Stephen A. Douglas persuaded the U.S. Congress to divide the unorganized territory east of the Continental Divide into two new organized territories, the Territory of Kansas and the Territory of Nebraska, and an unorganized southern region known as the Indian territory. Each new territory was to decide the fate of slavery within its boundaries, but this compromise merely served to fuel animosity between free soil and pro-slavery factions.
+
+The gold seekers organized the Provisional Government of the Territory of Jefferson on August 24, 1859, but this new territory failed to secure approval from the Congress of the United States embroiled in the debate over slavery. The election of Abraham Lincoln for the President of the United States on November 6, 1860, led to the secession of nine southern slave states and the threat of civil war among the states. Seeking to augment the political power of the Union states, the Republican Party-dominated Congress quickly admitted the eastern portion of the Territory of Kansas into the Union as the free State of Kansas on January 29, 1861, leaving the western portion of the Kansas Territory, and its gold-mining areas, as unorganized territory.
+
+Territory act
+
+Thirty days later on February 28, 1861, outgoing U.S. President James Buchanan signed an Act of Congress organizing the free Territory of Colorado. The original boundaries of Colorado remain unchanged except for government survey amendments. In 1776, Spanish priest Silvestre Vélez de Escalante recorded that Native Americans in the area knew the river as el Rio Colorado for the red-brown silt that the river carried from the mountains. In 1859, a U.S. Army topographic expedition led by Captain John Macomb located the confluence of the Green River with the Grand River in what is now Canyonlands National Park in Utah. The Macomb party designated the confluence as the source of the Colorado River.
+
+On April 12, 1861, South Carolina artillery opened fire on Fort Sumter to start the American Civil War. While many gold seekers held sympathies for the Confederacy, the vast majority remained fiercely loyal to the Union cause.
+
+In 1862, a force of Texas cavalry invaded the Territory of New Mexico and captured Santa Fe on March 10. The object of this Western Campaign was to seize or disrupt the gold fields of Colorado and California and to seize ports on the Pacific Ocean for the Confederacy. A hastily organized force of Colorado volunteers force-marched from Denver City, Colorado Territory, to Glorieta Pass, New Mexico Territory, in an attempt to block the Texans. On March 28, the Coloradans and local New Mexico volunteers stopped the Texans at the Battle of Glorieta Pass, destroyed their cannon and supply wagons, and dispersed 500 of their horses and mules. The Texans were forced to retreat to Santa Fe. Having lost the supplies for their campaign and finding little support in New Mexico, the Texans abandoned Santa Fe and returned to San Antonio in defeat. The Confederacy made no further attempts to seize the Southwestern United States.
+
+In 1864, Territorial Governor John Evans appointed the Reverend John Chivington as Colonel of the Colorado Volunteers with orders to protect white settlers from Cheyenne and Arapaho warriors who were accused of stealing cattle. Colonel Chivington ordered his troops to attack a band of Cheyenne and Arapaho encamped along Sand Creek. Chivington reported that his troops killed more than 500 warriors. The militia returned to Denver City in triumph, but several officers reported that the so-called battle was a blatant massacre of Indians at peace, that most of the dead were women and children, and that the bodies of the dead had been hideously mutilated and desecrated. Three U.S. Army inquiries condemned the action, and incoming President Andrew Johnson asked Governor Evans for his resignation, but none of the perpetrators was ever punished. This event is now known as the Sand Creek massacre.
+
+In the midst and aftermath of the Civil War, many discouraged prospectors returned to their homes, but a few stayed and developed mines, mills, farms, ranches, roads, and towns in Colorado Territory. On September 14, 1864, James Huff discovered silver near Argentine Pass, the first of many silver strikes. In 1867, the Union Pacific Railroad laid its tracks west to Weir, now Julesburg, in the northeast corner of the Territory. The Union Pacific linked up with the Central Pacific Railroad at Promontory Summit, Utah, on May 10, 1869, to form the First transcontinental railroad. The Denver Pacific Railway reached Denver in June of the following year, and the Kansas Pacific arrived two months later to forge the second line across the continent. In 1872, rich veins of silver were discovered in the San Juan Mountains on the Ute Indian reservation in southwestern Colorado. The Ute people were removed from the San Juans the following year.
+
+Statehood
+
+The United States Congress passed an enabling act on March 3, 1875, specifying the requirements for the Territory of Colorado to become a state. On August 1, 1876 (four weeks after the Centennial of the United States), U.S. President Ulysses S. Grant signed a proclamation admitting Colorado to the Union as the 38th state and earning it the moniker "Centennial State".
+
+The discovery of a major silver lode near Leadville in 1878 triggered the Colorado Silver Boom. The Sherman Silver Purchase Act of 1890 invigorated silver mining, and Colorado's last, but greatest, gold strike at Cripple Creek a few months later lured a new generation of gold seekers. Colorado women were granted the right to vote on November 7, 1893, making Colorado the second state to grant universal suffrage and the first one by a popular vote (of Colorado men). The repeal of the Sherman Silver Purchase Act in 1893 led to a staggering collapse of the mining and agricultural economy of Colorado, but the state slowly and steadily recovered. Between the 1880s and 1930s, Denver's floriculture industry developed into a major industry in Colorado. This period became known locally as the Carnation Gold Rush.
+
+Twentieth and twenty-first centuries
+
+Poor labor conditions and discontent among miners resulted in several major clashes between strikers and the Colorado National Guard, including the 1903–1904 Western Federation of Miners Strike and Colorado Coalfield War, the latter of which included the Ludlow massacre that killed a dozen women and children. Both the 1913–1914 Coalfield War and the Denver streetcar strike of 1920 resulted in federal troops intervening to end the violence. In 1927, the 1927-28 Colorado coal strike occurred and was ultimately successful in winning a dollar a day increase in wages. During it however the Columbine Mine massacre resulted in six dead strikers following a confrontation with Colorado Rangers. In a separate incident in Trinidad the mayor was accused of deputizing members of the KKK against the striking workers. More than 5,000 Colorado miners—many immigrants—are estimated to have died in accidents since records were first formally collected following an 1884 accident in Crested Butte that killed 59.
+
+In 1924, the Ku Klux Klan Colorado Realm achieved dominance in Colorado politics. With peak membership levels, the Second Klan levied significant control over both the local and state Democrat and Republican parties, particularly in the governor's office and city governments of Denver, Cañon City, and Durango. A particularly strong element of the Klan controlled the Denver Police. Cross burnings became semi-regular occurrences in cities such as Florence and Pueblo. The Klan targeted African-Americans, Catholics, Eastern European immigrants, and other non-White Protestant groups. Efforts by non-Klan lawmen and lawyers including Philip Van Cise lead to a rapid decline in the organization's power, with membership waning significantly by the end of the 1920s.
+
+Colorado became the first western state to host a major political convention when the Democratic Party met in Denver in 1908. By the U.S. census in 1930, the population of Colorado first exceeded one million residents. Colorado suffered greatly through the Great Depression and the Dust Bowl of the 1930s, but a major wave of immigration following World War II boosted Colorado's fortune. Tourism became a mainstay of the state economy, and high technology became an important economic engine. The United States Census Bureau estimated that the population of Colorado exceeded five million in 2009.
+
+On September 11, 1957, a plutonium fire occurred at the Rocky Flats Plant, which resulted in the significant plutonium contamination of surrounding populated areas.
+
+From the 1940s and 1970s, many protest movements gained momentum in Colorado, predominantly in Denver. This included the Chicano Movement, a civil rights, and social movement of Mexican Americans emphasizing a Chicano identity that is widely considered to have begun in Denver. The National Chicano Liberation Youth Conference was held in Colorado in March 1969.
+
+In 1967, Colorado was the first state to loosen restrictions on abortion when governor John Love signed a law allowing abortions in cases of rape, incest, or threats to the woman's mental or physical health. Many states followed Colorado's lead in loosening abortion laws in the 1960s and 1970s.
+
+Since the late 1990s, Colorado has been the site of multiple major mass shootings, including the infamous Columbine High School massacre in 1999 which made international news, where two gunmen killed 12 students and one teacher, before committing suicide. The incident has since spawned many copycat incidents. On July 20, 2012, a gunman killed 12 people in a movie theater in Aurora. The state responded with tighter restrictions on firearms, including introducing a limit on magazine capacity. On March 22, 2021, a gunman killed 10 people, including a police officer, in a King Soopers supermarket in Boulder. In an instance of anti-LGBT violence, a gunman killed 5 people at a nightclub in Colorado Springs during the night of November 19–20, 2022.
+
+Four warships of the U.S. Navy have been named the USS Colorado. The first USS Colorado was named for the Colorado River and served in the Civil War and later the Asiatic Squadron, where it was attacked during the 1871 Korean Expedition. The later three ships were named in honor of the state, including an armored cruiser and the battleship USS Colorado, the latter of which was the lead ship of her class and served in World War II in the Pacific beginning in 1941. At the time of the attack on Pearl Harbor, the battleship USS Colorado was located at the naval base in San Diego, California, and thus went unscathed. The most recent vessel to bear the name USS Colorado is Virginia-class submarine USS Colorado (SSN-788), which was commissioned in 2018.
+
+Geography
+
+Colorado is notable for its diverse geography, which includes alpine mountains, high plains, deserts with huge sand dunes, and deep canyons. In 1861, the United States Congress defined the boundaries of the new Territory of Colorado exclusively by lines of latitude and longitude, stretching from 37°N to 41°N latitude, and from 102°02′48″W to 109°02′48″W longitude (25°W to 32°W from the Washington Meridian). After  years of government surveys, the borders of Colorado were officially defined by 697 boundary markers and 697 straight boundary lines. Colorado, Wyoming, and Utah are the only states that have their borders defined solely by straight boundary lines with no natural features. The southwest corner of Colorado is the Four Corners Monument at 36°59′56″N, 109°2′43″W. The Four Corners Monument, located at the place where Colorado, New Mexico, Arizona, and Utah meet, is the only place in the United States where four states meet.
+
+Plains
+
+Approximately half of Colorado is flat and rolling land. East of the Rocky Mountains are the Colorado Eastern Plains of the High Plains, the section of the Great Plains within Colorado at elevations ranging from roughly . The Colorado plains are mostly prairies but also include deciduous forests, buttes, and canyons. Precipitation averages  annually.
+
+Eastern Colorado is presently mainly farmland and rangeland, along with small farming villages and towns. Corn, wheat, hay, soybeans, and oats are all typical crops. Most villages and towns in this region boast both a water tower and a grain elevator. Irrigation water is available from both surface and subterranean sources. Surface water sources include the South Platte, the Arkansas River, and a few other streams. Subterranean water is generally accessed through artesian wells. Heavy usage of these wells for irrigation purposes caused underground water reserves to decline in the region. Eastern Colorado also hosts a considerable amount and range of livestock, such as cattle ranches and hog farms.
+
+Front Range
+
+Roughly 70% of Colorado's population resides along the eastern edge of the Rocky Mountains in the Front Range Urban Corridor between Cheyenne, Wyoming, and Pueblo, Colorado. This region is partially protected from prevailing storms that blow in from the Pacific Ocean region by the high Rockies in the middle of Colorado. The "Front Range" includes Denver, Boulder, Fort Collins, Loveland, Castle Rock, Colorado Springs, Pueblo, Greeley, and other townships and municipalities in between. On the other side of the Rockies, the significant population centers in western Colorado (which is known as "The Western Slope") are the cities of Grand Junction, Durango, and Montrose.
+
+Mountains
+
+To the west of the Great Plains of Colorado rises the eastern slope of the Rocky Mountains. Notable peaks of the Rocky Mountains include Longs Peak, Mount Blue Sky, Pikes Peak, and the Spanish Peaks near Walsenburg, in southern Colorado. This area drains to the east and the southeast, ultimately either via the Mississippi River or the Rio Grande into the Gulf of Mexico.
+
+The Rocky Mountains within Colorado contain 53 true peaks with a total of 58 that are  or higher in elevation above sea level, known as fourteeners. These mountains are largely covered with trees such as conifers and aspens up to the tree line, at an elevation of about  in southern Colorado to about  in northern Colorado. Above this tree line, only alpine vegetation grows. Only small parts of the Colorado Rockies are snow-covered year-round.
+
+Much of the alpine snow melts by mid-August except for a few snow-capped peaks and a few small glaciers. The Colorado Mineral Belt, stretching from the San Juan Mountains in the southwest to Boulder and Central City on the front range, contains most of the historic gold- and silver-mining districts of Colorado. Mount Elbert is the highest summit of the Rocky Mountains. The 30 highest major summits of the Rocky Mountains of North America are all within the state.
+
+The summit of Mount Elbert at  elevation in Lake County is the highest point in Colorado and the Rocky Mountains of North America. Colorado is the only U.S. state that lies entirely above 1,000 meters elevation. The point where the Arikaree River flows out of Yuma County, Colorado, and into Cheyenne County, Kansas, is the lowest in Colorado at  elevation. This point, which is the highest low elevation point of any state, is higher than the high elevation points of 18 states and the District of Columbia.
+
+Continental Divide
+
+The Continental Divide of the Americas extends along the crest of the Rocky Mountains. The area of Colorado to the west of the Continental Divide is called the Western Slope of Colorado. West of the Continental Divide, water flows to the southwest via the Colorado River and the Green River into the Gulf of California.
+
+Within the interior of the Rocky Mountains are several large parks which are high broad basins. In the north, on the east side of the Continental Divide is the North Park of Colorado. The North Park is drained by the North Platte River, which flows north into Wyoming and Nebraska. Just to the south of North Park, but on the western side of the Continental Divide, is the Middle Park of Colorado, which is drained by the Colorado River. The South Park of Colorado is the region of the headwaters of the South Platte River.
+
+South Central region
+
+In south-central Colorado is the large San Luis Valley, where the headwaters of the Rio Grande are located. The northern part of the valley is the San Luis Closed Basin, an endorheic basin that helped created the Great Sand Dunes. The valley sits between the Sangre De Cristo Mountains and San Juan Mountains. The Rio Grande drains due south into New Mexico, Texas, and Mexico. Across the Sangre de Cristo Range to the east of the San Luis Valley lies the Wet Mountain Valley. These basins, particularly the San Luis Valley, lie along the Rio Grande Rift, a major geological formation of the Rocky Mountains, and its branches.
+
+Western Slope
+
+The Western Slope of Colorado includes the western face of the Rocky Mountains and all of the area to the western border. This area includes several terrains and climates from alpine mountains to arid deserts. The Western Slope includes many ski resort towns in the Rocky Mountains and towns west to Utah. It is less populous than the Front Range but includes a large number of national parks and monuments.
+
+The northwestern corner of Colorado is a sparsely populated region, and it contains part of the noted Dinosaur National Monument, which not only is a paleontological area, but is also a scenic area of rocky hills, canyons, arid desert, and streambeds. Here, the Green River briefly crosses over into Colorado.
+
+The Western Slope of Colorado is drained by the Colorado River and its tributaries (primarily the Gunnison River, Green River, and the San Juan River). The Colorado River flows through Glenwood Canyon, and then through an arid valley made up of desert from Rifle to Parachute, through the desert canyon of De Beque Canyon, and into the arid desert of Grand Valley, where the city of Grand Junction is located.
+
+Also prominent is the Grand Mesa, which lies to the southeast of Grand Junction; the high San Juan Mountains, a rugged mountain range; and to the north and west of the San Juan Mountains, the Colorado Plateau.
+
+Grand Junction, Colorado, at the confluence of the Colorado and Gunnison Rivers, is the largest city on the Western Slope. Grand Junction and Durango are the only major centers of television broadcasting west of the Continental Divide in Colorado, though most mountain resort communities publish daily newspapers. Grand Junction is located at the juncture of Interstate 70 and US 50, the only major highways in western Colorado. Grand Junction is also along the major railroad of the Western Slope, the Union Pacific. This railroad also provides the tracks for Amtrak's California Zephyr passenger train, which crosses the Rocky Mountains between Denver and Grand Junction.
+
+The Western Slope includes multiple notable destinations in the Colorado Rocky Mountains, including Glenwood Springs, with its resort hot springs, and the ski resorts of Aspen, Breckenridge, Vail, Crested Butte, Steamboat Springs, and Telluride.
+
+Higher education in and near the Western Slope can be found at Colorado Mesa University in Grand Junction, Western Colorado University in Gunnison, Fort Lewis College in Durango, and Colorado Mountain College in Glenwood Springs and Steamboat Springs.
+
+The Four Corners Monument in the southwest corner of Colorado marks the common boundary of Colorado, New Mexico, Arizona, and Utah; the only such place in the United States.
+
+Climate
+
+The climate of Colorado is more complex than states outside of the Mountain States region. Unlike most other states, southern Colorado is not always warmer than northern Colorado. Most of Colorado is made up of mountains, foothills, high plains, and desert lands. Mountains and surrounding valleys greatly affect the local climate.  Northeast, east, and southeast Colorado are mostly the high plains, while Northern Colorado is a mix of high plains, foothills, and mountains. Northwest and west Colorado are predominantly mountainous, with some desert lands mixed in. Southwest and southern Colorado are a complex mixture of desert and mountain areas.
+
+Eastern Plains
+
+The climate of the Eastern Plains is semi-arid (Köppen climate classification: BSk) with low humidity and moderate precipitation, usually from  annually, although many areas near the rivers are semi-humid climate. The area is known for its abundant sunshine and cool, clear nights, which give this area a great average diurnal temperature range. The difference between the highs of the days and the lows of the nights can be considerable as warmth dissipates to space during clear nights, the heat radiation not being trapped by clouds. The Front Range urban corridor, where most of the population of Colorado resides, lies in a pronounced precipitation shadow as a result of being on the lee side of the Rocky Mountains.
+
+In summer, this area can have many days above 95 °F (35 °C) and often 100 °F (38 °C). On the plains, the winter lows usually range from 25 to −10 °F (−4 to −23 °C). About 75% of the precipitation falls within the growing season, from April to September, but this area is very prone to droughts. Most of the precipitation comes from thunderstorms, which can be severe, and from major snowstorms that occur in the winter and early spring. Otherwise, winters tend to be mostly dry and cold.
+
+In much of the region, March is the snowiest month. April and May are normally the rainiest months, while April is the wettest month overall. The Front Range cities closer to the mountains tend to be warmer in the winter due to Chinook winds which warms the area, sometimes bringing temperatures of 70 °F (21 °C) or higher in the winter. The average July temperature is 55 °F (13 °C) in the morning and 90 °F (32 °C) in the afternoon. The average January temperature is 18 °F (−8 °C) in the morning and 48 °F (9 °C) in the afternoon, although variation between consecutive days can be 40 °F (-40 °C).
+
+Front Range foothills
+
+Just west of the plains and into the foothills, there is a wide variety of climate types. Locations merely a few miles apart can experience entirely different weather depending on the topography. Most valleys have a semi-arid climate, not unlike the eastern plains, which transitions to an alpine climate at the highest elevations. Microclimates also exist in local areas that run nearly the entire spectrum of climates, including subtropical highland (Cfb/Cwb), humid subtropical (Cfa), humid continental (Dfa/Dfb), Mediterranean (Csa/Csb) and subarctic (Dfc).
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+Extreme weather
+
+Extreme weather changes are common in Colorado, although a significant portion of the extreme weather occurs in the least populated areas of the state. Thunderstorms are common east of the Continental Divide in the spring and summer, yet are usually brief. Hail is a common sight in the mountains east of the Divide and across the eastern Plains, especially the northeast part of the state. Hail is the most commonly reported warm-season severe weather hazard, and occasionally causes human injuries, as well as significant property damage. The eastern Plains are subject to some of the biggest hail storms in North America. Notable examples are the severe hailstorms that hit Denver on July 11, 1990, and May 8, 2017, the latter being the costliest ever in the state.
+
+The Eastern Plains are part of the extreme western portion of Tornado Alley; some damaging tornadoes in the Eastern Plains include the 1990 Limon F3 tornado and the 2008 Windsor EF3 tornado, which devastated a small town. Portions of the eastern Plains see especially frequent tornadoes, both those spawned from mesocyclones in supercell thunderstorms and from less intense landspouts, such as within the Denver convergence vorticity zone (DCVZ).
+
+The Plains are also susceptible to occasional floods and particularly severe flash floods, which are caused both by thunderstorms and by the rapid melting of snow in the mountains during warm weather. Notable examples include the 1965 Denver Flood, the Big Thompson River flooding of 1976 and the 2013 Colorado floods. Hot weather is common during summers in Denver. The city's record in 1901 for the number of consecutive days above 90 °F (32 °C) was broken during the summer of 2008. The new record of 24 consecutive days surpassed the previous record by almost a week.
+
+Much of Colorado is very dry, with the state averaging only  of precipitation per year statewide. The state rarely experiences a time when some portion is not in some degree of drought. The lack of precipitation contributes to the severity of wildfires in the state, such as the Hayman Fire of 2002. Other notable fires include the Fourmile Canyon Fire of 2010, the Waldo Canyon Fire and High Park Fire of June 2012, and the Black Forest Fire of June 2013. Even these fires were exceeded in severity by the Pine Gulch Fire, Cameron Peak Fire, and East Troublesome Fire in 2020, all being the three largest fires in Colorado history (see 2020 Colorado wildfires). And the Marshall Fire which started on December 30, 2021, while not the largest in state history, was the most destructive ever in terms of property loss (see Marshall Fire).
+
+However, some of the mountainous regions of Colorado receive a huge amount of moisture from winter snowfalls. The spring melts of these snows often cause great waterflows in the Yampa River, the Colorado River, the Rio Grande, the Arkansas River, the North Platte River, and the South Platte River.
+
+Water flowing out of the Colorado Rocky Mountains is a very significant source of water for the farms, towns, and cities of the southwest states of New Mexico, Arizona, Utah, and Nevada, as well as the Midwest, such as Nebraska and Kansas, and the southern states of Oklahoma and Texas. A significant amount of water is also diverted for use in California; occasionally (formerly naturally and consistently), the flow of water reaches northern Mexico.
+
+Climate change
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+Records
+
+The highest official ambient air temperature ever recorded in Colorado was  on July 20, 2019, at John Martin Dam. The lowest official air temperature was  on February 1, 1985, at Maybell.
+
+Extreme temperatures
+
+Earthquakes
+
+Despite its mountainous terrain, Colorado is relatively quiet seismically. The U.S. National Earthquake Information Center is located in Golden.
+
+On August 22, 2011, a 5.3 magnitude earthquake occurred  west-southwest of the city of Trinidad. There were no casualties and only a small amount of damage was reported. It was the second-largest earthquake in Colorado's history. A magnitude 5.7 earthquake was recorded in 1973.
+
+In the early morning hours of August 24, 2018, four minor earthquakes rattled Colorado, ranging from magnitude 2.9 to 4.3.
+
+Colorado has recorded 525 earthquakes since 1973, a majority of which range 2 to 3.5 on the Richter scale.
+
+Fauna
+
+A process of extirpation by trapping and poisoning of the gray wolf (Canis lupus) from Colorado in the 1930s saw the last wild wolf in the state shot in 1945. A wolf pack recolonized Moffat County, Colorado in northwestern Colorado in 2019. Cattle farmers have expressed concern that a returning wolf population potentially threatens their herds. Coloradans voted to reintroduce gray wolves in 2020, with the state committing to a plan to have a population in the state by 2022 and permitting non-lethal methods of driving off wolves attacking livestock and pets.
+
+While there is fossil evidence of Harrington's mountain goat in Colorado between at least 800,000 years ago and its extinction with megafauna roughly 11,000 years ago, the mountain goat is not native to Colorado but was instead introduced to the state over time during the interval between 1947 and 1972. Despite being an artificially-introduced species, the state declared mountain goats a native species in 1993. In 2013, 2014, and 2019, an unknown illness killed nearly all mountain goat kids, leading to a Colorado Parks and Wildlife investigation.
+
+The native population of pronghorn in Colorado has varied wildly over the last century, reaching a low of only 15,000 individuals during the 1960s. However, conservation efforts succeeded in bringing the stable population back up to roughly 66,000 by 2013. The population was estimated to have reached 85,000 by 2019 and had increasingly more run-ins with the increased suburban housing along the eastern Front Range. State wildlife officials suggested that landowners would need to modify fencing to allow the greater number of pronghorns to move unabated through the newly developed land. Pronghorns are most readily found in the northern and eastern portions of the state, with some populations also in the western San Juan Mountains.
+
+Common wildlife found in the mountains of Colorado include mule deer, southwestern red squirrel, golden-mantled ground squirrel, yellow-bellied marmot, moose, American pika, and red fox, all at exceptionally high numbers, though moose are not native to the state. The foothills include deer, fox squirrel, desert cottontail, mountain cottontail, and coyote. The prairies are home to black-tailed prairie dog, the endangered swift fox, American badger, and white-tailed jackrabbit.
+
+Counties 
+
+The State of Colorado is divided into 64 counties. Two of these counties, the City and County of Broomfield and the City and County of Denver, have consolidated city and county governments. Counties are important units of government in Colorado since there are no civil townships or other minor civil divisions.
+
+The most populous county in Colorado is El Paso County, the home of the City of Colorado Springs. The second most populous county is the City and County of Denver, the state capital. Five of the 64 counties now have more than 500,000 residents, while 12 have fewer than 5,000 residents. The ten most populous Colorado counties are all located in the Front Range Urban Corridor. Mesa County is the most populous county on the Colorado Western Slope.
+
+Municipalities
+
+Colorado has 272 active incorporated municipalities, comprising 197 towns, 73 cities, and two consolidated city and county governments. At the 2020 United States census, 4,299,942 of the 5,773,714 Colorado residents (74.47%) lived in one of these 272 municipalities. Another 714,417 residents (12.37%) lived in one of the 210 census-designated places, while the remaining 759,355 residents (13.15%) lived in the many rural and mountainous areas of the state.
+
+Colorado municipalities operate under one of five types of municipal governing authority. Colorado currently has two consolidated city and county governments, 61 home rule cities, 12 statutory cities, 35 home rule towns, 161 statutory towns, and one territorial charter municipality.
+
+The most populous municipality is the City and County of Denver. Colorado has 12 municipalities with more than 100,000 residents, and 17 with fewer than 100 residents. The 16 most populous Colorado municipalities are all located in the Front Range Urban Corridor. The City of Grand Junction is the most populous municipality on the Colorado Western Slope. The Town of Carbonate has had no year-round population since the 1890 census due to its severe winter weather and difficult access.
+
+Unincorporated communities
+
+In addition to its 272 municipalities, Colorado has 210 unincorporated census-designated places (CDPs) and many other small communities. The most populous unincorporated community in Colorado is Highlands Ranch south of Denver. The seven most populous CDPs are located in the Front Range Urban Corridor. The Clifton CDP is the most populous CDP on the Colorado Western Slope.
+
+Special districts
+Colorado has more than 4,000 special districts, most with property tax authority. These districts may provide schools, law enforcement, fire protection, water, sewage, drainage, irrigation, transportation, recreation, infrastructure, cultural facilities, business support, redevelopment, or other services.
+
+Some of these districts have the authority to levy sales tax as well as property tax and use fees. This has led to a hodgepodge of sales tax and property tax rates in Colorado. There are some street intersections in Colorado with a different sales tax rate on each corner, sometimes substantially different.
+
+Some of the more notable Colorado districts are:
+ The Regional Transportation District (RTD), which affects the counties of Denver, Boulder, Jefferson, and portions of Adams, Arapahoe, Broomfield, and Douglas Counties
+ The Scientific and Cultural Facilities District (SCFD), a special regional tax district with physical boundaries contiguous with county boundaries of Adams, Arapahoe, Boulder, Broomfield, Denver, Douglas, and Jefferson Counties
+ It is a 0.1% retail sales and uses tax (one penny on every $10).
+ According to the Colorado statute, the SCFD distributes the money to local organizations on an annual basis. These organizations must provide for the enlightenment and entertainment of the public through the production, presentation, exhibition, advancement, or preservation of art, music, theater, dance, zoology, botany, natural history, or cultural history.
+ As directed by statute, SCFD recipient organizations are currently divided into three "tiers" among which receipts are allocated by percentage.
+ Tier I includes regional organizations: the Denver Art Museum, the Denver Botanic Gardens, the Denver Museum of Nature and Science, the Denver Zoo, and the Denver Center for the Performing Arts. It receives 65.5%.
+ Tier II currently includes 26 regional organizations. Tier II receives 21%.
+ Tier III has more than 280 local organizations such as small theaters, orchestras, art centers, natural history, cultural history, and community groups. Tier III organizations apply for funding from the county cultural councils via a grant process. This tier receives 13.5%.
+ An 11-member board of directors oversees the distributions by the Colorado Revised Statutes. Seven board members are appointed by county commissioners (in Denver, the Denver City Council) and four members are appointed by the Governor of Colorado.
+ The Football Stadium District (FD or FTBL), approved by the voters to pay for and help build the Denver Broncos' stadium Empower Field at Mile High.
+ Local Improvement Districts (LID) within designated areas of Jefferson and Broomfield counties.
+ The Metropolitan Major League Baseball Stadium District, approved by voters to pay for and help build the Colorado Rockies' stadium Coors Field.
+ Regional Transportation Authority (RTA) taxes at varying rates in Basalt, Carbondale, Glenwood Springs, and Gunnison County.
+
+Statistical areas
+
+Most recently on March 6, 2020, the Office of Management and Budget defined 21 statistical areas for Colorado comprising four combined statistical areas, seven metropolitan statistical areas, and ten micropolitan statistical areas.
+
+The most populous of the seven metropolitan statistical areas in Colorado is the 10-county Denver-Aurora-Lakewood, CO Metropolitan Statistical Area with a population of 2,963,821 at the 2020 United States census, an increase of +15.29% since the 2010 census.
+
+The more extensive 12-county Denver-Aurora, CO Combined Statistical Area had a population of 3,623,560 at the 2020 census, an increase of +17.23% since the 2010 census.
+
+The most populous extended metropolitan region in Rocky Mountain Region is the 18-county Front Range Urban Corridor along the northeast face of the Southern Rocky Mountains. This region with Denver at its center had a population of 5,055,344 at the 2020 census, an increase of +16.65% since the 2010 census.
+
+Demographics
+
+The United States Census Bureau estimated the population of Colorado on July 1, 2022, at 5,839,926, a 1.15% increase since the  2020 United States census.
+
+People of Hispanic and Latino American (of any race made) heritage made up 20.7% of the population. According to the 2000 census, the largest ancestry groups in Colorado are German (22%) including those of Swiss and Austrian descent, Mexican (18%), Irish (12%), and English (12%). Persons reporting German ancestry are especially numerous in the Front Range, the Rockies (west-central counties), and Eastern parts/High Plains.
+
+Colorado has a high proportion of Hispanic, mostly Mexican-American, citizens in Metropolitan Denver, Colorado Springs, as well as the smaller cities of Greeley and Pueblo, and elsewhere. Southern, Southwestern, and Southeastern Colorado have a large number of Hispanos, the descendants of the early settlers of colonial Spanish origin. In 1940, the U.S. Census Bureau reported Colorado's population as 8.2% Hispanic and 90.3% non-Hispanic white. The Hispanic population of Colorado has continued to grow quickly over the past decades. By 2019, Hispanics made up 22% of Colorado's population, and Non-Hispanic Whites made up 70%. Spoken English in Colorado has many Spanish idioms.
+
+Colorado also has some large African-American communities located in Denver, in the neighborhoods of Montbello, Five Points, Whittier, and many other East Denver areas. The state has sizable numbers of Asian-Americans of Mongolian, Chinese, Filipino, Korean, Southeast Asian, and Japanese descent. The highest population of Asian Americans can be found on the south and southeast side of Denver, as well as some on Denver's southwest side. The Denver metropolitan area is considered more liberal and diverse than much of the state when it comes to political issues and environmental concerns.
+
+The majority of Colorado's immigrants are from Mexico, India, China, Vietnam, Korea, Germany and Canada.
+
+There were a total of 70,331 births in Colorado in 2006. (Birth rate of 14.6 per thousand.) In 2007, non-Hispanic whites were involved in 59.1% of all births. Some 14.06% of those births involved a non-Hispanic white person and someone of a different race, most often with a couple including one Hispanic. A birth where at least one Hispanic person was involved counted for 43% of the births in Colorado. As of the 2010 census, Colorado has the seventh highest percentage of Hispanics (20.7%) in the U.S. behind New Mexico (46.3%), California (37.6%), Texas (37.6%), Arizona (29.6%), Nevada (26.5%), and Florida (22.5%). Per the 2000 census, the Hispanic population is estimated to be 918,899, or approximately 20% of the state's total population. Colorado has the 5th-largest population of Mexican-Americans, behind California, Texas, Arizona, and Illinois. In percentages, Colorado has the 6th-highest percentage of Mexican-Americans, behind New Mexico, California, Texas, Arizona, and Nevada.
+
+Birth data
+In 2011, 46% of Colorado's population younger than the age of one were minorities, meaning that they had at least one parent who was not non-Hispanic white.
+
+Note: Births in table do not add up, because Hispanics are counted both by their ethnicity and by their race, giving a higher overall number.
+
+ Since 2016, data for births of White Hispanic origin are not collected, but included in one Hispanic group; persons of Hispanic origin may be of any race.
+
+In 2017, Colorado recorded the second-lowest fertility rate in the United States outside of New England, after Oregon, at 1.63 children per woman. Significant, contributing factors to the decline in pregnancies were the  Title X Family Planning Program and an intrauterine device grant from Warren Buffett's family.
+
+Language
+English, the official language of the state, is the most commonly spoken in Colorado. One Native American language still spoken in Colorado is the Colorado River Numic language also known as the Ute dialect.
+
+Religion
+
+Major religious affiliations of the people of Colorado as of 2014 were 64% Christian, of whom there are 44% Protestant, 16% Roman Catholic, 3% Mormon, and 1% Eastern Orthodox. Other religious breakdowns according to the Pew Research Center were 1% Jewish, 1% Muslim, 1% Buddhist and 4% other. The religiously unaffiliated made up 29% of the population. In 2020, according to the Public Religion Research Institute, Christianity was 66% of the population. Judaism was also reported to have increased in this separate study, forming 2% of the religious landscape, while the religiously unaffiliated were reported to form 28% of the population in this separate study. In 2022, the same organization reported 61% was Christian (39% Protestant, 19% Catholic, 2% Mormon, 1% Eastern Orthodox), 2% New Age, 1% Jewish, 1% Hindu, and 34% religiously unaffiliated.
+
+According to the Association of Religion Data Archives, the largest Christian denominations by the number of adherents in 2010 were the Catholic Church with 811,630; multi-denominational Evangelical Protestants with 229,981; and the Church of Jesus Christ of Latter-day Saints with 151,433. In 2020, the Association of Religion Data Archives determined the largest Christian denominations were Catholics (873,236), non/multi/inter-denominational Protestants (406,798), and Mormons (150,509). Throughout its non-Christian population, there were 12,500 Hindus, 7,101 Hindu Yogis, and 17,369 Buddhists at the 2020 study.
+
+Our Lady of Guadalupe Catholic Church was the first permanent Catholic parish in modern-day Colorado and was constructed by Spanish colonists from New Mexico in modern-day Conejos. Latin Church Catholics are served by three dioceses: the Archdiocese of Denver and the Dioceses of Colorado Springs and Pueblo.
+
+The first permanent settlement by members of the Church of Jesus Christ of Latter-day Saints in Colorado arrived from Mississippi and initially camped along the Arkansas River just east of the present-day site of Pueblo.
+
+Health
+Colorado is generally considered among the healthiest states by behavioral and healthcare researchers. Among the positive contributing factors is the state's well-known outdoor recreation opportunities and initiatives. However, there is a stratification of health metrics with wealthier counties such as Douglas and Pitkin performing significantly better relative to southern, less wealthy counties such as Huerfano and Las Animas.
+
+Obesity
+According to several studies, Coloradans have the lowest rates of obesity of any state in the US. , 24% of the population was considered medically obese, and while the lowest in the nation, the percentage had increased from 17% in 2004.
+
+Life expectancy
+According to a report in the Journal of the American Medical Association, residents of Colorado had a 2014 life expectancy of 80.21 years, the longest of any U.S. state.
+
+Homelessness 
+According to HUD's 2022 Annual Homeless Assessment Report, there were an estimated 10,397 homeless people in Colorado.
+
+Economy
+
+ Total employment (2019): 2,473,192
+ Number of employer establishments: 174,258
+
+The total state product in 2015 was $318.6 billion. Median Annual Household Income in 2016 was $70,666, 8th in the nation. Per capita personal income in 2010 was $51,940, ranking Colorado 11th in the nation. The state's economy broadened from its mid-19th-century roots in mining when irrigated agriculture developed, and by the late 19th century, raising livestock had become important. Early industry was based on the extraction and processing of minerals and agricultural products. Current agricultural products are cattle, wheat, dairy products, corn, and hay.
+
+The federal government operates several federal facilities in the state, including NORAD (North American Aerospace Defense Command), United States Air Force Academy, Schriever Air Force Base located approximately 10 miles (16 kilometers) east of Peterson Air Force Base, and Fort Carson, both located in Colorado Springs within El Paso County; NOAA, the National Renewable Energy Laboratory (NREL) in Golden, and the National Institute of Standards and Technology in Boulder; U.S. Geological Survey and other government agencies at the Denver Federal Center near Lakewood; the Denver Mint, Buckley Space Force Base, the Tenth Circuit Court of Appeals, and the Byron G. Rogers Federal Building and United States Courthouse in Denver; and a federal Supermax Prison and other federal prisons near Cañon City. In addition to these and other federal agencies, Colorado has abundant National Forest land and four National Parks that contribute to federal ownership of  of land in Colorado, or 37% of the total area of the state.
+In the second half of the 20th century, the industrial and service sectors expanded greatly. The state's economy is diversified and is notable for its concentration on scientific research and high-technology industries. Other industries include food processing, transportation equipment, machinery, chemical products, the extraction of metals such as gold (see Gold mining in Colorado), silver, and molybdenum. Colorado now also has the largest annual production of beer in any state. Denver is an important financial center.
+
+The state's diverse geography and majestic mountains attract millions of tourists every year, including 85.2 million in 2018. Tourism contributes greatly to Colorado's economy, with tourists generating $22.3 billion in 2018.
+
+Several nationally known brand names have originated in Colorado factories and laboratories. From Denver came the forerunner of telecommunications giant Qwest in 1879, Samsonite luggage in 1910, Gates belts and hoses in 1911, and Russell Stover Candies in 1923. Kuner canned vegetables began in Brighton in 1864. From Golden came Coors beer in 1873, CoorsTek industrial ceramics in 1920, and Jolly Rancher candy in 1949. CF&I railroad rails, wire, nails, and pipe debuted in Pueblo in 1892. Holly Sugar was first milled from beets in Holly in 1905, and later moved its headquarters to Colorado Springs. The present-day Swift packed meat of Greeley evolved from Monfort of Colorado, Inc., established in 1930. Estes model rockets were launched in Penrose in 1958. Fort Collins has been the home of Woodward Governor Company's motor controllers (governors) since 1870, and Waterpik dental water jets and showerheads since 1962. Celestial Seasonings herbal teas have been made in Boulder since 1969. Rocky Mountain Chocolate Factory made its first candy in Durango in 1981.
+
+Colorado has a flat 4.63% income tax, regardless of income level. On November 3, 2020, voters authorized an initiative to lower that income tax rate to 4.55 percent. Unlike most states, which calculate taxes based on federal adjusted gross income, Colorado taxes are based on taxable income—income after federal exemptions and federal itemized (or standard) deductions. Colorado's state sales tax is 2.9% on retail sales. When state revenues exceed state constitutional limits, according to Colorado's Taxpayer Bill of Rights legislation, full-year Colorado residents can claim a sales tax refund on their individual state income tax return. Many counties and cities charge their own rates, in addition to the base state rate. There are also certain county and special district taxes that may apply.
+
+Real estate and personal business property are taxable in Colorado. The state's senior property tax exemption was temporarily suspended by the Colorado Legislature in 2003. The tax break was scheduled to return for the assessment year 2006, payable in 2007.
+
+, the state's unemployment rate was 4.2%.
+
+The West Virginia teachers' strike in 2018 inspired teachers in other states, including Colorado, to take similar action.
+
+Agriculture
+Corn is grown in the Eastern Plains of Colorado. Arid conditions and drought negatively impacted yields in 2020 and 2022.
+
+Natural resources
+
+Colorado has significant hydrocarbon resources. According to the Energy Information Administration, Colorado hosts seven of the largest natural gas fields in the United States, and two of the largest oil fields. Conventional and unconventional natural gas output from several Colorado basins typically accounts for more than five percent of annual U.S. natural gas production. Colorado's oil shale deposits hold an estimated  of oil—nearly as much oil as the entire world's proven oil reserves. Substantial deposits of bituminous, subbituminous, and lignite coal are found in the state.
+
+Uranium mining in Colorado goes back to 1872, when pitchblende ore was taken from gold mines near Central City, Colorado. Not counting byproduct uranium from phosphate, Colorado is considered to have the third-largest uranium reserves of any U.S. state, behind Wyoming and New Mexico. When Colorado and Utah dominated radium mining from 1910 to 1922, uranium and vanadium were the byproducts (giving towns like present-day Superfund site Uravan their names). Uranium price increases from 2001 to 2007 prompted several companies to revive uranium mining in Colorado. During the 1940s, certain communities–including Naturita and Paradox–earned the moniker of "yellowcake towns" from their relationship with uranium mining. Price drops and financing problems in late 2008 forced these companies to cancel or scale back the uranium-mining project. As of 2016, there were no major uranium mining operations in the state, though plans existed to restart production.
+
+Electricity generation
+
+Colorado's high Rocky Mountain ridges and eastern plains offer wind power potential, and geologic activity in the mountain areas provides the potential for geothermal power development. Much of the state is sunny and could produce solar power. Major rivers flowing from the Rocky Mountains offer hydroelectric power resources.
+
+Culture
+
+Arts and film
+
+ List of museums in Colorado
+ List of theaters in Colorado
+ Music of Colorado
+
+Several film productions have been shot on location in Colorado, especially prominent Westerns like True Grit, The Searchers, and Butch Cassidy and the Sundance Kid. Several historic military forts, railways with trains still operating, and mining ghost towns have been used and transformed for historical accuracy in well-known films. There are also several scenic highways and mountain passes that helped to feature the open road in films such as Vanishing Point, Bingo and Starman. Some Colorado landmarks have been featured in films, such as The Stanley Hotel in Dumb and Dumber and The Shining and the Sculptured House in Sleeper. In 2015, Furious 7 was to film driving sequences on Pikes Peak Highway in Colorado. The TV adult-animated series South Park takes place in central Colorado in the titular town. Additionally, The TV series Good Luck Charlie was set, but not filmed, in Denver, Colorado. The Colorado Office of Film and Television has noted that more than 400 films have been shot in Colorado.
+
+There are also several established film festivals in Colorado, including Aspen Shortsfest, Boulder International Film Festival, Castle Rock Film Festival, Denver Film Festival, Festivus Film Festival, Mile High Horror Film Festival, Moondance International Film Festival, Mountainfilm in Telluride, Rocky Mountain Women's Film Festival, and Telluride Film Festival.
+
+Many notable writers have lived or spent extended periods in Colorado. Beat Generation writers Jack Kerouac and Neal Cassady lived in and around Denver for several years each. Irish playwright Oscar Wilde visited Colorado on his tour of the United States in 1882, writing in his 1906 Impressions of America that Leadville was "the richest city in the world.  It has also got the reputation of being the roughest, and every man carries a revolver."
+
+Cuisine
+
+Colorado is known for its Southwest and Rocky Mountain cuisine, with Mexican restaurants found throughout the state.
+
+Boulder was named America's Foodiest Town 2010 by Bon Appétit. Boulder, and Colorado in general, is home to several national food and beverage companies, top-tier restaurants and farmers' markets. Boulder also has more Master Sommeliers per capita than any other city, including San Francisco and New York. Denver is known for steak, but now has a diverse culinary scene with many restaurants.
+
+Polidori Sausage is a brand of pork products available in supermarkets, which originated in Colorado, in the early 20th century.
+
+The Food & Wine Classic is held annually each June in Aspen. Aspen also has a reputation as the culinary capital of the Rocky Mountain region.
+
+Wine and beer
+
+Colorado wines include award-winning varietals that have attracted favorable notice from outside the state. With wines made from traditional Vitis vinifera grapes along with wines made from cherries, peaches, plums, and honey, Colorado wines have won top national and international awards for their quality. Colorado's grape growing regions contain the highest elevation vineyards in the United States, with most viticulture in the state practiced between  above sea level. The mountain climate ensures warm summer days and cool nights. Colorado is home to two designated American Viticultural Areas of the Grand Valley AVA and the West Elks AVA, where most of the vineyards in the state are located. However, an increasing number of wineries are located along the Front Range. In 2018, Wine Enthusiast Magazine named Colorado's Grand Valley AVA in Mesa County, Colorado, as one of the Top Ten wine travel destinations in the world.
+
+Colorado is home to many nationally praised microbreweries, including New Belgium Brewing Company, Odell Brewing Company, Great Divide Brewing Company, and Bristol Brewing Company. The area of northern Colorado near and between the cities of Denver, Boulder, and Fort Collins is known as the "Napa Valley of Beer" due to its high density of craft breweries.
+
+Marijuana and hemp
+
+Colorado is open to cannabis (marijuana) tourism. With the adoption of the 64th state amendment in 2012, Colorado became the first state in the union to legalize marijuana for medicinal (2000), industrial (referring to hemp, 2012), and recreational (2012) use. Colorado's marijuana industry sold $1.31 billion worth of marijuana in 2016 and $1.26 billion in the first three-quarters of 2017. The state generated tax, fee, and license revenue of $194 million in 2016 on legal marijuana sales. Colorado regulates hemp as any part of the plant with less than 0.3% THC.
+
+On April 4, 2014, Senate Bill 14–184 addressing oversight of Colorado's industrial hemp program was first introduced, ultimately being signed into law by Governor John Hickenlooper on May 31, 2014.
+
+Medicinal use
+
+On November 7, 2000, 54% of Colorado voters passed Amendment 20, which amends the Colorado State constitution to allow the medical use of marijuana. A patient's medical use of marijuana, within the following limits, is lawful:
+ (I) No more than  of a usable form of marijuana; and
+ (II) No more than twelve marijuana plants, with six or fewer being mature, flowering plants that are producing a usable form of marijuana.
+Currently, Colorado has listed "eight medical conditions for which patients can use marijuana—cancer, glaucoma, HIV/AIDS, muscle spasms, seizures, severe pain, severe nausea and cachexia, or dramatic weight loss and muscle atrophy". While governor, John Hickenlooper allocated about half of the state's $13 million "Medical Marijuana Program Cash Fund" to medical research in the 2014 budget. By 2018, the Medical Marijuana Program Cash Fund was the "largest pool of pot money in the state" and was used to fund programs including research into pediatric applications for controlling autism symptoms.
+
+Recreational use
+
+On November 6, 2012, voters amended the state constitution to protect "personal use" of marijuana for adults, establishing a framework to regulate marijuana in a manner similar to alcohol. The first recreational marijuana shops in Colorado, and by extension the United States, opened their doors on January 1, 2014.
+
+Sports
+
+Colorado has five major professional sports leagues, all based in the Denver metropolitan area. Colorado is the least populous state with a franchise in each of the major professional sports leagues.
+
+The Colorado Springs Snow Sox professional baseball team is based in Colorado Springs. The team is a member of the Pecos League, an independent baseball league which is not affiliated with Major or Minor League Baseball.
+
+The Pikes Peak International Hill Climb is a major hill climbing motor race held on the Pikes Peak Highway.
+
+The Cherry Hills Country Club has hosted several professional golf tournaments, including the U.S. Open, U.S. Senior Open, U.S. Women's Open, PGA Championship and BMW Championship.
+
+Professional sports teams
+
+College athletics
+
+The following universities and colleges participate in the National Collegiate Athletic Association Division I. The most popular college sports program is the University of Colorado Buffaloes, who used to play in the Big-12 but now play in the Pac-12. They have won the 1957 and 1991 Orange Bowl, 1995 Fiesta Bowl, and 1996 Cotton Bowl Classic.
+
+Transportation
+
+Colorado's primary mode of transportation (in terms of passengers) is its highway system. Interstate 25 (I-25) is the primary north–south highway in the state, connecting Pueblo, Colorado Springs, Denver, and Fort Collins, and extending north to Wyoming and south to New Mexico. I-70 is the primary east–west corridor. It connects Grand Junction and the mountain communities with Denver and enters Utah and Kansas. The state is home to a network of US and Colorado highways that provide access to all principal areas of the state. Many smaller communities are connected to this network only via county roads.
+
+Denver International Airport (DIA) is the third-busiest domestic U.S. and international airport in the world by passenger traffic. DIA handles by far the largest volume of commercial air traffic in Colorado and is the busiest U.S. hub airport between Chicago and the Pacific coast, making Denver the most important airport for connecting passenger traffic in the western United States.
+
+Public transportation bus services are offered both intra-city and inter-city—including the Denver metro area's RTD services. The Regional Transportation District (RTD) operates the popular RTD Bus & Rail transit system in the Denver Metropolitan Area.  the RTD rail system had 170 light-rail vehicles, serving  of track. In addition to local public transit, intercity bus service is provided by Burlington Trailways, Bustang, Express Arrow, and Greyhound Lines.
+
+Amtrak operates two passenger rail lines in Colorado, the California Zephyr and Southwest Chief. Colorado's contribution to world railroad history was forged principally by the Denver and Rio Grande Western Railroad which began in 1870 and wrote the book on mountain railroading. In 1988 the "Rio Grande" was acquired, but was merged into, the Southern Pacific Railroad by their joint owner Philip Anschutz. On September 11, 1996, Anschutz sold the combined company to the Union Pacific Railroad, creating the largest railroad network in the United States. The Anschutz sale was partly in response to the earlier merger of Burlington Northern and Santa Fe which formed the large Burlington Northern and Santa Fe Railway (BNSF), Union Pacific's principal competitor in western U.S. railroading. Both Union Pacific and BNSF have extensive freight operations in Colorado.
+
+Colorado's freight railroad network consists of 2,688 miles of Class I trackage. It is integral to the U.S. economy, being a critical artery for the movement of energy, agriculture, mining, and industrial commodities as well as general freight and manufactured products between the East and Midwest and the Pacific coast states.
+
+In August 2014, Colorado began to issue driver licenses to aliens not lawfully in the United States who lived in Colorado. In September 2014, KCNC reported that 524 non-citizens were issued Colorado driver licenses that are normally issued to U.S. citizens living in Colorado.
+
+Education
+
+The first institution of higher education in the Colorado Territory was the Colorado Seminary, opened on November 16, 1864, by the Methodist Episcopal Church. The seminary closed in 1867 but reopened in 1880 as the University of Denver. In 1870, the Bishop George Maxwell Randall of the Episcopal Church's Missionary District of Colorado and Parts Adjacent opened the first of what become the Colorado University Schools which would include the Territorial School of Mines opened in 1873 and sold to the Colorado Territory in 1874. These schools were initially run by the Episcopal Church. An 1861 territorial act called for the creation of a public university in Boulder, though it would not be until 1876 that the University of Colorado was founded. The 1876 act also renamed Territorial School of Mines as the Colorado School of Mines. An 1870 territorial act created the Agricultural College of Colorado which opened in 1879. The college was renamed the Colorado State College of Agriculture and Mechanic Arts in 1935, and became Colorado State University in 1957.
+
+The first Catholic college in Colorado was the Jesuit Sacred Heart College, which was founded in New Mexico in 1877, moved to Morrison in 1884, and to Denver in 1887. The college was renamed Regis College in 1921 and Regis University in 1991. On April 1, 1924, armed students patrolled the campus after a burning cross was found, the climax of tensions between Regis College and the locally-powerful Ku Klux Klan.
+
+Following a 1950 assessment by the Service Academy Board, it was determined that there was a need to supplement the U.S. Military and Naval Academies with a third school that would provide commissioned officers for the newly independent Air Force. On April 1, 1954, President Dwight Eisenhower signed a law that moved for the creation of a U.S. Air Force Academy. Later that year, Colorado Springs was selected to host the new institution. From its establishment in 1955, until the construction of appropriate facilities in Colorado Springs was completed and opened in 1958, the Air Force Academy operated out of Lowry Air Force Base in Denver. With the opening of the Colorado Springs facility, the cadets moved to the new campus, though not in the full-kit march that some urban and campus legends suggest. The first class of Space Force officers from the Air Force Academy commissioned on April 18, 2020.
+
+Military installations
+
+The major military installations in Colorado include:
+ Buckley Space Force Base (1938–)
+ Air Reserve Personnel Center (1953–)
+ Fort Carson (U.S. Army 1942–) 
+ Piñon Canyon Maneuver Site (1983–)
+ Peterson Space Force Base (1942–)
+ Cheyenne Mountain Space Force Station (1961–)
+ Pueblo Chemical Depot (U.S. Army 1942–)
+ Schriever Space Force Base (1983–)
+ United States Air Force Academy (1954–)
+Former military posts in Colorado include:
+ Spanish Fort (Spanish Army 1819–1821)
+ Fort Massachusetts (U.S. Army 1852–1858)
+ Fort Garland (U.S. Army 1858–1883)
+ Camp Collins (U.S. Army 1862–1870)
+ Fort Logan (U.S. Army 1887–1946)
+ Colorado National Guard Armory (1913–1933)
+ Fitzsimons Army Hospital (U.S. Army 1918–1999)
+ Denver Medical Depot (U.S. Army 1925–1949)
+ Lowry Air Force Base (1938–1994)
+ Pueblo Army Air Base (1941-1948)
+ Rocky Mountain Arsenal (U.S. Army 1942–1992)
+ Camp Hale (U.S. Army 1942–1945)
+ La Junta Army Air Field (1942–1946)
+ Leadville Army Air Field (1943–1944)
+
+Government
+
+State government
+
+Like the federal government and all other U.S. states, Colorado's state constitution provides for three branches of government: the legislative, the executive, and the judicial branches.
+
+The Governor of Colorado heads the state's executive branch. The current governor is Jared Polis, a Democrat. Colorado's other statewide elected executive officers are the Lieutenant Governor of Colorado (elected on a ticket with the Governor), Secretary of State of Colorado, Colorado State Treasurer, and Attorney General of Colorado, all of whom serve four-year terms.
+
+The seven-member Colorado Supreme Court is the state's highest court, with seven justices. The Colorado Court of Appeals, with 22 judges, sits in divisions of three judges each. Colorado is divided into 22 judicial districts, each of which has a district court and a county court with limited jurisdiction. The state also has specialized water courts, which sit in seven distinct divisions around the state and which decide matters relating to water rights and the use and administration of water.
+
+The state legislative body is the Colorado General Assembly, which is made up of two houses – the House of Representatives and the Senate. The House has 65 members and the Senate has 35. , the Democratic Party holds a 23 to 12 majority in the Senate and a 46 to 19 majority in the House.
+
+Most Coloradans are native to other states (nearly 60% according to the 2000 census), and this is illustrated by the fact that the state did not have a native-born governor from 1975 (when John David Vanderhoof left office) until 2007, when Bill Ritter took office; his election the previous year marked the first electoral victory for a native-born Coloradan in a gubernatorial race since 1958 (Vanderhoof had ascended from the Lieutenant Governorship when John Arthur Love was given a position in Richard Nixon's administration in 1973).
+
+Tax is collected by the Colorado Department of Revenue.
+
+Politics
+
+Colorado was once considered a swing state, but has become a relatively safe blue state in both state and federal elections. In presidential elections, it had not been won until 2020 by double digits since 1984 and has backed the winning candidate in 9 of the last 11 elections. Coloradans have elected 17 Democrats and 12 Republicans to the governorship in the last 100 years.
+
+In presidential politics, Colorado was considered a reliably Republican state during the post-World War II era, voting for the Democratic candidate only in 1948, 1964, and 1992. However, it became a competitive swing state in the 1990s. Since the mid-2000s, it has swung heavily to the Democrats, voting for Barack Obama in 2008 and 2012, Hillary Clinton in 2016, and Joe Biden in 2020.
+
+Colorado politics exhibits a contrast between conservative cities such as Colorado Springs and Grand Junction, and liberal cities such as Boulder and Denver. Democrats are strongest in metropolitan Denver, the college towns of Fort Collins and Boulder, southern Colorado (including Pueblo), and several western ski resort counties. The Republicans are strongest in the Eastern Plains, Colorado Springs, Greeley, and far Western Colorado near Grand Junction.
+
+Colorado is represented by two members of the United States Senate:
+ Class 2, John Hickenlooper (Democratic), since 2021
+ Class 3, Michael Bennet (Democratic), since 2009
+
+Colorado is represented by eight members of the United States House of Representatives:
+ 1st district: Diana DeGette (Democratic), since 1997
+ 2nd district: Joe Neguse (Democratic), since 2019
+ 3rd district: Lauren Boebert (Republican), since 2021
+ 4th district: Ken Buck (Republican), since 2015
+ 5th district: Doug Lamborn (Republican), since 2007
+ 6th district: Jason Crow (Democratic), since 2019
+ 7th district: Brittany Pettersen (Democratic), since 2023
+ 8th district: Yadira Caraveo (Democratic), since 2023
+
+In a 2020 study, Colorado was ranked as the seventh easiest state for citizens to vote in.
+
+Significant initiatives and legislation enacted in Colorado
+
+In 1881 Colorado voters approved a referendum that selected Denver as the state capital.
+
+Colorado was the first state in the union to enact, by voter referendum, a law extending suffrage to women. That initiative was approved by the state's voters on November 7, 1893.
+
+On the November 8, 1932, ballot, Colorado approved the repeal of alcohol prohibition more than a year before the Twenty-first Amendment to the United States Constitution was ratified.
+
+Colorado has banned, via C.R.S. section 12-6-302, the sale of motor vehicles on Sunday since at least 1953.
+
+In 1972 Colorado voters rejected a referendum proposal to fund the 1976 Winter Olympics, which had been scheduled to be held in the state. Denver had been chosen by the International Olympic Committee as the host city on May 12, 1970.
+
+In 1992, by a margin of 53 to 47 percent, Colorado voters approved an amendment to the state constitution (Amendment 2) that would have prevented any city, town, or county in the state from taking any legislative, executive or judicial action to recognize homosexuals or bisexuals as a protected class. In 1996, in a 6–3 ruling in Romer v. Evans, the U.S. Supreme Court found that preventing protected status based upon homosexuality or bisexuality did not satisfy the Equal Protection Clause.
+
+In 2006, voters passed Amendment 43, which banned gay marriage in Colorado. That initiative was nullified by the U.S. Supreme Court's 2015 decision in Obergefell v. Hodges.
+
+In 2012, voters amended the state constitution protecting the "personal use" of marijuana for adults, establishing a framework to regulate cannabis like alcohol. The first recreational marijuana shops in Colorado, and by extension the United States, opened their doors on January 1, 2014.
+
+On May 29, 2019, Governor Jared Polis signed House Bill 1124 immediately prohibiting law enforcement officials in Colorado from holding undocumented immigrants solely based on a request from U.S. Immigration and Customs Enforcement.
+
+Native American reservations
+The two Native American reservations remaining in Colorado are the Southern Ute Indian Reservation (1873; Ute dialect: Kapuuta-wa Moghwachi Núuchi-u) and Ute Mountain Ute Indian Reservation (1940; Ute dialect: Wʉgama Núuchi). The two abolished Indian reservations in Colorado were the Cheyenne and Arapaho Indian Reservation (1851–1870) and Ute Indian Reservation (1855–1873).
+
+Protected areas
+
+Colorado is home to 4 national parks, 9 national monuments, 3 national historic sites, 2 national recreation areas, 4 national historic trails, 1 national scenic trail, 11 national forests, 2 national grasslands, 44 national wildernesses, 3 national conservation areas, 8 national wildlife refuges, 3 national heritage areas, 26 national historic landmarks, 16 national natural landmarks, more than 1,500 National Register of Historic Places, 1 wild and scenic river, 42 state parks, 307 state wildlife areas, 93 state natural areas, 28 national recreation trails, 6 regional trails, and numerous other scenic, historic, and recreational areas.
+
+See also
+
+Bibliography of Colorado
+Geography of Colorado
+History of Colorado
+Index of Colorado-related articles
+List of Colorado-related lists
+List of ships named the USS Colorado
+Outline of Colorado
+
+Footnotes
+
+References
+
+Further reading
+
+ Explore Colorado, A Naturalist's Handbook, The Denver Museum of Natural History and Westcliff Publishers, 1995,  for an excellent guide to the ecological regions of Colorado.
+ The Archeology of Colorado, Revised Edition, E. Steve Cassells, Johnson Books, Boulder, Colorado, 1997, trade paperback, .
+ Chokecherry Places, Essays from the High Plains, Merrill Gilfillan, Johnson Press, Boulder, Colorado, trade paperback, .
+ 
+ The Tie That Binds, Kent Haruf, 1984, hardcover, , a fictional account of farming in Colorado.
+ Railroads of Colorado: Your Guide to Colorado's Historic Trains and Railway Sites, Claude Wiatrowski, Voyageur Press, 2002, hardcover, 160 pages,
+
+External links
+
+State government
+State of Colorado
+Colorado Tourism Office
+History Colorado
+
+Federal government
+ Energy & Environmental Data for Colorado
+ USGS Colorado state facts, real-time, geographic, and other scientific resources of Colorado
+ United States Census Bureau
+ Colorado QuickFacts
+ 2000 Census of Population and Housing for Colorado
+ USDA ERS Colorado state facts
+ Colorado State Guide, from the Library of Congress
+
+Other
+ List of searchable databases produced by Colorado state agencies hosted by the American Library Association Government Documents Roundtable
+ Colorado County Evolution
+ Ask Colorado
+ Colorado Historic Newspapers Collection (CHNC)
+ Mountain and Desert Plants of Colorado and the Southwest,
+ Climate of Colorado 
+ 
+ 
+ Holocene Volcano in Colorado (Smithsonian Institution Global Volcanism Program) 
+
+ 
+Contiguous United States
+Former Spanish colonies
+Colorado, Territory of
+Colorado, State of
+States of the United States
+Western United States
+1861 establishments in Colorado Territory
+The Carboniferous ( ) is a geologic period and system of the Paleozoic that spans 60 million years from the end of the Devonian Period  million years ago (mya), to the beginning of the Permian Period,  mya. The name Carboniferous means "coal-bearing", from the Latin  ("coal") and  ("bear, carry"), and refers to the many coal beds formed globally during that time.
+
+The first of the modern 'system' names, it was coined by geologists William Conybeare and William Phillips in 1822, based on a study of the British rock succession. The Carboniferous is often treated in North America as two geological periods, the earlier Mississippian and the later Pennsylvanian.
+
+Terrestrial animal life was well established by the Carboniferous Period. Tetrapods (four limbed vertebrates), which had originated from lobe-finned fish during the preceding Devonian, became pentadactylous in and diversified during the Carboniferous, including early amphibian lineages such as temnospondyls, with the first appearance of amniotes, including synapsids (the group to which modern mammals belong) and reptiles during the late Carboniferous. The period is sometimes called the Age of Amphibians, during which amphibians became dominant land vertebrates and diversified into many forms including lizard-like, snake-like, and crocodile-like.
+
+Insects underwent a major radiation during the late Carboniferous. Vast swaths of forest covered the land, which eventually fell and became the coal beds characteristic of the Carboniferous stratigraphy evident today.
+
+The later half of the period experienced glaciations, low sea level, and mountain building as the continents collided to form Pangaea. A minor marine and terrestrial extinction event, the Carboniferous rainforest collapse, occurred at the end of the period, caused by climate change.
+
+Etymology and history 
+The term "Carboniferous" had first been used as an adjective by Irish geologist Richard Kirwan in 1799, and later used in a heading entitled "Coal-measures or Carboniferous Strata" by John Farey Sr. in 1811, becoming an informal term referring to coal-bearing sequences in Britain and elsewhere in Western Europe. Four units were originally ascribed to the Carboniferous, in ascending order, the Old Red Sandstone, Carboniferous Limestone, Millstone Grit and the Coal Measures. These four units were placed into a formalised Carboniferous unit by William Conybeare and William Phillips in 1822, and later into the Carboniferous System by Phillips in 1835. The Old Red Sandstone was later considered Devonian in age. Subsequently, separate stratigraphic schemes were developed in Western Europe, North America, and Russia. The first attempt to build an international timescale for the Carboniferous was during the Eighth International Congress on Carboniferous Stratigraphy and Geology in Moscow in 1975, when all of the modern ICS stages were proposed.
+
+Stratigraphy 
+The Carboniferous is divided into two subsystems, the lower Mississippian and upper Pennsylvanian, which are sometimes treated as separate geological periods in North American stratigraphy.
+
+Stages can be defined globally or regionally. For global stratigraphic correlation, the International Commission on Stratigraphy (ICS) ratify global stages based on a Global Boundary Stratotype Section and Point (GSSP) from a single formation (a stratotype) identifying the lower boundary of the stage. The ICS subdivisions from youngest to oldest are as follows:
+
+ICS units 
+The Mississippian was first proposed by Alexander Winchell, and the Pennsylvanian was proposed by J. J. Stevenson in 1888, and both were proposed as distinct and independent systems by H. S. Williams in 1881.
+
+The Tournaisian was named after the Belgian city of Tournai. It was introduced in scientific literature by Belgian geologist André Hubert Dumont in 1832. The GSSP for the base of the Tournaisian is located at the La Serre section in Montagne Noire, southern France. It is defined by the first appearance datum of the conodont Siphonodella sulcata, which was ratified in 1990. However, the GSSP was later shown to have issues, with Siphonodella sulcata being shown to occur 0.45 m below the proposed boundary.
+
+The Viséan Stage was introduced by André Dumont in 1832. Dumont named this stage after the city of Visé in Belgium's Liège Province. The GSSP for the Visean is located in Bed 83 at the Pengchong section, Guangxi, southern China, which was ratified in 2012. The GSSP for the base of the Viséan is the first appearance datum of fusulinid (an extinct group of forams) Eoparastaffella simplex.
+
+The Serpukhovian Stage was proposed in 1890 by Russian stratigrapher Sergei Nikitin. It is named after the city of Serpukhov, near Moscow. The Serpukhovian Stage currently lacks a defined GSSP. The proposed definition for the base of the Serpukhovian is the first appearance of conodont Lochriea ziegleri.
+
+The Bashkirian was named after Bashkiria, the then Russian name of the republic of Bashkortostan in the southern Ural Mountains of Russia. The stage was introduced by Russian stratigrapher Sofia Semikhatova in 1934. The GSSP for the base of the Bashkirian is located at Arrow Canyon in Nevada, US, which was ratified in 1996. The GSSP for the base of the Bashkirian is defined by the first appearance of the conodont Declinognathodus noduliferus.
+
+The Moscovian is named after Moscow, Russia, and was first introduced by Sergei Nikitin in 1890. The Moscovian currently lacks a defined GSSP.
+
+The Kasimovian is named after the Russian city of Kasimov, and originally included as part of Nikitin's original 1890 definition of the Moscovian. It was first recognised as a distinct unit by A.P. Ivanov in 1926, who named it the "Tiguliferina" Horizon after a kind of brachiopod. The Kasimovian currently lacks a defined GSSP.
+
+The Gzhelian is named after the Russian village of Gzhel (), nearby Ramenskoye, not far from Moscow. The name and type locality were defined by Sergei Nikitin in 1890. The base of the Gzhelian currently lacks a defined GSSP.
+
+The GSSP for the base of the Permian is located in the Aidaralash River valley near Aqtöbe, Kazakhstan, which was ratified in 1996. The beginning of the stage is defined by the first appearance of the conodont Streptognathodus postfusus.
+
+Regional stratigraphy
+
+North America 
+
+In North American stratigraphy, the Mississippian is divided, in ascending order, into the Kinderhookian, Osagean, Meramecian and Chesterian series, while the Pennsylvanian is divided into the Morrowan, Atokan, Desmoinesian, Missourian and Virgilian series.
+
+The Kinderhookian is named after the village of Kinderhook, Pike County, Illinois. It corresponds to the lower part of the Tournasian.
+
+The Osagean is named after the Osage River in St. Clair County, Missouri. It corresponds to the upper part of the Tournaisian and the lower part of the Viséan.
+
+The Meramecian is named after the Meramec Highlands Quarry, located the near the Meramec River, southwest of St. Louis, Missouri. It corresponds to the mid Viséan.
+
+The Chesterian is named after the Chester Group, a sequence of rocks named after the town of Chester, Illinois. It corresponds to the upper Viséan and all of the Serpukhovian.
+
+The Morrowan is named after the Morrow Formation located in NW Arkansas, it corresponds to the lower Bashkirian.
+
+The Atokan was originally a formation named after the town of Atoka in southwestern Oklahoma. It corresponds to the upper Bashkirian and lower Moscovian
+
+The Desmoinesian is named after the Des Moines Formation found near the Des Moines River in central Iowa. It corresponds to the middle and upper Moscovian and lower Kasimovian.
+
+The Missourian was named at the same time as the Desmoinesian. It corresponds to the middle and upper Kasimovian.
+
+The Virgilian is named after the town of Virgil, Kansas, it corresponds to the Gzhelian.
+
+Europe 
+The European Carboniferous is divided into the lower Dinantian and upper Silesian, the former being named for the Belgian city of Dinant, and the latter for the Silesia region of Central Europe. The boundary between the two subdivisions is older than the Mississippian-Pennsylvanian boundary, lying within the lower Serpukhovian. The boundary has traditionally been marked by the first appearance of the ammonoid Cravenoceras leion. In Europe, the Dinantian is primarily marine, the so-called "Carboniferous Limestone", while the Silesian is known primarily for its coal measures.
+
+The Dinantian is divided up into two stages, the Tournaisian and Viséan. The Tournaisian is the same length as the ICS stage, but the Viséan is longer, extending into the lower Serpukhovian.
+
+The Silesian is divided into three stages, in ascending order, the Namurian, Westphalian, Stephanian. The Autunian, which corresponds to the middle and upper Gzhelian, is considered a part of the overlying Rotliegend.
+
+The Namurian is named after the city of Namur in Belgium. It corresponds to the middle and upper Serpukhovian and the lower Bashkirian.
+
+The Westphalian is named after the region of Westphalia in Germany it corresponds to the upper Bashkirian and all but the uppermost Moscovian.
+
+The Stephanian is named after the city of Saint-Étienne in eastern France. It corresponds to the uppermost Moscovian, the Kasimovian, and the lower Gzhelian.
+
+Palaeogeography
+A global drop in sea level at the end of the Devonian reversed early in the Carboniferous; this created the widespread inland seas and the carbonate deposition of the Mississippian. There was also a drop in south polar temperatures; southern Gondwanaland was glaciated for much of the period, though it is uncertain if the ice sheets were a holdover from the Devonian or not. These conditions apparently had little effect in the deep tropics, where lush swamps, later to become coal, flourished to within 30 degrees of the northernmost glaciers.
+
+Mid-Carboniferous, a drop in sea level precipitated a major marine extinction, one that hit crinoids and ammonites especially hard. This sea level drop and the associated unconformity in North America separate the Mississippian Subperiod from the Pennsylvanian Subperiod. This happened about 323 million years ago, at the onset of the Permo-Carboniferous Glaciation.
+
+The Carboniferous was a time of active mountain-building as the supercontinent Pangaea came together. The southern continents remained tied together in the supercontinent Gondwana, which collided with North America–Europe (Laurussia) along the present line of eastern North America. This continental collision resulted in the Hercynian orogeny in Europe, and the Alleghenian orogeny in North America; it also extended the newly uplifted Appalachians southwestward as the Ouachita Mountains. In the same time frame, much of present eastern Eurasian plate welded itself to Europe along the line of the Ural Mountains. Most of the Mesozoic supercontinent of Pangea was now assembled, although North China (which collided in the Latest Carboniferous), and South China continents were still separated from Laurasia. The Late Carboniferous Pangaea was shaped like an "O".
+
+There were two major oceans in the Carboniferous: Panthalassa and Paleo-Tethys, which was inside the "O" in the Carboniferous Pangaea. Other minor oceans were shrinking and eventually closed: the Rheic Ocean (closed by the assembly of South and North America), the small, shallow Ural Ocean (which was closed by the collision of Baltica and Siberia continents, creating the Ural Mountains), and the Proto-Tethys Ocean (closed by North China collision with Siberia/Kazakhstania). In the Late Carboniferous, a shallow epicontinental sea covered a significant part of what is today northwestern Europe.
+
+Climate
+
+Average global temperatures in the Early Carboniferous Period were high: approximately 20 °C (68 °F). However, cooling during the Middle Carboniferous reduced average global temperatures to about 12 °C (54 °F). Atmospheric carbon dioxide levels fell during the Carboniferous Period from roughly 8 times the current level in the beginning, to a level similar to today's at the end. The Carboniferous is considered part of the Late Palaeozoic Ice Age, which began in the latest Devonian with the formation of small glaciers in Gondwana. During the Tournaisian the climate warmed, before cooling, there was another warm interval during the Viséan, but cooling began again during the early Serpukhovian. At the beginning of the Pennsylvanian around 323 million years ago, glaciers began to form around the South Pole, which grew to cover a vast area of Gondwana. This area extended from the southern reaches of the Amazon basin and covered large areas of southern Africa, as well as most of Australia and Antarctica. Cyclothems, which began around 313 million years ago, and continue into the following Permian indicate that the size of the glaciers were controlled by Milankovitch cycles akin to recent ice ages, with glacial periods and interglacials. Deep ocean temperatures during this time were cold due to the influx of cold bottom waters generated by seasonal melting of the ice cap.
+
+The cooling and drying of the climate led to the Carboniferous Rainforest Collapse (CRC) during the late Carboniferous. Tropical rainforests fragmented and then were eventually devastated by climate change.
+
+Rocks and coal
+
+Carboniferous rocks in Europe and eastern North America largely consist of a repeated sequence of limestone, sandstone, shale and coal beds. In North America, the early Carboniferous is largely marine limestone, which accounts for the division of the Carboniferous into two periods in North American schemes. The Carboniferous coal beds provided much of the fuel for power generation during the Industrial Revolution and are still of great economic importance.
+
+The large coal deposits of the Carboniferous may owe their existence primarily to two factors. The first of these is the appearance of wood tissue and bark-bearing trees. The evolution of the wood fiber lignin and the bark-sealing, waxy substance suberin variously opposed decay organisms so effectively that dead materials accumulated long enough to fossilise on a large scale. The second factor was the lower sea levels that occurred during the Carboniferous as compared to the preceding Devonian Period. This fostered the development of extensive lowland swamps and forests in North America and Europe. Based on a genetic analysis of basidiomycetes, it was proposed that large quantities of wood were buried during this period because animals and decomposing bacteria and fungi had not yet evolved enzymes that could effectively digest the resistant phenolic lignin polymers and waxy suberin polymers. They suggest that fungi that could break those substances down effectively became dominant only towards the end of the period, making subsequent coal formation much rarer. The delayed fungal evolution hypothesis has been challenged by other researchers, who conclude that tectonic and climatic conditions during the formation of Pangaea, which created water filled basins alongside developing mountain ranges, resulted in the development of widespread humid, tropical conditions and the burial of massive quantities of organic matter, were responsible for the high rate of coal formation, with large amounts of coal also being formed during the Mesozoic and Cenozoic well after lignin digesting fungi had become well established, and that fungal degredation of lignin had likely already evolved by the end of the Devonian, even if the specific enzymes used by basidiomycetes had not.
+
+Although it is often asserted that Carboniferous atmospheric oxygen concentrations were signficiantly higher than today, at around 30% of total atmospheric concentration, prehistoric atmospheric oxygen concentration estimates are highly uncertain, with other estimates suggesting that the amount of oxygen was actually lower than that present in todays atmosphere.
+
+In eastern North America, marine beds are more common in the older part of the period than the later part and are almost entirely absent by the late Carboniferous. More diverse geology existed elsewhere, of course. Marine life is especially rich in crinoids and other echinoderms. Brachiopods were abundant. Trilobites became quite uncommon. On land, large and diverse plant populations existed. Land vertebrates included large amphibians.
+
+Life
+
+Plants
+
+Early Carboniferous land plants, some of which were preserved in coal balls, were very similar to those of the preceding Late Devonian, but new groups also appeared at this time.
+The main Early Carboniferous plants were the Equisetales (horse-tails), Sphenophyllales (scrambling plants), Lycopodiales (club mosses), Lepidodendrales (scale trees), Filicales (ferns), Medullosales (informally included in the "seed ferns", an assemblage of a number of early gymnosperm groups) and the Cordaitales. These continued to dominate throughout the period, but during late Carboniferous, several other groups, Cycadophyta (cycads), the Callistophytales (another group of "seed ferns"), and the Voltziales, appeared.
+
+The Carboniferous lycophytes of the order Lepidodendrales, which are cousins (but not ancestors) of the tiny club-moss of today, were huge trees with trunks 30 meters high and up to 1.5 meters in diameter. These included Lepidodendron (with its cone called Lepidostrobus), Anabathra, Lepidophloios and Sigillaria. The roots of several of these forms are known as Stigmaria. Unlike present-day trees, their secondary growth took place in the cortex, which also provided stability, instead of the xylem. The Cladoxylopsids were large trees, that were ancestors of ferns, first arising in the Carboniferous.
+
+The fronds of some Carboniferous ferns are almost identical with those of living species. Probably many species were epiphytic. Fossil ferns and "seed ferns" include Pecopteris, Cyclopteris, Neuropteris, Alethopteris, and Sphenopteris; Megaphyton and Caulopteris were tree ferns.
+
+The Equisetales included the common giant form Calamites, with a trunk diameter of 30 to  and a height of up to . Sphenophyllum was a slender climbing plant with whorls of leaves, which was probably related both to the calamites and the lycopods.
+
+Cordaites, a tall plant (6 to over 30 meters) with strap-like leaves, was related to the cycads and conifers; the catkin-like reproductive organs, which bore ovules/seeds, is called Cardiocarpus. These plants were thought to live in swamps. True coniferous trees (Walchia, of the order Voltziales) appear later in the Carboniferous, and preferred higher drier ground.
+
+Marine invertebrates
+In the oceans the marine invertebrate groups are the Foraminifera, corals, Bryozoa, Ostracoda, brachiopods, ammonoids, hederelloids, microconchids and echinoderms (especially crinoids). The diversity of brachiopods and fusilinid foraminiferans, surged beginning in the Visean, continuing through the end of the Carboniferous, although cephalopod and nektonic conodont diversity declined. This evolutionary radiation was known as the Carboniferous-Earliest Permian Biodiversification Event. For the first time foraminifera take a prominent part in the marine faunas. The large spindle-shaped genus Fusulina and its relatives were abundant in what is now Russia, China, Japan, North America; other important genera include Valvulina, Endothyra, Archaediscus, and Saccammina (the latter common in Britain and Belgium). Some Carboniferous genera are still extant. The first true priapulids appeared during this period.
+
+The microscopic shells of radiolarians are found in cherts of this age in the Culm of Devon and Cornwall, and in Russia, Germany and elsewhere. Sponges are known from spicules and anchor ropes, and include various forms such as the Calcispongea Cotyliscus and Girtycoelia, the demosponge Chaetetes, and the genus of unusual colonial glass sponges Titusvillia.
+
+Both reef-building and solitary corals diversify and flourish; these include both rugose (for example, Caninia, Corwenia, Neozaphrentis), heterocorals, and tabulate (for example, Chladochonus, Michelinia) forms. Conularids were well represented by Conularia
+
+Bryozoa are abundant in some regions; the fenestellids including Fenestella, Polypora, and Archimedes, so named because it is in the shape of an Archimedean screw. Brachiopods are also abundant; they include productids, some of which  reached very large for brachiopods size and had very thick shells (for example, the -wide Gigantoproductus), while others like Chonetes were more conservative in form. Athyridids, spiriferids, rhynchonellids, and terebratulids are also very common. Inarticulate forms include Discina and Crania. Some species and genera had a very wide distribution with only minor variations.
+
+Annelids such as Serpulites are common fossils in some horizons. Among the mollusca, the bivalves continue to increase in numbers and importance. Typical genera include Aviculopecten, Posidonomya, Nucula, Carbonicola, Edmondia, and Modiola. Gastropods are also numerous, including the genera Murchisonia, Euomphalus, Naticopsis. Nautiloid cephalopods are represented by tightly coiled nautilids, with straight-shelled and curved-shelled forms becoming increasingly rare. Goniatite ammonoids such as Aenigmatoceras are common.
+
+Trilobites are rarer than in previous periods, on a steady trend towards extinction, represented only by the proetid group. Ostracoda, a class of crustaceans, were abundant as representatives of the meiobenthos; genera included Amphissites, Bairdia, Beyrichiopsis, Cavellina, Coryellina, Cribroconcha, Hollinella, Kirkbya, Knoxiella, and Libumella.
+
+Crinoids were highly numerous during the Carboniferous, though they suffered a gradual decline in diversity during the middle Mississippian. Dense submarine thickets of long-stemmed crinoids appear to have flourished in shallow seas, and their remains were consolidated into thick beds of rock. Prominent genera include Cyathocrinus, Woodocrinus, and Actinocrinus. Echinoids such as Archaeocidaris and Palaeechinus were also present. The blastoids, which included the Pentreinitidae and Codasteridae and superficially resembled crinoids in the possession of long stalks attached to the seabed, attain their maximum development at this time.
+
+Freshwater and lagoonal invertebrates
+Freshwater Carboniferous invertebrates include various bivalve molluscs that lived in brackish or fresh water, such as Anthraconaia, Naiadites, and Carbonicola; diverse crustaceans such as Candona, Carbonita, Darwinula, Estheria, Acanthocaris, Dithyrocaris, and Anthrapalaemon.
+
+The eurypterids were also diverse, and are represented by such genera as Adelophthalmus, Megarachne (originally misinterpreted as a giant spider, hence its name) and the specialised very large Hibbertopterus. Many of these were amphibious.
+
+Frequently a temporary return of marine conditions resulted in marine or brackish water genera such as Lingula, Orbiculoidea, and Productus being found in the thin beds known as marine bands.
+
+Terrestrial invertebrates 
+Fossil remains of air-breathing insects, myriapods and arachnids are known from the Carboniferous. Their diversity when they do appear, however, shows that these arthropods were both well-developed and numerous. Some arthropods grew to large sizes with the up to  millipede-like Arthropleura being the largest-known land invertebrate of all time. Among the insect groups are the huge predatory Protodonata (griffinflies), among which was Meganeura, a giant dragonfly-like insect and with a wingspan of ca. —the largest flying insect ever to roam the planet. Further groups are the Syntonopterodea (relatives of present-day mayflies), the abundant and often large sap-sucking Palaeodictyopteroidea, the diverse herbivorous Protorthoptera, and numerous basal Dictyoptera (ancestors of cockroaches).  Many insects have been obtained from the coalfields of Saarbrücken and Commentry, and from the hollow trunks of fossil trees in Nova Scotia. Some British coalfields have yielded good specimens: Archaeoptilus, from the Derbyshire coalfield, had a large wing with  preserved part, and some specimens (Brodia) still exhibit traces of brilliant wing colors. In the Nova Scotian tree trunks land snails (Archaeozonites, Dendropupa) have been found.
+
+Fish
+Many fish inhabited the Carboniferous seas; predominantly Elasmobranchs (sharks and their relatives). These included some, like Psammodus, with crushing pavement-like teeth adapted for grinding the shells of brachiopods, crustaceans, and other marine organisms. Other groups of elasmobranchs, like the ctenacanthiformes grew to large sizes, with some genera like Saivodus reaching around 6-9 meters (20-30 feet). Other fish had piercing teeth, such as the Symmoriida; some, the petalodonts, had peculiar cycloid cutting teeth. Most of the other cartilaginous fish were marine, but others like the Xenacanthida, and several genera like Bandringa invaded fresh waters of the coal swamps. Among the bony fish, the Palaeonisciformes found in coastal waters also appear to have migrated to rivers. Sarcopterygian fish were also prominent, and one group, the Rhizodonts, reached very large size.
+
+Most species of Carboniferous marine fish have been described largely from teeth, fin spines and dermal ossicles, with smaller freshwater fish preserved whole.
+
+Freshwater fish were abundant, and include the genera Ctenodus, Uronemus, Acanthodes, Cheirodus, and Gyracanthus.
+
+Chondrichthyes  (especially holocephalans like the Stethacanthids) underwent a major evolutionary radiation during the Carboniferous. It is believed that this evolutionary radiation occurred because the decline of the placoderms at the end of the Devonian Period caused many environmental niches to become unoccupied and allowed new organisms to evolve and fill these niches. As a result of the evolutionary radiation Carboniferous holocephalans assumed a wide variety of bizarre shapes including Stethacanthus which possessed a flat brush-like dorsal fin with a patch of denticles on its top. Stethacanthus unusual fin may have been used in mating rituals. Other groups like the eugeneodonts filled in the niches left by large predatory placoderms. These fish were unique as they only possessed one row of teeth in their upper or lower jaws in the form of elaborate tooth whorls. The first members of the helicoprionidae, a family eugeneodonts that were characterized by the presence of one circular tooth whorl in the lower jaw, appeared during the lower Carboniferous. Perhaps the most bizarre radiation of holocephalans at this time was that of the iniopterygiformes, an order of holocephalans that greatly resembled modern day flying fish that could have also "flown" in the water with their massive, elongated pectoral fins. They were further characterized by their large eye sockets, club-like structures on their tails, and spines on the tips of their fins.
+
+Tetrapods
+Carboniferous amphibians were diverse and common by the middle of the period, more so than they are today; some were as long as 6 meters, and those fully terrestrial as adults had scaly skin. They included a number of basal tetrapod groups classified in early books under the Labyrinthodontia. These had long bodies, a head covered with bony plates and generally weak or undeveloped limbs. The largest were over 2 meters long. They were accompanied by an assemblage of smaller amphibians included under the Lepospondyli, often only about  long. Some Carboniferous amphibians were aquatic and lived in rivers (Loxomma, Eogyrinus, Proterogyrinus); others may have been semi-aquatic (Ophiderpeton, Amphibamus, Hyloplesion) or terrestrial (Dendrerpeton, Tuditanus, Anthracosaurus).
+
+The Carboniferous Rainforest Collapse slowed the evolution of amphibians who could not survive as well in the cooler, drier conditions. Amniotes, however, prospered due to specific key adaptations. One of the greatest evolutionary innovations of the Carboniferous was the amniote egg, which allowed the laying of eggs in a dry environment, as well as keratinized scales and claws, allowing for the further exploitation of the land by certain tetrapods. These included the earliest sauropsid reptiles (Hylonomus), and the earliest known synapsid (Archaeothyris). Synapsids quickly became huge and diversified in the Permian, only for their dominance to stop during the Mesozoic Era. Sauropsids (reptiles, and also, later, birds) also diversified but remained small until the Mesozoic, during which they dominated the land, as well as the water and sky, only for their dominance to stop during the Cenozoic Era.
+
+Reptiles underwent a major evolutionary radiation in response to the drier climate that preceded the rainforest collapse. By the end of the Carboniferous Period, amniotes had already diversified into a number of groups, including several families of synapsid pelycosaurs, protorothyridids, captorhinids, saurians and araeoscelids.
+
+Fungi
+As plants and animals were growing in size and abundance in this time (for example, Lepidodendron), land fungi diversified further. Marine fungi still occupied the oceans. All modern classes of fungi were present in the Late Carboniferous (Pennsylvanian Epoch).
+
+During the Carboniferous, animals and bacteria had great difficulty with processing the lignin and cellulose that made up the gigantic trees of the period. Microbes had not evolved that could process them. The trees, after they died, simply piled up on the ground, occasionally becoming part of long-running wildfires after a lightning strike, with others very slowly degrading into coal. White rot fungus were the first organisms to be able to process these and break them down in any reasonable quantity and timescale. Thus, some have proposed that fungi helped end the Carboniferous Period, stopping accumulation of undegraded plant matter, although this idea remains highly controversial.
+
+Extinction events
+
+Romer's gap
+
+The first 15 million years of the Carboniferous had very limited terrestrial fossils. This gap in the fossil record is called Romer's gap after the American palaentologist Alfred Romer. While it has long been debated whether the gap is a result of fossilisation or relates to an actual event, recent work indicates the gap period saw a drop in atmospheric oxygen levels, indicating some sort of ecological collapse. The gap saw the demise of the Devonian fish-like ichthyostegalian labyrinthodonts, and the rise of the more advanced temnospondyl and reptiliomorphan amphibians that so typify the Carboniferous terrestrial vertebrate fauna.
+
+Carboniferous rainforest collapse
+
+Before the end of the Carboniferous Period, an extinction event occurred. On land this event is referred to as the Carboniferous Rainforest Collapse (CRC). Vast tropical rainforests collapsed suddenly as the climate changed from hot and humid to cool and arid. This was likely caused by intense glaciation and a drop in sea levels.
+
+The new climatic conditions were not favorable to the growth of rainforest and the animals within them. Rainforests shrank into isolated islands, surrounded by seasonally dry habitats. Towering lycopsid forests with a heterogeneous mixture of vegetation were replaced by much less diverse tree-fern dominated flora.
+ 
+Amphibians, the dominant vertebrates at the time, fared poorly through this event with large losses in biodiversity; reptiles continued to diversify due to key adaptations that let them survive in the drier habitat, specifically the hard-shelled egg and scales, both of which retain water better than their amphibian counterparts.
+
+See also
+ List of Carboniferous tetrapods
+ Carboniferous rainforest collapse
+ Important Carboniferous Lagerstätten
+ Granton Shrimp Bed; 359 mya; Edinburgh, Scotland 
+ East Kirkton Quarry; c. 350 mya; Bathgate, Scotland
+ Bear Gulch Limestone; 324 mya; Montana, US
+ Mazon Creek; 309 mya; Illinois, US
+ Hamilton Quarry; 300 mya; Kansas, US
+ List of fossil sites (with link directory)
+
+References
+
+Sources
+
+ 
+ 
+ 
+
+ 
+ 
+ 
+
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+Rainer Zangerl and Gerard Ramon Case: Iniopterygia: a new order of Chondrichthyan fishes from the Pennsylvanian of North America. Fieldiana Geology Memoirs, v. 6, Field Museum of Natural History, 1973 Biodiversity Heritage Library (Volltext, engl.)
+
+External links
+
+ 
+ Examples of Carboniferous Fossils
+60+ images of Carboniferous Foraminifera
+Carboniferous (Chronostratography scale)
+
+ 
+Geological periods
+The Comoros, officially the Union of the Comoros, is an archipelagic country made up of three islands in Southeastern Africa, located at the northern end of the Mozambique Channel in the Indian Ocean. Its capital and largest city is Moroni. The religion of the majority of the population, and the official state religion, is Sunni Islam. Comoros proclaimed its independence from France on 6 July 1975. A member of the Arab League, it is the only country in the Arab world which is entirely in the Southern Hemisphere. It is a member state of the African Union, the Organisation internationale de la Francophonie, the Organisation of Islamic Cooperation, and the Indian Ocean Commission. The country has three official languages: Shikomori, French and Arabic.
+
+The sovereign state consists of three major islands and numerous smaller islands, all of the volcanic Comoro Islands with the exception of Mayotte. Mayotte voted against independence from France in a referendum in 1974, and continues to be administered by France as an overseas department. France has vetoed United Nations Security Council resolutions that would affirm Comorian sovereignty over the island. Mayotte became an overseas department and a region of France in 2011 following a referendum which was passed overwhelmingly.
+
+At , the Comoros is the third-smallest African country by area. In 2019, its population was estimated to be 850,886.
+
+The Comoros were likely first settled by Austronesian/Malagasy peoples, Bantu speakers from East Africa, and seafaring Arab traders. It became part of the French colonial empire during the 19th century, before its independence in 1975. It has experienced more than 20 coups or attempted coups, with various heads of state assassinated. Along with this constant political instability, it has one of the worst levels of income inequality of any nation, and ranks in the lowest quartile on the Human Development Index. , about half the population lived below the international poverty line of US$1.25 a day.
+
+Etymology 
+The name "Comoros" derives from the Arabic word  qamar ("moon").
+
+History
+
+Settlement 
+
+According to mythology, a jinni (spirit) dropped a jewel, which formed a great circular inferno. This became the Karthala volcano, which created the island of Ngazidja (Grande Comore). King Solomon is also said to have visited the island accompanied by his queen Bilqis.
+
+The first attested human inhabitants of the Comoro Islands are now thought to have been Austronesian settlers travelling by boat from islands in Southeast Asia. These people arrived no later than the eighth century AD, the date of the earliest known archaeological site, found on Mayotte, although settlement beginning as early as the first century has been postulated.
+
+Subsequent settlers came from the east coast of Africa, the Arabian Peninsula and the Persian Gulf, the Malay Archipelago, and Madagascar. Bantu-speaking settlers were present on the islands from the beginnings of settlement, probably brought to the islands as slaves.
+
+Development of the Comoros is divided into phases. The earliest reliably recorded phase is the Dembeni phase (eighth to tenth centuries), during which there were several small settlements on each island. From the eleventh to the fifteenth centuries, trade with the island of Madagascar and merchants from the Swahili coast and the Middle East flourished, more villages were founded and existing villages grew. Many Comorians can trace their genealogies to ancestors from the Arabian peninsula, particularly Hadhramaut, who arrived during this period.
+
+Medieval Comoros 
+According to legend, in 632, upon hearing of Islam, islanders are said to have dispatched an emissary, Mtswa-Mwindza, to Mecca—but by the time he arrived there, the Islamic prophet Muhammad had died. Nonetheless, after a stay in Mecca, he returned to Ngazidja, where he built a mosque in his home town of Ntsaweni, and led the gradual conversion of the islanders to Islam.
+
+In 933, the Comoros was referred to by Omani sailors as the Perfume Islands.
+
+Among the earliest accounts of East Africa, the works of Al-Masudi describe early Islamic trade routes, and how the coast and islands were frequently visited by Muslims including Persian and Arab merchants and sailors in search of coral, ambergris, ivory, tortoiseshell, gold and slaves. They also brought Islam to the people of the Zanj including the Comoros. As the importance of the Comoros grew along the East African coast, both small and large mosques were constructed. The Comoros are part of the Swahili cultural and economic complex and the islands became a major hub of trade and an important location in a network of trading towns that included Kilwa, in present-day Tanzania, Sofala (an outlet for Zimbabwean gold), in Mozambique, and Mombasa in Kenya.
+
+The Portuguese arrived in the Indian Ocean at the end of the 15th century and the first Portuguese visit to the islands seems to have been that of Vasco da Gama's second fleet in 1503. For much of the 16th century the islands provided provisions to the Portuguese fort at Mozambique and although there was no formal attempt by the Portuguese crown to take possession, a number of Portuguese traders settled and married local women.
+
+By the end of the 16th century local rulers on the African mainland were beginning to push back and, with the support of the Omani Sultan Saif bin Sultan they began to defeat the Dutch and the Portuguese. One of his successors, Said bin Sultan, increased Omani Arab influence in the region, moving his administration to nearby Zanzibar, which came under Omani rule. Nevertheless, the Comoros remained independent, and although the three smaller islands were usually politically unified, the largest island, Ngazidja, was divided into a number of autonomous kingdoms (ntsi).
+
+The islands were well placed to meet the needs of Europeans, initially supplying the Portuguese in Mozambique, then ships, particularly the English, on the route to India, and, later, slaves to the plantation islands in the Mascarenes.
+
+European contact and French colonisation 
+
+In the last decade of the 18th century, Malagasy warriors, mostly Betsimisaraka and Sakalava, started raiding the Comoros for slaves and the islands were devastated as crops were destroyed and the people were slaughtered, taken into captivity or fled to the African mainland: it is said that by the time the raids finally ended in the second decade of the 19th century only one man remained on Mwali. The islands were repopulated by slaves from the mainland, who were traded to the French in Mayotte and the Mascarenes. On the Comoros, it was estimated in 1865 that as much as 40% of the population consisted of slaves.
+
+France first established colonial rule in the Comoros by taking possession of Mayotte in 1841 when the Sakalava usurper sultan  (also known as Tsy Levalo) signed the Treaty of April 1841, which ceded the island to the French authorities. After its annexation, France attempted to convert Mayotte into a sugar plantation colony. 
+
+Meanwhile, Ndzwani (or Johanna as it was known to the British) continued to serve as a way station for English merchants sailing to India and the Far East, as well as American whalers, although the British gradually abandoned it following their possession of Mauritius in 1814, and by the time the Suez Canal opened in 1869 there was no longer any significant supply trade at Ndzwani. Local commodities exported by the Comoros were, in addition to slaves, coconuts, timber, cattle and tortoiseshell. British and American settlers, as well as the island's sultan, established a plantation-based economy that used about one-third of the land for export crops. In addition to sugar on Mayotte, ylang-ylang and other perfume plants, vanilla, cloves, coffee, cocoa beans, and sisal were introduced.
+
+In 1886, Mwali was placed under French protection by its Sultan Mardjani Abdou Cheikh. That same year, Sultan Said Ali of Bambao, one of the sultanates on Ngazidja, placed the island under French protection in exchange for French support of his claim to the entire island, which he retained until his abdication in 1910. In 1908 the four islands were unified under a single administration (Colonie de Mayotte et dépendances) and placed under the authority of the French colonial Governor-General of Madagascar. In 1909, Sultan Said Muhamed of Ndzwani abdicated in favour of French rule and in 1912 the protectorates were abolished and the islands administered as a single colony. Two years later the colony was abolished and the islands became a province of the colony of Madagascar.
+
+Agreement was reached with France in 1973 for the Comoros to become independent in 1978, despite the deputies of Mayotte voting for increased integration with France. A referendum was held on all four of the islands. Three voted for independence by large margins, while Mayotte voted against. On 6 July 1975, however, the Comorian parliament passed a unilateral resolution declaring independence. Ahmed Abdallah proclaimed the independence of the Comorian State (État comorien; دولة القمر) and became its first president. France did not recognise the new state until 31 December, and retained control of Mayotte.
+
+Independence (1975) 
+
+The next 30 years were a period of political turmoil. On 3 August 1975, less than one month after independence, president Ahmed Abdallah was removed from office in an armed coup and replaced with United National Front of the Comoros (FNUK) member Said Mohamed Jaffar. Months later, in January 1976, Jaffar was ousted in favour of his Minister of Defence Ali Soilihi.
+
+The population of Mayotte voted against independence from France in three referendums during this period. The first, held on all the islands on 22 December 1974, won 63.8% support for maintaining ties with France on Mayotte; the second, held in February 1976, confirmed that vote with an overwhelming 99.4%, while the third, in April 1976, confirmed that the people of Mayotte wished to remain a French territory. The three remaining islands, ruled by President Soilihi, instituted a number of socialist and isolationist policies that soon strained relations with France. On 13 May 1978, Bob Denard, once again commissioned by the French intelligence service (SDECE), returned to overthrow President Soilihi and reinstate Abdallah with the support of the French, Rhodesian and South African governments. Ali Soilihi was captured and executed a few weeks later.
+
+In contrast to Soilihi, Abdallah's presidency was marked by authoritarian rule and increased adherence to traditional Islam and the country was renamed the Federal Islamic Republic of the Comoros (République Fédérale Islamique des Comores; جمهورية القمر الإتحادية الإسلامية). Bob Denard served as Abdallah's first advisor; nicknamed the "Viceroy of the Comoros," he was sometimes considered the real strongman of the regime. Very close to South Africa, which financed his "presidential guard," he allowed Paris to circumvent the international embargo on the apartheid regime via Moroni. He also set up from the archipelago a permanent mercenary corps, called upon to intervene at the request of Paris or Pretoria in conflicts in Africa. Abdallah continued as president until 1989 when, fearing a probable coup, he signed a decree ordering the Presidential Guard, led by Bob Denard, to disarm the armed forces. Shortly after the signing of the decree, Abdallah was allegedly shot dead in his office by a disgruntled military officer, though later sources claim an antitank missile was launched into his bedroom and killed him. Although Denard was also injured, it is suspected that Abdallah's killer was a soldier under his command.
+
+A few days later, Bob Denard was evacuated to South Africa by French paratroopers. Said Mohamed Djohar, Soilihi's older half-brother, then became president, and served until September 1995, when Bob Denard returned and attempted another coup. This time France intervened with paratroopers and forced Denard to surrender. The French removed Djohar to Reunion, and the Paris-backed Mohamed Taki Abdoulkarim became president by election. He led the country from 1996, during a time of labour crises, government suppression, and secessionist conflicts, until his death in November 1998. He was succeeded by Interim President Tadjidine Ben Said Massounde.
+
+The islands of Ndzwani and Mwali declared their independence from the Comoros in 1997, in an attempt to restore French rule. But France rejected their request, leading to bloody confrontations between federal troops and rebels. In April 1999, Colonel Azali Assoumani, Army Chief of Staff, seized power in a bloodless coup, overthrowing the Interim President Massounde, citing weak leadership in the face of the crisis. This was the Comoros' 18th coup, or attempted coup d'état since independence in 1975.
+
+Azali failed to consolidate power and reestablish control over the islands, which was the subject of international criticism. The African Union, under the auspices of President Thabo Mbeki of South Africa, imposed sanctions on Ndzwani to help broker negotiations and effect reconciliation. Under the terms of the Fomboni Accords, signed in December 2001 by the leaders of all three islands, the official name of the country was changed to the Union of the Comoros; the new state was to be highly decentralised and the central union government would devolve most powers to the new island governments, each led by a president. The Union president, although elected by national elections, would be chosen in rotation from each of the islands every five years.
+
+Azali stepped down in 2002 to run in the democratic election of the President of the Comoros, which he won. Under ongoing international pressure, as a military ruler who had originally come to power by force, and was not always democratic while in office, Azali led the Comoros through constitutional changes that enabled new elections. A Loi des compétences law was passed in early 2005 that defines the responsibilities of each governmental body, and is in the process of implementation. The elections in 2006 were won by Ahmed Abdallah Mohamed Sambi, a Sunni Muslim cleric nicknamed the "Ayatollah" for his time spent studying Islam in Iran. Azali honoured the election results, thus allowing the first peaceful and democratic exchange of power for the archipelago.
+
+Colonel Mohammed Bacar, a French-trained former gendarme elected President of Ndzwani in 2001, refused to step down at the end of his five-year mandate. He staged a vote in June 2007 to confirm his leadership that was rejected as illegal by the Comoros federal government and the African Union. On 25 March 2008 hundreds of soldiers from the African Union and the Comoros seized rebel-held Ndzwani, generally welcomed by the population: there have been reports of hundreds, if not thousands, of people tortured during Bacar's tenure.
+Some rebels were killed and injured, but there are no official figures. At least 11 civilians were wounded. Some officials were imprisoned. Bacar fled in a speedboat to Mayotte to seek asylum. Anti-French protests followed in the Comoros (see 2008 invasion of Anjouan). Bacar was eventually granted asylum in Benin.
+
+Since independence from France, the Comoros experienced more than 20 coups or attempted coups.
+
+Following elections in late 2010, former Vice-president Ikililou Dhoinine was inaugurated as president on 26 May 2011. A member of the ruling party, Dhoinine was supported in the election by the incumbent President Ahmed Abdallah Mohamed Sambi. Dhoinine, a pharmacist by training, is the first President of the Comoros from the island of Mwali. Following the 2016 elections, Azali Assoumani, from Ngazidja, became president for a third term. In 2018 Azali held a referendum on constitutional reform that would permit a president to serve two terms. The amendments passed, although the vote was widely contested and boycotted by the opposition, and in April 2019, and to widespread opposition, Azali was re-elected president to serve the first of potentially two five-year terms.
+
+In January 2020, the legislative elections in Comoros were dominated by President Azali Assoumani's party, the Convention for the Renewal of the Comoros, CRC. It took an overwhelming majority in the parliament, meaning his hold on power strengthened. CRC took 17 out of 24 seats of the parliament.
+
+In 2021, Comoros signed and ratified the Treaty on the Prohibition of Nuclear Weapons, making it a nuclear-weapon-free state. and in 2023, Comoros was invited as a non-member guest to the G7 summit in Hiroshima.
+
+On 18 February 2023 the Comoros assumed the presidency of the African Union.
+
+Geography 
+
+The Comoros is formed by Ngazidja (Grande Comore), Mwali (Mohéli) and Ndzwani (Anjouan), three major islands in the Comoros Archipelago, as well as many minor islets. The islands are officially known by their Comorian language names, though international sources still use their French names (given in parentheses above). The capital and largest city, Moroni, is located on Ngazidja. The archipelago is situated in the Indian Ocean, in the Mozambique Channel, between the African coast (nearest to Mozambique and Tanzania) and Madagascar, with no land borders.
+
+At , it is one of the smallest countries in the world. The Comoros also has claim to  of territorial seas. The interiors of the islands vary from steep mountains to low hills.
+
+The areas and populations (at the 2017 Census) of the main islands are as follows:
+
+Ngazidja is the largest of the Comoros Archipelago, with an area of 1,024 km2. It is also the most recent island, and therefore has rocky soil. The island's two volcanoes, Karthala (active) and La Grille (dormant), and the lack of good harbours are distinctive characteristics of its terrain. Mwali, with its capital at Fomboni, is the smallest of the four major islands. Ndzwani, whose capital is Mutsamudu, has a distinctive triangular shape caused by three mountain chains – Shisiwani, Nioumakele and Jimilime – emanating from a central peak,  ().
+
+The islands of the Comoros Archipelago were formed by volcanic activity. Mount Karthala, an active shield volcano located on Ngazidja, is the country's highest point, at . It contains the Comoros' largest patch of disappearing rainforest. Karthala is currently one of the most active volcanoes in the world, with a minor eruption in May 2006, and prior eruptions as recently as April 2005 and 1991. In the 2005 eruption, which lasted from 17 to 19 April, 40,000 citizens were evacuated, and the crater lake in the volcano's  caldera was destroyed.
+
+The Comoros also lays claim to the Îles Éparses or Îles éparses de l'océan indien (Scattered Islands in the Indian Ocean) – Glorioso Islands, comprising Grande Glorieuse, Île du Lys, Wreck Rock, South Rock,  (three islets) and three unnamed islets – one of France's overseas districts. The Glorioso Islands were administered by the colonial Comoros before 1975, and are therefore sometimes considered part of the Comoros Archipelago. Banc du Geyser, a former island in the Comoros Archipelago, now submerged, is geographically located in the Îles Éparses, but was annexed by Madagascar in 1976 as an unclaimed territory. The Comoros and France each still view the Banc du Geyser as part of the Glorioso Islands and, thus, part of its particular exclusive economic zone.
+
+Climate 
+
+The climate is generally tropical and mild, and the two major seasons are distinguishable by their raininess. The temperature reaches an average of  in March, the hottest month in the rainy season (called kashkazi/kaskazi [meaning north monsoon], which runs from November to April), and an average low of  in the cool, dry season (kusi (meaning south monsoon), which proceeds from May to October). The islands are rarely subject to cyclones.
+
+Biodiversity 
+
+The Comoros constitute an ecoregion in their own right, Comoros forests. It had a 2018 Forest Landscape Integrity Index mean score of 7.69/10, ranking it 33rd globally out of 172 countries.
+
+In December 1952 a specimen of the West Indian Ocean coelacanth fish was re-discovered off the Comoros coast. The 66 million-year-old species was thought to have been long extinct until its first recorded appearance in 1938 off the South African coast. Between 1938 and 1975, 84 specimens were caught and recorded.
+
+Protected areas
+There are six national parks in the Comoros – Karthala, Coelacanth, and Mitsamiouli Ndroudi on Grande Comore, Mount Ntringui and Shisiwani on Anjouan, and Mohéli National Park on Mohéli. Karthala and Mount Ntrigui national parks cover the highest peaks on the respective islands, and Coelacanth, Mitsamiouli Ndroudi, and Shisiwani are marine national parks that protect the island's coastal waters and fringing reefs. Mohéli National Park includes both terrestrial and marine areas.
+
+Government 
+
+Politics of the Comoros takes place in a framework of a federal presidential republic, whereby the President of the Comoros is both head of state and head of government, and of a multi-party system. The Constitution of the Union of the Comoros was ratified by referendum on 23 December 2001, and the islands' constitutions and executives were elected in the following months. It had previously been considered a military dictatorship, and the transfer of power from Azali Assoumani to Ahmed Abdallah Mohamed Sambi in May 2006 was a watershed moment as it was the first peaceful transfer in Comorian history.
+
+Executive power is exercised by the government. Federal legislative power is vested in both the government and parliament. The preamble of the constitution guarantees an Islamic inspiration in governance, a commitment to human rights, and several specific enumerated rights, democracy, "a common destiny" for all Comorians. Each of the islands (according to Title II of the Constitution) has a great amount of autonomy in the Union, including having their own constitutions (or Fundamental Law), president, and Parliament. The presidency and Assembly of the Union are distinct from each of the islands' governments. The presidency of the Union rotates between the islands. Despite widespread misgivings about the durability of the system of presidential rotation, Ngazidja holds the current presidency rotation, and Azali is President of the Union; Ndzwani is in theory to provide the next president.
+
+Legal system 
+The Comorian legal system rests on Islamic law, an inherited French (Napoleonic Code) legal code, and customary law (mila na ntsi). Village elders, kadis or civilian courts settle most disputes. The judiciary is independent of the legislative and the executive. The Supreme Court acts as a Constitutional Council in resolving constitutional questions and supervising presidential elections. As High Court of Justice, the Supreme Court also arbitrates in cases where the government is accused of malpractice. The Supreme Court consists of two members selected by the president, two elected by the Federal Assembly, and one by the council of each island.
+
+Political culture 
+Around 80 percent of the central government's annual budget is spent on the country's complex administrative system which provides for a semi-autonomous government and president for each of the three islands and a rotating presidency for the overarching Union government. A referendum took place on 16 May 2009 to decide whether to cut down the government's unwieldy political bureaucracy. 52.7% of those eligible voted, and 93.8% of votes were cast in approval of the referendum. Following the implementation of the changes, each island's president became a governor and the ministers became councillors.
+
+Foreign relations 
+
+In November 1975, the Comoros became the 143rd member of the United Nations. The new nation was defined as comprising the entire archipelago, although the citizens of Mayotte chose to become French citizens and keep their island as a French territory.
+
+The Comoros has repeatedly pressed its claim to Mayotte before the United Nations General Assembly, which adopted a series of resolutions under the caption "Question of the Comorian Island of Mayotte", opining that Mayotte belongs to the Comoros under the principle that the territorial integrity of colonial territories should be preserved upon independence. As a practical matter, however, these resolutions have little effect and there is no foreseeable likelihood that Mayotte will become de facto part of the Comoros without its people's consent. More recently, the Assembly has maintained this item on its agenda but deferred it from year to year without taking action. Other bodies, including the Organization of African Unity, the Movement of Non-Aligned Countries and the Organisation of Islamic Cooperation, have similarly questioned French sovereignty over Mayotte. To close the debate and to avoid being integrated by force in the Union of the Comoros, the population of Mayotte overwhelmingly chose to become an overseas department and a region of France in a 2009 referendum. The new status was effective on 31 March 2011 and Mayotte has been recognised as an outermost region by the European Union on 1 January 2014. This decision legally integrates Mayotte in the French Republic.
+
+The Comoros is a member of the United Nations, the African Union, the Arab League, the World Bank, the International Monetary Fund, the Indian Ocean Commission and the African Development Bank. On 10 April 2008, the Comoros became the 179th nation to accept the Kyoto Protocol to the United Nations Framework Convention on Climate Change. The Comoros signed the UN treaty on the Prohibition of Nuclear Weapons. Azali Assoumani, President of the Comoros and Chair of the African Union, attended the 2023 Russia–Africa Summit in Saint Petersburg.
+
+In May 2013 the Union of the Comoros became known for filing a referral to the Office of the Prosecutor of the International Criminal Court (ICC) regarding the events of "the 31 May 2010 Israeli raid on the Humanitarian Aid Flotilla bound for [the] Gaza Strip". In November 2014 the ICC Prosecutor eventually decided that the events did constitute war crimes but did not meet the gravity standards of bringing the case before ICC.
+
+The emigration rate of skilled workers was about 21.2% in 2000.
+
+Military 
+
+The military resources of the Comoros consist of a small standing army and a 500-member police force, as well as a 500-member defence force. A defence treaty with France provides naval resources for protection of territorial waters, training of Comorian military personnel, and air surveillance. France maintains the presence of a few senior officers in the Comoros at government request, as well as a small maritime base and a Foreign Legion Detachment (DLEM) on Mayotte.
+
+Once the new government was installed in May–June 2011, an expert mission from UNREC (Lomé) came to the Comoros and produced guidelines for the elaboration of a national security policy, which were discussed by different actors, notably the national defence authorities and civil society. By the end of the programme in end March 2012, a normative framework agreed upon by all entities involved in SSR will have been established. This will then have to be adopted by Parliament and implemented by the authorities.
+
+Human rights 
+
+Both male and female same-sex sexual acts are illegal in Comoros. Such acts are punished with up to five years imprisonment.
+
+Economy 
+
+The level of poverty in the Comoros is high, but "judging by the international poverty threshold of $1.9 per person per day, only two out of every ten Comorians could be classified as poor, a rate that places the Comoros ahead of other low-income countries and 30 percentage points ahead of other countries in Sub-Saharan Africa." Poverty declined by about 10% between 2014 and 2018, and living conditions generally improved. Economic inequality remains widespread, with a major gap between rural and urban areas. Remittances through the sizable Comorian diaspora form a substantial part of the country's GDP and have contributed to decreases in poverty and increases in living standards.
+
+According to ILO's ILOSTAT statistical database, between 1991 and 2019 the unemployment rate as a percent of the total labor force ranged from 4.38% to 4.3%. An October 2005 paper by the Comoros Ministry of Planning and Regional Development, however, reported that "registered unemployment rate is 14.3 percent, distributed very unevenly among and within the islands, but with marked incidence in urban areas."
+
+In 2019, more than 56% of the labor force was employed in agriculture, with 29% employed in industry and 14% employed in services. The islands' agricultural sector is based on the export of spices, including vanilla, cinnamon, and cloves, and thus susceptible to price fluctuations in the volatile world commodity market for these goods. The Comoros is the world's largest producer of ylang-ylang, a plant whose extracted essential oil is used in the perfume industry; some 80% of the world's supply comes from the Comoros.
+
+High population densities, as much as 1000 per square kilometre in the densest agricultural zones, for what is still a mostly rural, agricultural economy may lead to an environmental crisis in the near future, especially considering the high rate of population growth. In 2004 the Comoros' real GDP growth was a low 1.9% and real GDP per capita continued to decline. These declines are explained by factors including declining investment, drops in consumption, rising inflation, and an increase in trade imbalance due in part to lowered cash crop prices, especially vanilla.
+
+Fiscal policy is constrained by erratic fiscal revenues, a bloated civil service wage bill, and an external debt that is far above the HIPC threshold. Membership in the franc zone, the main anchor of stability, has nevertheless helped contain pressures on domestic prices.
+
+The Comoros has an inadequate transportation system, a young and rapidly increasing population, and few natural resources. The low educational level of the labour force contributes to a subsistence level of economic activity, high unemployment, and a heavy dependence on foreign grants and technical assistance. Agriculture contributes 40% to GDP and provides most of the exports.
+
+The government is struggling to upgrade education and technical training, to privatise commercial and industrial enterprises, to improve health services, to diversify exports, to promote tourism, and to reduce the high population growth rate.
+
+The Comoros is a member of the Organization for the Harmonization of Business Law in Africa (OHADA).
+
+Demographics 
+
+With about 850,000 residents, the Comoros is one of the least-populous countries in the world, but its population density is high, with an average of . In 2001, 34% of the population was considered urban, but the urban population has since grown; in recent years rural population growth has been negative, while overall population growth is still relatively high. In 1958 the population was 183,133.
+
+Almost half the population of the Comoros is under the age of 15. Major urban centres include Moroni, Mitsamihuli, Fumbuni, Mutsamudu, Domoni, and Fomboni. There are between 200,000 and 350,000 Comorians in France.
+
+Ethnic groups 
+The islands of the Comoros are 97.1% ethnically Comorian, which is a mixture of Bantu, Malagasy, and Arab people. Minorities include Makua and Indian (mostly Ismaili). There are recent immigrants of Chinese origin in Grande Comore (especially Moroni). Although most French left after independence in 1975, a small Creole community, descended from settlers from France, Madagascar and Réunion, lives in the Comoros.
+
+Languages 
+
+The most common languages in the Comoros are the Comorian languages, collectively known as Shikomori. They are related to Swahili, and the four different variants (Shingazidja, Shimwali, Shindzwani and Shimaore) are spoken on each of the four islands. Arabic and Latin scripts are both used, Arabic being the more widely used, and an official orthography has recently been developed for the Latin script.
+
+Arabic and French are also official languages, along with Comorian. Arabic is widely known as a second language, being the language of Quranic teaching. French is the administrative language and the language of most non-Quranic formal education.
+
+Religion 
+
+Sunni Islam is the dominant religion, followed by as much as 99% of the population. Comoros is the only Muslim-majority country in Southern Africa and the third southernmost Muslim-majority territory after Mayotte and the Australian territory of Cocos Islands.
+A minority of the population of the Comoros are Christian, both Catholic and Protestant denominations are represented, and most Malagasy residents are also Christian. Immigrants from metropolitan France are mostly Catholic.
+
+Health 
+
+There are 15 physicians per 100,000 people. The fertility rate was 4.7 per adult woman in 2004. Life expectancy at birth is 67 for females and 62 for males.
+
+Education 
+
+Almost all children attend Quranic schools, usually before, although increasingly in tandem with regular schooling. Children are taught about the Qur'an, and memorise it, and learn the Arabic script. Most parents prefer their children to attend Koran schools before moving on to the French-based schooling system. Although the state sector is plagued by a lack of resources, and the teachers by unpaid salaries, there are numerous private and community schools of relatively good standard. The national curriculum, apart from a few years during the revolutionary period immediately post-independence, has been very much based on the French system, both because resources are French and most Comorians hope to go on to further education in France. There have recently been moves to Comorianise the syllabus and integrate the two systems, the formal and the Quran schools, into one, thus moving away from the secular educational system inherited from France.
+
+Pre-colonization education systems in Comoros focused on necessary skills such as agriculture, caring for livestock and completing household tasks. Religious education also taught children the virtues of Islam. The education system underwent a transformation during colonization in the early 1900s which brought secular education based on the French system. This was mainly for children of the elite. After Comoros gained independence in 1975, the education system changed again. Funding for teachers' salaries was lost, and many went on strike. Thus, the public education system was not functioning between 1997 and 2001. Since gaining independence, the education system has also undergone a democratization and options exist for those other than the elite. Enrollment has also grown.
+
+In 2000, 44.2% of children aged 5 to 14 years were attending school. There is a general lack of facilities, equipment, qualified teachers, textbooks and other resources. Salaries for teachers are often so far in arrears that many refuse to work.
+
+Prior to 2000, students seeking a university education had to attend school outside of the country. However, in the early 2000s a university was created in the country. This served to help economic growth and to fight the "flight" of many educated people who were not returning to the islands to work.
+
+Comorian has no native script, but both the Arabic and Latin alphabets are used. In 2004, about 57 percent of the population was literate in the Latin script while more than 90 percent were literate in the Arabic script.
+
+Culture 
+
+Traditionally, women on Ndzwani wear red and white patterned garments called shiromani, while on Ngazidja and Mwali colourful shawls called leso are worn. Many women apply a paste of ground sandalwood and coral called msindzano to their faces. Traditional male clothing is a long white shirt known as a nkandu, and a bonnet called a kofia.
+
+Marriage 
+There are two types of marriages in Comoros, the little marriage (known as Mna daho on Ngazidja) and the customary marriage (known as ada on Ngazidja, harusi on the other islands). The little marriage is a simple legal marriage. It is small, intimate, and inexpensive, and the bride's dowry is nominal. A man may undertake a number of Mna daho marriages in his lifetime, often at the same time, a woman fewer; but both men and women will usually only undertake one ada, or grand marriage, and this must generally be within the village. The hallmarks of the grand marriage are dazzling gold jewelry, two weeks of celebration and an enormous bridal dowry. Although the expenses are shared between both families as well as with a wider social circle, an ada wedding on Ngazidja can cost up to €50,000. Many couples take a lifetime to save for their ada, and it is not uncommon for a marriage to be attended by a couple's adult children.
+
+The ada marriage marks a man's transition in the Ngazidja age system from youth to elder. His status in the social hierarchy greatly increases, and he will henceforth be entitled to speak in public and participate in the political process, both in his village and more widely across the island. He will be entitled to display his status by wearing a mharuma, a type of shawl, across his shoulders, and he can enter the mosque by the door reserved for elders, and sit at the front. A woman's status also changes, although less formally, as she becomes a "mother" and moves into her own house. The system is less formalised on the other islands, but the marriage is nevertheless a significant and costly event across the archipelago. The ada is often criticized because of its great expense, but at the same time it is a source of social cohesion and the main reason why migrants in France and elsewhere continue to send money home. Increasingly, marriages are also being taxed for the purposes of village development.
+
+Kinship and social structure 
+
+Comorian society has a bilateral descent system. Lineage membership and inheritance of immovable goods (land, housing) is matrilineal, passed in the maternal line, similar to many Bantu peoples who are also matrilineal, while other goods and patronymics are passed in the male line. However, there are differences between the islands, the matrilineal element being stronger on Ngazidja.
+
+Music 
+
+Twarab music, imported from Zanzibar in the early 20th century, remains the most influential genre on the islands and is popular at ada marriages.
+
+Media 
+
+There are two daily national newspapers published in the Comoros, the government-owned Al-Watwan, and the privately owned La Gazette des Comores, both published in Moroni. There are a number of smaller newsletters published on an irregular basis as well as a variety of news websites. The government-owned ORTC (Office de Radio et Télévision des Comores) provides national radio and television service. There is a TV station run by the Anjouan regional government, and regional governments on the islands of Grande Comore and Anjouan each operate a radio station. There are also a few independent and small community radio stations that operate on the islands of Grande Comore and Mohéli, and these two islands have access to Mayotte Radio and French TV.
+
+See also 
+
+Index of Comoros-related articles
+
+Notes
+
+References
+
+Citations
+
+Sources 
+
+This article incorporates text from the Library of Congress Country Studies, which is in the public domain.
+
+External links 
+
+Union des Comores – Official government website
+
+Tourism website 
+Embassy des Comores – The Federal and Islamic Republic of the Comoros in New York, United States
+
+Comoros from the BBC News
+Key Development Forecasts for Comoros from International Futures
+
+ 
+Countries in Africa
+1975 establishments in Africa
+Countries and territories where Arabic is an official language
+Comoros archipelago
+East African countries
+Federal republics
+French-speaking countries and territories
+Island countries of the Indian Ocean
+Island countries
+Least developed countries
+Member states of the African Union
+Member states of the Arab League
+Member states of the Organisation internationale de la Francophonie
+Member states of the Organisation of Islamic Cooperation
+Member states of the United Nations
+Small Island Developing States
+States and territories established in 1503
+States and territories established in 1975
+The critical philosophy () movement, attributed to Immanuel Kant (1724–1804), sees the primary task of philosophy as criticism rather than justification of knowledge. Criticism, for Kant, meant judging as to the possibilities of knowledge before advancing to knowledge itself (from the Greek kritike (techne), or "art of judgment"). The basic task of philosophers, according to this view, is not to establish and demonstrate theories about reality, but rather to subject all theories—including those about philosophy itself—to critical review, and measure their validity by how well they withstand criticism.
+
+"Critical philosophy" is also used as another name for Kant's philosophy itself. Kant said that philosophy's proper inquiry is not about what is out there in reality, but rather about the character and foundations of experience itself. We must first judge how human reason works, and within what limits, so that we can afterwards correctly apply it to sense experience and determine whether it can be applied at all to metaphysical objects.
+
+The principal three sources on which the critical philosophy is based are the three critiques, namely Critique of Pure Reason, Critique of Practical Reason and Critique of Judgement, published between 1781 and 1790 and mostly concerned, respectively, with metaphysics, ethics and aesthetics.
+
+See also 
+Critical idealism
+Critical thinking
+Charles Bernard Renouvier
+Léon Brunschvicg
+
+References
+ Stanford Encyclopedia of Philosophy: Immanuel Kant
+
+Kantianism
+China (), officially the People's Republic of China (PRC), is a country in East Asia. It is the world's second-most-populous country, with a population exceeding 1.4 billion. China spans the equivalent of five time zones and borders fourteen countries by land, tied with Russia as having the most of any country in the world. With an area of nearly , it is the world's third-largest country by total land area. The country is divided into 22 provinces, five autonomous regions, four municipalities, and two semi-autonomous special administrative regions. The national capital is Beijing, and the most populous city and largest financial center is Shanghai.
+
+The region that is now China has been inhabited since the Paleolithic era. The earliest Chinese dynastic states, such as the Shang and the Zhou, emerged in the basin of the Yellow River before the late second millennium BCE. The eighth to third centuries BCE saw a breakdown in Zhou authority and significant conflict, as well as the emergence of Classical Chinese literature and philosophy. In 221 BCE, China was unified under an emperor, ushering in more than two millennia in which China was governed by one or more imperial dynasties, including the Han, Tang, Ming and Qing. Some of China's most notable achievements—such as the invention of gunpowder and paper, the establishment of the Silk Road, and the building of the Great Wall—occurred during this period. The Chinese culture—including languages, traditions, architecture, philosophy and more—has heavily influenced East Asia during this imperial period.
+
+In 1912, the Chinese monarchy was overthrown and the Republic of China established. The Republic saw consistent conflict for most of the mid-20th century, including a civil war between the Kuomintang government and the Chinese Communist Party (CCP), which began in 1927, as well as the Second Sino-Japanese War that began in 1937 and continued until 1945, therefore becoming involved in World War II. The latter led to a temporary stop in the civil war and numerous Japanese atrocities such as the Nanjing Massacre, which continue to influence China–Japan relations. In 1949, the CCP established control over China as the Kuomintang fled to Taiwan. Early communist rule saw two major projects: the Great Leap Forward, which resulted in a sharp economic decline and massive famine; and the Cultural Revolution, a movement to purge all non-communist elements of Chinese society that led to mass violence and persecution. Beginning in 1978, the Chinese government began economic reforms that moved the country away from planned economics, but political reforms were cut short by the 1989 Tiananmen Square protests, which ended in a massacre. Despite the event, the economic reform continued to strengthen the nation's economy in the following decades while raising China's standard of living significantly.
+
+China is a unitary one-party socialist republic led by the CCP. It is one of the five permanent members of the UN Security Council and a founding member of several multilateral and regional organizations such as the Asian Infrastructure Investment Bank, the Silk Road Fund, the New Development Bank, and the RCEP. It is also a member of the BRICS, the G20, APEC, and the East Asia Summit. China ranks poorly in measures of democracy, transparency, and human rights, including for press freedom, religious freedom, and ethnic equality. Making up around one-fifth of the world economy, China is the world's largest economy by GDP at purchasing power parity, the second-largest economy by nominal GDP, and the second-wealthiest country. The country is one of the fastest-growing major economies and is the world's largest manufacturer and exporter, as well as the second-largest importer. China is a nuclear-weapon state with the world's largest standing army by military personnel and the second-largest defense budget.
+
+Etymology 
+
+The word "China" has been used in English since the 16th century; however, it was not a word used by the Chinese themselves during this period. Its origin has been traced through Portuguese, Malay, and Persian back to the Sanskrit word Cīna, used in ancient India. "China" appears in Richard Eden's 1555 translation of the 1516 journal of the Portuguese explorer Duarte Barbosa. Barbosa's usage was derived from Persian Chīn (), which was in turn derived from Sanskrit Cīna (). Cīna was first used in early Hindu scripture, including the Mahābhārata (5th century BCE) and the Laws of Manu (2nd century BCE). In 1655, Martino Martini suggested that the word China is derived ultimately from the name of the Qin dynasty (221–206 BCE). Although usage in Indian sources precedes this dynasty, this derivation is still given in various sources. The origin of the Sanskrit word is a matter of debate, according to the Oxford English Dictionary.
+
+Alternative suggestions include the names for Yelang and the Jing or Chu state. The official name of the modern state is the "People's Republic of China" (). The shorter form is "China"  () from  ("central") and  ("state"), a term which developed under the Western Zhou dynasty in reference to its royal demesne. It was then applied to the area around Luoyi (present-day Luoyang) during the Eastern Zhou and then to China's Central Plain before being used in official documents as an synonym for the state under the Qing. It was sometimes also used as a cultural concept to distinguish the Huaxia people from perceived "barbarians". The name Zhongguo is also translated as  in English. China (PRC) is sometimes referred to as the Mainland when distinguishing the ROC from the PRC.
+
+History
+
+Prehistory 
+
+China is regarded as one of the world's oldest civilizations. Archaeological evidence suggests that early hominids inhabited the country 2.25 million years ago. The hominid fossils of Peking Man, a Homo erectus who used fire, were discovered in a cave at Zhoukoudian near Beijing; they have been dated to between 680,000 and 780,000 years ago. The fossilized teeth of Homo sapiens (dated to 125,000–80,000 years ago) have been discovered in Fuyan Cave in Dao County, Hunan. Chinese proto-writing existed in Jiahu around 6600 BCE, at Damaidi around 6000 BCE, Dadiwan from 5800 to 5400 BCE, and Banpo dating from the 5th millennium BCE. Some scholars have suggested that the Jiahu symbols (7th millennium BCE) constituted the earliest Chinese writing system.
+
+Early dynastic rule 
+
+According to Chinese tradition, the first dynasty was the Xia, which emerged around 2100 BCE. The Xia dynasty marked the beginning of China's political system based on hereditary monarchies, or dynasties, which lasted for a millennium. The Xia dynasty was considered mythical by historians until scientific excavations found early Bronze Age sites at Erlitou, Henan in 1959. It remains unclear whether these sites are the remains of the Xia dynasty or of another culture from the same period. The succeeding Shang dynasty is the earliest to be confirmed by contemporary records. The Shang ruled the plain of the Yellow River in eastern China from the 17th to the 11th century BCE. Their oracle bone script (from  BCE) represents the oldest form of Chinese writing yet found and is a direct ancestor of modern Chinese characters.
+
+The Shang was conquered by the Zhou, who ruled between the 11th and 5th centuries BCE, though centralized authority was slowly eroded by feudal warlords. Some principalities eventually emerged from the weakened Zhou, no longer fully obeyed the Zhou king, and continually waged war with each other during the 300-year Spring and Autumn period. By the time of the Warring States period of the 5th–3rd centuries BCE, there were seven major powerful states left.
+
+Imperial China 
+The Warring States period ended in 221 BCE after the state of Qin conquered the other six kingdoms, reunited China and established the dominant order of autocracy. King Zheng of Qin proclaimed himself the First Emperor of the Qin dynasty. He enacted Qin's legalist reforms throughout China, notably the forced standardization of Chinese characters, measurements, road widths (i.e., the cart axles' length), and currency. His dynasty also conquered the Yue tribes in Guangxi, Guangdong, and Northern Vietnam. The Qin dynasty lasted only fifteen years, falling soon after the First Emperor's death, as his harsh authoritarian policies led to widespread rebellion.
+
+Following a widespread civil war during which the imperial library at Xianyang was burned, the Han dynasty emerged to rule China between 206 BCE and CE 220, creating a cultural identity among its populace still remembered in the ethnonym of the modern Han Chinese. The Han expanded the empire's territory considerably, with military campaigns reaching Central Asia, Mongolia, South Korea, and Yunnan, and the recovery of Guangdong and northern Vietnam from Nanyue. Han involvement in Central Asia and Sogdia helped establish the land route of the Silk Road, replacing the earlier path over the Himalayas to India. Han China gradually became the largest economy of the ancient world. Despite the Han's initial decentralization and the official abandonment of the Qin philosophy of Legalism in favor of Confucianism, Qin's legalist institutions and policies continued to be employed by the Han government and its successors.
+
+After the end of the Han dynasty, a period of strife known as Three Kingdoms followed, whose central figures were later immortalized in one of the Four Classics of Chinese literature. At its end, Wei was swiftly overthrown by the Jin dynasty. The Jin fell to civil war upon the ascension of a developmentally disabled emperor; the Five Barbarians then invaded and ruled northern China as the Sixteen States. The Xianbei unified them as the Northern Wei, whose Emperor Xiaowen reversed his predecessors' apartheid policies and enforced a drastic sinification on his subjects, largely integrating them into Chinese culture. In the south, the general Liu Yu secured the abdication of the Jin in favor of the Liu Song. The various successors of these states became known as the Northern and Southern dynasties, with the two areas finally reunited by the Sui in 581. The Sui restored the Han to power through China, reformed its agriculture, economy and imperial examination system, constructed the Grand Canal, and patronized Buddhism. However, they fell quickly when their conscription for public works and a failed war in northern Korea provoked widespread unrest.
+
+Under the succeeding Tang and Song dynasties, Chinese economy, technology, and culture entered a golden age. The Tang dynasty retained control of the Western Regions and the Silk Road, which brought traders to as far as Mesopotamia and the Horn of Africa, and made the capital Chang'an a cosmopolitan urban center. However, it was devastated and weakened by the An Lushan Rebellion in the 8th century. In 907, the Tang disintegrated completely when the local military governors became ungovernable. The Song dynasty ended the separatist situation in 960, leading to a balance of power between the Song and Khitan Liao. The Song was the first government in world history to issue paper money and the first Chinese polity to establish a permanent standing navy which was supported by the developed shipbuilding industry along with the sea trade.
+
+Between the 10th and 11th century CE, the population of China doubled in size to around 100 million people, mostly because of the expansion of rice cultivation in central and southern China, and the production of abundant food surpluses. The Song dynasty also saw a revival of Confucianism, in response to the growth of Buddhism during the Tang, and a flourishing of philosophy and the arts, as landscape art and porcelain were brought to new levels of maturity and complexity. However, the military weakness of the Song army was observed by the Jurchen Jin dynasty. In 1127, Emperor Huizong of Song and the capital Bianjing were captured during the Jin–Song Wars. The remnants of the Song retreated to southern China.
+
+The Mongol conquest of China began in 1205 with the gradual conquest of Western Xia by Genghis Khan, who also invaded Jin territories. In 1271, the Mongol leader Kublai Khan established the Yuan dynasty, which conquered the last remnant of the Song dynasty in 1279. Before the Mongol invasion, the population of Song China was 120 million citizens; this was reduced to 60 million by the time of the census in 1300. A peasant named Zhu Yuanzhang led a rebellion that overthrew the Yuan in 1368 and founded the Ming dynasty as the Hongwu Emperor. Under the Ming dynasty, China enjoyed another golden age, developing one of the strongest navies in the world and a rich and prosperous economy amid a flourishing of art and culture. It was during this period that admiral Zheng He led the Ming treasure voyages throughout the Indian Ocean, reaching as far as East Africa.
+
+In the early years of the Ming dynasty, China's capital was moved from Nanjing to Beijing. With the budding of capitalism, philosophers such as Wang Yangming further critiqued and expanded Neo-Confucianism with concepts of individualism and equality of four occupations. The scholar-official stratum became a supporting force of industry and commerce in the tax boycott movements, which, together with the famines and defense against Japanese invasions of Korea (1592–1598) and Later Jin incursions led to an exhausted treasury. In 1644, Beijing was captured by a coalition of peasant rebel forces led by Li Zicheng. The Chongzhen Emperor committed suicide when the city fell. The Manchu Qing dynasty, then allied with Ming dynasty general Wu Sangui, overthrew Li's short-lived Shun dynasty and subsequently seized control of Beijing, which became the new capital of the Qing dynasty.
+
+The Qing dynasty, which lasted from 1644 until 1912, was the last imperial dynasty of China. The Ming-Qing transition (1618–1683) cost 25 million lives in total, but the Qing appeared to have restored China's imperial power and inaugurated another flowering of the arts. After the Southern Ming ended, the further conquest of the Dzungar Khanate added Mongolia, Tibet and Xinjiang to the empire. Meanwhile, China's population growth resumed and shortly began to accelerate. It is commonly agreed that pre-modern China's population experienced two growth spurts, one during the Northern Song period (960-1127), and other during the Qing period (around 1700–1830). By the High Qing era China was possibly the most commercialized country in the world, and imperial China experienced a second commercial revolution in the economic history of China by the end of the 18th century. On the other hand, the centralized autocracy was strengthened in part to suppress anti-Qing sentiment with the policy of valuing agriculture and restraining commerce, like the Haijin during the early Qing period and ideological control as represented by the literary inquisition, causing some social and technological stagnation.
+
+Fall of the Qing dynasty 
+
+In the mid-19th century, the Qing dynasty experienced Western imperialism in the Opium Wars with Britain and France. China was forced to pay compensation, open treaty ports, allow extraterritoriality for foreign nationals, and cede Hong Kong to the British under the 1842 Treaty of Nanking, the first of the Unequal Treaties. The First Sino-Japanese War (1894–1895) resulted in Qing China's loss of influence in the Korean Peninsula, as well as the cession of Taiwan to Japan.
+The Qing dynasty also began experiencing internal unrest in which tens of millions of people died, especially in the White Lotus Rebellion, the failed Taiping Rebellion that ravaged southern China in the 1850s and 1860s and the Dungan Revolt (1862–1877) in the northwest. The initial success of the Self-Strengthening Movement of the 1860s was frustrated by a series of military defeats in the 1880s and 1890s.
+
+In the 19th century, the great Chinese diaspora began. Losses due to emigration were added to by conflicts and catastrophes such as the Northern Chinese Famine of 1876–1879, in which between 9 and 13 million people died. The Guangxu Emperor drafted a reform plan in 1898 to establish a modern constitutional monarchy, but these plans were thwarted by the Empress Dowager Cixi. The ill-fated anti-foreign Boxer Rebellion of 1899–1901 further weakened the dynasty. Although Cixi sponsored a program of reforms known as the late Qing reforms, the Xinhai Revolution of 1911–1912 brought an end to the Qing dynasty and established the Republic of China. Puyi, the last Emperor of China, abdicated in 1912.
+
+Establishment of the Republic and World War II 
+
+On 1 January 1912, the Republic of China was established, and Sun Yat-sen of the Kuomintang (the KMT or Nationalist Party) was proclaimed provisional president. On 12 February 1912, regent Empress Dowager Longyu sealed the imperial abdication decree on behalf of 4 year old Puyi, the last emperor of China, ending 5,000 years of monarchy in China. In March 1912, the presidency was given to Yuan Shikai, a former Qing general who in 1915 proclaimed himself Emperor of China. In the face of popular condemnation and opposition from his own Beiyang Army, he was forced to abdicate and re-establish the republic in 1916.
+
+After Yuan Shikai's death in 1916, China was politically fragmented. Its Beijing-based government was internationally recognized but virtually powerless; regional warlords controlled most of its territory. In the late 1920s, the Kuomintang under Chiang Kai-shek, the then Principal of the Republic of China Military Academy, was able to reunify the country under its own control with a series of deft military and political maneuverings, known collectively as the Northern Expedition. The Kuomintang moved the nation's capital to Nanjing and implemented "political tutelage", an intermediate stage of political development outlined in Sun Yat-sen's San-min program for transforming China into a modern democratic state. The political division in China made it difficult for Chiang to battle the communist-led People's Liberation Army (PLA), against whom the Kuomintang had been warring since 1927 in the Chinese Civil War. This war continued successfully for the Kuomintang, especially after the PLA retreated in the Long March, until Japanese aggression and the 1936 Xi'an Incident forced Chiang to confront Imperial Japan.
+
+The Second Sino-Japanese War (1937–1945), a theater of World War II, forced an uneasy alliance between the Kuomintang and the Communists. Japanese forces committed numerous war atrocities against the civilian population; in all, as many as 20 million Chinese civilians died. An estimated 40,000 to 300,000 Chinese were massacred in the city of Nanjing alone during the Japanese occupation. During the war, China, along with the UK, the United States, and the Soviet Union, were referred to as "trusteeship of the powerful" and were recognized as the Allied "Big Four" in the Declaration by United Nations. Along with the other three great powers, China was one of the four major Allies of World War II, and was later considered one of the primary victors in the war. After the surrender of Japan in 1945, Taiwan, including the Pescadores, was handed over to Chinese control. However, the validity of this handover is controversial, in that whether Taiwan's sovereignty was legally transferred and whether China is a legitimate recipient, due to complex issues that arose from the handling of Japan's surrender. China emerged victorious but war-ravaged and financially drained. The continued distrust between the Kuomintang and the Communists led to the resumption of civil war. Constitutional rule was established in 1947, but because of the ongoing unrest, many provisions of the ROC constitution were never implemented in mainland China.
+
+Civil War and the People's Republic 
+
+Before the existence of the People's Republic, the CCP had declared several areas of the country as the Chinese Soviet Republic (Jiangxi Soviet), a predecessor state to the PRC, in November 1931 in Ruijin, Jiangxi. The Jiangxi Soviet was wiped out by the KMT armies in 1934 and was relocated to Yan'an in Shaanxi where the Long March concluded in 1935. It would be the base of the communists before major combat in the Chinese Civil War ended in 1949. Afterwards, the CCP took control of most of mainland China, and the Kuomintang retreating offshore to Taiwan, reducing its territory to only Taiwan, Hainan, and their surrounding islands.
+
+On 1 October 1949, CCP Chairman Mao Zedong formally proclaimed the establishment of the People's Republic of China at the new nation's founding ceremony and inaugural military parade in Tiananmen Square, Beijing. In 1950, the People's Liberation Army captured Hainan from the ROC and annexed Tibet. However, remaining Kuomintang forces continued to wage an insurgency in western China throughout the 1950s.
+
+The government consolidated its popularity among the peasants through the Land Reform Movement, which included the execution of between 1 and 2 million landlords. China developed an independent industrial system and its own nuclear weapons. The Chinese population increased from 550 million in 1950 to 900 million in 1974. However, the Great Leap Forward, an idealistic massive industrialization project, resulted in an estimated 15 to 55 million deaths between 1959 and 1961, mostly from starvation. In 1964, China's first atomic bomb exploded successfully. In 1966, Mao and his allies launched the Cultural Revolution, sparking a decade of political recrimination and social upheaval that lasted until Mao's death in 1976. In October 1971, the PRC replaced the Republic of China in the United Nations, and took its seat as a permanent member of the Security Council. This UN action also created the problem of the political status of Taiwan and the Two Chinas issue.
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+Reforms and contemporary history 
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+After Mao's death, the Gang of Four was quickly arrested by Hua Guofeng and held responsible for the excesses of the Cultural Revolution. Deng Xiaoping took power in 1978, and instituted large-scale political and economic reforms, together with the "Eight Elders", CCP members who held huge influence during this time. The CCP loosened governmental control over citizens' personal lives, and the communes were gradually disbanded in favor of working contracted to households. The Cultural Revolution was also rebuked, with millions of its victims being rehabilitated. Agricultural collectivization was dismantled and farmlands privatized, while foreign trade became a major new focus, leading to the creation of special economic zones (SEZs). Inefficient state-owned enterprises (SOEs) were restructured and unprofitable ones were closed outright, resulting in massive job losses. This marked China's transition from a planned economy to a mixed economy with an increasingly open-market environment. China adopted its current constitution on 4 December 1982.
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+In 1989, the country saw large pro-democracy protests, eventually leading to the Tiananmen Square massacre by the leadership, bringing condemnations and sanctions against the Chinese government from various foreign countries, though the effect on external relations was short-lived. Jiang Zemin, Party secretary of Shanghai at the time, was selected to replace Zhao Ziyang as the CCP general secretary; Zhao was put under house arrest for his sympathies to the protests. Jiang later additionally took the presidency and Central Military Commission chairmanship posts, effectively becoming China's top leader. Li Peng, who was instrumental in the crackdown, remained premier until 1998, after which Zhu Rongji became the premier. Under their administration, China continued economic reforms, further closing many SOEs and massively trimming down "iron rice bowl"; occupations with guaranteed job security. During Jiang's rule, China's economy grew sevenfold, and its performance pulled an estimated 150 million peasants out of poverty and sustained an average annual gross domestic product growth rate of 11.2%. British Hong Kong and Portuguese Macau returned to China in 1997 and 1999, respectively, as the Hong Kong and Macau special administrative regions under the principle of one country, two systems. The country joined the World Trade Organization in 2001.
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+Between 2002 and 2003, Hu Jintao and Wen Jiabao succeeded Jiang and Zhu as paramount leader and premier respectively; Jiang attempted to remain CMC chairman for longer before giving up the post entirely between 2004 and 2005. Under Hu and Wen, China maintained its high rate of economic growth, overtaking the United Kingdom, France, Germany and Japan to become the world's second-largest economy. However, the growth also severely impacted the country's resources and environment, and caused major social displacement. Hu and Wen also took a relatively more conservative approach towards economic reform, expanding support for SOEs.Additionally under Hu, China hosted the Beijing Olympics in 2008.
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+Xi Jinping and Li Keqiang succeeded Hu and Wen as paramount leader and premier respectively between 2012 and 2013; Li Keqiang was later succeeded by Li Qiang in 2023. Shortly after his ascension to power, Xi launched a vast anti-corruption crackdown, that prosecuted more than 2 million officials by 2022. Leading many new Central Leading Groups to bypass traditional bureaucracy, Xi consolidated power further than his predecessors. Xi has also pursued changes to China's economy, supporting SOEs and making eradicating extreme poverty through "targeted poverty alleviation" a key goal. In 2013, Xi launched the Belt and Road Initiative, a global infrastructure investment project. Xi has also taken a more assertive stance on foreign and security issues. Since 2017, the Chinese government has been engaged in a harsh crackdown in Xinjiang, with an estimated one million people, mostly Uyghurs, but including other ethnic and religious minorities, in internment camps. The National People's Congress in 2018 amended the constitution to remove the two-term limit on holding the Presidency, allowing for a third and further terms. In 2020, the Standing Committee of the National People's Congress (NPCSC) passed a national security law that authorize the Hong Kong government wide-ranging tools to crack down on dissent. From December 2019 to December 2022, the COVID-19 pandemic led the government to enforce strict public health measures intended to completely eradicate the virus, a goal that was eventually abandoned after protests against the policy in 2022.
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+Geography 
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+China's landscape is vast and diverse, ranging from the Gobi and Taklamakan Deserts in the arid north to the subtropical forests in the wetter south. The Himalaya, Karakoram, Pamir and Tian Shan mountain ranges separate China from much of South and Central Asia. The Yangtze and Yellow Rivers, the third- and sixth-longest in the world, respectively, run from the Tibetan Plateau to the densely populated eastern seaboard. China's coastline along the Pacific Ocean is  long and is bounded by the Bohai, Yellow, East China and South China seas. China connects through the Kazakh border to the Eurasian Steppe which has been an artery of communication between East and West since the Neolithic through the Steppe Route – the ancestor of the terrestrial Silk Road(s).
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+The territory of China lies between latitudes 18° and 54° N, and longitudes 73° and 135° E. The geographical center of China is marked by the Center of the Country Monument at . China's landscapes vary significantly across its vast territory. In the east, along the shores of the Yellow Sea and the East China Sea, there are extensive and densely populated alluvial plains, while on the edges of the Inner Mongolian plateau in the north, broad grasslands predominate. Southern China is dominated by hills and low mountain ranges, while the central-east hosts the deltas of China's two major rivers, the Yellow River and the Yangtze River. Other major rivers include the Xi, Mekong, Brahmaputra and Amur. To the west sit major mountain ranges, most notably the Himalayas. High plateaus feature among the more arid landscapes of the north, such as the Taklamakan and the Gobi Desert. The world's highest point, Mount Everest (8,848 m), lies on the Sino-Nepalese border. The country's lowest point, and the world's third-lowest, is the dried lake bed of Ayding Lake (−154 m) in the Turpan Depression.
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+Climate 
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+China's climate is mainly dominated by dry seasons and wet monsoons, which lead to pronounced temperature differences between winter and summer. In the winter, northern winds coming from high-latitude areas are cold and dry; in summer, southern winds from coastal areas at lower latitudes are warm and moist.
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+A major environmental issue in China is the continued expansion of its deserts, particularly the Gobi Desert. Although barrier tree lines planted since the 1970s have reduced the frequency of sandstorms, prolonged drought and poor agricultural practices have resulted in dust storms plaguing northern China each spring, which then spread to other parts of East Asia, including Japan and Korea. China's environmental watchdog, SEPA, stated in 2007 that China is losing  per year to desertification. Water quality, erosion, and pollution control have become important issues in China's relations with other countries. Melting glaciers in the Himalayas could potentially lead to water shortages for hundreds of millions of people. According to academics, in order to limit climate change in China to  electricity generation from coal in China without carbon capture must be phased out by 2045. With current policies, the GHG emissions of China will probably peak in 2025, and by 2030 they will return to 2022 levels. However, such pathway still leads to 3 degree temperature rise. Official government statistics about Chinese agricultural productivity are considered unreliable, due to exaggeration of production at subsidiary government levels. Much of China has a climate very suitable for agriculture and the country has been the world's largest producer of rice, wheat, tomatoes, eggplant, grapes, watermelon, spinach, and many other crops.
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+Biodiversity 
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