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Go is a strategic board game for two players. It is known as wéiqí in Chinese (Traditional: 圍棋; Simplified: 围棋), igo (囲碁?) or go (碁?) in Japanese, and baduk in Korean (hangul: 바둑). To differentiate it from the common English verb to go, it is sometimes capitalized. An alternate spelling is also used occasionally.[nb 1] Go originated in China, where it has been played for more than 2500 years. It is most popular in East Asia, but has gained some popularity in the rest of the world in recent years. Go is noted for being rich in strategic complexity despite its simple rules. Go is played by two players who alternately place black and white stones on the vacant intersections of a grid of 19×19 lines. For faster games or teaching purposes, a smaller grid, such as 13×13 lines or 9×9 lines, can be used. The object of the game is to control a larger part of the board than the opponent. To achieve this, players strive to place their stones in such a way that they cannot be captured, while mapping out territories the opponent cannot invade without being captured. A stone or a group of stones is captured and removed if it has no empty adjacent intersections, the result of being completely surrounded by stones of the opposing color. The adjacent intersections of a stone or group are known as "liberties". Placing stones close together helps them support each other and avoid capture. On the other hand, placing stones far apart creates influence across more of the board. Part of the strategic difficulty of the game stems from finding a balance between such conflicting interests. Players strive to serve both defensive and offensive purposes and choose between tactical urgency and strategic plans. The game ends, and the score is counted, when both players consecutively pass on a turn, indicating that neither side can make a play to increase its territory or reduce its opponent's. Despite the fact that Go originated in ancient China, it is commonly known in the West by its Japanese name, go. This stems from the fact that early Western players learned of the game from Japanese sources. As a result, many Go concepts for which there is no ready English equivalent have become known elsewhere by their Japanese names. The Japanese name igo is linked to the Japanese reading of its Chinese name wéiqí, which roughly translates as "board game of surrounding".[nb 2]
HistoryOrigin in China
Some legends trace the origin of the game to legendary Chinese emperor Yao (2337–2258 BC), who had his counselor Shun design it for his son, Danzhu—supposedly an unruly sort—to teach him discipline, concentration and balance. Other theories suggest that the game was derived from Chinese tribal warlords and generals, who used pieces of stone to map out attacking positions, or that Go equipment was originally a fortune-telling device.[1] The earliest written reference of the game is generally recognized as the historical annal Zuo Zhuan[2] (c. 4th century BC),[3] referring to a historical event of 548 BC. It is also mentioned in Book XVII of the Analects of Confucius (c. 3rd century BC)[3] and in two books written by Mencius[4] (c. 3rd century BC).[3] In all of these works, the game is referred to as yì (弈), a name that means "to play [Go]" today. Go was originally played on a 17×17 line grid,[5] but a 19×19 grid became standard by the Tang Dynasty (618–907). In China, Go was perceived as the popular game of the aristocracy, while Xiangqi (Chinese chess) was the game of the masses. Go was considered one of the four cultivated arts of the Chinese scholar gentleman, along with calligraphy, painting and playing the musical instrument guqin.[6] Spread to Korea and JapanBy the 5th century AD Baduk (Go) is present in Korea and expert Baduk players are even mentioned in Korean history, and also around this time it was becoming popular among the imperial court in Korea.[7][8] Baduk's popularity expanded from the Three Kingdoms of Korea period and even after the Goryeo period. The game evolved into the variant called Sunjang baduk by the 16th century. Sunjang baduk became the main variant played in Korea until the end of the 19th century.[9][10] 
The game reached Japan in the 7th century AD. The oldest Go board in Japan is a Korean board made of cotton rosewood, this board was sent by King Uija around 724 AD.[11][12] Go eventually gained popularity at the imperial court in the 8th century.[13] By the beginning of the 13th century, Go was played among the general public in Japan.[14] In 1603, Tokugawa Ieyasu re-established Japan's unified national government. In the same year, he assigned the then-best player in Japan, a Buddhist monk named Nikkai (né Kanō Yosaburo, 1559), to the post of Godokoro (Minister of Go).[15] Nikkai took the name Honinbo Sansa and founded the Honinbo Go school.[15] Several competing schools were founded soon after.[15] These officially recognized and subsidized Go schools greatly developed the level of play and introduced the dan/kyu style system of ranking players.[16] Players from the four schools (Honinbo, Yasui, Inoue and Hayashi) competed in the annual castle games, played in the presence of the shogun.[17] Go in the WestDespite its widespread popularity in East Asia, Go has been slow to spread to the rest of the world, unlike other games of ancient Asian origin, such as chess. Schadler[18] speculates that chess has more widespread appeal because culturally congruent game pieces can be created in chess (e.g. Queen and Bishop in Western Chess, Advisor and Elephant in Chinese Chess), while Go is totally abstract. Also, there is no climactic ending in Go (such as checkmate in chess). New players often have trouble figuring out when a game of Go is over. Other theories center around the existence of fundamental differences in the level and type of thinking required by Go players as opposed to chess players. While pure analytical thought and the ability to plan many moves in advance are advantageous in chess, in Go a more intuitive approach based on pattern recognition and experience is stressed. A purely analytical approach, due to the sheer number of moves available for consideration, can be paralyzing. The first detailed description of Go in a European language, De Circumveniendi Ludo Chinensium (About the Chinese encircling game), was written in Latin by Thomas Hyde, and included in his 1694 treatise on Oriental board games, De Ludis Orientalibus (About Oriental games); however, Go did not start to become popular in the West until the end of the 19th century, when German scientist Oskar Korschelt wrote a treatise on the game.[19] By the early 20th century, Go had spread throughout the German and Austro-Hungarian empires. In 1905, Edward Lasker learned the game while in Berlin. When he moved to New York, Lasker founded the New York Go Club together with (amongst others) Arthur Smith, who had learned of the game while touring the East and had published the book The Game of Go in 1908.[20] Lasker's book Go and Go-moku (1934) helped spread the game throughout the US,[20] and in 1935, the American Go Association was formed. Two years later, in 1937, the German Go Association was founded. World War II put a stop to most Go activity, but after the war, Go continued to spread.[21] For most of the 20th century, the Japan Go Association played a leading role in spreading Go outside East Asia by publishing the English-language magazine Go Review in the 1960s; establishing Go centers in the US, Europe and South America; and often sending professional teachers on tour to Western nations.[22] In 1996, NASA astronaut Daniel Barry and Japanese astronaut Koichi Wakata became the first people to play Go in space. Both astronauts were awarded honorary dan ranks by the Nihon Ki-in.[23] As of 2008[update], the International Go Federation has a total of 71 member countries.[24] It has been claimed that across the world 1 person in every 222 plays Go.[25] RulesAlthough there are some minor differences between rulesets used in different countries,[26] most notably in Chinese and Japanese scoring rules,[27] these differences do not seriously affect the tactics and strategy of the game. Except where noted otherwise, the basic rules presented here are valid independent of the scoring rules used. The scoring rules are explained separately. Basic rules
Two players, Black and White, take turns placing a stone (game piece) of their own color on a vacant point (intersection) of the grid on a Go board. Black moves first (If there is a large difference in playing level between the players, black is sometimes allowed to place two or more stones on the board for his first move, see Go handicaps for details). The official grid comprises 19×19 lines, though the rules can be applied to any grid size; 13×13 and 9×9 are popular choices to teach beginners.[28] Once played, a stone may not be moved to a different point.[29] Vertically and horizontally adjacent stones of the same color form a chain (also called a group) that shares its liberties (see below) in common, cannot subsequently be subdivided, and in effect becomes a single larger stone.[30] Only stones connected to one another by the lines on the board create a chain; stones that are diagonally adjacent are not connected. Chains may be expanded by playing additional stones on adjacent intersections or connected together by playing a stone on an intersection that is adjacent to two or more chains of the same color. 
A vacant point adjacent to a stone is called a liberty for that stone.[31] Chains of stones share their liberties. A chain of stones must have at least one liberty to remain on the board. When a chain is surrounded by opposing stones so that it has no liberties, it is captured and removed from the board. Most rule sets do not allow a player to play a stone in such a way that one of their own chains is left without liberties, subject to the following important exception.[32] The rule does not apply if playing the new stone results in the capture of one or more of the opponent's stones. In this case, the opponent's stones are captured first, leaving the newly played stone at least one liberty.[33] The rule just stated is said to prohibit suicide. (Since suicide is very rarely useful, making it legal does not significantly alter the nature of the game.)
An example of a situation in which the ko rule applies Players are not allowed to make a move that returns the game to the position before the opponent's last move. This rule, called the ko rule (from the Japanese 劫 kō "eon"), prevents unending repetition.[34] See the example to the right: Black has just played the stone marked 1, capturing a white stone at the intersection marked with a circle. If White were now allowed to play on the marked intersection, that move would capture the black stone marked 1 and recreate the situation before Black made the move marked 1. Allowing this would result in an unending cycle of captures by both players. The ko rule therefore prohibits White from playing at the marked intersection immediately. Instead White must play elsewhere; Black can then end the ko by filling at the marked intersection, creating a five-stone Black chain. If White wants to continue the ko, White will try to find a play that Black must answer; if Black answers, then White can retake the ko. A repetition of such exchanges is called a ko fight.[35] While the various rule sets agree on the ko rule prohibiting returning the board to an immediately previous position, they deal in different ways with the relatively uncommon situation in which a player might recreate a past position that is further removed. See Rules of Go: Repetition for further information. Instead of placing a stone, a player may pass. This usually occurs when they believe no useful moves remain. When both players pass consecutively, the game ends and is then scored. Scoring rulesThere are two basic scoring systems used to determine the winner at the end of a game. These very occasionally lead to different results. The first is territory scoring, which is used in Japan and Korea. It is also believed to have been the method originally used in China. The other system, known as area scoring, is used in China. It is thought to have been developed in the 15th century.[36] In Western countries, players have in most cases customarily used Japanese rules, though practice varies, particularly at an official level. New Zealand has long used area scoring, while national Go federations in the US, France and the UK have shifted more recently to an area scoring system.[37] The latter countries have adopted a counting method (a method of calculating the score) designed to resemble that of territory scoring—while nonetheless giving the same result as if the normal area counting method had been applied—so as to minimize the practical effect of the change. Detailed descriptionAfter both players have passed consecutively, the stones that are still on the board but unable to avoid capture, called dead stones, are removed. (When both sides have passed, skilled players will usually agree which stones are dead and which are alive.) Area scoring (including Chinese): A player's score is the number of stones they have on the board, plus the number of empty intersections surrounded by that player's stones. Territory scoring (including Japanese and Korean): In the course of the game, each player retains the stones they capture, termed prisoners. Any dead stones removed at the end of the game become prisoners. The score is the number of empty points enclosed by a player's stones, plus the number of prisoners captured by that player. (Exceptionally, in Japanese and Korean rules, empty points, even those surrounded by stones of a single colour, may count as neutral territory if some of them are alive by seki. See "Life and Death" below for seki.) If there is disagreement about which stones are dead, then under area scoring rules, the players simply resume play to resolve the matter. The score is computed using the position after the next time the players pass consecutively. Under territory scoring, the rules are considerably more complex; however, in practice, players will generally play on, and, once the status of each stone has been determined, return to the position at the time the first two consecutive passes occurred and remove the dead stones. For further information, see Rules of Go. Comparison of the scoring methodsGiven that the number of stones a player has on the board is related to the number of prisoners the opponent has taken, the resulting net score (the difference between Black and White's respective scores) under both rulesets is often identical and rarely differs by more than a point.[38] Each of these scoring methods has advantages and disadvantages.[39] There have been some efforts to agree on a standardized set of international rules. Those rules with a degree of recognition from the International Go Federation include the rules of the World Amateur Go Championship, based on the Japanese rules, and those of the First World Mind Sports Games of October 2008, essentially based on the Chinese rules with some compromise elements towards the Japanese and Korean rules.[40] Life and death
While not actually mentioned in the rules of Go (at least in simpler rule sets, such as those of New Zealand and the US), the concept of a living group of stones is necessary for a practical understanding of the game.[41]
Examples of eyes When a group of stones is mostly surrounded and has no options to connect with friendly stones elsewhere, the status of the group is either alive, dead or unsettled. A group of stones is said to be alive if it cannot be captured, even if the opponent is allowed to move first. Conversely, a group of stones is said to be dead if it cannot avoid capture, even if the owner of the group is allowed the first move. If the status of a group depends on whether the owner or their opponent moves first, the group is said to be unsettled. In such a situation, the player that moves first may either make it alive if they are the owner, or kill it if it is the opponent's group.[41]
Example of seki (mutual life) For a group to be alive, it needs to be able to create at least two eyes if threatened. An eye is an empty point that is surrounded by friendly stones and where the opponent can never play due to the suicide rule. If two such eyes exist, the opponent can never capture a group of stones, because it will always have at least two liberties. One eye is not enough for life, because a point that would normally be suicide may be played upon if doing so fills the last liberty of opposing stones, thereby capturing those stones. In the "Examples of eyes" diagram, all the circled points are eyes. The two black groups in the upper corners are alive, as both have at least two eyes. The groups in the lower corners are dead, as both have only one eye. The group in the lower left may seem to have two eyes, but the surrounded empty point without a circle is not actually an eye. White can play there and take a black stone. Such a point is often called a false eye.[41] There is a rare exception to the requirement that a group must have two eyes to be alive, a situation called seki (or mutual life). Where different coloured groups are adjacent and share liberties, the situation may reach a position when neither player wants to move first, because doing so would allow the opponent to capture; such situations therefore remain on the board and are examples of a Nash equilibrium. Sekis can occur in many ways. The simplest are: (1) each player has a group without eyes and they share two liberties, and (2) each player has a group with one eye and they share one more liberty. In the "Example of seki (mutual life)" diagram, the circled points are liberties shared by both a black and a white group. Neither player wants to play on a circled point, because doing so would allow the opponent to capture. All the other groups in this example, both black and white, are alive with at least two eyes. Sekis are unusual, and usually result from an attempt by one player to invade and kill a nearly settled group of the other player.[41] Equipment
It is possible to play Go with a simple paper board and coins or plastic tokens for the stones. More popular midrange equipment includes cardstock, a laminated particle board, or wood boards with stones of plastic or glass. More expensive traditional materials are still used by many players. Traditional equipmentBoardsThe Go board typically measures between 45 cm (17.7 in) and 48 cm (18.9 in) in length (from one player's side to the other) and 42 cm (16.5 in) to 44 cm (17.3 in) in width. Chinese boards are slightly larger, as a traditional Chinese Go stone is slightly larger to match. The board is not square; there is a 15:14 ratio in length to width, because with a perfectly square board, from the player's viewing angle the perspective creates a foreshortening of the board. The added length compensates for this.[42] There are two main types of boards: a table board similar in most respects to other game boards like that used for chess, and a floor board, which is its own free-standing table and at which the players sit. The traditional Japanese goban is between 10 cm (3.9 in) and 18 cm (7.1 in) thick and has legs; it sits on the floor(see picture to right), as do the players .[42] It is preferably made from the rare golden-tinged Kaya tree (Torreya nucifera), with the very best made from Kaya trees up to 700 years old. More recently, the related California Torreya (Torreya californica) has been prized for its light color and pale rings, as well as its less expensive and more readily available stock. The natural resources of Japan have been unable to keep up with the enormous demand for the slow-growing Kaya trees; both T. nucifera and T. californica must be of sufficient age (many hundreds of years) to grow to the necessary size, and they are now extremely rare at the age and quality required, raising the price of such equipment tremendously.[43] In Japan, harvesting of live Kaya trees is banned, as the species is protected; the tree must die of natural causes before it is harvested. Thus, an old-growth, floor-standing Kaya goban can easily cost in excess of US$10,000 with the highest-quality examples approaching $20,000. Other, less expensive woods often used to make quality table boards in both Chinese and Japanese dimensions include Hiba (Thujopsis dolabrata), Katsura (Cercidiphyllum japonicum), Kauri (Agathis), and Shin Kaya (various varieties of spruce, commonly from Alaska, Siberia and China's Yunnan Province).[43] So-called Shin Kaya is a potentially confusing merchant's term: shin means "new", and thus shin kaya is best translated "faux kaya"—the woods so described are biologically unrelated to Kaya.[43] Beginning in the early 2000s, some boards have been made by compositing strips of bamboo to create a material called "bamboo plywood" or "plybamboo". The resulting board is very durable and has a unique aesthetic, while being relatively inexpensive. StonesA full set of Go stones (goishi) usually contains 181 black stones and 180 white ones; a 19×19 grid has 361 points, so there are enough stones to cover the board, and Black gets the extra odd stone because that player goes first. There are two main types of stones: single-convex, in which one side is flat, and double-convex, in which both sides have a similar curve. Each type has its pros and cons: single-convex stones, placed flat side down, are less prone to move out of position if the board is bumped or disturbed by nearby movement. In addition, during post-game analysis, players can try out variations using upside-down stones, making it easy to remember the actual game moves. On the other hand, flat stones are harder to clear from the board at the end of the game. Traditional Japanese stones are double-convex, and made of clamshell (white) and slate (black).[44] The classic slate is nachiguro stone mined in Wakayama Prefecture and the clamshell from the Hamaguri clam; however, due to a scarcity in the Japanese supply of this clam, the stones are most often made of shells harvested from Mexico.[44] Historically, the most prized stones were made of jade, often given to the reigning emperor as a gift.[44] In China, the game is traditionally played with single-convex stones[44] made of a composite called Yunzi. The material comes from Yunnan Province and is made by sintering a proprietary and trade-secret mixture of mineral compounds. This process dates to the Tang Dynasty and, after the knowledge was lost in the 1920s during the Chinese Civil War, was rediscovered in the 1960s by the now state-run Yunzi company. The material is prized for its colors, its pleasing sound as compared to glass or to synthetics such as melamine, and its lower cost as opposed to other materials such as slate/shell. The term "yunzi" can also refer to a single-convex stone made of any material; however, most English-language Go suppliers will specify Yunzi as a material and single-convex as a shape to avoid confusion, as stones made of Yunzi are also available in double-convex while synthetic stones can be either shape. Traditional stones are made so that black stones are slightly larger in diameter than white; this is to compensate for the optical illusion created by contrasting colors that would make equal-sized white stones appear larger on the board than black stones.[44] Bowls
The bowls for the stones are shaped like a flattened sphere with a level underside.[45] The lid is loose fitting and upturned before play to receive stones captured during the game. Chinese bowls are again slightly larger, and a little more rounded, a style known as Go Seigen; Japanese Kitani bowls tend to have a shape closer to that of the bowl of a snifter glass, such as for brandy. The bowls are usually made of turned wood. Rosewood is the traditional material for Japanese bowls, but is very expensive; wood from the Chinese jujube date tree, which has a lighter color (it is often stained) and slightly more visible grain pattern, is a common substitute for rosewood, and traditional for Go Seigen-style bowls. Other traditional Chinese bowls include lacquered wood bowls, or woven straw or rattan baskets. Stone bowls also are traditionally used. The names of the bowl shapes, Go Seigen and Kitani, pay homage to two 20th-century professional Go players by the same names, of Chinese and Japanese nationality, respectively, who are referred to as the "Fathers of modern Go".[46] Modern and low-cost alternativesIn clubs and at tournaments, where large numbers of sets must be purchased and maintained by one organization, expensive traditional sets are not usually used. For these situations, table boards are usually used instead of floor boards, and are either made of a lower-cost wood such as spruce or bamboo, or are flexible mats made of vinyl that can be rolled up. In such cases, the stones are usually made of glass, plastic or resin (such as melamine or Bakelite) rather than slate and shell. Bowls are often made of plastic. Common "novice" Go sets are all-inclusive kits made of particle board or plywood, with plastic or glass stones, that either fold up to enclose the stone containers or have pull-out drawers to keep stones. In relative terms, these sets are inexpensive, costing US$20–$40 depending on component quality, and thus are popular with casual Go players. Magnetic sets are also available, either as portable travel sets or in larger sizes for educational purposes. Playing technique and ettiquette
The traditional way to place a Go stone is to first take one from the bowl, gripping it between the index and middle fingers, with the middle finger on top, and then placing it directly on the desired intersection.[47] It is considered respectful of the opponent to place the first stone to the player's upper right-hand corner. Although it can be soothing and pleasant to run one's hand through the bowl or hold a handful of stones, this can be noisy and unnerving to one's opponent; it is considered good form to take only one stone at a time as one decides where to play. It is permissible to strike the board firmly to produce a sharp click. Many consider the acoustic properties of the board to be quite important.[43] The traditional goban usually has its underside carved with a pyramid called a heso recessed into the board. Tradition holds that this is to give a better resonance to the stone's click, but the more conventional explanation is it allows the board to expand and contract without splitting the wood.[43] In theory, the wood never fully dries, so fully sealing it threatens warping in varying conditions. The heso allows the board to breathe. Time control
A game of Go may be timed using a game clock. Formal time controls were introduced into the professional game during the 1920s and were controversial.[48] Adjournments and sealed moves began to be regulated in the 1930s. Go tournaments use a number of different time control systems. All common systems envisage a single main period of time for each player for the game, but they vary on the protocols for continuation (in overtime) after a player has finished that time allowance.[nb 3] The most widely used time control system is the so called byoyomi[nb 4] system. The top professional Go matches have timekeepers so that the players do not have to press their own clocks. Two widely used variants of the byoyomi system are:[49]
Notation and recording games
The standard way of recording a Go game is with a Kifu (棋譜). This is a diagram of the Go board position showing each stone numbered with the move it was placed. If more than one move occurred on the same point, annotations by the side of the diagram give this information in the form "57 at 51" or something comparable. Other notations comparable to algebraic chess notation also have been used in the past, especially by early Western players who were familiar with chess notation; however, most players have abandoned them in favor of the kifu system, which is easier to use. Nowadays game records can be stored on computer, with most software using the Smart Game Format. Competitive playRanks and ratings
In Go, rank indicates a player's skill in the game. Traditionally, ranks are measured using kyu and dan grades,[50] a system which also has been adopted by many martial arts. More recently, mathematical rating systems similar to the Elo rating system have been introduced.[51] Such rating systems often provide a mechanism for converting a rating to a kyu or dan grade.[51] Kyu grades (abbreviated k) are considered student grades and decrease as playing level increases, meaning 1st kyu is the strongest available kyu grade. Dan grades (abbreviated d) are considered master grades, and increase from 1st dan to 7th dan. First dan equals a black belt in eastern martial arts using this system. Top players can attain a professional dan grade (abbreviated p), with the very best reaching 9th dan professional. The difference among each amateur rank is one handicap stone. For the professional ranks, the difference is roughly one handicap stone for every three ranks. For example, if a 5k plays a game with a 1k, the 5k would need a handicap of four stones to even the odds. Top-level amateur players sometimes defeat professionals in tournament play.[52] The rank system comprises, from the lowest to highest ranks:
Tournament and match rules
Tournament and match rules deal with factors that may influence the game but are not part of the actual rules of play. Such rules may differ between events. Rules that influence the game include: the setting of compensation points (komi), handicap strategies, and time control parameters. Rules that do not generally influence the game are: the tournament system, pairing strategies, and placement criteria. Common tournament systems used in Go include the McMahon system,[53] Swiss system, league systems and the knockout system. Tournaments may combine multiple systems; many professional Go tournaments use a combination of the league and knockout systems.[54] Tournament rules may also set the following:
Top players
Although the game was developed in China, the establishment of the Four Go houses by Tokugawa Ieyasu at the start of the 17th century shifted the focus of the Go world to Japan. State sponsorship, allowing players to dedicate themselves full time to study of the game, and fierce competition between individual houses resulted in a significant increase in the level of play. During this period, the best player of his generation was given the prestigious title Meijin (master) and the post of Godokoro (minister of Go). Of special note are the players who were dubbed Kisei (Go Sage). The only three players to receive this honor were Dosaku, Jowa and Shusaku, all of the house Honinbo.[57] 
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