Go (board game)

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Go

Go is played on a grid of black painted lines (usually 19 × 19 of them). The playing pieces, called "stones", are played on the intersections of the lines.
Players	2
Age range	4+
Setup time	None
Playing time	casual: 20–90 minutes tournament: 2–6 hours*
Random chance	None
Skills required	Tactics, Strategy, Observation
Footnotes * Some professional games, especially in Japan, take over 16 hours, and are played in sessions spread over two days.

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, igo^?) or go (碁, go^?) in Japanese, and baduk in Korean (hangul: 바둑). To differentiate it from the common English verb go, it is sometimes capitalized. An alternate spelling is also used occasionally.^[1] Go originated in China, where it has been played for at least two thousand years. It is mostly popular in East Asia but has nowadays gained some popularity in the rest of the world as well. Go is noted for being rich in strategic complexity despite its simple rules.

Go is played by two players alternately placing black and white stones on the vacant intersections of a 19 × 19 grid board. 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.

On one hand, 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 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 weiqi, which roughly translates as "board game of surrounding".^[2]

In many East Asian cultures, Go was considered one of the most important skills a civilized person could learn. This 16th century screen by Kano Eitoku (狩野永徳) shows Chinese Go players in the Ming Dynasty.

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[edit] History

Main article: History of Go

[edit] Origin in China

General Guan Yu (160–219) being treated for a poisoned arm by the physician Hua Tuo while playing Go. 1853 Japanese woodblock print by Utagawa Kuniyoshi.

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.^[3]

The earliest written reference of the game is usually taken to be the historical annal Zuo Zhuan^[4] (c. 4th century BC),^[5] referring to a historical event of 548 BC. It is also mentioned in Book XVII of the Analects of Confucius (c. 3rd century BC)^[5] and in two of the books of Mencius^[6] (c. 3rd century BC).^[5] 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 grid^[7], 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.^[8]

[edit] Spread to Japan and Korea

Although Go may have reached Korea as early as the 5th century AD, more solid evidence stems from the 7th century AD.^[9] By this time, Go had also reached Japan, where it gained popularity at the imperial court in the 8th century.^[10] By the beginning of the 13th century, Go was played among the general public in Japan.^[11]

Korean players, in traditional dress, play in a photograph dated between 1910 and 1920.

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 (born Kano Yosaburo, 1559), to the post of Godokoro (Minister of Go).^[12] Nikkai took on the name of Honinbo Sansa and founded the Honinbo Go school.^[12] Several competing schools were founded soon after.^[12] These officially recognized and subsidized Go schools greatly developed the level of play and introduced the dan/kyu style system of ranking players.^[13] Players from the four schools (Honinbo, Yasui, Inoue, Hayashi) competed in the annual castle games, played in the presence of the shogun.^[14]

[edit] Go In The West

Despite its widespread popularity in Eastern Asia, Go has been slow to spread to the rest of the world, unlike other games of ancient Asian origin such as chess. Schadler ^[15] speculates that chess has more widespread appeal because on the one hand culturally congruent game pieces can be created in chess (e.g. Queen and Bishop in Western Chess, but Advisor and Elephant in Chinese Chess), and on the other hand there is no climactic ending in Go (such as checkmate in chess); indeed, new players often have trouble figuring out when a game of Go is over.

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.^[16] 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.^[17] Lasker's book Go and Go-moku (1934) helped spread the game throughout the US,^[17] 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.^[18] For most of the 20th century, the Japan Go Association played a leading role in spreading Go outside East Asia, 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.^[19] 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 Kiin.^[20] As of 2008, the International Go Federation has a total of 71 member countries.^[21] It has been claimed that across the world 1 person in every 222 plays Go.^[22]

[edit] Rules

Main article: Rules of Go

Although there are some minor differences between rulesets used in different countries,^[23] most notably in Chinese and Japanese scoring rules,^[24] these differences do not seriously affect the tactics and strategy of the game. The basic rules presented here are valid independent of the scoring rules used. The scoring rules are explained separately.

[edit] Basic rules

One black chain and two white chains, their liberties shown with dots. Note that liberties are shared among all stones of a chain.

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.^[25] Once played, a stone may not be moved to a different point.^[26]

Orthogonally 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.^[27] 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.

If white plays at A, the black chain loses its last liberty. It is captured and removed from the board.

A vacant point adjacent to a stone is called a liberty for that stone.^[28] 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.

Generally, it is not allowed to play a stone in such a way that one of your own chains is left without liberties.^[29] Such a move is dubbed suicide. An exception to this rule occurs if doing so captures 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.^[30]

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.^[31] 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. 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.^[32]

Instead of placing a stone, a player may pass, indicating that he sees no way to increase his territory or reduce his opponent's territory. When both players pass consecutively, the game ends and is then scored.

[edit] Scoring rules

There are two basic ways to count the score at the end of a game. The oldest scoring method is territory scoring which is used in Japan, Korea and most Western countries. The other scoring rules —invented in 15th-century China— are called area scoring and are used in China and some other countries.^[33] The USA, France and the UK use a scoring system that is a hybrid of these two systems.^[34]

With territory scoring, the score is the number of empty points enclosed by each player's stones (after dead stones have been removed), plus the number of prisoners. Prisoners are opponent's stones captured during the game, as well as those still on the board but unable to avoid capture (so-called dead stones).

With area scoring, the score is the number of stones each player has on the board, plus the number of surrounded empty intersections. Dead stones are removed at the end, as under "territory" scoring, but prisoners do not count toward the score under these rules.

Given the fact that the number of stones a player has on the board is directly related to the number of prisoners the opponent has taken, the resulting net score under both rules is often identical and is rarely more than one point different.^[35]

Each of these scoring methods has advantages and disadvantages.^[36] There have been some efforts to agree on a standardized set of international rules.^[37]

[edit] Important consequences

Although not actually part of the rules, there are some consequences of the basic go rules that are so important that they might be considered as derived rules.^[38]

Examples of eyes.

The most important of these consequences of the rules are the concepts of life and death. When a group of stones is mostly surrounded and has no options to connect with friendly stones elsewhere, we can describe the status of the group as either alive or dead. 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 his 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 he is the owner, or kill it if it is the opponent's group.^[38]

Example of seki (mutual life).

For a group to be alive, it needs to create at least two eyes. 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. Refer to the diagram labeled "Examples of eyes". All the circled points are eyes. The two black groups in the upper corners are alive, as they both have at least two eyes. The groups in the lower corners are dead, as they 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.^[38]

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). If two (or more) groups of the opposing players are adjacent and share liberties, the situation may reach a position where neither player wants to move first, because doing so would allow the opponent to capture. Such situations therefore remain on the board. 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. An example seki may be found in the diagram on the right, where 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 (perhaps one game in twenty finished games has one), and usually result from an attempt by one player to invade and kill a nearly settled group of the other player.^[38]

[edit] Equipment

Main article: Go equipment

A traditional Japanese set, with floor board (碁盤 goban), bowls (碁笥 goke) and stones (碁石 goishi)

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 also still used by many players.

[edit] Traditional equipment

The traditional Go board is solid wood, from 10 to 18 cm (4 to 7 in) thick.^[39] In Japan, 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 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. Other woods often used to make quality table boards include Hiba (Thujopsis dolabrata), Katsura (Cercidiphyllum japonicum), Kauri (Agathis), and Shin-Kaya (Spruce).^[40] 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.^[40]

In the Japanese style, the stones are kept in matching solid wood bowls and are made of clamshell (white) and slate (black).^[41] The classic slate is nachiguro stone mined in Wakayama prefecture and the clamshell from the Hamaguri clam. However, due to a scarcity in supplies, clamshells are being harvested from Mexico.^[41] The natural resources of Japan have been unable to keep up with the enormous demand for the native clams and slow-growing Kaya trees; both must be of sufficient age 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.^[40]

In China, the game is traditionally played with yunzi stones, which are single convex (i.e. flat on one side).^[41] The stone comes from Yunnan province. Historically, the most prized stones were made of jade, often given to the reigning emperor as a gift.^[41]

Yunzi stones are flat on one side; they can be turned upside-down (flat surface up) during post-game analysis to keep track of which moves were changed during analysis.

In clubs and at tournaments, where large numbers of sets must be maintained (and usually purchased) by one organization, expensive traditional sets are not usually used. For these situations, table boards (of the same design as floor boards, but only about 1–5 cm thick and without legs) are used, and the stones are made of glass or plastic rather than slate and shell. Bowls are often plastic if wooden bowls are not available.

Traditionally, in Japan, the board's grid is 1.5 shaku long by 1.4 shaku wide (455 mm by 424 mm) with space beyond to allow stones to be played on the edges and corners of the grid.^[39] Newcomers may be surprised at first to discover that the board is not a perfect square. It is longer than it is wide, in the proportion 15:14. The reason for this is that when the players sit at the board, the angle at which they view the board gives a foreshortening of the grid; the board is slightly longer between the players to compensate for this.^[39]

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.^[41]

The bowls for the stones are of a simple shape, like a flattened sphere with a level underside.^[42] The lid is loose-fitting and is upturned before play to receive stones captured during the game. The bowls are usually made of turned wood, although small lidded baskets of woven straw are a cheaper alternative from China.

[edit] Playing technique

A pair of Shanghaiese men demonstrate the traditional technique of holding a stone.

The traditional way to place a Go stone is to first take a stone 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.^[43] 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 best 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.^[40] The traditional goban will usually have 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 to allow the board to expand and contract without splitting the wood.^[40] In theory, the wood never fully dries, so fully sealing it threatens warping in varying conditions. The heso allows the board to breathe.

[edit] Time control

See also: time control and byoyomi

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.^[44] 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.^[45] The most widely used time control system in Go is the so called byoyomi^[46] 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:^[47]

• Standard byoyomi: After the main time is depleted, a player has a certain number of time periods (typically around thirty seconds). After each move, the number of full time periods that the player took (possibly zero) is subtracted. For example, if a player has three thirty-second time periods and takes thirty or more (but less than sixty) seconds to make a move, he loses one time period. With 60–89 seconds, he loses two time periods, and so on. If, however, he takes less than thirty seconds, the timer simply resets without subtracting any periods. Using up the last period means that the player has lost on time.
• Canadian byoyomi: After using all of his/her main time, a player must make a certain number of moves within a certain period of time, for example twenty moves within five minutes.^[47][48] If the time period expires without the required number of stones having been played, then the player has lost on time.^[49]

[edit] Competitive play

[edit] Ranks and ratings

Main article: Go ranks and ratings

Three Japanese professional Go players observe some younger amateurs as they dissect a life and death problem in the corner of the board, at the US Go Congress in Houston, 2003.

In Go, rank indicates a player's skill in the game. Traditionally, ranks are measured using kyu and dan grades,^[50] a system which has also 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 between 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:

[edit] 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:

• compensation points, called komi, which compensate the second player for the first move advantage of his opponent; Tournaments commonly use a compensation in the range of 5–8 points,^[55] generally including a half-point to prevent draws.
• compensation stones placed on the board before alternate play, allowing players of different strengths to play competitively (see Go handicap for more information);
• superko: Although the basic ko rule described above covers over 95% of all cycles occurring in games,^[56] there are some complex situations —triple ko, eternal life, etc.— that are not covered by it but would allow the game to cycle indefinitely. To prevent this, the ko rule is sometimes extended to disallow any previous position. This is called superko.^[56]

[edit] Top players

See also: Go players and Go professional

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 that were dubbed Kisei (Go Sage). The only three players to receive this honor were Dosaku, Jowa and Shusaku, all of the house Honinbo.^[57]

Honinbo Shusai (left), last head of house Honinbo, plays against then-up-and-coming Go Seigen in the game of the century.

After the end of the Tokugawa Shogunate and the Meiji Restoration period, the Go houses slowly disappeared, and in 1924, the Nihon Kiin (Japanese Go Association) was formed. Top players from this period often played newspaper-sponsored matches of 2–10 games.^[58] Of special note are Go Seigen (Chinese: Wu Qingyuan), who scored an impressive 80% in these matches,^[59] and Kitani Minoru, who dominated matches in the early 1930s.^[60] These two players are also recognized for their groundbreaking work on new opening theory (Shinfuseki).^[61]

For much of the twentieth century, Go continued to be dominated by players trained in Japan. Notable names included Sakata Eio, Rin Kaiho (Chinese: Lin Haifeng), Kato Masao, Kobayashi Koichi and Cho Chikun (born Cho Ch'i-hun, South Korea).^[62] As these names show, top Chinese and Korean talents would sometimes move to Japan, because the level of play there was high and funding was more lavish. One of the first Korean players to do so was Cho Namchul, who studied in the Kitani Dojo 1937–1944. After his return to Korea, the Hanguk Kiwon (Korean Go Association) was formed and caused the level of play in South Korea to rise significantly in the second half of the twentieth century.^[63] In China, the game suffered from the Cultural Revolution (1966-1976) but quickly recovered in the last quarter of the twentieth century, bringing Chinese players like Nie Weiping and Ma Xiaochun on par with their Japanese and Korean counterparts.^[64]

Korean player Lee Chang-ho, considered by many to be the best player of the late 20th and early 21st centuries, plays against Russian player Alexandre Dinerchtein, six-time European Champion and one of the few Western players to reach professional status.

With the advent of major international titles from 1989 onward, it became possible to compare the level of players from different countries more accurately. Korean players like Lee Chang-ho, Cho Hunhyun, Lee Sedol and Park Young-Hoon dominated international Go and won an impressive number of titles.^[65] Several Chinese players also rose to the top in international Go, most notably Ma Xiaochun, Chang Hao and Gu Li. Japan currently lags behind in the international Go scene.

Historically, as with most sports and games, more men than women have played Go. Special tournaments for women exist, but until recently, men and women did not compete together at the highest levels. However, the creation of new, open tournaments and the rise of strong female players, most notably Rui Naiwei, have in recent years highlighted the strength and competitiveness of emerging female players.^[66]

The level in other countries has traditionally been much lower, except for some players who had preparatory professional training in Asia.^[67] Knowledge of the game has been scant elsewhere for most of the game's history. A German scientist, Oskar Korschelt, is credited with the first systematic description of the game in a Western language in 1880.^[68] A famous player of the 1920s was Emanuel Lasker, a former world chess champion during that time.^[69] It was not until the 1950s that more than a few Western players took up the game as other than a passing interest. In 1978, Manfred Wimmer became the first Westerner to receive a professional player's certificate from an Asian professional Go association.^[70] In 2000, a Westerner, Michael Redmond, finally achieved the top rank awarded by an Asian Go association, 9 dan. In total, as of 2008, only nine non-Asian Go players have ever turned professional.

[edit] Tactics

Main article: Go strategy and tactics

In Go, tactics deal with immediate fighting between stones, capturing and saving stones, life, death and other issues localized to a specific part of the board. Larger issues, not limited to only part of the board, are referred to as strategy, and are covered in their own section.

[edit] Capturing tactics

There are several tactical constructs aimed at capturing stones.^[71] These are among the first things a player learns after understanding the rules. Recognizing the possibility that stones can be captured using these techniques is an important step forward.