Go (game)
Abstract strategy board game for two players / From Wikipedia, the free encyclopedia
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Go is an abstract strategy board game for two players in which the aim is to capture more territory than the opponent by fencing off empty space. The game was invented in China more than 2,500 years ago and is believed to be the oldest board game continuously played to the present day.[1][2][3][4][5] A 2016 survey by the International Go Federation's 75 member nations found that there are over 46 million people worldwide who know how to play Go, and over 20 million current players, the majority of whom live in East Asia.[6]
Years active | Spring and Autumn period to present |
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Genres | |
Players | 2 |
Setup time | Minimal |
Playing time |
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Chance | None |
Skills | Strategy, tactics, elementary arithmetic |
Synonyms | |
a Some professional games exceed 16 hours and are played in sessions spread over two days. |
Go | |||||||||||||||||||||||||||||||||||||||||
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Chinese name | |||||||||||||||||||||||||||||||||||||||||
Traditional Chinese | 圍棋 | ||||||||||||||||||||||||||||||||||||||||
Simplified Chinese | 围棋 | ||||||||||||||||||||||||||||||||||||||||
Literal meaning | 'encirclement board game' | ||||||||||||||||||||||||||||||||||||||||
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Tibetan name | |||||||||||||||||||||||||||||||||||||||||
Tibetan | མིག་མངས | ||||||||||||||||||||||||||||||||||||||||
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Vietnamese name | |||||||||||||||||||||||||||||||||||||||||
Vietnamese alphabet | cờ vây | ||||||||||||||||||||||||||||||||||||||||
Hán-Nôm | 碁圍 | ||||||||||||||||||||||||||||||||||||||||
Korean name | |||||||||||||||||||||||||||||||||||||||||
Hangul | 바둑 | ||||||||||||||||||||||||||||||||||||||||
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Japanese name | |||||||||||||||||||||||||||||||||||||||||
Kanji | |||||||||||||||||||||||||||||||||||||||||
Hiragana |
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Katakana |
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The playing pieces are called stones. One player uses the white stones and the other black. The players take turns placing their stones on the vacant intersections (points) on the board. Once placed, stones may not be moved, but captured stones are immediately removed from the board. A single stone (or connected group of stones) is captured when surrounded by the opponent's stones on all orthogonally adjacent points. [7] The game proceeds until neither player wishes to make another move.
When a game concludes, the winner is determined by counting each player's surrounded territory along with captured stones and komi (points added to the score of the player with the white stones as compensation for playing second).[8] Games may also end by resignation.[9]
The standard Go board has a 19×19 grid of lines, containing 361 points. Beginners often play on smaller 9×9 and 13×13 boards,[10] and archaeological evidence shows that the game was played in earlier centuries on a board with a 17×17 grid. Boards with a 19×19 grid had become standard, however, by the time the game reached Korea in the 5th century CE and Japan in the 7th century CE.[11]
Go was considered one of the four essential arts of the cultured aristocratic Chinese scholars in antiquity. The earliest written reference to the game is generally recognized as the historical annal Zuo Zhuan[12][13] (c. 4th century BCE).[14]
Despite its relatively simple rules, Go is extremely complex. Compared to chess, Go has both a larger board with more scope for play and longer games and, on average, many more alternatives to consider per move. The number of legal board positions in Go has been calculated to be approximately 2.1×10170,[15][lower-alpha 1] which is far greater than the number of atoms in the observable universe, which is estimated to be on the order of 1080.[17]
The name Go is a short form of the Japanese word igo (囲碁; いご), which derives from earlier wigo (ゐご), in turn from Middle Chinese ɦʉi gi (圍棋, Mandarin: wéiqí, lit. 'encirclement board game' or 'board game of surrounding'). In English, the name Go when used for the game is often capitalized to differentiate it from the common word go.[18] In events sponsored by the Ing Chang-ki Foundation, it is spelled goe.[19]
The Korean word baduk (바둑) derives from the Middle Korean word Badok, the origin of which is controversial; the more plausible etymologies include the suffix dok added to Ba to mean 'flat and wide board', or the joining of Bat, meaning 'field', and Dok, meaning 'stone'. Less plausible etymologies include a derivation of Badukdok, referring to the playing pieces of the game, or a derivation from Chinese páizi (排子), meaning 'to arrange pieces'.[20]
Go is an adversarial game between two players with the objective of capturing territory. That is, occupying and surrounding a larger total empty area of the board with one's stones than the opponent.[21] As the game progresses, the players place stones on the board creating stone "formations" and enclosing spaces. Stones are never moved on the board, but when "captured" are removed from the board. Stones are linked together into a formation by being adjacent along the black lines, not on diagonals (of which there are none). Contests between opposing formations are often extremely complex and may result in the expansion, reduction, or wholesale capture and loss of formations and their enclosed empty spaces (called "eyes"). Another essential component of the game is control of the sente (that is, controlling the offense, so that one's opponent is forced into defensive moves); this usually changes several times during play.
Initially the board is bare, and players alternate turns to place one stone per turn. As the game proceeds, players try to link their stones together into "living" formations (meaning that they are permanently safe from capture), as well as threaten their opponent's stones and formations. Stones have both offensive and defensive characteristics, depending on the situation.
An essential tactic is that a formation of stones must incorporate at least two open points (known as eyes) to preserve itself from elimination on the board. Two or more eyes incorporated into a group (called a liberty) and a group with two or more eyes cannot be captured, even if it's surrounded on the outside. [23] Such groups are said to be unconditionally alive.[24]
The general strategy is to place stones to fence-off territory, attack the opponent's weak groups (trying to kill them so they will be removed), and always stay mindful of the life status of one's own groups.[25][26] The liberties of groups are countable. Situations where mutually opposing groups must capture each other or die are called capturing races, or semeai.[27] In a capturing race, the group with more liberties will ultimately be able to capture the opponent's stones.[27][28][lower-alpha 2] Capturing races and the elements of life or death are the primary challenges of Go.
In the end game players may pass rather than place a stone if they think there are no further opportunities for profitable play.[29] The game ends when both players pass[30] or when one player resigns. In general, to score the game, each player counts the number of unoccupied points surrounded by their stones and then subtracts the number of stones that were captured by the opponent. The player with the greater score (after adjusting for handicapping called komi) wins the game.
In the opening stages of the game, players typically establish groups of stones (or bases) near the corners and around the sides of the board, usually starting on the third or fourth line in from the board edge rather than at the very edge of the board. The edges and corners make it easier to develop groups which have better options for life (self-viability for a group of stones that prevents capture) and establish formations for potential territory.[31] Players usually start near the corners because establishing territory is easier with the aid of two edges of the board.[32] Established corner opening sequences are called joseki and are often studied independently.[33] However, in the mid-game, stone groups must also reach in towards the large central area of the board to capture more territory.
Dame are points that lie in between the boundary walls of black and white, and as such are considered to be of no value to either side. Seki are mutually alive pairs of white and black groups where neither has two eyes.
Ko (Chinese and Japanese: 劫) is a potentially indefinitely repeated stone-capture position. The rules do not allow a board position to be repeated. Therefore, any move which would restore the previous board position would not be allowed, and the next player would be forced to play somewhere else. If the play requires a strategic response by the first player, further changing the board, then the second player could "retake the ko," and the first player would be in the same situation of needing to change the board before trying to take the ko back. And so on. [34] Some of these ko fights may be important and decide the life of a large group, while others may be worth just one or two points. Some ko fights are referred to as picnic kos when only one side has a lot to lose.[35] The Japanese call it a hanami (flower-viewing) ko.[36]
Playing with others usually requires a knowledge of each player's strength, indicated by the player's rank (increasing from 30 kyu to 1 kyu, then 1 dan to 7 dan, then 1 dan pro to 9 dan pro). A difference in rank may be compensated by a handicap—Black is allowed to place two or more stones on the board to compensate for White's greater strength.[37][38] There are different rulesets (Korean, Japanese, Chinese, AGA, etc.), which are almost entirely equivalent, except for certain special-case positions and the method of scoring at the end.
Basic concepts
This section needs additional citations for verification. (February 2016) |
Basic strategic aspects include the following:
- Connection: Keeping one's own stones connected means that fewer groups need to make living shape, and one has fewer groups to defend.
- Cut: Keeping opposing stones disconnected means that the opponent needs to defend and make living shape for more groups.
- Stay alive: The simplest way to stay alive is to establish a foothold in the corner or along one of the sides. At a minimum, a group must have two eyes (separate open points) to be alive.[9] An opponent cannot fill in either eye, as any such move is suicidal and prohibited in the rules.
- Mutual life (seki) is better than dying: A situation in which neither player can play on a particular point without then allowing the other player to play at another point to capture. The most common example is that of adjacent groups that share their last few liberties—if either player plays in the shared liberties, they can reduce their own group to a single liberty (putting themselves in atari), allowing their opponent to capture it on the next move.
- Death: A group that lacks living shape is eventually removed from the board as captured.
- Invasion: Set up a new living group inside an area where the opponent has greater influence, means one reduces the opponent's score in proportion to the area one occupies.
- Reduction: Placing a stone far enough into the opponent's area of influence to reduce the amount of territory they eventually get, but not so far that it can be cut off from friendly stones outside.
- Sente: A play that forces one's opponent to respond (gote). A player who can regularly play sente has the initiative and can control the flow of the game.
- Sacrifice: Allowing a group to die in order to carry out a play, or plan, in a more important area.
The strategy involved can become very abstract and complex. High-level players spend years improving their understanding of strategy, and a novice may play many hundreds of games against opponents before being able to win regularly.
Strategy deals with global influence, the interaction between distant stones, keeping the whole board in mind during local fights, and other issues that involve the overall game. It is therefore possible to allow a tactical loss when it confers a strategic advantage.
Novices often start by randomly placing stones on the board, as if it were a game of chance. An understanding of how stones connect for greater power develops, and then a few basic common opening sequences may be understood. Learning the ways of life and death helps in a fundamental way to develop one's strategic understanding of weak groups.[lower-alpha 3] A player who both plays aggressively and can handle adversity is said to display kiai, or fighting spirit, in the game.
Opening strategy
In the opening of the game, players usually play and gain territory in the corners of the board first, as the presence of two edges makes it easier for them to surround territory and establish the eyes they need.[39] From a secure position in a corner, it is possible to lay claim to more territory by extending along the side of the board.[40] The opening is the most theoretically difficult part of the game and takes a large proportion of professional players' thinking time.[41][42] The first stone played at a corner of the board is generally placed on the third or fourth line from the edge. Players tend to play on or near the 4–4 star point during the opening. Playing nearer to the edge does not produce enough territory to be efficient, and playing further from the edge does not safely secure the territory.[43]
In the opening, players often play established sequences called joseki, which are locally balanced exchanges;[44] however, the joseki chosen should also produce a satisfactory result on a global scale. It is generally advisable to keep a balance between territory and influence. Which of these gets precedence is often a matter of individual taste.
Middlegame and endgame
The middle phase of the game is the most combative, and usually lasts for more than 100 moves. During the middlegame, the players invade each other's territories, and attack formations that lack the necessary two eyes for viability. Such groups may be saved or sacrificed for something more significant on the board.[45] It is possible that one player may succeed in capturing a large weak group of the opponent's, which often proves decisive and ends the game by a resignation. However, matters may be more complex yet, with major trade-offs, apparently dead groups reviving, and skillful play to attack in such a way as to construct territories rather than kill.[46]
The end of the middlegame and transition to the endgame is marked by a few features. Near the end of a game, play becomes divided into localized fights that do not affect each other,[47] with the exception of ko fights, where before the central area of the board related to all parts of it. No large weak groups are still in serious danger. Moves can reasonably be attributed some definite value, such as 20 points or fewer, rather than simply being necessary to compete. Both players set limited objectives in their plans, in making or destroying territory, capturing or saving stones. These changing aspects of the game usually occur at much the same time, for strong players. In brief, the middlegame switches into the endgame when the concepts of strategy and influence need reassessment in terms of concrete final results on the board.
Aside from the order of play (alternating moves, Black moves first or takes a handicap) and scoring rules, there are essentially only two rules in Go:
- Liberty rule states that every stone remaining on the board must have at least one open point (a liberty) directly orthogonally adjacent (up, down, left, or right), or must be part of a connected group that has at least one such open point (liberty) next to it. Stones or groups of stones which lose their last liberty are removed from the board.
- Repetition Rule (the ko rule) states that a stone on the board must never immediately repeat a previous position of a captured stone, thus only a move elsewhere on the board is permitted that turn. Since without this rule such a pattern of the two players repeating their prior moves (capturing stones in same places) could continue indefinitely, this rule prevents a stalemate.
Almost all other information about how the game is played is heuristic, meaning it is learned information about how the patterns of the stones on the board function, rather than a rule. Other rules are specialized, as they come about through different rulesets, but the above two rules cover almost all of any played game.
Although there are some minor differences between rulesets used in different countries,[48] most notably in Chinese and Japanese scoring rules,[49] these differences do not greatly affect the tactics and strategy of the game.
Except where noted, the basic rules presented here are valid independent of the scoring rules used. The scoring rules are explained separately. Go terms for which there is no ready English equivalent are commonly called by their Japanese names.
Basic rules
The two players, Black and White, take turns placing stones of their color on the intersections of the board, one stone at a time. The usual board size is a 19×19 grid, but for beginners or for playing quick games,[50] the smaller board sizes of 13×13[51] and 9×9 are also popular.[52] The board is empty to begin with.[53] Black plays first unless given a handicap of two or more stones, in which case White plays first. The players may choose any unoccupied intersection to play on except for those forbidden by the ko and suicide rules (see below). Once played, a stone can never be moved and can be taken off the board only if it is captured.[54] A player may pass their turn, declining to place a stone, though this is usually only done at the end of the game when both players believe nothing more can be accomplished with further play. When both players pass consecutively, the game ends[55] and is then scored.
Liberties and capture
Vertically and horizontally adjacent stones of the same color form a chain (also called a string or group),[56] forming a discrete unit that cannot then be divided.[57] 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 placing additional stones on adjacent intersections, and they can be connected together by placing a stone on an intersection that is adjacent to two or more chains of the same color.[58]
A vacant point adjacent to a stone, along one of the grid lines of the board, is called a liberty for that stone.[59][60] Stones in a chain share their liberties.[56] 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.[61]
Ko rule
Players are not allowed to make a move that returns the game to the immediately prior position. This rule, called the ko rule, prevents unending repetition (a stalemate).[62] As shown in the example pictured: White had a stone where the red circle was, and Black has just captured it by playing a stone at 1 (so the White stone has been removed). However, it is readily apparent that now Black's stone at 1 is immediately threatened by the three surrounding White stones. If White were allowed to play again on the red circle, it would return the situation to the original one, but the ko rule forbids that kind of endless repetition. Thus, White is forced to move elsewhere, or pass. If White wants to recapture Black's stone at 1, White must attack Black somewhere else on the board so forcefully that Black moves elsewhere to counter that, giving White that chance. If White's forcing move is successful, it is termed "gaining the sente"; if Black responds elsewhere on the board, then White can retake Black's stone at 1, and the ko continues, but this time Black must move elsewhere. A repetition of such exchanges is called a ko fight.[63] To stop the potential for ko fights, two stones of the same color would need to be added to the group, making either a group of 5 Black or 5 White stones.
While the various rulesets 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.
Suicide
A player may not place a stone such that it or its group immediately has no liberties unless doing so immediately deprives an enemy group of its final liberty. In the second case, the enemy group is captured, leaving the new stone with at least one liberty, so the new stone can be placed.[66] This rule is responsible for the all-important difference between one and two eyes: if a group with only one eye is fully surrounded on the outside, it can be killed with a stone placed in its single eye. (An eye is an empty point or group of points surrounded by a group of stones).
The Ing and New Zealand rules do not have this rule,[67] and there a player might destroy one of its own groups (commit suicide). This play would only be useful in limited sets of situations involving a small interior space or planning.[68] In the example at right, it may be useful as a ko threat.
Komi
Because Black has the advantage of playing the first move, the idea of awarding White some compensation came into being during the 20th century. This is called komi, which gives white a 5.5-point compensation under Japanese rules, 6.5-point under Korean rules, and 15/4 stones, or 7.5-point under Chinese rules(number of points varies by rule set).[69] Under handicap play, White receives only a 0.5-point komi, to break a possible tie (jigo).
Scoring rules
Two general types of scoring procedures are used, and players determine which to use before play. Both procedures almost always give the same winner.
- Area scoring procedure (including Chinese): counts the number of points a player's stones occupy and surround. It is associated with contemporary Chinese play and was probably established there during the Ming dynasty in the 15th or 16th century.[70] Beginner-friendly, but takes longer to count. A player's score is the number of stones that the player has on the board, plus the number of empty intersections surrounded by that player's stones. 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.
- Territory scoring procedure (including Japanese and Korean): counts the number of empty points a player's stones surround, together with the number of stones the player captured. 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.[lower-alpha 4] Under territory scoring there can be an extra penalty for playing inside ones' territory, so if there is a disagreement extra play to resolve it would, in tournament settings, happen on a separate board, where the player claiming a group is dead would play first, and would demonstrate how to capture those stones. For further information, see Rules of Go.
Both procedures are counted after both players have passed consecutively, the stones that are still on the board but unable to avoid capture, called dead stones, are removed. Given that the number of stones a player has on the board is directly related to the number of prisoners their opponent has taken, the resulting net score, that is, the difference between Black's and White's scores is identical under both rulesets (unless the players have passed different numbers of times during the course of the game). Thus, the net result given by the two scoring systems rarely differs by more than a point.[71]
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 U.S.), the concept of a living group of stones is necessary for a practical understanding of the game.[72]
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. Otherwise, the group is said to be unsettled: the defending player can make it alive or the opponent can kill it, depending on who gets to play first.[72]
An eye is an empty point or group of points surrounded by a group of stones. If the eye is surrounded by Black stones, White cannot play there unless such a play would take Black's last liberty and capture the Black stones. (Such a move is forbidden according to the suicide rule in most rule sets, but even if not forbidden, such a move would be a useless suicide of a White stone.)
If a Black group has two eyes, White can never capture it because White cannot remove both liberties simultaneously. If Black has only one eye, White can capture the Black group by playing in the single eye, removing Black's last liberty. Such a move is not suicide because the Black stones are removed first. 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 marked a is not actually an eye. White can play there and take a black stone. Such a point is often called a false eye.[72]
Seki (mutual life)
There is an exception to the requirement that a group must have two eyes to be alive, a situation called seki (or mutual life). Where different colored 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; in such situations therefore both players' stones remain on the board (in seki). Neither player receives any points for those groups, but at least those groups themselves remain living, as opposed to being captured.[lower-alpha 5]
Seki can occur in many ways. The simplest are:
- each player has a group without eyes and they share two liberties, and
- each player has a group with one eye and they share one more liberty.
In the "Example of seki (mutual life)" diagram, the two circled points are liberties shared by both a black and a white group. Both of these interior groups are at risk, and neither player wants to play on a circled point, because doing so would allow the opponent to capture their group on the next move. The outer groups in this example, both black and white, are alive. Seki can result from an attempt by one player to invade and kill a nearly settled group of the other player.[72]