Rules of Go

This is an in-depth discussion of the rules of Go.

Note: While the basic idea of go, conveyed by the outline rules given first, is not particularly complex, there are numerous subtle points which are not required to be studied when first starting to play.

Basic rules

Players

Rule: There are two players, called Black and White.

Go is a game between two players.

The equipment

The board

The board, or "goban"

Rule: Go is played on a board. The board is a grid of 19 horizontal and 19 vertical lines.

Beginners might prefer to play on a small board with 9 horizontal and 9 vertical lines (9 × 9 board). On this board learning tactics is easier and one is not confused by the complex strategies seen on big boards.

After having gained some experience (having played, say, 100 games), one can switch to the regular 19x19 board. Some teachers recommend moving up to a 13 × 13 board as an intermediate step, and this board is adequate for social players.

A point on the grid where a horizontal line meets a vertical line is called an intersection.

There are 361 intersections on the regular 19 × 19 board. In the following diagram, the mark (red circle) indicates one of the 25 intersections of the small 5 × 5 board:

(To save space, most diagrams show small boards. Here we have a 5 × 5 board.)

Stones

Rule: There are black and white stones.

The player Black uses black stones, the player White uses white stones. There is an unlimited supply of stones. The diagram shows some stones on some intersections of the board:

The state of stones on the board

Chain of connected stones

Definition: A chain consists of one stone or of several stones that are of the same colour and mutually connected via lines of the grid.

This is a chain of 6 black stones:

Liberty

Definition: A liberty of a chain is an empty intersection adjacent to it.

The marked intersections (red circles) are the liberties of the black chain:

Removal

Rule: A play removes any chains without liberties.

Before		Black plays		After removal

In most cases a play does not remove a chain. A play might remove a large chain of several stones. It is possible for a play to remove up to four groups if it takes away the last liberty of each of them. Removing an opponent's chain(s) is also called a capture.

Existence

Rule: A stone, once played, remains on the board until the game's end, unless taken by an opponent.

Play

Turn-based play

Rule: The players alternate. Black starts.

Before Black plays first, the board is empty. Black makes a first play on one of the intersections. Then White makes a second play somewhere:

Start		Black plays		White plays

The game will continue with Black and White alternating.

Play or pass

Rule: On his turn, a player makes either a play or a pass.

Normally, the player having the turn makes a play.

Empty intersection

Rule: When a player makes a play, he or she puts one stone of his or her colour on an empty intersection.

The following diagram shows how Black could make a play:

No suicide (not present in some variations!)

Rule: You cannot place a stone where it would have no liberties (or be a part of a larger chain with no liberties), unless the play completes a removal of opposite stones.

For example, in the above diagram, black can't play at the circled point.

For example, in the above diagram, white can't play at the circled point.

Note: Some Go rulesets allow suicide. The chain with no liberties is removed from the board.

Ko (no repetition of the same shape)

Rule: If recapturing a stone would recreate the same board position from the previous move, the position is called ko, and the recapturing move is illegal.

In the position above, Black has just captured a stone at the circled point by playing to the right of that point. White could now recapture Black's stone, and so on in infinite stalemate. The ko rule prevents this situation and enables the game to keep moving. This "basic ko rule" is adequate for the simplest kind of ko, which occurs when two single stones could otherwise recapture each other indefinitely. This situation occurs in most games and often has a major or even decisive effect on the result. To prevent endless repetition, the rule of ko forbids plays that would repeat the previous board position. A player may not recapture on their next move and must play elsewhere (or pass). After a new move, the board position will be different, and the stone may then be recaptured.

Other positions which could lead to an endlessly repeating position are rare enough that many frequent players never encounter them; their treatment depends on what rule set is being used. Under some rule sets, such games may be considered drawn if neither player opts to escape the loop by playing elsewhere (as a player with an overwhelming lead might be inclined to do). The AGA and New Zealand rule sets have a "superko" rule forbidding any move that repeats any previous board position. The Ing rules feature a complicated distinction between "fighting" and "disturbing" ko.

The word ko (Japanese: 劫 kō; usually written with katakana コウ) means "eternity" in Japanese [1], and is pronounced with a double-length "o", making it sound somewhat like 'kou' does in English.

Seki

Rule: When adjacent groups of black and white are neither alive nor able to capture each other, the situation is called seki.

If either black or white were to play at the captured point, either side would then capture the other group by playing in their eye.

This corollary to all rule sets applies to situations in which groups of black and white stones have mutually dependent life, although neither Black nor White is alive independently. In most rule sets, the vacant points in a seki are treated as neutral points for counting purposes. The Ing rules have a complicated formula for allocating them to each side, based on the number of black and white stones that are touching the neutral points.

Pass

Rule: When a player does not wish to play a move, he or she says "pass." This generally happens at the end of the game, when all territory has been claimed and further moves seem useless, or even harmful to a player's position. Alternation continues with his or her opponent.

End

Rule: Alternate play ends when a player makes a pass and then his opponent also passes.

Winner

The player with the higher score is the winner. Margin of victory does not matter; one point is as good as 100. Different scoring rules exist which in practice almost always determine the same winner, see Scoring section below. You choose a rule set before starting the game.

Optional rules

Compensation

To allow players of different skills to compete fairly, handicaps and komi are used. These are considered a part of the game and, unlike in many other games, they do not distort the nature of the game. Players at all levels employ handicaps to make the game more balanced.

Komi

Main article: Komidashi

In an "even", or non-handicap game, Black's initial advantage of moving first can be offset by komi (compensation points): a fixed number of points, agreed before the game, added to White's score at the end of the game. The correct value of komi (to properly compensate for Black's advantage) is controversial, but common values are 5.5, 6.5 or 7.5 -- the fractional value avoids a tied game. In a handicap game, komi is usually set to 0.5 (i.e. White wins if the game is tied). A handicap game with a handicap of 1 starts like an even game, but White receives only 0.5 komi (i.e. a White player who is stronger by one rank is handicapped only by Black's first-move advantage).

Handicap

Main article: Go handicaps

Handicaps are given by allowing the weaker player to take Black, and declaring White's first few moves as mandatory "pass" moves. In practice, this means that Black's first move is to place a set number of stones (usually the number is equal to the difference in the players' ranks) on the board before allowing White to play. Traditionally, the hoshi ("star points") -- strategically-important intersections marked with small dots -- are used to place these handicap stones. On the 19x19 board, there are nine star points: at the four 4-4 points in the corners, at the four 4-10 points along the sides, and one at the 10-10 point (the centre of the board, or tengen in Japanese). Smaller boards such as the 13x13 and 9x9 also have star points. The 13x13 has 9 at the 3-3 points, 3-6 points, and the center. The 9x9 board has only 5 points: the 3-3 points and the center.

When Black is only one rank weaker (also known as one stone weaker, due to the close relationship between ranks and the handicap system) he or she is given the advantage of playing Black, perhaps without komi, but without any mandatory White passes. For rank differences from two through nine stones, the appropriate number of handicap stones are used. Beyond nine stones, the difference in strength between the players is usually considered great enough that the game is more a lesson, with White teaching Black, so nine stones is the nominal upper limit on handicap stones regardless of the difference in rank (though higher numbers of stones, up to 41 stones in some cases, can be given if the teacher wants more of a challenge).

Thinking times

See the Time control section of the main Go article.

Variations

Go is an ancient game and as such the rules are not entirely set in stone. The two main variations in use today are the Japanese-style ruleset and the Chinese-style ruleset (the description above is for the Japanese rules). Sadly this is rather time- , fashion- and philosophy-dependent, resulting in the fact that the age of almost all rules is very young compared to the age of the game Go. See for a short concise overview the Go rule dialects.

Scoring

The defining difference between rulesets is the scoring method, where three different principal aims or philosophies exist:

In territory scoring (Japanese traditional method), a player's score is determined by the number of empty locations that player has surrounded minus the number of stones their opponent has captured. At the end of the game, each player places prisoners in the opponent's territory and rearranges them into easy-to-count shapes as much as possible.

In stone scoring (Chinese traditional method) a player's score is determined by the number of stones that player has on the board. At the end of the game, the players use black stones to fill the black territory, and all white stones are removed from the board. Score is determined by counting the black stones. Since the board contains 361 intersections, Black must have 181 or more stones to win. This method was spread in mainland of China for many hundreds of years until at least the beginning of the 20th century.

In area scoring (Chinese modern method) a player's score is determined by the number of empty locations that player has surrounded plus the number of stones that player has on the board. At the end of the game, the players use black stones to fill the black territory, and all white stones are removed from the board. Score is determined by counting the black stones. Since the board contains 361 intersections, Black must have 181 or more stones to win. It was invented/defined in the 70th year of the 20th century in the main land of China. A practical modification of counting the score is to arrange black's territory in rectangles of ten, then count that total aloud, then count aloud black's stones in groups of ten (five plus five) while ignoring the white stones. This is a popular method of counting because the rectangles are aesthetically appealing and it builds tension as the count approaches the critical number 181.

Around 1975, Taiwanese player and industrialist Ing Chang-ki invented a method of scoring based on the "area" method. each player begins the game with exactly 180 stones (Mr. Ing also invented special stone containers that count each player's stones). At the end, all stones are placed on the board. One vacant intersection will remain, appearing in the winner's area; the number of stones of one color in the other color's area will indicate the margin of victory.

If the game ends with both players having passed the same number of times, then the score will be identical no matter which method is used. AGA rules call for a player to give the opponent a stone when passing. This "passing stone" ensures a correct result under any counting method.

The tradition of agreeing upon certain outcomes without playing them out is notably more complicated under Japanese-style rulesets where stones are removed and territory counted (or not) even though such an outcome could not be reached under normal play.

Repetition

The major division in rules to prevent repetition is between the simple ko rule and the super ko rule: the simple ko rule (typically part of the Japanese ruleset) prevents repetition of the last previous board; while the super ko rule (typically part of Chinese derived rulesets) prevents repetition of any previous board. The super ko rule is further differentiated into situational super ko (includes whose turn it is) and positional super ko (ignores whose turn it is). The simple ko rule (contrary to the name) generally includes additional rules to handle other undesirable repetitions (e.g. long cycles can lead to no result where the game must be replayed).

Suicide

Currently most major rulesets forbid playing such that a play results in that player's own stones being removed from the board, however some rulesets (notably, New Zealand derived rules and ING rules) allow suicide of more than one stone. The suicide of the nakade can be sometimes used as a ko threat. Sometimes suicides can be used strategically to win a large area or territory versus the alternative of neither player getting anything or for both to be in a standstill.

Compensation

The major rulesets differ in how handicap stones are placed on the board: free placement(Chinese), where stones can be placed anywhere (as if the player's turn repeated); and fixed placement(Japanese), where tradition dictates the stone placement (according to the handicap). Area scoring rules and territory scoring rules also differ in the compensation given for each handicap stone (since each handicap stone would count under area scoring). Komi (compensation for going first) also varies, ranging from several fixed values (commonly 5.5, 6.5, or 7.5) to various meta-games to determine a value (notably Auction Komi).

Board sizes

Most Go is played on a 19x19 board, but 13x13 and 9x9 are also popular sizes. Historically other board sizes were commonly used (notably 17x17, which is thought to have evolved into the current 19x19 board). Go is also sometimes played on various novelty sized boards (usually very large). Generally all rules apply to all board sizes, with the exception of handicaps and compensation (whose placement and values vary according to board size).

Rule sets

There are many official rule sets for playing Go. These vary in significant ways, such as the method used to count the final score, and in very small ways, such as whether the two kinds of "bent four in the corner" positions result in removal of the dead stones automatically at the end of the game or whether the position must be played out, and whether the players must start the game with a fixed number of stones or with an unbounded number.

Rule sets include Japanese, Chinese, AGA (American Go Association), Ing, and New Zealand rules.

Further detailed information may be found at the following external links.

Japanese rules

These are rules used in Japan and Korea, and are in wide use throughout the West, sometimes known as "territory" rules. The scoring is based on territory and captured stones. At the end of the game, prisoners are placed in the opponent's territory and players rearrange the board so that territories are easy to count, leaving a visual image resembling the game, which some players find aesthetically pleasing. There is no superko (the triple ko leads to an undecided game.) Suicide is always forbidden. Komi is 6.5.

Chinese rules

This is the other major set of rules in widespread use, also known as "area" rules. At the end, one player (usually Black) fills in all of his/her captured territory, and the other (White) stones are removed from the board. Prisoners do not count. Black stones are then arranged in groups of ten -- eighteen such groups, plus half the komi, plus at least one additional stone = victory for Black. So for example with a komi of 7.5 points, under chinese rules Black needs at least 185 stones on the board at the end to win. Komi is usually 7.5 points.

AGA rules

These are used by the American Go Association. Some special rules (like giving the opponent a prisoner when passing) are added, which make the area scoring and territory scoring equal.

ING rules

The scoring is basically the same as area scoring, but is done with a special technique involving "Ing bowls". Both players must start with exactly 180 stones; the Ing Foundation makes special bowls that allow players to count their stones easily. Prisoners come back to the owner. After the game finishes, both players fill their empty territory with their stones. The one that gets rid of all of them is the winner. White pays Black eight points (komi) by placing four white stones in Black's territory at the beginning of the counting phase. As Black wins ties it is 7.5 in effect. There is a superko rule. Multi-stone suicide is allowed. This ruleset was invented and promoted by Ing Chang-ki.

Differences

In most cases the differences between the rule sets are a few points which only makes a difference in professional games that are close and nearly a draw. Strategy wise, since players are discouraged to continue playing lost positions in Japanese rules, they will most likely stop (they lose territory, and thus points by putting in their own territory and lose a point if it becomes a prisoner), while in Chinese rules, since there is no point loss for prisoners, players can keep playing until they are satisfied with an area (the only caveat is that they may be wasting moves and thus there is only an opportunity cost to moves where they could have gotten more points or lessened the damage, compared to the move they made). It's because of the design of the Chinese rules that players using this rule set will be more able to take greater risks than compared to playing under Japanese rules; this may draw games out a little longer and at certain times seem dishonorable.

See also

• Go (board game)
• Go concepts
• Go strategy and tactics

External links

Rules comparisons

• A listing of rules pages
• Another listing of rules pages
• Brief descriptions of different rule sets
• Comparison of some go rules summarized in a table
• Go (Weiqi, Baduk) rules
• Go rule dialects

Specific rule sets

• Official American Go Association rules
• Official Japanese rules as amended in 1989
• Official Chinese rules
• Ing's SST laws of Goe
• “Logical” rules (Tromp-Taylor ruleset, also known as "New Zealand rules")
• “Simple” rules
• Click here for a collection of essays assessing and comparing the various rule sets