Rules of Go
The rules of Go have seen some variation over time and from place to place. This article discusses those sets of rules broadly similar to the ones currently in use in East Asia. Even among these, there is a degree of variation.
Notably, Chinese and Japanese rules differ in a number of aspects. The most significant of these are the scoring method, together with attendant differences in the manner of ending the game.
While differences between sets of rules may have moderate strategic consequences on occasion, they do not change the character of the game. The different sets of rules usually lead to the same game result, so long as the players make minor adjustments near the end of the game. Differences in the rules are said to cause problems in perhaps one in every 10,000 games in competition.
This article first presents a simple set of rules which are, except for wording, identical to those usually referred to as the Tromp–Taylor Rules, themselves close in most essential respects to the Chinese rules. These rules are then discussed at length, in a way that does not assume prior knowledge of go on the part of the reader. The discussion is for the most part applicable to all sets of rules, with exceptions noted. Later sections of the article address major areas of variation in the rules of go, and individual sets of rules.
A set of rules suitable for beginners is presented here. In some respects, these differ from the rules most commonly used. However, the basic rules are simply stated, and provide a convenient basis on which to discuss differences in rulesets. The rules are studied more fully in § Explanation of the basic rules below.
Two statements of the same basic rules, differing only in wording, are given here. The first is a concise one due to James Davies. The second is a formulation of the basic rules used for expository purposes in this article.
Except for terminology, the basic rules are identical to the Logical Rules first proposed in their current form in September 1996 by John Tromp and Bill Taylor. They are also quite close to the Simplified Ing Rules of the European Go Federation, the only exception being the method of ending the game.
- The board is empty at the onset of the game (unless players agree to place a handicap).
- Black makes the first move, after which White and Black alternate.
- A move consists of placing one stone of one's own color on an empty intersection on the board.
- A player may pass their turn at any time.
- A stone or solidly connected group of stones of one color is captured and removed from the board when all the intersections directly adjacent to it are occupied by the enemy. (Capture of the enemy takes precedence over self-capture.)
- No stone may be played so as to recreate a former board position.
- Two consecutive passes end the game.
- A player's area consists of all the points the player has either occupied or surrounded.
- The player with more area wins.
These rules rely on common sense to make notions such as "connected group" and "surround" precise. What is here called a "solidly connected group of stones" is also called a chain.
The basic rules are formulated here in a more detailed way to ease their presentation in § Explanation of the basic rules below. (Each rule and definition links to a detailed explanation in that section.)
An optional rule prohibiting suicide is included as Rule 7A.
Players and equipmentEdit
- Rule 1. Players: Go is a game between two players, called Black and White.
- Rule 2. Board: Go is played on a plain grid of 19 horizontal and 19 vertical lines, called a board.
- Rule 3. Stones: Go is played with playing tokens known as stones. Each player has at their disposal an adequate supply (usually 180) of stones of the same color.
- Rule 4. Positions: At any time in the game, each intersection on the board is in one and only one of the following three states: 1) empty; 2) occupied by a black stone; or 3) occupied by a white stone. A position consists of an indication of the state of each intersection.
- Definition. ("Connected") Two placed stones of the same color (or two empty intersections) are said to be connected if it is possible to draw a path from one intersection to the other by passing through adjacent intersections of the same state (empty, occupied by white, or occupied by black).
- Definition. ("Liberty") In a given position, a liberty of a stone is an empty intersection adjacent to that stone or adjacent to a stone which is connected to that stone.
- Rule 5. Initial position: At the beginning of the game, the board is empty.
- Rule 6. Turns: Black moves first. The players alternate thereafter.
- Rule 7. Moving: When it is their turn, a player may either pass (by announcing "pass" and performing no action) or play. A play consists of the following steps (performed in the prescribed order):
- Step 1. (Playing a stone) Placing a stone of their color on an empty intersection (chosen subject to Rule 8 and, if it is in effect, to Optional Rule 7A). It can never be moved to another intersection after being played.
- Step 2. (Capture) Removing from the board any stones of their opponent's color that have no liberties.
- Step 3. (Self-capture) Removing from the board any stones of their own color that have no liberties.
- Optional Rule 7A. Prohibition of suicide: A play is illegal if one or more stones of that player's color would be removed in Step 3 of that play.
- Rule 8. Prohibition of repetition: A play is illegal if it would have the effect (after all steps of the play have been completed) of creating a position that has occurred previously in the game.
- Rule 9. End: The game ends when both players have passed consecutively. The final position is the position on the board at the time the players pass consecutively.
- Definition. ("Territory") In the final position, an empty intersection is said to belong to a player's territory if all stones adjacent to it or to an empty intersection connected to it are of that player's color.
- Definition. ("Area") In the final position, an intersection is said to belong to a player's area if either: 1) it belongs to that player's territory; or 2) it is occupied by a stone of that player's color.
- Definition. ("Score") A player's score is the number of intersections in their area in the final position.
- Rule 10. Winner: If one player has a higher score than the other, then that player wins. Otherwise, the game is drawn.
Comparative features of the basic rulesEdit
The essential features of these basic rules relative to other rulesets are summarized here. Each of the differences is discussed in greater detail in a later section of the article.
What variation exists among rulesets concerns primarily Rules 7A, 8, 9 and 10.
- The basic rules use area scoring, as in China and Taiwan, and as in the official rules of many Western countries. The main alternative is territory scoring. Though territory scoring is the system used in Japan and Korea, and is customarily used in the West, it is not possible to use territory scoring unless Rule 9 is replaced by a much more complex end-of-game rule. The goal of these basic rules is to present a simple system first. See § Scoring systems below.
- The basic rules require the players to "play the game out" entirely. Virtually all rulesets used in practice provide some mechanism that allows players to begin scoring the game before the final position (the one used to score the game) has been reached. In some cases, this is merely a convenience intended to save time. In others, it may be an essential feature of the game. In any case, explaining these rules might obscure the nature of the game somewhat for a person unfamiliar with it. See § Counting phase below.
- The basic rules allow suicide (or self-capture). This is unusual outside of Taiwan and New Zealand. Inclusion of Optional Rule 7A is in line with practice elsewhere. See § Suicide below.
- The basic rules apply the rule of positional superko. This, or a similar rule, is common in official Western rulesets, but not in East Asia. See § Repetition below.
- The basic rules do not contain any special exceptions for territory in a seki. This agrees with most practice outside Japan and Korea. See § Seki below.
- The basic rules do not have a komi. This is now unusual in even-strength games, but was common practice until the mid-twentieth century. A komi is a number of points, usually five to eight, awarded to White in compensation for moving second. See § Komi below.
- The basic rules make no provision for the use of handicap stones. See § Handicap below.
- The basic rules do not specify a counting system. A counting system is a conventional method for calculating the difference in score between the players (hence determining the winner). It may incorporate various devices, such as filling in one's territory after the game, or shifting stones on the board into patterns, which allow quicker calculation of the difference in scores.
Explanation of the basic rulesEdit
The object of the game of go is, in rough terms, to control more territory at the end of the game than one's opponent does.
Elements of the gameEdit
Rule 1. Go is a game between two players, called Black and White.
The choice of black or white is traditionally done by chance between players of even strength. The method of selection is called nigiri. One player, whom we will call Player A, takes a handful of white stones; Player B then places either one or two black stones on the board, indicating "even" or "odd". Player A counts the number stones in their hand to determine whether there is an odd or even number. If the number of stones matches the other player's selection of "even" or "odd", Player B will play the black stones; if not, they will take the white stones.
When players are of different strengths, the weaker player takes black. Black may also pre-place several handicap stones before play begins, to compensate for the difference in strength—see below.
Rule 2. Go is played on a plane grid of 19 horizontal and 19 vertical lines, called a board.
Definition: A point on the board where a horizontal line meets a vertical line is called an intersection. Two intersections are said to be adjacent if they are distinct and connected by a horizontal or vertical line with no other intersections between them.
The condition that the intersections be "distinct" is included to ensure that an intersection is not considered to be adjacent to itself.
Intersections are also called points.
There are 361 points on a regular 19 × 19 board.
For simplicity, we will illustrate the rules mostly using 5 × 5 boards.
Each of the following diagrams shows two points on a 5 × 5 board:
|Adjacent points.||Adjacent points.||Non-adjacent points.||Non-adjacent points.|
In the first two diagrams, the points are adjacent; in the third and fourth, they are not.
Though 19 × 19 boards are standard, go can be played on another size board. Particularly common sizes for quick games are 9 × 9 and 13 × 13. (See also "Board size" below.)
Beginners might prefer to play on a 9 × 9 board to start. The nature of the game remains similar enough to make this worthwhile, yet the games are shorter. For beginners, playing longer games is less important than playing a greater number of games.
Rule 3. Go is played with playing tokens known as stones. Each player has at their disposal an adequate supply of stones of their color.
Traditionally, Black is given 181 stones, and White, 180, to start the game. This is almost always sufficient, but if it turns out to be insufficient, extra stones will be used.
Rule 4. At any time in the game, each intersection on the board is in one and only one of the following three states: 1) empty; 2) occupied by a black stone; or 3) occupied by a white stone. A position consists of an indication of the state of each intersection.
Specifying a position involves only the current state of the board. It requires no indication of whose turn it is, nor any information relating to previous moves or states of the board. This definition of "position" is used in Rule 8 ("positional superko").
The diagram shows a possible position:
Naturally, two stones are said to be adjacent if they occupy adjacent intersections. Similarly, a stone and an intersection are adjacent if the stone occupies an intersection adjacent to that intersection.
Connected stones and pointsEdit
Definition. Two placed stones of the same color (or two empty intersections) are said to be connected if it is possible to draw a path from one to the other by passing only through adjacent intersections of the same state (empty, occ. by white, or occ. by black).
The concept of connected stones is used to describe (via the concept of liberties, defined below) the conditions in which stones are captured by a move. The concept of connected empty points is used only at the end of the game, to define a player's score.
In the following position, the stones 1 and 7 are connected by the sequence of black stones 1, 2, ..., 7, in which each stone (other than 1) is adjacent to the stone before it. The empty points a and k are connected by the sequence of empty points a, b, ..., k, in which each point (other than a) is adjacent to the one before it. In fact, it is easy to see in this position that all the black stones are connected to each other and that all the empty points are connected to each other.
Let us examine the following position and determine which stones and empty points are connected.
In the diagram, stones and empty points are marked with the same number or letter, respectively, whenever they are connected to each other.
A chain is a set of one or more stones (necessarily of the same color) that are all connected to each other and that are not connected to any other stones. Although it is not necessary to define the word chain in order to state the rules, the concept is important for an understanding of the game.
For example, Black and White each have four chains in the diagram above. Black has one three-stone chain, one two-stone chain, and two one-stone chains. White has one four-stone chain and three one-stone chains.
It follows from the definitions that any stone on the board belongs to exactly one chain. Furthermore, saying that two distinct stones of the same color are connected is the same as saying that they belong to the same chain.
In a given position, a liberty of a stone is an empty intersection adjacent to that stone or adjacent to a stone which is connected to that stone.
We study some examples.
In the above position, the points a, b, c, d, e, are the liberties of the black stone at 1.
- a is a liberty of Black 1 because it is adjacent to Black 1 itself.
- b is a liberty of Black 1 because it is adjacent to Black 2, which is connected to Black 1. Alternatively, b is adjacent to Black 3.
- c is a liberty of Black 1 because it is adjacent to Black 3, which is connected to Black 1.
- d is a liberty of Black 1 because it is adjacent to Black 4, which is connected to Black 1.
- e is a liberty of Black 1 because it is adjacent to Black 5, which is connected to Black 1. Alternatively, e is adjacent to Black 4.
The result would have been the same if we had determined the liberties of Black 2, or of any other stone belonging to the black chain.
In this position:
- The black stones marked 1 have the liberties c, d and h.
- The black stones marked 2 have the liberties d, e, f, g and h.
- The black stone marked 3 has the liberties g and h.
- The white stones marked 4 have the liberties a, b and c.
- The white stone marked 5 has the single liberty c.
- The white stone marked 6 has the liberties d and h.
- The white stone marked 7 has the liberties e and f.
Since any two stones belonging to the same chain have the same liberties, we often speak of the liberties of that chain. For example, in the first diagram, the points a, b, c, d and e are the liberties of the lone black chain. In the second diagram, the liberties of the black chain in the lower right are c, d and h.
Rule 5. At the beginning of the game, the board is empty.
Alternation of turnsEdit
Rule 6. Black moves first. The players alternate thereafter.
What players may do when they move is the object of Rules 7 and 8.
Rule 7. On their turn, a player may either pass (by announcing "pass" and performing no action) or play. A play consists of the following steps (performed in the prescribed order):
- Step 1. Placing a stone of their color on an empty intersection (chosen subject to Rule 8 and, if it is in effect, to Optional Rule 7A).
- Step 2. Removing from the board any stones of their opponent's color that have no liberties.
- Step 3. Removing from the board any stones of their own color that have no liberties.
A move is defined as a play or a pass. Thus, on each turn a player moves once.
A player may pass on any move. Usually, passing is beneficial only at the end of the game, when all territory has been claimed and further moves would be useless, or even harmful to a player's position.
The following three sections discuss the successive steps of a play in greater detail. Let us observe immediately however that, in view of Steps 2 and 3, all stones remaining on the board after any move must have at least one liberty.
Placing a stone on the boardEdit
Step 1 of a play. The player places a stone of their color on an empty intersection (chosen subject to Rule 8 and, if it is in effect, to Optional Rule 7A).
As indicated by the reference to Rules 8 and 7A (respectively the superko rule and prohibition of suicide, to be discussed later), there are some restrictions on the choice of point at which to play.
The following diagrams show a possible sequence of moves at the beginning of the game:
|Start||Black plays||White plays|
The following diagrams show how Black might play later in the same game:
Numbers are often used, as here, to indicate new moves in printed diagrams.
Once a stone has been played, it remains on the board in the same location, until the end of the game or until it is captured (removed from the board as part of Step 2 or Step 3 of a play).
Step 2 of a play. (After playing their stone) a player removes from the board any stones of their opponent's color that have no liberties.
We say that the stones removed from the board have been captured by the player moving.
We now give some examples in which the capture rule is applied.
The diagrams below show the capture of a white stone by Black. To begin with, the white stone has a single liberty at a. By playing a stone at a, Black removes the last remaining liberty of the white stone. It is subsequently removed from the board.
|Before||Black plays||After removal|
At the edge of the board and especially in the corners, stones have fewer liberties to start with and are more easily captured.
|Before||Black plays||After removal|
Next, White captures a chain of four black stones by playing at a.
|Before||White plays||After removal|
Black captures the white chain by playing at a. The black stone is not captured, because the white stones are removed first, providing it with two liberties.
|Before||Black plays||After removal|
Black captures the marked white chain at the edge of the board by playing at a. Then White captures the black stone in the corner by playing at b.
|Before||Black plays||After capture||White plays||After capture|
Here, White captures the three marked black chains by playing at a.
|Before||White plays||After capture|
Step 3 of a play. (After playing their stone and capturing any opposing stones) a player removes from the board any stones of their own color that have no liberties.
Optional Rule 7A. A play is illegal if one or more stones would be removed in Step 3 of that play.
The removal of one or more stones in Step 3 is called self-capture, or suicide. Before discussing self-capture further, let us note that most rulesets give effect to Optional Rule 7A, which prohibits it. This means that, in those rulesets, any play which under the basic rules would require a self-capture to be performed is illegal. For further information, see § Suicide below.
We begin with an example which, it is emphasized, does not involve self-capture. When Black plays at a, the capture of the marked white stones results in the black chain at the bottom right acquiring liberties. This move is legal (with the same result) whatever the rules.
|Before||Black plays||After capture|
The previous example shows that it is important that Step 2 of a play (capture) precedes Step 3 (self-capture). If the order were reversed, then self-capture would occur here.
It is not difficult to convince oneself that if a play results in the capture of opposing stones, self-capture does not occur.
We now present some examples of plays in which self-capture occurs. These moves would be illegal under the optional rule prohibiting suicide.
In this example, if Black plays at a, then the stone played by them is removed immediately. This move has the same effect on the position as a pass, though it would not allow White to end the game by passing next (Rule 9). The move is in any event illegal by Rule 8. (This is the positional superko rule. This move might be legal under other versions of the superko rule. See § Repetition below.)
|Before||Black plays||After self-capture; violates Rule 8|
In the next example, Black plays at a, resulting in the self-capture of the marked black stones.
|Before||Black plays||After self-capture|
Ko and SuperkoEdit
Rule 8. A play is illegal if it would have the effect (after all steps of the play have been completed) of creating a position that has occurred previously in the game.
Though a pass is a kind of "move", it is not a "play". Therefore, Rule 8 never bars a player from passing. Before going further, we state a consequence of Rule 8 called the ko rule:
Consequence (ko rule). One may not play in such a way as to recreate the board position following one's previous move.
Whereas Rule 8 prohibits repetition of any previous position, the ko rule prohibits only immediate repetition.
Rule 8 is known as the positional superko rule. The word "positional" is used to distinguish it from slightly different superko rules that are sometimes used. While the ko rule is observed in all forms of go, not all rulesets have a superko rule. The practical effects of the ko rule and the superko rule are similar; situations governed by the superko rule but not by the ko rule arise relatively infrequently. For further information, see § Repetition below.
The superko rule is designed to ensure the game eventually comes to an end, by preventing indefinite repetition of the same positions. While its purpose is similar to that of the threefold repetition rule of chess, it differs from it significantly in nature; the superko rule bans moves that would cause repetition, whereas chess allows such moves as one method of forcing a draw. The ko rule has important strategic consequences in go.
Some examples follow in which Rule 8 applies. These examples cover only the most important case, namely the ko rule.
The first diagram shows the board immediately after White has played at 1, and it is Black's turn. Black captures the marked white stone by playing at a. If White responds by capturing at b with 3, the board position is identical to that immediately following White 1. White 3 is therefore prohibited by the ko rule.
|Black to move||Black captures||Illegal recapture|
Another example of ko follows. Here, Black 3 is illegal by the ko rule.
|White to move||White captures||Illegal recapture|
As noted in the section "Self-capture", Rule 8 prohibits the suicide of a single stone. This is something of a triviality since such a move would not be strategically useful. Taking it for granted that no suicide of a single stone has occurred, a moment's thought will convince the reader that the ko rule can be engaged in only one situation:
Restatement of the ko rule: One may not capture just one stone if that stone was played on the previous move and that move also captured just one stone.
Furthermore, this can occur only when one plays in the location at which one's stone was captured in the previous move. The two points where consecutive captures might occur, but for the ko rule, are said to be in ko. For example, in the first two diagrams above, the points a and b are in ko.
The next two examples involve capture and immediate recapture, but the ko rule is not engaged, because either the first or second capture takes more than one stone.
In the first diagram below, White must prevent Black from playing at a, and does this with 1 in the second diagram. Black can capture the three stones in White 1's group by playing at b. Black does this with Black 2 in the third diagram. White may recapture Black 2 by playing at a again, because the resulting position, shown in the fourth diagram, has not occurred previously. It differs from the position after White 1 by the absence of the two marked white stones.
|White to move||White sacrifices||Black captures||Recapture legal|
In the first diagram below, it is White's turn. White must prevent Black from connecting the marked stones to the others by playing at a. The second diagram shows White's move. White is threatening to kill the marked black stones by playing at b. In the third diagram, Black plays at b to prevent this, capturing White 1. However, by playing at a again, White can capture Black 2's group. This is not barred by the ko rule because the resulting position, shown in the fourth diagram, differs from the one after White 1 by the absence of the marked black stones. This kind of capture is called a snapback.
|White to move||White sacrifices||Black captures||White snaps back|
The next example is typical of real games. It shows how the ko rule can sometimes be circumvented by first playing elsewhere on the board.
The first diagram below shows the position after Black 1. White can capture the marked black stone by playing at a. The second diagram shows the resulting position. Black cannot immediately recapture at b because of the ko rule. So Black instead plays 3 in the third diagram. For reasons that will become clear, Black 3 is called a "ko threat".