Introduction to the game of Go

How to play Go

Although the normal size of a Go board is 19 by 19 lines, it is possible to use smaller sizes. Beginners can learn the basics on a 9 by 9 board, and a quick game can be played on a 13 by 13 board without losing the essential character of the game. The following examples all use a 9 by 9 board.

The rules and an example game

A game of Go starts with an empty board. Each player has an effectively unlimited supply of stones, one taking the black stones, the other taking white. The basic object of the game is to use one's stones to form territories by surrounding vacant areas of the board. It is also possible to capture the opponent's stones by completely surrounding them.

The players take turns, placing one of their stones on a vacant point at each turn. Black plays first. Note that the stones are placed on the intersections of the lines rather than in the squares. Once played, stones are not moved. However they may be captured, in which case they are removed from the board, and kept by the capturing player as prisoners.

Diagram 1

At the end of the game the players count one point for each vacant point inside their own territory, and one point for every stone they have captured. The player with the larger total of territory plus prisoners is the winner.

Diagram 1 shows the position at the end of a game on a 9 by 9 board, during which Black captured one white stone which had been at a.

Black has surrounded 15 points of territory, 10 in the lower right corner and 5 towards the top of the board. Black's territory includes the point a formerly occupied by the stone he has captured. Adding his prisoner, Black has a total of 16 points.

White's territory is 17 points, so White wins the game by one point.

Capturing stones and counting liberties

The points which are horizontally and vertically
adjacent to a stone, or a group of stones, are
known as liberties. An isolated stone or group
of stones is captured when all of its liberties
are occupied by enemy stones.

Diagram 2

Diagram 3

Diagram 4

Diagram 2 shows three isolated white stones with their liberties marked by crosses. Stones which are on the edge of the board have fewer liberties than those in the centre of the board. A single stone on the side has three liberties, and a stone in the corner has only two liberties.

Diagram 3 shows the same three stones of Diagram 2 each with only one liberty left and therefore subject to capture on Black's next move. Each of these white stones is said to be in atari, meaning they are about to be captured.

Diagram 4 shows the position which would arise if Black went on to play at b in Diagram 3. Black has taken the captured stone from the board, and in a real game would keep it as a prisoner. The same remarks would apply to the other two white stones, should Black play at c or d in Diagram 4.

Diagram 5

Groups

Stones occupying adjacent points constitute a solidly connected group. Two examples of such solidly connected groups of stones are shown in Diagram 5. It is important to remember that only stones which are horizontally or vertically adjacent are solidly connected; diagonals don't count as connections. Thus, for example, the two marked black stones in the top left of Diagram 5 are not solidly connected.

Diagram 6


Diagram 7

Capturing groups of stones

As far as capturing is concerned, a solidly connected group of stones is treated as a single unit. As with isolated stones, a group is captured when all of its liberties are occupied by enemy stones.

In Diagram 6 the groups of Diagram 5 have both been reduced to just one liberty. Note that the Black group in the top right is not yet captured because of the internal liberty at f. The two stones at the top left of Diagram 6 can each be captured independently at g or h.

In Diagram 7 we see the position which would result if Black captured at e and White captured at f and at g. The remaining black stone could be captured at h. As with the capture of a single stone, the points formerly occupied by the Black group have become White territory, and vice versa.

A player may not 'commit suicide', that is
play a stone into a position where it would
have no liberties or form part of a group
which would thereby have no liberties,
unless, as a result, one or more of the
stones surrounding it is captured.

Diagrams 8 and 9 illustrate the rule governing capture. In Diagram 8, White may not play at i or j, since either of these plays would amount to suicide; the stones would then have no liberties. However, if the outside liberties have been filled, as shown in diagram 9, then the plays at i and j become legal; they fill the last black liberty in each case, and result in the black stones being captured and removed from the board as White's prisoners.

Diagram 8	Diagram 9

Diagram 10

Life and death and the concept of eyes

In Diagram 9, White was able to play at i and j because these plays result in the capture of the adjacent black stones. Since White's plays make captures, they don't count as suicide.

A different situation is shown in Diagram 10. The black group here could only be captured if White were able to play at both m and n. Since the first of these plays would be suicide, there is no way that White can carry out the capture. These two separate spaces within the group are known as eyes.

Any group of stones which has two or more eyes
is permanently safe from capture and is referred
to as a live group. Conversely, a group of stones
which is unable to make two eyes, and is cut off
and surrounded by live enemy groups, is called a
dead group since it is unable to avoid
eventual capture.

Diagram 11

In Diagram 11, the black group at the bottom is in danger of being captured. To ensure that his group has two eyes, Black needs to play at o. If White plays at o, the black group will no longer be able to make two eyes, and cannot avoid eventual capture; White can always fill in the outside liberties and then play at p and at q. Black plays at p or q would only hasten the group's death.

The black group at the top left of Diagram 11 is already alive even though there is a white stone inside one of its eyes. Since White can never capture the black stones, the white stone caught inside the group can't be saved.

In the course of a real game, players are not obliged to complete the capture of an isolated dead group once it is clear to both players that the group is dead. In this case, once White has played at o in Diagram 11, the situation may be left as it is until the end of the game. Then, the dead stones are simply removed from the board and counted together with the capturing player's other prisoners.

Diagram 12

The ko rule

At the top of Diagram 12, Black can capture a stone by playing at r. This results in the situation at the top of Diagram 13. However, this stone is itself vulnerable to capture by a White play at u in Diagram 13. If White were allowed to recapture immediately at u, the position would revert to that in Diagram 12, and there would be nothing to prevent this capture and recapture continuing indefinitely. This pattern of stones is called ko - a term meaning eternity. Two other possible shapes for a ko, on the edge of the board and in the corner, are also shown in this diagram.

Diagram 13

The ko rule removes this possibility of indefinite repetition by forbidding the recapture of the ko, in this case a play at u in Diagram 13, until White has played at least one move elsewhere. Black may then fill the ko, but if he chooses not to do so, instead answering White's intervening move elsewhere, White is then permitted to retake the ko. Similar remarks apply to the other two positions in these diagrams; the corresponding moves at w and v in Diagram 13 must also be delayed by one turn.

Diagram 14

Seki - a kind of local stalemate

Usually a group which can't make two eyes will die unless one of the surrounding enemy groups also lacks two eyes. This often leads to a race to capture, but can also result in a stand-off situation, known as seki, in which neither group has two eyes, but neither can capture the other due to a shortage of liberties. Two examples of seki are shown in Diagram 14. Neither player can afford to play at x, y or z, since to do so would enable the other to make a capture.

Note that even though the groups involved in a seki may have an eye, as a general rule none of the points inside a seki count as territory for either player.

The end of the game

The game ends by agreement. When neither player believes that he can make more territory, capture more stones, or reduce his opponent's territory by playing on, he will pass instead of making a move on the board. Two consecutive passes end the game.

The handicap system

As remarked in the introduction, one of the best features of the game of Go is its handicap system. A weaker player may be given an advantage of anything up to nine stones. These are placed on the board in lieu of his first move.

Through the grading system, any two players can easily establish the difference in their strength, and therefore how many stones the weaker player should take in order to compensate for this difference. Since a player's grade is measured in terms of stones, the number of stones for the handicap is simply the difference in grade between the two players.

There is an established pattern for the placement of handicap stones, shown by the dots which are marked on any Go board. This is shown in Diagram 15, seen from the Black player's point of view. For handicaps of two or three stones, where the stones can't be placed symmetrically, the convention is that the far left corner is left vacant.

Diagram 15

Japanese and Chinese rules of Go

The rules described in this page are the Japanese rules. These are the rules most commonly used in the West. The Chinese use a different system of rules which are essentially the same but which involve a different method of counting the score. The two sets of rules usually lead to the same game result.

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This page is part of the British Go Association web site.

It is taken from the BGA's Play Go leaflet, 2004 edition.

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