How to Play | British Go Association

Capturing strings

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

In Diagram 6 the strings of Diagram 5 have both been reduced to just one liberty. Note that the black string 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 string have become white territory, and vice versa.

A player may not self-capture, that is play a stone into a position where it would have no liberties or form part of a string 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 self-capture. In Diagram 8, White may not play at i or j, since either of these plays would be self-capture; 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 capture some stones, they do not count as self-capture.

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

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

Diagram 11

In Diagram 11, the black string at the bottom is in danger of being captured. To ensure that Black's string has two eyes, Black needs to play at o. If White plays at o, the black string 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 string's death.

The black string 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 string cannot be saved.

In the course of a real game, players are not obliged to complete the capture of an isolated dead string once it is clear to both players that the string is dead. We call this a hopeless string. In Diagram 11, once White has played at o, the situation may be left as it is until the end of the game. Then, the hopeless strings 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 Japanese 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 made at least one play elsewhere. Black may then fill the ko, but if Black chooses not to do so, instead answering White's intervening turn elsewhere, White is then permitted to retake the ko. Similar remarks apply to the other two positions in these diagrams; the corresponding plays at w and v in Diagram 13 must also be delayed by one turn.

Diagram 14

Seki - a kind of local stalemate

Usually a string which cannot make two eyes will die unless one of the surrounding enemy strings 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 string 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.

The end of the game

When you think your territories are all safe, you can't gain any more territory, reduce your opponent's territory or capture more strings, instead of playing a stone on the board you pass and hand a stone to your opponent as a prisoner. Two consecutive passes ends the game.

Any hopeless strings are removed and become prisoners. If you cannot agree whether a string is dead or not, then continue playing; you can then complete capture of disputed strings or confirm they are alive. (Playing during a continuation does not change the score as each play is the same as a pass.) Since Black played first, White must play last and may need to make a further pass.

Now you know how to play. However there are a few other things you should know:

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 Black's first turn. Once all the handicap stones have been placed in position it is White's turn to play.

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 (Black is facing the board from the bottom), for each of 1 to 9 stones handicap.

Diagram 15

Komi

Black has a natural advantage in playing first. So in games between players of the same strength, it is usual to compensate White for the disadvantage of playing second by adding points to White's score. These points are called komi. From experience the value of playing first is about 7 points, so this is the normal size of komi. In tournaments, komi is often set at 7.5 points to avoid draws.

In a 1 stone handicap the weaker player is Black but no komi is given to White.

Next: An Example Game

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