The concept of Life and death is a consequence of two basic Go rules.
- A group of stones with no liberties is captured.
- A stone may not be played on a position where it will be captured directly, unless it directly captures another group.
Because of these rules, some groups can never be captured (alive), while others can’t avoid capture (dead).
See the diagram on the right, and suppose white tries to capture the black groups:
- a: White is not allowed to play a, because a white stone at a would be captured immediately.
- b: White may play b, because the black group will be captured first.
- c+d: White can not play c, because the white stone at c would be captured immediately, while the black group still has another liberty at d, so it won’t be captured. The same logic holds for playing d.
The black group with the letters c and d can never be captured, and is called alive. The group can live because it has two — separated — inner liberties, where white can’t play. A group such as b that cannot become alive is called dead. Groups that are neither alive, nor dead, are called unsettled.
Liberties inside a group, where the opponent can not play, are called eyes. In the previous example, a, b, c and d are eyes. An eye may be a single empty intersection, or more of them. In the diagram on the left, the intersections marked e form a single eye, and f forms another eye. The group has two — separated — eye spaces. Even though white can make a move in these eyes, black could eventually capture the white stones, and each eye would thereby be reduced to a single intersection.
Life and death situations and issues occur when an area with a group of stones surrounds a small area (<7 points) so that it may not be possible to form two separate independent “eyes”. As the board fills up during the course of the game, certain groups will survive, and others may not. A group with a single eye can normally be captured, in the end, by filling first round the outside. The purpose of making two eyes is to prevent this. Novices sometimes interpret making two eyes in a narrow way, and form ‘explicit’ eyes one by one. This is often the wrong approach, and it is better to play generally to make a territory inside a group out of which two eyes can surely be made, if and when the opponent attacks it. Groups with seven or more points of territory will be able to form two eyes easily when attacked, unless there are some serious structural weaknesses.
Because the loss of a group can mean the loss of the game, and because the efficient use of each move is important, knowing the life and death status of one’s own groups (as well as one’s opponent’s) is an important skill to cultivate, if one is to become a strong player. The correct, accurate plays with which to make a group secure, or to kill the opponent’s group, are studied deeply by all strong players.
Virtually all games will have at least a few dead stones, which remain on the board at the end of the game, when both players pass. Those dead stones are then removed, in an operation often called ‘cleaning’, which is a separate phase of the game. The stones removed are treated exactly like other captured stones. Under Chinese rules, which use area counting, stones removed during the cleaning phase are returned to their bowls.
It is a novice mistake to carry out the capture of dead stones before it is of tactical importance to do so. Such plays, during the game, waste a turn and may also cost points.
Single stones and small groups are often sacrificed. In cases where a group is more than of sacrificial value, that group typically must make life in order for one to have a chance at winning the overall game.
Generally each side will have at most 4-5 living groups on the board at the end of the game. There is a go proverb that says that “Five groups may live, but the sixth will die”  which in a nutshell describes the need to emphasise connection between developing groups. The struggle for life can be solved by connection. Since each group needs two eyes, (and eyes are sometimes hard to come by) the alternative is to connect out to another group, thereby sharing both liberties and eyes.