Life and death
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Life and death is a fundamental concept in the game of Go, where the status of a distinct group of stones is determined as either being "alive", and may remain on the board, or "dead," where the group will be lost as "captured". The basic idea can be simply but slightly inaccurately put in the form that:
- A group must have two eyes (meaning secured internal liberties) to live (meaning to survive through to the end of the game).
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[edit] Importance
Life and death situations and issues occur when an area with a group of stones is contained closely by the opponent's stones, so as to make the status of that group questionable. As the board fills up during the course of the game, certain groups will survive, and others will 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 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. Most groups with ten 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 developed group can often 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.
[edit] Status of a group
The concept of 'status' is discussed in Life and Death by James Davies. The idea, naturally enough, is traditional. Groups of stones are divided into those that are alive, dead or unsettled. Here alive, for example, is an unconditional judgement made, that with best play from both players, the group can survive to the end of the game. That assumes the opponent starts: the alive status means that, whatever the attack made, there is an adequate defensive answer.
The unsettled status is therefore most worthy of attention. By playing first, the attacking player can kill such a group. By playing first, the defending player can save such a group. There is an enormous range of formations that are unsettled.
[edit] Caveats
Because of the possibility of seki positions, the basic doctrine on two eyes is not to be applied absolutely literally. It is not precisely the case that the necessity of two eyes is a derived rule of the basic rules. That being said, mastery of the principle of two eyes is completely fundamental for go players.
Groups that are alive may yet die. One reason is that they may be sacrificed, in the course of a ko fight.
Another way in which the ko rule enters the discussion is through the complications ko adds to the classification by status. It is quite possible for a group to be alive in ko: that is, the group is conditionally alive, the condition being to be able to win a particular ko fight relating to the control of a key intersection.
[edit] Dead stones
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. Under Japanese and Korean rules 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, there is no need for a separate cleaning phase, and captured stones are returned to 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" [1] 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.
[edit] Aji
Even if a group is lost, one can still use one's own dead stones for aji (potential). Ko threats are just one way in which apparently dead stones are put to good use. Expert players use a variety of 'squeezing' tactics, of which semedori, an advanced endgame technique, and shibori are two that have recognised Japanese-language names.
[edit] See also
[edit] References
- James Davies, Life and Death: Elementary Go Series, Vol. 4, The Ishi Press, Inc., Tokyo, Japan, 1975.
[edit] External links
- Goproblems.com site has over 3000 life and death and other Go puzzles, in an interactive applet. (Requires Java)
- GoTools, free (but a password will be required) Java applet for solving life-and-death problems, of professional level (those problems, set in limited spaces, with a clear objective, are essentially the only subdomain of go where real progress have been made in Artificial Intelligence)
