Suicide
The term suicide (or self-capture) refers to a move which is played such that the stone just placed has no liberties, but all opposing stones still have.
Suicide moves are forbidden under Japanese rules and Chinese rules; but some other rulesets, such as Ing rules, New Zealand rules and Tromp-Taylor rules, do allow suicide, at least when it is suicide of more than one stone.
A suicide of one stone does not change the position on the board, and therefore may be forbidden or equivalent to passing, depending on the ruleset [1].
For the vast majority of the cases, even if suicide is allowed, it only causes a loss of stones and/or points to oneself.
However, in rare cases, suicide of more than one stone can be a useful move. The rest of this article gives examples of how suicide can be useful.
The simplest, and best known, situation where suicide can make a difference is as a ko threat. In this position, the black group is alive. However, if White is allowed to play the suicide move of , taking three white stones off the board, Black will have to come back at the same point to make two eyes. If suicide is forbidden, then White has no ko threat here.
But sometimes suicide also makes a difference for the outcome of a capturing race. In this diagram, if White is not allowed to play suicide, she is dead. There is no way for White to avoid that: Black first fills up two liberties with to
, then captures at
, resulting in the next diagram.
Playing at to prevent Black from getting two eyes will not help White.
Black plays atari at , and White is dead.
Note that these diagrams are just used to show that White is indeed dead - Black need not hurry to take the stones off the board.
...but, if suicides were permitted....
If suicide is allowed, White does have a resource in this situation. She can play the suicide move of . The result is shown in the next diagram.
After , the position is a seki; neither player can make any useful move - so this time, White lives. If Black plays
or
at
or
or a, the position is still seki, each player having one eye and no external liberties.
[1] The status of self-capture of a single stone in various rulesets which allow suicide is as follows:
- Ing rules explicitly forbid suicide of a single stone.
- Tromp-Taylor rules have the positional superko rule, so suicide of a single stone is not allowed.
- New Zealand rules have only situational superko, so suicide of a single stone is usually allowed. When allowed, it is equivalent to passing. It is not allowed after a pass.
A very unusual incident occurred in the first round of the
15th Korean Kiseong tournament (2003-10-02). Cho Hunhyun 9p was forced to lose a game
(against Choi Cheolhan) because of an illegal move. You can see the game record at the time of the infraction at go4go (or at illegal move). Cho obviously intended to take the ko in the lower left corner when he made an illegal suicide play instead (on the lower edge). Such a mistake is extremely rare in professional tournaments.
Main author:
- Andre Engels (2D Europe)