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SelfCapture

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EyeDefinitionDisc...
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TrompTaylorRules
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Suicide
  Difficulty: Advanced   Keywords: Tactics, Rules

The term suicide (or self-capture) refers to a move which is played such that the stone that is played has no liberties.

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]. Suicide of more than one stone can, however, be a useful move.


[Diagram]
Suicide as a ko threat

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 W1, 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.



[Diagram]
A capturing race

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 B1 to B5, then captures at B7, resulting in the next diagram.


[Diagram]
Black wins

Playing at W1 to prevent Black from getting two eyes will not help White. Black plays atari at B2, 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.

[Diagram]
Suicide permitted

If suicide is allowed, White does have a resource in this situation. She can play the suicide move of W2. The result is shown in the next diagram.


[Diagram]
White wins

After W4, the position is a seki; neither player can make any useful move - so this time, White lives. If Black plays B1 or B3 at W2 or W4 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.

Robert Pauli: Please make it more clear, Andre. After the suicide move the stone you're talking about is gone. So it hardly makes sense to refer to this point in time when talking about missing liberties. My humble suggestion therefore:

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.

Main author:



This is a copy of the living page "Suicide" at Sensei's Library.
(OC) 2003 the Authors, published under the OpenContent License V1.0.