The Ko Rule in Go
“Ko” is Japanese for eternity, and the ko rule exists to stop the game from lasting forever. It is one of the few rules that surprises new players, so here is exactly how it works.
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The problem ko solves
In certain shapes, a single stone can be captured, and the opponent could then immediately recapture, returning the board to exactly where it was. Without a rule, the two players could repeat this forever.
The rule
You may not play a move that recreates the board position as it was immediately before your opponent's last move. So after your stone is captured in a ko, you must play somewhere else first; you can only retake the ko on a later turn.
Ko fights and ko threats
Because you must play elsewhere before retaking, players make “ko threats” — moves the opponent must answer. If your threat is big enough, your opponent responds, and you can then retake the ko. Ko fights are some of the most exciting moments in Go.
Superko
Superko is a stronger version of the rule that forbids recreating any previous whole-board position, not just the most recent one. GoingBoard enforces positional superko, which cleanly handles rare multi-stage repetition.
Frequently asked questions
- Why is it called ko?
- Ko (劫) is a Buddhist term for an immense span of time. It refers to the endless repetition the rule prevents.
- What is a ko threat?
- A move played elsewhere that your opponent must respond to. It buys you the turn you need before you are allowed to retake the ko.
- Does GoingBoard enforce ko automatically?
- Yes. GoingBoard tracks the board's history and won't allow an illegal ko recapture — it uses the positional superko rule.
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