The Ko Rule in Go: Why You Can't Immediately Recapture
⏱ Read ~5 min · Updated July 2026 · Part of: Learn Go
The ko rule exists for one reason: to stop the same capture repeating forever. It's the only rule in Go that ever forbids a move, and once you see the picture it creates, it's unforgettable.
| English | 中文 | Plain meaning |
|---|---|---|
| ko | 劫／打劫 | a single-stone capture that can't be instantly retaken |
| ko threat | 劫材 | a forcing move played elsewhere to gain time |
| ko fight | 打劫（過程） | back-and-forth over a ko |
| sente | 先手 | having the initiative — opponent must respond |
| gote | 後手 | losing the initiative — you respond |
1. The infinite loop ko prevents
Picture this exact shape: one Black stone and one White stone, each with one liberty, sitting so that either player could capture the other.
Without a rule, this loops forever:
- Black captures the White stone. ♻️
- White recaptures the Black stone. ♻️
- Black recaptures again… and the board never changes.
The ko rule breaks the cycle with one line: after you capture a single stone in a ko, your opponent cannot immediately recapture that same stone. They must play somewhere else first.
2. The ko picture (one shape to recognize)
🔁 A ko looks like two single stones that have just captured each other's neighbor — a tight 1-vs-1 trade. When you see it, remember: the player who just got captured must tenuki (play elsewhere) before they can take the stone back.
🛑 Analogy: two people grabbing the same parking spot. If they could yank the keys back instantly, they'd fight forever. The rule is "let go, go do something else, then come back."
3. Ko threats (how kos actually play out)
Since the recapturer must play elsewhere first, they play a ko threat — a forcing move somewhere else on the board that the opponent should answer. If the opponent answers, the recapturer is now free to retake the ko.
This back-and-forth — capture ko → play threat → answer threat → retake ko → opponent plays a threat → … — is called a ko fight. Whoever has more (or bigger) ko threats usually wins the ko.
4. Sente and gote (the engine under ko threats)
Ko threats work because of sente and gote:
- 🥇 Sente (先手): a move so urgent the opponent must answer it. You keep the initiative.
- 🥈 Gote (後手): a move the opponent can ignore. You lose the initiative.
A good ko threat is sente — it forces a response, which buys you the right to retake the ko. This is the same sente/gote idea that runs through the entire game; ko is just where beginners first meet it.
5. Ko on a 4×4 board
On a 4×4 board kos appear fast and resolve fast, because there's little room for big ko threats elsewhere. That makes ko a clean teaching shape: you see the loop risk, you see the threat mechanic, and the fight ends quickly. (Full superko rules — "no board position may ever repeat" — matter on big boards; on 4×4 the simple "no instant recapture" version is what you'll meet.)
Try it
The ko rule clicks when you see the loop once — then break it.
👉 Play brainGO — meet your first ko
Related guides
- Learn Go: the visual beginner's guide
- Capture in Go — the move that starts a ko
- Atari in Go — stones in a ko are in atari