Most groups in Go either live, with two eyes, or die. But there is a third possibility that surprises many new players: seki, sometimes translated as mutual life. In a seki, two groups of opposite colours are locked together, sharing liberties, and neither player can attack without destroying their own group. The result is that both groups stay on the board until the end of the game.
This article explains how seki arises, how to recognise it, when you should aim for it, and how it is counted under the area scoring used on this site.
How seki happens
Seki usually comes out of a capturing race. Two groups are surrounding each other. Each has few liberties, and some of those liberties are shared: they touch both groups.
Normally, the player to move fills the opponent's liberties and wins the race. But sometimes the only liberties left are shared ones, and filling any of them would put the filler's own group in atari. If you fill a shared liberty, your opponent captures you. If your opponent fills one, you capture them. So neither player moves there, and the position freezes.
That frozen state is seki. Both groups are alive, even though neither has two eyes.
Recognising seki
Look for these features:
- Two groups of opposite colours, adjacent to each other.
- Neither group has two eyes; often neither has any eye, or each has exactly one.
- All remaining liberties of at least one group are shared with the other.
- Any move on a shared liberty would reduce the mover's own group to one liberty and let the opponent capture.
When you see this, stop and read. If filling a shared point is self-destructive for both sides, it is seki, and neither side should play there.
The two common kinds
- Seki with no eyes. Two groups share two liberties and have no other liberties. Whoever fills one of the two shared points is left in atari and captured. So neither fills.
- Seki with one eye each. Each group has one eye and they share one liberty. Filling the shared liberty would leave the filler with only its eye, and the opponent then captures by playing in that eye. So neither fills.
There are also more complex forms involving larger eyes or edge shapes. The principle is always the same: attacking is self-destructive for both.
When to aim for seki
Seki is a tool, not only an accident.
- When your group is losing a capturing race, look for a way to reach seki instead. Saving a group through seki is a big success, because otherwise it would die and give your opponent all the area around it.
- When your opponent's group can live with two eyes, sometimes you can reduce it to seki instead, denying it the territory inside its eyes.
- When you are winning a race, make sure you do not accidentally allow seki. Fill outside liberties first and count carefully.
Scoring seki under area scoring
This site uses area scoring with komi 7.5: each player counts stones on the board plus empty points reachable only from their stones. For seki, that means:
- Stones in the seki count for their owners. They are on the board, so they are points.
- Shared liberties count for nobody. A shared liberty touches both colours, so it is not surrounded by either player.
- An eye inside a seki group is an empty point surrounded by that group's stones. Under the area count used here, if it is reachable only from that group's stones, it counts for the group's owner.
Under territory scoring, the traditional treatment of seki is different in some rule sets, where points inside seki groups are not counted as territory. That is one of the small places where territory and area scoring differ; see territory versus area scoring.
Seki and the end of the game
On this site, the game ends when both players pass in a row, and the board is counted as it stands. Seki groups are simply left on the board. You do not capture them and you do not need to fill the shared liberties. In fact, trying to fill them is the mistake that seki punishes.
Before passing, make sure:
- Dead stones in your area are captured.
- Neutral points that can be filled safely are filled.
- Shared liberties in seki are left empty.
The article on capture dead stones before passing explains the first step in detail.
A common beginner mistake
New players who see a seki often think: "My opponent's group has no eyes, so I should be able to capture it." They fill a shared liberty, and immediately their own group is captured. The group that looked dead was in fact alive, and the attacker turned a standoff into a loss.
The fix is to count liberties before attacking. If filling a liberty would leave your own group in atari, stop. The position is probably seki.
Seki in capturing races
Because seki grows out of races, understanding races helps with seki. The article on capturing races explains how to count outside, shared and eye liberties. A race where each side has no outside liberties left and only shared liberties remain is a prime candidate for seki.
How often does seki appear?
Seki is less common than ordinary life and death, but it appears regularly, especially in corners and in games with many fights. On small boards like 9×9, where groups are often cramped, seki can come up surprisingly often. Being able to recognise it quickly saves groups and prevents costly mistakes.
Practice
Seki is best learned by meeting it in games. In fights against the computer on the home page, watch for races where both groups run low on liberties. When you think you see seki, stop and check whether either side can safely fill a shared point.
Against people on the online page, seki often decides close games. If you sign in on the account page, your games are saved, and you can replay any race to see whether seki was possible.
Frequently asked questions
What is seki?
A position where two groups of opposite colours share liberties and neither can capture the other without being captured first. Both groups live.
Can a group in seki be captured later?
Not unless the surrounding situation changes, for example if one side gains extra liberties from elsewhere. In a stable seki, neither side can safely attack.
How is seki counted here?
Under area scoring, the stones in seki count for their owners and the shared liberties count for nobody.
Should I fill the shared liberties before passing?
No. Filling a shared liberty in seki puts your own group in atari. Leave them empty.
Is seki good or bad for me?
It depends. If your group was going to die, reaching seki saves it. If your opponent's group was going to die, allowing seki means you missed a win.
