Eyes in Go — Why Two Eyes Mean Life
An eye is an empty point completely surrounded by stones of one colour. Eyes are the heart of life and death in Go: a group with two separate real eyes can never be captured, no matter what the opponent does, because they can't fill both at once without playing an illegal self-capture. Learning to make two eyes — and to tell a real eye from a false one — is the single biggest step from beginner to confident player.
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What is an eye?
An eye is an empty point, or a small enclosed empty space, entirely surrounded by one player's stones. To capture a group you must fill all of its liberties — but if a liberty is an eye, your opponent can only fill it by playing inside their own enclosure, which is normally self-capture and therefore illegal. That is what makes an eye such a powerful liberty: it's one the attacker usually can't take.
Why two eyes mean life
A single eye is not enough. The opponent can fill all the outside liberties and then, on the very last move, play into the one eye — that move captures, so it's legal. With two separate eyes the attacker would have to fill both, but filling the first eye is self-capture while the second eye still gives the group a liberty, so it can never be played legally. Two real eyes is unconditional life.
- One eye: the group can still be killed on the last move.
- Two separate eyes: the group is unconditionally alive.
- Making two eyes is the goal of any group under attack.
Real eyes vs false eyes
Not every surrounded point is a real eye. A false eye looks enclosed, but the diagonal points around it are not all controlled, so the surrounding stones can be cut apart and the eye collapses. Rule of thumb: to be real, an eye needs you to control three of the four diagonal points in the centre, and all of them on the edge or in the corner. A group that depends on false eyes can be killed.
Frequently asked questions
- What is an eye in Go?
- An eye is an empty point surrounded by one colour's stones. Because filling it is normally self-capture, an eye is a liberty the opponent usually can't take — which is why eyes keep groups alive.
- Why do you need two eyes?
- With two separate eyes the opponent can never fill both: filling the first would be self-capture while the second still gives a liberty, so it's illegal. Two real eyes make a group unconditionally alive.
- What is a false eye?
- A false eye looks enclosed but its diagonal points aren't secured, so the surrounding stones can be cut and the eye collapses. A group relying on false eyes can still be captured.
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