Living Groups
The fundamentals of life and death in Go
What Makes a Group Alive?
In Go, a group of stones is considered "alive" when it cannot be captured by the opponent regardless of how they play. The most reliable way to ensure life is to create two separate "eyes."
An eye is an enclosed empty space completely surrounded by a group of stones. Three, four, even more connected empty points can form a single eye. However, a large eye alone does not guarantee safety. The opponent can enter and fill interior points one by one, reducing the eye's size. Once it is down to one empty point, the final point can be played — and the group captured.
A group with two eyes cannot be captured. To remove it, the opponent would have to fill both eyes at once — but filling one still leaves the other, and attempting to fill the second eye would leave their own stones with no liberties, making it illegal. Because both eyes can never be gone simultaneously, the group lives unconditionally.
One Eye — Dead
A group with only one enclosed space cannot survive. The opponent can play in that space to capture the whole group.
Even if the eye is larger, the opponent can progressively fill in the space and eventually capture when it fills the last square. One eye is not enough.
Two Eyes — Alive
Two separate eyes generally guarantees life. Unless the opponent can create their own eye-space inside, it will be impossible for them to capture. Filling up the last space inside either eye would be self-capture, and they cannot play both simultanously.
In this example, white is unable to place stones at either 1 or 2 because they would have no liberties.
Here black has a two larger eyes. White can start filling them in, but will hit the same situation.
In this example, the group will live or die dependeing on who plays first. If black plays d4, it has 2 eyes, but if white plays there first it is dead.
False Eyes
False eyes look like eyes, but the surrounding shapes are not fully connected. This flaw lets the opponent fill them in. In this example white can play at 1 to take the eye
This black group isn't yet solid. Its fate depends on who plays at 1 first.
Large Enclosed Areas
A group that controls a large open area of the board is often effectively alive even without two formed eyes, because it has room to make them at any time. As long as the opponent cannot reduce the interior and form two eyes of their own inside your group, you can always carve out the eye space you need before the critical moment arrives.
The danger is when the opponent invades a large area early and begins building their own shapes inside it. If they can make two eyes of their own they can take the territory and even threaten the outer group. Watching for early invasions and limiting the opponent's eye-making options inside your territory is a key part of mid-game play.
Life and Death Problems (Tsumego)
Studying life and death problems — called "tsumego" in Japanese — is one of the most effective ways to improve at Go. Even 10-15 minutes of daily practice builds the pattern recognition that carries into every phase of the game. Start with simple problems and work up; the skill compounds quickly.
Recognizing which eye shapes live and which die — and special positions like ko and seki — is covered in Tactics 101.