Go Life and Death Basics: Two Eyes, False Eyes and Vital Points

What life and death means

Life and death is about whether a group of stones surrounded by the opponent can stay on the board without being captured. Stones are captured when all their liberties are filled, and that does not change as a group grows. A large group, however, is rarely killed just by closing off its outside liberties, so what really matters is whether it can make empty points inside that the opponent cannot play on. Knowing life and death lets you give up stones that are already lost and fight on for stones that can live, which changes how you count the whole game.

Why two eyes

An eye is an empty point surrounded by your stones. A stone played there by the opponent would have no liberties, so unless it captures your stones it counts as suicide and is not allowed. With only one eye, though, the opponent can fill all the outside liberties and then play in the eye last. At that moment your group has no liberties left and the whole thing is captured, so the move is legal. Two separate eyes are a different story. The opponent can only play in one at a time, and a stone in either one captures nothing and has no liberties of its own, so it cannot be played. That is why a group with two real eyes can never be captured, whatever the opponent does.

False eyes: points that only look like eyes

A false eye looks enclosed, but the stones around it are not all connected, so it eventually gets filled. If the surrounding stones are split, the opponent can put the cut-off part in atari. To save it you have to play in the eye yourself to connect, and the eye disappears. If you do not connect, those stones are captured and the eye is broken anyway. A group that seems to have two eyes but where one of them is false is no better off than a group with one eye. False eyes are the most common reason a group that looked alive suddenly gets captured.

Telling real eyes from false ones

Looking at the diagonal points around the eye gives a quick answer. An eye in the middle of the board is real if you keep the opponent off at least three of its four diagonals; if the opponent holds two, it is false. An eye on the edge has only two diagonals, so giving up either one makes it false, and an eye in the corner has a single diagonal, which you must keep. Treat this as a quick rule of thumb and still read out the moves, taking the state of nearby stones into account.

• Centre eye: hold at least three of four diagonals
• Edge eye: hold both diagonals
• Corner eye: hold the single diagonal

Eye space and vital points

The empty area inside a group is its eye space. A wide, elongated eye space makes two eyes easy, while a small or compact one can be reduced to a single eye with one move. The key point that divides the space into two eyes is called the vital point, and an opponent stone placed there to prevent two eyes is a placement. Assuming the outside is completely sealed and there is no outside help, these basic shapes are worth learning by heart.

• Straight three: the middle is vital; you play it and live, the opponent plays it and you die
• Bent three: the point at the bend is vital
• Straight four: if the opponent takes one of the two middle points, take the other and live
• Square four: dead no matter who plays first
• T-shaped four: the centre point is vital

Seki: both groups live

Sometimes two groups that surround each other share liberties in such a way that whoever fills one first puts their own stones in atari and gets captured. This is called seki. Since neither side will touch it, both groups live even without two eyes. It looks like an exception, but the principle is the same: the move that reduces the opponent's liberties also reduces your own. Whether the empty points inside a seki count as territory depends on the scoring method, so check the rules of the tournament or the place where you play.

Capturing races and who moves first

When two groups without eyes are locked together, a capturing race decides who captures whom first. The basic method is to count each side's liberties: more liberties wins, and with equal numbers the side to move wins. A group with one eye has a big advantage, because the opponent can only fill that eye at the very end. This is also why problems state who plays first and whether the goal is to live or to kill. Many groups live if you move first and die if the opponent does, so decide early whether to secure them before the opponent touches them.

How to study and common mistakes

Life and death is more about reading than memorising. Start with easy problems involving small groups in the corner and on the edge, and read the answer through in your head before placing any stones. There is a proverb that six stones in a row on the second line die and eight live, but the result depends on both ends and the surroundings, so use it only as a starting point for reading.

• If you see two eyes, check the diagonals for a false eye first
• Consider both widening the eye space and taking the vital point
• Avoid adding extra moves to groups that are already alive
• Let go of groups that are hard to save and play big points elsewhere