Living with Two Eyes: The Basics of Life and Death in Go

In your first games of go, you may know the rules and still not know which stones are going to be captured and which ones you can leave alone. This is where the words “alive” and “dead” come in. Whether a group lives or dies is called life and death.

At the centre of life and death is one rule: a group with two eyes lives. In this post I explain why that rule holds, step by step from the rules themselves. How capturing works and where you cannot play are in Go Rules for Beginners.

The diagrams are in text. ● is Black, ○ is White and ・ is an empty point. In the first two diagrams, the top row and the left column are the edges of the board, so the top left is a corner.

What an eye is

The empty points directly next to a stone, up, down, left and right, are its liberties. When all of a group’s liberties are filled, it is captured.

An eye is an empty point surrounded only by your own stones. If the opponent plays there, the new stone has no liberties. Under the rules of go you cannot play a stone with no liberties. The one exception is when the move captures opposing stones.

One eye is not enough

●・●●●○
●●●●●○
○○○○○○

Black’s group has just one liberty, the empty point at the top left. That is Black’s eye. Can White play there?

The white stone would have no liberties. But it fills Black’s last liberty, so it captures all the black stones. Because it captures, the move is allowed. A group with only one eye, once it is surrounded, is captured by a final move inside the eye.

Two eyes cannot be taken

●・●・●○
●●●●●○
○○○○○○

Now Black has two eyes. If White plays in either one, Black still has the other eye as a liberty, so nothing is captured. Since the move captures nothing and has no liberties, White cannot play it. The same goes for the other eye.

White cannot play in either eye, so there is no way to take away Black’s liberties. Unless Black fills its own eyes, this group can never be captured. That is what “living with two eyes” means.

The two eyes must be separate. Two empty points side by side and connected count as one eye. White can play into them one at a time and capture on the last one.

False eyes

Something that looks like an eye but is not a real one is called a false eye.

If all the black stones around the eye are connected, the eye is real. But if White holds the diagonal points of the eye, the black stones around it may be split into two groups. Then White can put one of those groups in atari and capture it by playing inside the eye. The eye disappears.

The diagonal points are what to check.

• An eye in the middle of the board: false if the opponent holds two of its four diagonal points
• An eye on the edge: false if the opponent holds one of its two diagonal points
• An eye in the corner: false if the opponent holds its one diagonal point

While you are learning, I think it helps to make a habit of looking at the diagonals whenever you count eyes.

Vital points

When a group’s inside space is small, just three or four points, where you play decides whether it lives. That point is called the vital point. Below, I assume the group is surrounded by the opponent and cannot run out.

Straight three: three empty points in a line.

●●●●●
●・・・●
●●●●●

The middle is the vital point. If Black plays there, it makes one eye on each side and lives. If White plays there first, Black cannot split the space into two eyes and dies.

Bent three: three empty points in an L shape. The vital point is the corner of the bend. It works the same way as straight three.

Straight four: four empty points in a line are alive. If White plays on one of the two inner points, Black plays on the other and makes two eyes. There are two vital points, and if one is taken the other remains. In Japanese this relationship is called miai.

Square four: four empty points in a two-by-two square are dead even without a move. Wherever Black plays, it cannot split the space into two eyes.

Shapes with five or six empty points have their own vital points too. There are not many of them, but I do not think you need to learn them all at once. If you start by remembering the middle of straight three, you can think about the others with the same question: which point splits the space into two eyes?

Seki

There is one case where stones without two eyes are not captured. Black and White stones surround each other, and whichever side plays first would be captured, so neither side plays. This is called seki. Stones in seki stay on the board. Under Japanese rules, the empty points inside a seki count as territory for neither side.

Seki does not come up much in beginners’ games. At first, “two eyes to live” is enough.

How to learn life and death

For practice, I think tsumego are best. A tsumego is a problem that asks only about life and death, like a mate problem in chess. “Black to play and live” asks you to find the move that makes Black alive. “Black to play and kill” asks for the move that kills White.

I suggest starting with problems that have few empty points and an answer you can see in one move. You will see vital points like the middle of straight three again and again. When you solve, check not only the first move but whether two eyes are made, or prevented, whatever the opponent does next. Thinking that far is what builds skill in life and death.

In real games, when your stones look like they are about to be surrounded, make room for two eyes early. If you try to make eyes after you are surrounded, with only a few empty points left, the opponent plays the vital point and that is the end. The other way round, when you have surrounded a group, do not miss the turn when you can play its vital point first.

Written in the words of the rules, all this is simple. But once you can tell living stones from dead ones, I think you will suddenly see where to play. The Nihon Ki-in’s beginner page (in Japanese) also has lessons on minimum life and false eyes, and sets of life and death problems.

Learning life and death in Mindsports

StudyX Mindsports is an app with 12 strategy games, including go. Go is played on a 9x9 board. The go beginner lessons include a chapter called “Living with two eyes”, where tap-to-answer quizzes and real game positions let you check the ideas in this post on the board. The advanced lessons also include “Vital points of life and death”.

After the lessons, you can play the CPU from Lv.1 to Lv.50. It goes up one level when you win and down one when you lose, so the opponent adjusts to your results. After a game you can step through it with Review. On a 9x9 board, life and death quickly decides the game. I wrote about the small board in The 9x9 Go Board.

The games and beginner lessons are free, with ads. Each game’s first advanced lesson is free too, and a one-time purchase opens the rest and removes the ads. How to use Mindsports is in Getting Started with Mindsports.