Go Basic Rules: Territory, Capture, Ko and Illegal Moves

Placing stones

Go is played by Black and White placing one stone at a time in turn, and Black moves first. Stones go on the intersections of the lines, not inside the squares, and once placed a stone never moves unless it is captured. If you see no useful move, you may pass. The standard board has 19 lines, but starting on a 9 by 9 board is strongly recommended. A game takes around ten minutes, so you can see the rules in action many times over, and you also practise seeing the whole board at once.

Liberties and capture

Life and death in Go comes down to liberties. A liberty is an empty intersection directly adjacent to a stone, above, below, left or right; diagonal points do not count. A single stone in the middle of the board has four liberties, three on the edge and two in the corner. Stones of the same colour connected along the lines form one group and share their liberties. When your opponent fills the last liberty of one of your groups, every stone in it is captured and removed from the board. A group with only one liberty left is said to be in atari, and you need to decide at once whether to run or to cut your losses elsewhere.

• Liberties are adjacent empty points, not diagonal ones
• Connected stones of one colour share liberties
• Filling the last liberty captures the whole group
• A group with one liberty left is in atari

Points where you cannot play

You may not play a stone that would leave itself, or the group it joins, with no liberties at all. This is often called suicide, and such a point is an illegal move. There is one exception: if the move fills the last liberty of an opposing group and captures it, it is allowed. Removing the opposing stones first opens up space, which gives your stone a liberty. This exception is what lets you play inside an area your opponent surrounds when the move captures, and it also explains the principle of two eyes described below.

Ko: preventing endless repetition

Sometimes a shape appears where each side could capture a single stone back and forth. Without a rule, both players could keep retaking at the same spot forever. The ko rule prevents this. If your opponent captures one stone and creates a ko, you cannot recapture immediately; you must play elsewhere first and only then retake. The move played elsewhere only works if it is threatening enough that your opponent must answer it, and such a move is called a ko threat. A ko fight can turn on who has more threats and requires weighing gains and losses across the whole board, which makes ko the rule beginners find hardest.

Two eyes means life

An empty point inside a group that the opponent cannot safely enter is called an eye. If a group has only one eye, the opponent can fill all the outside liberties and then play in the eye last to capture, because a capturing move is the exception to the suicide rule. But if a group has two separate eyes, a stone played in either one would have no liberties and would be illegal, so that group can never be captured. That is why living in Go means making two eyes, and a group that cannot make two eyes is eventually treated as dead. A position where neither side can attack the other and both groups survive together is called seki.

Territory and counting

Territory means the empty intersections surrounded by your stones. When the game ends you count territory to decide the result. The method widely used in Korea and Japan counts your territory and subtracts the stones your opponent captured, along with your stones judged dead at the end. The Chinese method counts your living stones on the board together with your territory. The two methods usually give the same result or differ only very slightly. Because Black gains an advantage by moving first, White receives a set number of extra points, called komi. Komi usually includes a half point so the game cannot end in a draw, and its size varies between rule sets, so check it before you play.

How the game ends

The game ends when both players decide there is nothing more to gain and pass in succession. The players then agree on which stones cannot live, remove them as dead stones and count. If they disagree about whether a group is dead, the standard approach is to resume play and settle it on the board. It is also common for one player to resign before counting, conceding the game. At first it is easy to miss whether a boundary is fully closed, so get into the habit of filling every empty boundary point between your territory and your opponent's before counting, which cuts down on mistakes.

Checklist for your first games

When you are learning the rules, checking in the following order prevents most mistakes. Looking first at whether any of your own stones are in atari, before hunting for captures, is an especially valuable habit.

• Do any of my groups have only one liberty left
• Can I capture any of my opponent's stones right now
• Is the point I want to play an illegal suicide move
• Am I trying to retake a ko immediately
• Did we agree on komi and the counting method beforehand