Basic Game Play

Go is a game of territory. Two players, black and white, take turns placing pieces or stones, trying to surround as much territory as possible.

On a player's turn they can place a stone on almost any unoccupied grid point. Stones are never moved on the board, however they can be captured (described below), in which case they are removed from the board. The game continues until both players pass in succession.

A players score at the end of the game is the sum of the number of pieces captured and the total area surrounded (not occupied). White is additionally awarded komi, typically around 6, for the disadvantage of having to go second.

Capture

Chains of stones are captured when all of their adjacent points, or liberties, are occupied by the the opponent. Note that the chain does not span diagonal connections. A threatened chain of stones is said to be in atari.

In the following example, white plays the stone marked with a square resulting in the capture of the black stones.

 


One important principal in the game of go is that of the double eye. In the following figure, a formation such as black's is impossible to capture. Why? For white to capture black they must first place a stone in either of the two eyes, which would results in its immediate capture.

Ko & Suicide


There are two restrictions on moves. The first is the rule of suicide. Namely, you cannot place a stone in a position that results in your capture. However, such a play is legal if results in the capture of your opponents stones.

For example, on the left black cannot play at the space marked with an X since that would result in its immediate capture. However, on the right, the same play would capture some of white's stones, so it is legal.

 


The rule of Ko says that after a stone is captured you cannot immediately play the captured position if it results in the same board state. This is best illustrated by example. Black is not allowed to capture the white stone since it would recreate the board state on the left.

 

Note that this restriction only lasts for a turn, after which you are allowed to play this position. If its critical to control that position then you can threaten your opponent elsewhere on the board so they do not have time to fill in the eye.