Go in five minutes flat

Go is a game for two players. The aim is to surround territory. The equipment consists of a board, on which there is a 19x19 square grid, and a collection of black and white stones. One player takes white, the other black.

Starting with an empty board, and with black going first, they each take it in turns to make a move. A move consists of placing a stone at an intersection, like so:

Once a stone is played, it does not move, although it may get captured, in which case it will be removed from the board (more on capturing later). The board will thus gradually be filled with more and more stones. Later on, players may decide that they can get no further territory by playing another move and they may elect to pass instead. When both players pass consecutively, the game is over and the score is counted.

So how do you count territory?

Imagine the game had just ended and the bottom left hand corner of the board looks like this:

Black would be said to have the 15 points of territory marked here. Actually, even if the situation was like this:

Black would still have the 15 points. The diagonals do not have to be played in order to claim the territory. By the way, territory does not have to be attached to the edge of the board, it's perfectly valid in the centre too.

And what about capturing?

Stones may be captured, but before this can be explained it is necessary to define a couple of terms. First of all "armies". Armies are collections of stones in direct contact with each other. For example these are all armies:

a three man army

a four man army

Note this is NOT a three-man army (it is a two man army and a one-man army), diagonal connections do not count with regard to connecting stones into armies.

Next we have to define "liberties". Liberties are the neighbouring points of the stones. So for example here is a two-man army with it's six liberties shown:

And here is a one-man army on the edge of the board with three liberties.

In order to capture an army the opponent must place stones on all its liberties. So for example in the following diagram, if it were white's turn to play, he could play at the point marked and then capture the two black stones.

The two stones would then be removed from the board and become whites "prisoners".

Prisoners are worth one point each and your final score is one point for each point of territory plus one point for each prisoner you have captured. There is then one small adjustment that is made: Playing first is an advantage, so in compensation for this, white gets an additional six and a half points. The purpose of half being to remove the possibility of a draw. This compensation is called the "komi".

The "suicide" rule:

You are not allowed to capture yourself. In the following diagrams it would be illegal for black to play at either of the marked points because in both cases his armies would be without liberties:

Note

The rules, as stated so far, leave an ambiguity that needs to be resolved. Take a look at the following position:

Black to play: in this position the marked point looks like an illegal move because if black played there it would have no liberties. But also notice that the marked point is the last liberty of the five-man white army. The rules state that you should do any capturing first before you determine the legality of the move. So in other words, black CAN play the move, capturing the white stones.

The Ko rule

The "Ko" rule states that you may not play a move that repeats an earlier position. This rule was added to prevent an awkward never-ending cycle of moves. Consider the following position:

Black to play: Black can play at A capturing the white stone at B. This is legal, no problem. Now it will be white to play, but white will not be allowed to play back at B immediately, because it would repeat the original board position. White is thus obliged to play his move elsewhere. Now it is blacks turn. It may be that black decides to play at B in which case there are no further issues to be resolved, but it is interesting to note that if black also plays elsewhere, then white IS then allowed to play back at B capturing the black stone at A. This is because the two moves played "elsewhere" have changed the board and so whites move no longer repeats any earlier position.

Tidying up at the end of the game:

Imagine the game is drawing to a close and the situation in the bottom left hand corner is like this:

The white stone A is in a dire situation. It has only one liberty so can be captured by black at any moment. Not only that, but it can not play any move to rescue itself. It is hopelessly lost. In this situation black is not actually obliged to capture the stone in order to claim the 11 points of territory here. As long as both players agree that the stone is dead then at the end of the game the stone is removed and counted as one of black's prisoners.