Meaningful Stones: Life Lessons in the Game of Go

Recall that stones that are next to each other along horizontal or vertical lines (but NOT diagonally) are connected and form a single group. In the following figure, how many black groups are there? How many white groups?

Remember that spaces next to a group of stones (along horizontal or vertical lines) are called the liberties of the group. There are two groups in the figure below. How many liberties does each have?

In order to talk about the location of stones on the board, it is helpful to have a notation for the intersections. To do this we number the rows from bottom to top, and we use letters (starting with A and skipping I) across the bottom.

The nine small dots on the board are called star points. They are simply there as reference points. We reference intersections by listing the letter first followed by the number. For example, the white stone is at the D8 point. The black stone is at the M17 point. The center star point, at K10, is sometimes referred to by its Japanese name tengen. The corner star points are called 4-4 points (four lines from the two nearest sides), but if we want to name a specific 4-4 point we can use the label D4, D16, Q4, or Q16.

Consider white’s move in this corner situation. White can capture the black stone in the corner with a move at T2.

The result is

Now black cannot play in the corner at T1, as that would be an illegal self-capture. Instead black plays at T3.

Now white cannot play at T1 as that would result in the self-capture of the four white stones. Let’s say white plays at R3.

Can black now play in the corner at T1? Yes! Enemy captures happen before self-captures. If black was not capturing stones, the move would be illegal, but since black is capturing stones, it is a legal move.

Here is an example of a game that has finished on a 7 × 7 board.

Why is the game completed? Neither side has any meaningful moves remaining. (Meaningful moves either increase your territory or reduce your opponent’s territory, threaten to capture stones or protect your stones from being captured.) You might ask, "Why doesn’t black play at B1?" Well, white will immediately play at B2, capturing the black stone. The end result is that white’s territory is reduced by one since they placed an extra stone inside their own territory, but they increase their captures by one, resulting in no change to their overal score (territory plus captures). In general, there is no benefit to placing stones in your opponent’s territory unless you have an opportunity to capture some stones.

Suppose that white has captured 4 black stones and black has captured 3 white stones. What is the final score of the game?

Suppose that white has just captured a black stone by placing the marked stone below.

Black cannot immediately recapture with a move at D4 (the star point) because of the ko rule.

Black must play somewhere else on the board. Suppose black plays at F3, extending their weak stone. White now has a choice. White can play elsewhere on the board, or they can play at D4 ending the "ko fight."

Here white has ended the ko. White is left with an inefficient clump of stones, but they have lots of liberties and are not in immediate danger.

Here’s a more complicated example of a ko. As before, white has just taken the stone at D4 to start the ko. This time black has a better move, the marked stone at G3. This kind of move is called a "ko threat." It threatens to take something more valuable than the ko, forcing your opponent to respond away from the ko and allowing you to retake the ko.

In this case black is threatening the four white stones. White has to choose between saving the four white stones and ending the ko. If white saves the four stones, then black can re-take the ko with a stone at D4.

Now it’s white’s turn to look for a ko threat somewhere else on the board. If they can force black to respond elsewhere, then white can re-take the ko. If they can’t find a ko threat, then black can play at D3 ending the ko. This process of taking turns looking for ko threats and retaking the ko is called a ko fight. It is a natural consequence of the ko rule.