Most beginners have trouble knowing when the game is over. The game is said to be over "when neither player can make further profitable moves." But it is often hard to see when that time comes.
Here is another look at the sample 9x9 game we saw before.
Assuming it is Black's turn, there are four possibilities:
Let's look at that last choice in more detail. First ask what is Black's object in continuing to play?
Suppose Black decides to attack the lower left white group - hoping to prevent
White from making two eyes.
What might be a good place to play? There is an old Go proverb that says "my
opponent's best move is my best move."
You can probably see that if White had a stone at
as in this diagram, it would be easy to make two eyes. So that makes it a good
point for Black to evaluate.
Let's assume that Black plays there and then look at White's response.
White's problem is to ensure that there are two eyes. There is quite a bit of empty space so this should not be difficult. Dividing the interior of the group in two by building a little two-stone wall in the center seems to be an easy way. The wall could be on the second line or the third line. I will illustrate the third line choice. (There are certainly other possibilties too.) Certainly if White played there, the white group would have two eyes.
But supposing White decides not to play...?
Does this mean the exercise is over for Black? Maybe not. The interior White wall is not yet built. Perhaps Black can block it, by playing the same place.
If White ignores this last move, is it possible that Black may be able to deprive White
of two eyes? White can certainly reply to Black's move and stay out of trouble.
Now White plays to resolve the situation, but let's look what happend to the score. Black gave up two stones,but White responded to one of those moves, and reduced the territory by one point. Thus Black lost two and White lost one. Every similar move within an opposing territory loses a point, unless the opponent responds to it.
Note that this example is just that: an example. There is no real threat to the white group, even if White ignores five more moves. [I know, I know, there's a seki risk, but we haven't talked about that yet, and if you see it you shouldn't be reading this.]