This page is intended for non mathematicians and non computer scientists who are beginning to learn the game of Go and prefer a visual way to recognize an eye. While the technique discussed here works in most cases, it is not a foolproof way of determining whether the shape is a real eye or a false eye.
Table of contents | Table of diagrams At the corner At the side In the middle At the corner At the side In the middle At the corner At the side In the middle At the corner At the side In the middle False eye False eye False eye False eye Two eyes |
The concept of eyes is central to the game of Go, since groups that have at least two eyes are alive and cannot be captured.
There are two conditions for determine whether there is an eye. Note that a real eye is an eye, while a false eye is not an eye.
1. The group must surround at least one empty point.
In each of the three cases above, the group surrounds an empty point a.
2. The group must be solidly connected.
If the above two conditions are satisfied, then we definitely have a real eye.
In each of the three cases above, the point a is a real eye.
Note that in the third case, it is not neccessary for black to occupy the point at b.
Some people may misunderstand the meaning of the two conditions above, so here is an illustration of what is not an eye.
In the three cases above, there is no eye. In each case, condition 2 is satisfied but condition 1 is not, as the group did not surround any empty points.
Some people may prefer this alternative for condition 2.
At the corner, for a to be a real eye, the point marked x must be occupied by a black stone.
At the side, for a to be a real eye, both the points marked x must be occupied by black stones.
In the middle, for a to be a real eye, three out of four points marked x must be occupied by black stones.
False eyes are shapes that look like eyes, but are not eyes. Otherwise, we call them real eyes.
Using the eye in the middle as an illustration, we say that this shape that looks like an eye is a false eye. Either version of condition 2 is violated: the stones are not having solid connection; and white managed to occupy the two points, so black only occupied two out of the four x points.
Here we assume that the two stones cannot be captured.
To illustrate this, we shall have white surround the three stones such that these stones are under atari.
If black saves the three stones, then condition 1 is violated, since
is no longer an empty point. Thus, this is not an eye.
On the other hand, if we allow to capture the three black stones, then obviously there is no eye here.
A more precise way of stating the alternative for condition 2 is to change
to
so that we recognize more possible kinds of real eyes, such as the example below.
This group has two real eyes, one at a and one at b. a is a real eye because white cannot play at b, and b is also a real eye because white cannot play at a as well as the points.
This technique for differentiating between real eyes from false eyes generally works in the majority of the games, but it is not totally foolproof. There are a few counterexamples to this technique, but these are rare and seldom found in games. I would say that this technique is good enough for people who are just beginning to learn the game of Go.
For those interested, the when false eyes are eyes and eye definition discussion pages lists some exceptions to the technique discussed above.
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