Evpsych: I don't get this rule, although it is correct. Why are corners special? It seems to me that any 2 of the 8 points that form a square around the eye will "falsify" it. Perhaps others are as confused as I am about this.

unkx80: Maybe because if White occupies any of the four non-corner points, then the Black stones will not surround a point, so it should be obvious that there is no eye there. I think this is used for differentiating between a real eye and a false eye.

Evpsych: It might be worth pointing out the rationale in any master edit.

Bill: Maybe you don't get it because it is wrong. You cannot decide whether an eye is false or not just by looking at these points. However, on the assumption that the White stones in these diagrams are alive, the eyes will very often be false. And, in terms of the life or death of the Black stones, it is rare that the eye will be necessary for life, even if it need not be filled. So, normally, you might as well consider it to be false.

Proof for the above statement can be seen here: http://senseis.xmp.net/?topic=673

Guo Juan afair calls these "shoulders" in a beginner lesson. Having a name for it allows for some handy rules of thumb. "An eye needs 3 shoulders in the center, 2 at the edge and 1 in the corner."