Capture three to make an eye

The proverb capture three to make an eye refers to capturing three stones in a closed corridor, which normally ensures an eye if the corridor has no cutting points.

Table of contents Capturing three stones suffices to make an eye Exceptions Heuristic See also Notes and discussion

Capturing three stones suffices to make an eye

An example at the edge of the board.

Capture three to make an eye  

When White captures at ...

Capture three to make an eye  

...even when Black throws in with , White can make a second eye with .

This works away from the edge, too.

Capture three to make an eye  

Capturing three White stones at makes an eye too, so Black lives.

Exceptions

However, this proverb has exceptions too, such as the following, where the corridor has a cutting point.

Exception  

In this case, despite capturing three Black stones at ...

Exception  

... kills. Since a and b are miai, White dies.

Here is another counter-example, where the corridor has already been cut. Such counter-examples can also be found away from the side.

Exception  

If Black captures the three stones with , then...

Exception  

... recaptures. Because of and the eye around a is a false eye.

Heuristic

A possible heuristic to see whether the "capture three to make an eye" proverb applies is to look at the position immediately after capturing. In each of the four cases below, we see whether we can form an Black eye at either the a points. If White can occupy all the b points after Black's capture, then Black has no eye here.

Heuristic for corner.  

Heuristic for side.  

Heuristic for side.  

Heuristic for center.  

Heuristic for center.  

See also

• Capture Two Recapture One (a somewhat similar shape)
• The pages in the Eyes Collection, for other ways to make eyes
• Doug's Go Blog/Februari2004 (§ 8 March) for remarks on a case where the rule fails

Notes and discussion

PJT 2019-12-16: The Korean text “석점을 잡으면 한 눈을 만들 수 있다” was substituted for the title of the first section. If this means the same, we might put it in a CJK box; if it uses a colourful image, it would be nice to know; if it was vandalism, we should lose it.

PJT 2023-11-06 DeepL suggests that it means “Score a point to make an eye”, which seems a bit off, unless there are nuances in the the context of Go.