Diagonal attachment - as inferior shape

  Difficulty: Beginner   Keywords: Shape

According to Cho Hun-hyeon, the White kosumi is a weak player's diagonal. There is a star point joseki in which this shape occurs, but in general it should be avoided [1][2].

Completing the shape  

Charles One way to understand the issue here is to see that Black a is a good way to play after B3. Therefore in general W4 should be played now. Instead W4 at b is a play to attack Black more strongly, but Black at a will then remain as a weakness.

That's just one aspect of the problem for White with this shape: it tends to concede some influence.

Actually, if you analyse continuations after the diagonal contact then tenuki you can see two good follow-ups.


Here B1 and B3 build influence while leaving White a cutting point at a.

Knight's move as good shape  

This B1 is a gentler and lighter way to play. White's attempts to cut it will end in bad shape.

Cut (1)  

The cut with W1 is bad shape since White will lose a stone after B4.

Cut (2)  

If White tries to cut the other way, with W1 here, Black could answer with a or b. Black at a, White at b to cut and White has an empty triangle.


And here it seems like White has more worries than Black. Usually W2 will look like an overplay.

To add to that, Black has the option to play B1 in the diagram above some time as a kikashi, protecting the cut.

Weak point  

Bill: B1 hits the basic weak point of White's formation. It takes away potential eye shape for White and threatens to connect via a.

[1] See joseki as a source of bad habits.

[2] Charles This one shape should be studied in relation to its subsets, in fact.

The fundamental 'weak player's diagonal' is W1 here.

Diagonal attachment - as inferior shape last edited by Bill on July 16, 2008 - 19:34
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