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Extension

 

Extending from a Single Stone
   

A single stone on the side has no territory and no base. Extending from such a stone should always be at the front of your mind. (An exception is a single stone on the 3-3 point, which does not urgently need an extension.)

[Diagram]
Diag.: 3rd line extension

In general, the 'safe' distance to extend from one stone is only one point. However, because of the edge effect, a stone on the third line can usually support a two-point extension, such as shown in the diagram. Black cannot cut this apart without stones around which can support this.
Not only is this a stable extension, it is also the minimum amount of space needed to have any hope of creating a living group.


[Diagram]
Diag.: Bad extension

Of course, there are exceptions to the two-space rule.

The diagram here shows an example where a two-point extension should not be made. Making the two-point extension to '1' would mean touching a stone already there. Since black will probably respond with '2', white will be forced to play '3', which gives her a very flat position. It is clear that this result is not good for her.

However, in general a two-space extension from a single stone on the third line is a good, stabilising move.


[Diagram]
Diag.: Extension from stone on 4th line

In general, the reasons for wanting to extend from a stone on the fourth line are not the same as for extending from a stone on the third line. Having played a stone on the fourth line, you have played a stone which aims at influence more than territory. You should therefore be less worried about securing your territory than about extending your influence. Furthermore, no single extension from a stone on the fourth line will settle it as nicely as a two-space extension from a third-line stone. As shown in the diagram, extending to 'a' or 'b' leaves the group open to attack at 'x' or 'y'. Even if white extends to 'x', he can still be attacked by 'y' (or vice-versa).

For these reasons, extensions from fourth line stones tend to be longer and less safe, aiming more at influence.


[Diagram]
Diag.: Corner hoshi extensions

The diagram shows some possible extensions from the corner hoshi point stone:

'a' at the hoshi point is the most extensive. The link between these two stones is weak, but the influence of the stones on the bottom left is very large. If this extension is left alone, white can easily construct a large territory here. Sometimes this extension is made on the third line instead.

'b' can be played and is actually a safe extension in that it cannot be cut. However, the group is still open at one side, and e.g. a play by black on the 3-4 point will take a big chunk out of it. But this is OK, white was not playing directly for territory.

However, by playing 'b' on the third line he does indicate that he wants to settle his group some, otherwise he would have played 'c' instead, which is a very influential move, partly so also towards the left side. However, the extension to 'c' is easily cut and invites battles.

Extending to 'd' after playing the hoshi point stone is not consistent with the high position of the hoshi stone. Although it is safer than an extension to 'b', it suffers the same drawbacks but has a smaller, less ambitious scope.

The extension to 'e' is often played as a respose to a kakari - aiming for influence on the left side, keeping a good connection with the hoshi stone. However, the thus created group is still open to attack from both sides.

Note that, as already stated, extending from a corner hoshi stone is not urgent.

Extensions from stones on the fourth line which are not corner hoshi stones can be made as well. However, in almost all of these cases, it is more important to evaluate what you are extending towards than what you are extending from. I.e. the length and height of your extension will depend on the position of your opponent in the direction you are extending. (This is of course true for all extensions).



This is a copy of the living page "Extending from a Single Stone" at Sensei's Library.
(C) the Authors, published under the OpenContent License V1.0.