I was looking through some professional games, and here are two different positions I found:

Click Here To Show Diagram Code

[go]$$B Position A
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . . . . . . . 2 O . . O . . X . . |
$$ | . . . O . O . 3 . 1 . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . . . . . . . . . . X . . . X . . . |
$$ | . . X . . . . . . . O X . . O X O X . |
$$ | . . . . . . . . . X X O O . O O X . . |
$$ | . . . , . . . . . , . . . O X X X X . |
$$ | . . X . . . . . . . X . O O O O X O . |
$$ | . . . . . . . . . X O . . . X X O . . |
$$ | . . . . . . . . . . O . O X . . O . . |
$$ | . . X . . . . . . . . . . X X O . O . |
$$ | . . . . . . . . . . . X X . O X O . . |
$$ | . . O , . . . . O , O O O X . X X O X |
$$ | . . . O . . . . . . . . X O . X . X . |
$$ | . . . . . . . . . . . . O . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Click Here To Show Diagram Code

[go]$$W Position B
$$ ---------------------------------------
$$ | . . . . O . . . . . . . . . . . . . . |
$$ | . . O O X X O . X . . . . . . . . . . |
$$ | . . X . O X O O O X . . . . X O X . . |
$$ | . . . O O O X X X X . . . . . X . . . |
$$ | . . . . . X . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . X X O . . |
$$ | . . . . . . . . . . . . X X O O O . . |
$$ | . . . . . . . . . . . . . O . . X O . |
$$ | . . . . . . . . . . . . . O X . . . . |
$$ | . . . , . . . . . , . . . . . , O . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . X O . . |
$$ | . . . . . . . . . . . . . . . . O . . |
$$ | . . O . . . . . . . . . . . X . . . . |
$$ | . . . . . . . . . . . . . . . O . . . |
$$ | . . . O . . . . . 1 3 C . X . , X . . |
$$ | . . O . . X . . X 2 . . . . X . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

Both games feature a shoulder hit reduction on some third line stones, however in Position A, I feel the reducer plays lightly with a one-space jump. In my own games, I am more likely to play a shoulder hit this way. In position B, feels heavier to me than if it were at the marked intersection to the right.

Why does one pro play one space jump after shoulder hit, and the other play solid extension? There might be relative merits specific to these particular positions that I don't see, but in general, how does one decide which of these to play?

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be immersed

That's a question I have as well. For those two examples, could it be because in the second diagram white didn't want black to peep?

One thing I see- in the top example, if the shoulder hitter is allowed to descend to the third line, it threatens the corner, while in the bottom example the shoulder hittee is thick on both sides.

Could you elaborate on your idea a bit? Are you saying that, when the opponent is thick, it might be good to extend solidly? This one isn't intuitive to me (though the illluck's peep idea does seem to make sense).

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be immersed

I agree with the peep idea too.

Yes, me too. But could you explain more about your idea?

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be immersed

As Shaddy notes, is an attacking play.



In this diagram a jump to would not be particularly light, but would approach Black's thickness for no good reason. It would be thin, therefore. If and are too heavy, then White should not begin with .

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The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

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Everything with love. Stay safe.

I didn't have a good explanation for the second one, only the first one.

I spoke with a pro about this.

He said that the solid extension was good when the reducer has supporting stones nearby and you are trying to put pressure on the reducee. In this case, you are not worried about your stones being heavy, because you are not in danger of being attacked.

In contrast, the one space jump is flexible, and is good for situations where there are more enemy stones in the area. You are not trying to put pressure on the reducee so much as to be flexible and able to go about in the area without being attacked severely.

I don't get that impression so much in Position A, but perhaps in this particular situation, the one space jump actually puts more pressure than the extension, so the idea is similar (kind of like what Shaddy mentioned).

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be immersed

Did you show him these examples? I did not get the impression that they were typical of situations where there is a real choice between the extension and the jump.

_________________
The Adkins Principle:
At some point, doesn't thinking have to go on?
— Winona Adkins

Visualize whirled peas.

Everything with love. Stay safe.

No, I didn't show him these particular examples, so his opinion may be different from these particular positions.

_________________
be immersed

I was thinking that in the second example there are no nearby supporting stones (and when I read the pro oppinion I was "what?"), and preventing the peep/keeping the shape as clean as possible makes it easier for that group to survive. Whereas in the 1-jump, there is some supporting thickness close by, so by jumping he can maximise the reduced area.

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Geek of all trades, master of none: the motto for my blog mostlymaths.net

In position A I think is correct because there is no way for white to link his stones together.

My thoughts on position A:



For position B there doesn't seem to be a good way to attack these 2 stones. If you were to play the jump instead, that wouldn't be the case.

My thoughts on position B:



Your general thinking of how to choose a follow up for a shoulder hit isn't wrong. If you want to play lightly, then you should jump; if you want to play solidly, then you should extend. However, general principles are often broken at high levels of Go because of slight changes in positions and thorough reading.