John Fairbairn wrote:
I chose the title of this thread with care. Shape was the first word. I'll bet that made quite a few eyes light up. After many decades of go I have learned that nothing gets amateur juices going better than the word 'shape.' Yet it is hardly ever mentioned in pro commentaries. So, is obsession with shape an amateurs' flaw (like obsession with joseki), or is it something pros got from their mother's milk and just do it, instead of talking about it?
A lot of players got strong through fighting, and it seems to me that they don't particularly care about shape. For an example see the commentary on

by Kato Masao in
How is your positional judgement? Game 16 at
https://lifein19x19.com/viewtopic.php?p=250450#p250450 . Kato willingly takes bad shape (an empty triangle) to threaten to capture a couple of stones and save one of his own. Elf thinks that

loses 30%!
Some years ago I did a search for some go terms in the online digital collection of go books in the Library of the Japanese National Diet, and found a book,
Shape and Tesuji by Iwasa Kei (1925) at
http://dl.ndl.go.jp/info:ndljp/pid/932263 . Iwasa starts off by saying that the most important thing in go is shape (囲棋で一番大切なのは何と云っても形である). An overstatement, I expect, but he seems to have a broader view of shape than other writers. Here is his first example of bad shape.
- Click Here To Show Diagram Code
[go]$$Bc Bad shape
$$ --------------------
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .
$$ | . . O 2 . . . . . .
$$ | . . X 1 W . . . . .
$$ | . . . . . . . . . .
$$ | . . . . . . . . . .[/go]
I hadn't looked at the book before, I just made a bookmark. But seeing this bolsters my view that shape is about local efficiency.
John Fairbairn wrote:
I can across an example today of a Meijin (Honinbo Shuei) commenting on a move by Nozawa Chikucho 3-dan which, if nothing else, knocks the mother's milk idea on the head. But it also seems to call into question the whole amateur approach to shape (monkey see, monkey do).
In the position below Nozawa played the triangled move (24( and Shuei commented simply: "For White 24 it is better to jump to A." Commentaries in those days were for instruction, not therapy sessions. Players had to work out the reasons for their mistakes on their own.
There was no actual mention of shape, but even as an amateur I feel confident in saying that shape is behind this comment. So, a pro 3-dan good enough to sit at the feet of the master (and to improve very significantly later on) made a shape mistake. How do we explain the mistake?
It's easy enough to fall into the trap of saying 24 makes an empty triangle, tout court. But if Shuei had said 24 was better than A, we would all just as confidently quote another proverb and say it was because of five alive - White is filling in a liberty of a weaker enemy group. Those ways of looking at things are just like writing an essay at school by copying paragraphs from different books and calling it research.
But what is the proper way to look at it? Again it's easy to sound magisterial and say it depends on the aji or overconcentration left behind, or something like that. But then how do we evaluate the results?
I don't know. Remember my question was "How do we explain the mistake?" Not "what is the mistake?" - although that is stage we may have to go through.
(If you want to see how the game actually unfolded, it is game 1906-04-16a in the GoGoD database, and it is also in my e-book of Shuei's commentaries.)
Iwasa's bad shape example is relevant to the present discussion, because

in the game makes the same kind of mistake. Elf thinks that

loses 13% by comparison with
25.
- Click Here To Show Diagram Code
[go]$$Wcm24 White gives Black an extra dame
$$ ---------------------------------------
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . 5 a . . . . . . . . . . . . . . . |
$$ | . 3 . O . . . . O . X . . . O . . . . |
$$ | . 2 1 O X X X . . , . . . . . , X . . |
$$ | . 4 X X O O . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . O . . . . |
$$ | . . . . . . . . . . . . . . . . X . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . , . . . . . , . . . . . , . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . O . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . X . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . X . . . |
$$ | . . X , . . . . . , . . . . . , . . . |
$$ | . . . . O . . . . O . . . . . X . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ | . . . . . . . . . . . . . . . . . . . |
$$ ---------------------------------------[/go]

allows

to hane at the head of White's stones, reducing them to 3 dame. After

Black has 5 dame while White needs protecting. BTW, Elf thinks that

is a minor mistake, which would be better at
a. Once you see it it is kind of obvious that
a is at least as good as

.
If

is at
25, Black does not get that fifth dame, and in this case that makes a big difference. In Elf's mainline variation Black sacrifices the corner stones. A full explanation would probably get into the complexities of the possible fight scenarios. I think the fact that

gives Black an extra dame is the main point.

Edit: Corrected

and

to
