Why does white have to play at a in order to get two eyes there?

Hi there. Absolute beginner question. I’m reading Cho Chikun’s ‘Go a Complete Introduction to the Game’, chapter 3, page 26. It’s in a section introducing false eyes.

At the point in the narrated example game where I’m puzzled, the text explains “When black plays 19 in FIgure 3 (which is not the image I’m including here), the white group is confined to the upper right corner, so White must play 20 [at a] in order to get two eyes there.”

I feel this is an important point to grasp, but I’m not seeing it. Why must White play at a?


Thank you in anticipation,


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I’m not going to answer your question, but I hope that my reply might at least be a consolation. :slight_smile:
I’m not an absolute beginner, 8k at the moment. Seeing this diagram I can see immediately that white is in trouble and intuitively the spot a looks like a good candidate to me. Directly right of a also looks tempting. I’d have a fair chance of getting it right in a game, but I can’t see directly that this is the only move that works. So asking a beginner to see that is a bit much. Once you do a bunch of tsumego you will build some intuition for such situations.

It will be interesting to see if some stronger player can give an explanation why a is the only move in a way that a beginner can understand.

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The turn at A for white is a pretty common shape to have to make in order make the corner live. ‘A’ is a key point because if you flip this problem around, and it’s blacks turn to play. The ‘clamp’ tesuji at A becomes a real problem for white.


Because if black gets to play there first the corner dies.

Why does white need to play in the corner? Because otherwise, black will kill the whole group in the next move.

The vital point of the position is at a (as @_oopsImStoned pointed out).

So, you might ask, why make life at the “vital point” and not, say, at the 1-2 point right next to it? Just because the vital point “looks nice”?

The more thorough answer is aji. Life at 1-2 works only because white has the outside liberty at 3-4. The move at a makes life even without outside liberties. That is the advantage of playing the proper move.

I leave reading out the moves to you as an exercise :wink:

Edit: sorry @smurph, we posted at the same moment, but you have the more thorough explanation :smiley:


Thank you! That’s an amazing explanation. Will go complete some of those exercises left for the reader tonight.

By the way, the lightbulb comment for me in your analysis, @smurph, was this one:

I am perhaps focussing only (or at least too much) on the stones already on the board, and not paying enough attention to the unoccupied points. This brilliant step from your analysis shows that both are important, and then the reason that ‘a’ is so important (‘3’ in this picture - or ‘4’) becomes much more clear. Thank you.


My vision is very simple and probably incomplete, but what I see is that “a” makes already two eyes: one in the corner (1-1) and one immediately below “a” (3-2).
I can’t see a sequence to falsify one of them.

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