This puzzle on chesstempo caught my eye (we play as White):

[FEN "2b2rk/1p3ppp/r/p1p/3pP1Pq/1P1P/P3BPK/1RB1QR2 b - - 0 1"]

1. Bg4

I reckon Black needs to try skewering the rook with the bishop that captured the pawn.

I made a wrong move. It doesn't much matter to the question, yet I wanted to show this nice way Black may mate after my mistake:

[FEN "2b2rk/1p3ppp/r/p1p/3pP1Pq/1P1P/P3BPK/1RB1QR2 b - - 0 1"]

1. Bg4 Bg4
2. Qg4 Kh2
3. Qh4 Kg2
4. Rg6 Kf3
5. Qg4

Anyway, the right move was this:

[FEN "2b2rk/1p3ppp/r/p1p/3pP1Pq/1P1P/P3BPK/1RB1QR2 b - - 0 1"]

1. Bg4 Rh1

I see no point to Bh3+ now, yet Black plays just that and gets the bishop captured:

[FEN "2b2rk/1p3ppp/r/p1p/3pP1Pq/1P1P/P3BPK/1RB1QR2 b - - 0 1"]

1. Bg4 Rh1
2. Bh3+ Rh3

The king protects the rook, therefore it shan't be captured by the queen.

Why does Black play Bh3+?

  • 2
    It's one of those positions where Black is just lost - There are 4 ways to save the queen all of which drop the bishop and all of which rate as about +6.6 - +6.9 to white on my version of Stockfish. In practice these are all the same evaluation. And so the reason Bh3+ was chosen was because, on the day the puzzle was set, it was that that the software on the computer being used chose. – Ian Bush Nov 23 '20 at 11:00
  • 1
    Every time you want to find a reason for a move, think of what the alternatives are. Which move can you find that is better than ...Bh3+? – David Nov 23 '20 at 15:12

Black is going to lose the bishop regardless. White is attacking the queen in such a way that it will have to move (or be captured), and there are no available safe squares from which it can continue to protect black's bishop. After the queen retreats, white will be free to capture the bishop with his bishop. By playing Bh3 first, black can at least generate some small counterplay by opening up the file so his rook can come check the white king, while white's bishop remains on a somewhat passive square.

  • 3
    Welcome to Chess.SE! Thank you for your answer - that's a fine first post :). – Zhiltsoff Igor Nov 23 '20 at 21:45

You haven't understood the puzzle. The puzzle asks you to find the best move for white after Bxg4 by black. It does not ask you to find the best move for black after Rh1 by white.

Having found Rh1 for white the moves that follow are illustrative only. They do not show all the possible black replies and there is no suggestion that the line chosen for black is a lot better for black than the alternatives.

In the computer's evaluation the position after 2...Bh3+ 3. Rxh3 Rg6+ will count as marginally better because the rook is more actively placed. The difference is irrelevant because both positions are equally lost.

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