Bishop and Pawn vs Bishop: The Short Diagonal Wins
White to play and win
PlayBoth bishops run on dark squares, and f8 is dark too, so Black's bishop can guard the queening square itself. Two diagonals lead to f8: a long one, and a short one of only three squares. The rule: put your king where it covers two squares of the short diagonal, and your bishop covers the rest.
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The Three-Square Diagonal
White to play and win · Win against perfect defense
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The theory
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Ke8 throws the win away. After Ke8 Ke6 Bf8 Bf4 the black king stands behind yours, your king covers only one square of the short diagonal, and the game is a draw.
In same-colored bishop endings with the defending king in place, the draw depends on the length of the bishop's diagonals. Four squares or more on both sides holds. A diagonal shorter than four can be lost, if the attacking king helps cover it.
Count the short diagonal. Here the pawn is stopped on f8, and the short diagonal f8-g7-h6 is only three squares. The bishop cannot hold three squares alone once the king pitches in.
Choose the good side. With the move, 1.Kg8 puts the king where it controls g7, a square of that short diagonal. Sent the other way, toward e8, the king covers only f8, one of the three, and Black draws by keeping rear opposition, always ready to step back to e6. That single tempo, and that single square, decide the game.
In this drill the defender clings to the long diagonal. Take the g8 side, force the bishop short, and push the pawn through.
Keep going
The Wrong Bishop
Black to play and draw
Centurini: Deflect, Then Interfere
White to play and win
The King Guards the Interference Square
Black to play and draw
All 24 bishop endgames positionsFollow the full curriculum (free)