What Is the Wrong Bishop in Chess? Why Bishop and Rook Pawn Can't Win

The wrong bishop is the most famous "extra material that can't win" in the endgame: with a bishop and an a- or h-pawn, if the bishop can't control the color of the promotion square, the defending king just hides in that corner and it's a draw. An extra bishop and pawn looks like an easy win, but even the tablebase says it can't be done. When it comes up while you play chess for free, the attacker should think it through first, and the defender should remember to run for the corner.

The key position

Swap in a dark-squared bishop and the result is completely different:

The same position, only the bishop is on e1 and runs on dark squares. This bishop controls h8 and can drive the black king out of the corner. Tablebase: White wins.

How it works

The defender: run straight for the corner

The black king heads for the h8 corner. Once it reaches g7, h7 or h8, White's light-squared bishop can't drive it away. Tablebase: draw.

Why not? h8 is a dark square, so the light-squared bishop can never give check there. The white king can only come closer and box the black king in, but if it boxes it in too tightly, the black king has no moves and it's stalemate.

If the attacker just pushes, it's stalemate

The white pawn reaches h7 and the black king goes back to h8. Now nothing White does helps: as long as the white king guards the pawn on h7, the black king has no moves and it's stalemate. As soon as the white king steps away, the black king takes the pawn on h7.

The whole idea of the wrong bishop fits in one sentence: the corner is dark, the bishop is light, so the bishop can't help.

Common mistakes

The defender's most common mistake is not heading for the corner right away:

The black king goes to e5? That's even further from the corner. The white pawn runs straight up the board and the black king can't catch it. Tablebase: Black loses.

The attacker's mistake is forgetting about this when trading pieces: if you have an extra bishop and a rook pawn and the bishop is the wrong color, trading off everything else may leave you with just a draw.

Practice puzzles

Black to move. Black has only the king left; White has a light-squared bishop and an h-pawn. How do you draw?

Show answer

1... Ke7 For example Ke7, heading for the h8 corner (Ke6 works too). Going the other way with Kd5 or Kc5 loses according to the tablebase.

White to move. The bishop is the wrong color, but the black king isn't in the corner yet. How do you keep it out?

Show answer

1. Bc4 Bc4! The bishop covers g8, the white king covers g7 and f7, the black king can't get into the corner, and the pawn promotes. Kh7 also wins, but after h6 the black king goes to g8, reaches the corner, and the tablebase says draw.

FAQ

What is a "wrong bishop"?

A bishop only moves on squares of one color. If the rook pawn's promotion square is dark and your bishop is light-squared (or the other way round), the bishop can't control the promotion square. That's called the wrong bishop.

Does this only happen with a- and h-pawns?

Yes. The other pawns don't promote in a corner, so once the defending king is driven out it has nowhere to hide. Only the rook pawn's corner is a dead end where the wrong bishop can't drive the king away.

Can't you win with two h-pawns either?

In many cases you still can't, because both pawns have to go through the same corner. The defending king sits in the corner, and it often ends in stalemate anyway.

Try it yourself

The wrong bishop often appears after trades, so go back to chess endgames and look at opposite-colored bishops and queen vs pawn, other endings that "look won but are drawn". Or play online chess against the computer, and next time before you trade, check: does my bishop match my rook pawn?

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