Opposite-Coloured Bishops

The endings where two pawns up is often not enough to win and three pawns up is sometimes not enough either — the most paradoxical balance of forces in chess, and the practical rules that turn the paradox into useful conclusions.

The single most useful observation a club player can carry from study to practice is this: endgames of opposite-coloured bishops are drawish. Two pawns up against a competent defender is often a half-point at best; three pawns up sometimes only draws; the side defending with the wrong-coloured bishop holds positions that any other ending would lose. The reason is geometric and the consequences are deep — opposite-coloured bishops invert all the usual rules of the endgame, and the player who knows the inversion will save full points and steal full points his opponent thinks impossible.

Black king — White's bishop is light-squared, Black's pawn is on a dark square. Whatever the white bishop is doing, it cannot attack the black pawn directly, and the black king holds the dark-squared blockading square.

Black pawn — White's bishop is light-squared, Black's pawn is on a dark square. Whatever the white bishop is doing, it cannot attack the black pawn directly, and the black king holds the dark-squared blockading square.

The paradox

In every other endgame, an extra pawn is an enormous advantage. The classical lesson, repeated by every coach since Tarrasch, is that one extra pawn is sufficient to win a king-and-pawn ending; two extra pawns are sufficient to win virtually any minor-piece ending. Opposite-coloured bishops break this rule in a way that has irritated more grandmasters than any other single factor in chess.

The reason is the bishop’s colour-bound geometry. A light-squared bishop controls only the light squares; a dark-squared bishop only the dark. If the attacker’s bishop controls one colour and the defender’s bishop controls the other, the two pieces are simply doing different jobs in different parallel universes — neither can attack the other, and neither can dispute control of the squares the other controls. The defender’s bishop secures a series of blockade squares; the attacker’s bishop cannot remove the blockade.

Why pure endings draw

Concrete defensive technique in opposite-coloured-bishop endings: the defender places her king and bishop on the colour the attacker’s pawns are not on. If the attacker’s extra pawns are on dark squares, the defender’s bishop and king sit on dark squares — the bishop attacking and the king blockading, both jobs assigned to the dark-square defender. The attacker’s light-squared bishop is useless for breaking the blockade.

The mechanical case: with an attacker’s king on the sixth rank, an attacker’s pawn on the seventh, and a defender’s bishop one square away on a colour where the bishop sees the queening square, the position is a fortress. The attacker cannot make progress without an exchange of bishops — which would liquidate into a winning K+P vs K — but the defender simply will not allow her bishop to be traded.

White bishop — The white pawn is one move from promotion, but the black king holds d8 and the black bishop covers the diagonal. Without a way to remove the bishop, White cannot promote.

White pawn — The white pawn is one move from promotion, but the black king holds d8 and the black bishop covers the diagonal. Without a way to remove the bishop, White cannot promote.

The defender’s task in opposite-coloured-bishop positions is not to make threats but to choose her squares. Sit on the colour the attacker’s pawns are not on, place the king on a blockading square the bishop defends, refuse the exchange. There is nothing for the attacker to do.

When the attacker wins

Two factors push opposite-coloured-bishop endings into the win column.

Two connected pawns on the right colours. If the attacker has two passed pawns one file apart, with one on a light square and one on a dark, the defender’s single-colour bishop cannot blockade both. The dark-squared bishop stops the dark-squared pawn but lets the light-squared one through. With two such pawns far enough advanced and a king nearby, the attacker wins.

An invasion route to the defender’s pawns. If the attacker can use her king to attack the defender’s pawns directly, the bishop’s colour-blindness becomes irrelevant — kings have no colour preference. Endings where the attacker has a route in for her king (an open file, a route around the pawn chain) often win for the attacker.

The defender’s pawns on the wrong colour. If the defender has pawns on the colour her own bishop controls, those pawns become weaknesses — the bishop cannot defend them, and the attacker’s bishop can attack them. A defender with both passed pawns and weak pawns on her bishop’s colour is usually losing.

These three factors define what to look for. In practice the attacker often has two extra pawns and still draws; in the rare positions where one extra pawn wins, all three of these factors are present.

The reversal with heavy pieces

The famous inversion: opposite-coloured bishops with queens or rooks on the board often favour the attacker. The reason is that the defender’s bishop is colour-bound and cannot disrupt an attack on the colour it does not control. If the attacker can target the defender’s king on the colour the defender’s bishop does not cover, the bishop’s blockading magic disappears — there is nothing for it to blockade.

The practical rule has two halves:

Pure opposite-coloured-bishop endings (no other pieces) are drawish. Opposite-coloured-bishop endings with queens or rooks are dynamic and often favour the attacker.

Both halves are useful at the board. Trade down to a pure ending if you are the weaker side; keep the queens and rooks if you are the stronger side. Most strong players, when ahead, are happy to trade pieces for any combination except the trade that leaves an opposite-coloured-bishop ending. Most weaker players make the mistake of accepting trades into the drawn position, and the half-point lost is precisely the half-point opposite-coloured-bishops are notorious for taking away.