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Ponderchess / Glossary

Double check in chess

A double check is a check given by two pieces at once. It almost always arises from a discovered check in which the moving piece also gives check. No single move can block or capture both checking pieces, so the king must move, and if it cannot, it is checkmate.

White to move. The bishop on e2 blocks the rook on e1 from the black king. Bb5 moves it with check along the diagonal and uncovers the rook at the same time. Black could block either check alone, with ...c6 or ...Nd7 against the bishop or ...Be7 against the rook, but not both. The king has no square: d8, f8 and f7 are occupied, d7 is covered by the bishop and e7 by the rook. Bb5 is checkmate.1.Bb5#

How a double check arises

A piece moves off a line and uncovers a check by the bishop, rook or queen behind it, and the moving piece gives check as well. Typical pairs are a rook on the e-file with a bishop in front of it, or a queen on a diagonal with a knight in front of it.

Why only a king move helps

Against a single check there are three defences: capture the checking piece, block the line or move the king. Against two checks, a capture or block can deal with only one of them, so the only legal replies are king moves. That is why a double check is so dangerous even when both checking pieces are attacked: neither can be taken.

It also means the checking pieces can stand on squares where they could normally be captured. A knight or bishop can check from a defended square, because the opponent has no time to take it.

Typical double-check patterns

Many double checks end the game at once against an uncastled king on the e-file: a rook on e1 and a bishop moving off the file with check. The knight and queen combine in Philidor's smothered mate pattern, where Nh6 gives double check with the queen on the a2-g8 diagonal. A windmill often begins or ends with a double check.

To defend, avoid leaving the king on a line with an enemy line piece when only one enemy piece stands in between, and give the king squares to move to.

Common mistakes

  • Looking for a block or capture against a double check; only a king move is legal.
  • Keeping the king on an open file behind a single enemy piece that can move away with check.

Questions about double check

Can you block a double check?

No. A block or capture can stop only one of the two checks, so the king must move. If it has no safe square, it is checkmate.

Can a double check be given without a discovered check?

In practice it always involves a piece moving off a line and uncovering a second attacker. A single piece can never give check twice on its own.

Practise it