Double check — what it means in chess
A check from two pieces at once, forcing the king to move.
A check from two pieces at once, forcing the king to move.
A double check is the rare case where two pieces give check on the same move: the piece that moves and the piece it unveils, both checking at once. Here is what makes it special — you cannot block two checks or capture two checkers in one move, so the king is forced to move, no matter what. Even a queen sitting en prise cannot be taken if the king has to step away first. Double check is the engine behind smothered mate.
Double check is the reason the smothered mate combination works, and it is also the reason so many "impossible" sacrifices go through. The mover cannot be captured, because capturing it does not answer the second check. The intervening squares cannot be blocked, because blocking one line leaves the other open. Only the king moves. That collapses the defender's options from dozens to a handful — sometimes to one — and that is what lets a single knight or bishop hop into the middle of the enemy camp and survive. Any position with two of your pieces aimed at the king through the same square is worth a hard second look.
[[board startfen="4k3/p6p/4N3/8/8/8/8/4R1K1 w - - 0 1" pgn="1. Ng7+ Kd8" caption="A double check: the king must move, because two checks can't both be answered at once." notes="White to move. A rook on e1 behind its own knight, the enemy king on e8. Ng7+ — the knight checks from g7, and stepping off the e-file it unveils the rook checking too. Two checkers at once. You can't block or capture your way out of two checks in one move, so the king is forced to move — no matter what else hangs."]]
The Endgame Society glossary defines more than 240 chess terms — rules, notation, tactics, strategy, pawn structures, endgames, and openings — in language a beginner can act on rather than dictionary shorthand.