Definition
In chess, a double check is a position in which the opposing king is simultaneously attacked by two of the opponent's pieces. Both checks begin on the same move, so two distinct lines of attack threaten the king at once. Because two checks exist at the same time, ordinary responses like blocking one attack or capturing a single attacker generally fail to remove the other threat.
How a double check arises
Most double checks occur as a result of a discovered check: a piece moves and gives direct check while uncovering another piece that also checks the king. For example, a knight may hop to give check and in doing so reveal a rook or bishop checking along an opened file or diagonal. Less commonly, promotions or unusual rules such as en passant can create positions where two attacks appear simultaneously.
Consequences and legal responses
The key practical consequence of a double check is that the only legal responses that can remove both threats at once are moves by the king itself. Interposition (placing a piece between attacker and king) cannot stop a non-line check such as a knight check, and capturing one of the checking pieces normally leaves the king exposed to the other. Thus double checks are potent tactical weapons that often force a decisive gain of material or checkmate.
Common patterns and examples
Typical piece pairings in double checks include combinations such as rook and bishop, queen and knight, or rook and knight: one piece delivers a direct attack while the other delivers the discovered attack. Double checks frequently arise in tactical sequences leading to mate, for instance when the attacking side sacrifices material to force the king into an exposed position. Because they are created by a single move, double checks are especially useful in combinations and mating nets.
Importance and practical notes
As a tactical motif, the double check is taught early in chess study because it illustrates ideas of discovery, coordination, and forcing moves. Players should be alert for opportunities to engineer discovered checks that simultaneously add a second threat. Conversely, defending players must recognize positions where a single move could produce a double check and take preventive measures when possible.