Double check

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This article uses algebraic notation to describe chess moves.

In chess, a double check is a check delivered by two pieces at the same time.

The most common form of one check involves one piece moving to deliver check, at the same time revealing a discovered check from a piece behind (such a check is an inherent part of the type of smothered mate known as Philidor's legacy). The only replies to a double check are king moves, as capturing the checking piece (except by the king, which in the process moves out of check-by-the-other-piece) is not an option since there are two of them, and interposition is likewise impossible as there would be two lines of attack to block.

Image:chess_zhor_26.png
Image:chess_zver_26.png
a8 b8 c8 d8 e8 f8 g8 h8
a7 b7 c7 d7 e7 f7 g7 h7
a6 b6 c6 d6 e6 f6 g6 h6
a5 b5 c5 d5 e5 f5 g5 h5
a4 b4 c4 d4 e4 f4 g4 h4
a3 b3 c3 d3 e3 f3 g3 h3
a2 b2 c2 d2 e2 f2 g2 h2
a1 b1 c1 d1 e1 f1 g1 h1
Image:chess_zver_26.png
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A position demonstrating how double check without the moved piece giving check is possible. Black's last move was pawn from g7-g5.

Exceptionally, the piece moved does not have to give check. The only way for this to happen in orthodox chess is by way of an en passant pawn capture. In the position shown to the right, Black has just played g7-g5; white replies hxg6 e.p.+. This is a double check, yet the pawn moved does not give check: one check is given by the rook, the other by the bishop; the former is discovered by the movement of the capturing pawn, the latter by that of the captured pawn. Such a double check is extremely rare in practical play, but is sometimes found in problems.

In chess with variant rules or fairy pieces, other ways of delivering a double check may be possible. Triple checks may also be possible, for example: White rook e1, bishop e4, moas d3 and f3, king h1; Black king e5; White plays 1.Ba8 triple check (the moa is a non-leaping knight which first takes a diagonal step, then an orthogonal one).