Discovered attack and double check in chess
In a discovered attack a piece moves out of the way and opens a line for the bishop, rook or queen behind it. Two pieces attack at once: the one that moved, and the one it unmasked.
When the unmasked piece gives check, it is a discovered check; when both give check, it is a double check.
Discovered check
The knight stands between the white rook and the black king. Wherever it goes, the king is in check, so it can go wherever it does the most damage.
Double check
A double check is the strongest check of all: two pieces attack the king, and no block or capture stops both. The king must move. Richard Réti used it to beat Savielly Tartakower in Vienna in 1910, in just eleven moves.
Exercise: win the queen
White to move and win the queen.
Make the move on the board: drag a piece, or click it and then a square.
Solved!
Bxh7+ takes a pawn with check and unmasks the rook on d1 against the queen on d8. Black has to answer the check, and Rxd8 takes the queen.
Key points
- In a discovered attack one piece moves and unmasks another: two attacks come at once.
- With a discovered check the moving piece can go anywhere, even where it can be taken.
- Only a king move answers a double check.