Double Check: Two Attackers, One Answer

Against a normal check there are three defences: move the king, capture the checking piece, or block the line. Against a double check only the first one works. No single move can capture two pieces or block two lines, so the king has to move.

Double check almost always comes from a discovered check. A piece moves off a line, uncovering a check from the bishop, rook or queen behind it, and lands on a square where it also gives check. Both pieces now attack the king.

Because blocking and capturing are illegal, the checking pieces can stand on squares where they are attacked, even by the queen. That freedom is what makes double check so strong: a piece can be "hanging" and still be perfectly safe for one move, which is all it needs.

Sometimes the king has no square at all, and the double check is mate. More often, the king has to step aside, and the piece that moved uses its free move to collect material: capturing a queen it was attacking, or taking a rook on the next move.

The king is also dragged around. After a double check it often lands on a worse square, where further checks or a fork finish the job.

Look for the same setup as a discovered attack, but aimed at the king: your bishop, rook or queen pointed at the enemy king through one of your own pieces. Then ask whether the front piece has a square from which it also checks the king. Knight moves are especially useful here because a knight can both clear the line and give a check from a completely different angle.

When you find a double check, do not dismiss it because the moving piece looks unprotected. Check what the opponent can legally do: only king moves. The double checks you miss in your own games are the ones worth drilling.