In chess, not all checks are created equal. While a single check requires the opponent to reply, a double check, in which two of your pieces attacking the opposing king at the same time, is a specially powerful tactical tool. The mere weight of a double check severely constrains your opponent, usually resulting in a material gain or rapid checkmate. As the venerable chess adage has it, “Even the most slothful king flees wildly from a double check.”
The unique power of the double check
Why is this move so good? The answer is in the limitations on the opponent’s play. Under a single check, the defender has three choices: move the king, block the check, or capture the checking piece. A double check, however, eliminates two such possibilities. It is impossible to cover up two simultaneous checks with one piece and impossible to capture two different attacking pieces at the same time. This leaves the opponent with only one legal move, namely to move their king. The forced king move is the potency of the double check’s power. By gaining control of your opponent’s move, you are able to stage a follow-up attack very accurately.
The discovered attack double check
The most common way of providing a double check is in the guise of a discovered attack, whereby one piece is shifted out of the line to reveal an attack from the piece behind it, as the moved piece checks simultaneously.
In this position, Black’s king on e5 is safe for the moment. White can execute the crushing move Rd1++. The rook on d1 now puts Black’s king in check, and in doing so, the bishop on e3 now gives a discovered check. Black is in double check and cannot block both checks, and therefor must move.
Double checks leading to checkmate
The double check, done in a timely manner, can checkmate itself when the squares of escape for the other king are few. By pushing the king to a specific square, you may be able to deliver checkmate.
Winning material from a double check
Aside from checkmate, the double check can also be used to obtain lots of material. With the king’s movement, the attacking pieces are often able to capture an invaluable, now vulnerable, piece on the next turn.
Here, White can move Bd6+. This exposes a check by the rook on g1 and gives and simultaneously attacks the queen on c5. Black will be forced to move the king. White can capture the queen after the king has moved.
Mastering the skill of seeing and executing double checks is a major milestone in tactical development. Through the resolution of these exercises, you become accustomed to enhancing your vision on the board and begin to pay attention to how sets of pieces can be combined to execute an irresistible attack. When you get into a position with a potential discovered check, consider whether you can add a little something to turn it into a winning double check.