Definitions: Double Check

The definition's in the name, but I want to have a quick look at some implications of giving a double check.

Double Check: A piece moves giving check while simultaneously uncovering a second check by another piece.

The two main implications of this:
1. To defend a double check, the King must move.
2. Therefore, giving a double check temporarily immobilises the entire defending army.

Here is an example which also makes an interesting point about Queens, Rooks, and Bishops.

Reinfeld position #406
White to move

1. Qd8+ Kxd8 2. Bg5++ and now Black's only legal moves are 2. ... Kc7 3. Bd8# or 2. ... Ke8 3. Rd8#.

Note that when the Queen, constructed of a Rook + Bishop in one piece, arrived on d8 it was not mate because She was undefended. Yet when Her power was split between two 'lesser' pieces to form a barrage against d8, their combined power delivered checkmate.

Our man Fred describes this next example as "The most beautiful double check ever played.".

Reinfeld position #407
White to move

1. Rxg5 clearance of the h-file for the Queen's penetration 1. ... hxg5 2. Qh7+ Nd7 if 2. ... Kd8 3. Qh8+ followed by capturing one of the rooks 3. Bxd7 a liquidating combination, since after 3. ... Qxd7 4. Qxd7 Kxd7 5. Rxb8 etc, White will have 5 extra pawns. 3. ... Qg8 defending against a discovered check by attacking the unprotected White Queen. Another diagram for the finale:

Reinfeld position #407
After 3. ... Qg8

4. Rb7+ either decoying the King to a square from which the double check can be delivered, or interference with the Rook's protection of the Queen Kxb7 5. Bc8++ Kxc8 6. Qxg8+ and now Kb7 or Kc7 meets Qg7+ winning a Rook.