Zwischenzug

Zwischenzug is also known as intermezzo. It is an in-between or intermediate move, often a check, thrown into the middle of a tactical sequence. Missing these can dramatically alter your calculation of variations.

It is the last entry in David Hooper, and Kenneth Whyld, The Oxford Companion to Chess (1992), where the authors define it as "a move interspersed during an exchange or series of exchanges" (460). They note that whether a given move is a zwischenzug may depend on one's point of view. It may be a natural part of the combination. Hooper and Whyld offer an interesting nuance in the definition, suggesting that the term is limited to failure of calculation.

Yasser Seirawan offers an instructive example in Winning Chess Tactics (2003), 118.

Black to move

Black intends to exchange rooks and then push the a-pawn. This plan fails because of an in-between check. After 1...Rxh4, White forces a draw with 2.Qd8+ Kh7 3.Qxh4+.

Two examples that I often use with my students are from Paul Morphy's first round games against James Thompson at the First American Chess Congress (1857).

White to move

In the first game, Thompson had planned a discovery as part of a series of exchanges on f5. 11.exf5 Bxf5 12.Nxf5 Rxf5 13.d4. However, Morphy interrupted the sequence with an in-between move.

11.exf5 d5! 12.Bb3 e4 13.dxe4 dxe4 and then Thompson missed the resource that could have kept him in the game, and so retreated the knight. Morphy won seven moves later.

In the second game against Thompson, Morphy used an intermezzo to win a pawn.

White to move

The Bishops will be exchanged, but White has some choice in the manner of exchange.

30.Bxb4 axb4 31.Rad7 and White (Morphy) went on to win an instructive endgame.

My young opponent at the Lou Domanski Chess Festival in Sandpoint, Idaho on Saturday found a slightly more sophisticated sequence involving an in-between move. It was not forcing, but offered me a series of unpleasant choices.

Black to move

After 16.e4

I played 16...dxe4, expecting 17.Nxe4 Nxe4 18.Bxe4 Rad8 with equality.

My opponent offered me the choice of a wrecked pawn structure on the queenside or on the kingside.

17.dxc5 Bxc5

I chose the wrecked kingside structure and the bishop pair.

18.Bxf6 gxf6 19.Nxe4 Be7 20.Qh5

I could have been only slightly worse after 20...Rad8, but instead blundered away my queen and resigned.