Anti-Forcing Moves: The Zwischenzug

Last time, we analyzed forcing moves: “A forcing move is one that limits the ways in which your opponent can respond, beginning with captures and checks.”

Checks are pretty universal forcing moves, because by the rules of chess, the opponent must respond to the threat to their king. As we move down the list, however, we find exceptions; captures, for example, we usually assume that if we take a piece, the opponent will recapture. But what if they don’t?

This is a classic example of a zwischenzug, or intermezzo, or “in-between” move, where a player rejects the traditional notion of an equal trade. Black has just taken White’s queen on d8, which White will take, 1. Bxd8. They are expecting 1. …Kxd8 2. Rxf5, further trading a pair of minor pieces, when White would be doing quite well in the endgame.

But after 1. Bxd8, Black plays 1. …Nge3!.

This zwischenzug has several effects: one, the rook on f1 is attacked, and if White moves their bishop, they will lose their rook instead, which is worse. Two, the knight on f5 is protected (and if White attacked the knight on e3, that one is protected too). Three, White has no rook moves that protect the bishop! The knight on e3 prevents Rd1, and Rf8 is blocked, so there is no solving both their problems at once.

The result: Black is going to win a piece, 2. Rf3 Kxd8.

In the next example, White is going to play 1. Bxb6. What would you play in response?

If you would recapture, 1. …cxb6, you have missed your chance! White would move their knight from g4, and have an equal game. Black should play 1. …hxg4!, a zwischenzug which opens a discovered attack on White’s queen. They can’t move their bishop without losing the queen, so let’s suppose 2. Qxg4.

Black’s queen is attacked. It will not retreat, which would allow White to do the same with their bishop. 2. …Qxg4 is a great example of a forcing move: White simply can’t afford not to recapture a queen. And then 3. hxg4 cxb6 finishes it off, with the result that Black is up a knight.

Zwischenzugs are very easy to miss, because almost by definition you are not expecting them. They are one of the fascinating challenges in chess, and in calculating accurately.