Zwischenzug

A zwischenzug, German for an in-between move, occurs when one action seems automatic, such as recapturing the piece that has just taken one of yours, but a more urgent move is played first. The opponent must answer that new threat, and only then does the player return to the expected action if it is still useful.

Move order is the whole point. Imagine that an enemy piece captures yours and you expect to take it back immediately. Before recapturing, you give check, directly attacking the king, or attack something more valuable. If the opponent must deal with that problem, you gain a tempo, one useful move, and may still recover the original piece afterward. An in-between move that gives check is also called a zwischenschach, or intermediate check.

A zwischenzug is not simply a delayed response. It must pose a concrete demand that cannot be ignored without a greater cost. Sound calculation therefore includes every legal reply, including the possibility that the opponent declines to meet the threat and creates a stronger one.