Dual

A composition contains a dual when, after its first move, two or more methods satisfy the stated task. That task appears with the diagram and may, for example, require mate within a specified number of moves.

In a directmate, where White must force mate against every defense, the typical case occurs after a Black move: two different White moves both mate or both preserve an equally valid continuation. The position is still solvable, but White's play is no longer unique. Because this can blur the composer's intended idea, an unintended dual is normally regarded as a flaw, especially in a variation carrying the main theme.

Its seriousness depends on the type of composition and where it occurs. Some forms tolerate duals in secondary branches away from the main idea, while others demand strict uniqueness. The corresponding positive theme is dual avoidance, where several replies seem possible but the position rules out all except one.