Corresponding squares

Corresponding squares are pairs or groups linked by a defensive obligation. When one king occupies a square in the system, the other king must answer on its matching square to preserve the result. If that reply is unavailable, the first king can often penetrate or reach a critical square.

They occur mainly in blocked pawn endings, where obstacles distort the simple geometry of opposition, a situation in which the kings face each other and prevent direct advance. Each pair represents a form of zugzwang, a position in which being required to move makes the outcome worse. Opposition is a simple case of correspondence, but corresponding squares may be far apart and show no obvious symmetry.

How to identify them

1. Find the entry squares that would win a pawn or break the blockade.
2. Determine where the defending king must stand to prevent each entry.
3. Work backward through both routes. If the defender cannot reach the matching reply, the defense fails.

Triangulation and a spare tempo can change which king must enter a paired square first. Labels alone are therefore not enough; the move order must also be checked.