Corresponding squares

Examples

In a king and pawn versus king endgame, corresponding squares offer a clear defensive plan. Imagine the black king sits in front of the white pawn, with the white king behind or beside it. The white king wants to reach a key square (marked with an x) to win. If both kings are on squares labeled "1" (black on c8, white on c6), the outcome depends on whose turn it is. If Black moves first, White wins: Black goes to d8, White pushes the pawn, and Black must move to e7. If White moves first, Black draws because pushing the pawn leads to stalemate. This is a reciprocal zugzwang—neither side wants to step onto a "1" square if the other can match it. The "2" squares work the same way. When the white king sits on d5 (the middle "3" square), he threatens to move to either a "1" or "2" square. To hold the draw, the black king must be on one of his own "3" squares, ready to respond. Black’s defense is straightforward: shuffle between the "3" squares until White commits to a "1" or "2", then move to the matching square. If Black moves to a "1" or "2" at the wrong time, White either moves to the corresponding square or, if blocked by the file, steps diagonally forward; then after Black’s move, White advances the pawn and promotes. The squares on the fifth rank are not corresponding to Black’s "3" squares—if both kings are on those squares, the game is a draw no matter who moves. They are marked only to show that while White is on one of them, Black must stay on a "3" square to draw. In another example, the key squares are e1, e2, e3, and f3. If the black king reaches any of these, Black wins. The white king must block him. White can protect e3 and f3 by moving back and forth between e2 and f2. The correct move is 1. Kf2, which keeps the black king off the key squares by using the corresponding squares.