One Way King — Pawn Endgame Basics | onewayking.com
The square rule settles a pawn race before you count a single tempo: draw one box and read the verdict.
Imagine the square whose side runs from the pawn to its promotion square. On its move, if the enemy king can step into that square, it can catch the pawn. The test needs no counting of tempi and no reference to the attacking king.
Worked race one: a pawn on e5 with the promotion square e8. The box runs e5–e8 as one side, so it covers the three ranks above the pawn and three files to either side. A defending king that cannot step into this box on its move cannot catch the pawn, and the pawn promotes.
On narrow screens, swipe or scroll the plate sideways.
Worked race two: the same pawn, but the defending king stands one square outside the box and can enter it on the next move. Now the pawn is caught, and the attacker must use the king to shoulder the defender away before the pawn can advance again.
Worked race three: a rook pawn on a2 heading to a1. The box is narrow — only the a- and b-files — and the defending king in the corner in front of the pawn cannot be forced out of it. The square rule gives a correct verdict here, but the verdict is a draw.
Because the rule is a test of one move rather than a count, it survives checks, distant kings and opposite wings. What it does not do is tell you how to win once the pawn is safe: for that, the opposition and key squares take over.
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