The Rule of the Square and Pawn Races
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In most endgames, everything hinges on one simple question: will this passed pawn promote, or will the enemy king have time to stop it? Counting the moves one by one is slow and error-prone under time pressure. Masters, however, don’t count: they look at an imaginary square and know the answer instantly.
That is exactly what this article is about. You will learn to draw that square on the board, to know its crucial exception, then to see how this simple tool leads to ideas of rare elegance: the king escorting its pawn, the outside passed pawn that lures the enemy king away, and Réti’s diagonal race, one of the most beautiful feats in endgame play. Master these ideas and you stop suffering pawn races and start winning them.
The Rule of the Square: Judging at a Glance
Picture a passed pawn racing toward promotion. Mentally draw a square with one side running from the pawn to its promotion square, and the perpendicular side reaching out toward the enemy king. That square is the decisive zone of the race.
The rule is clear: if the enemy king stands inside the square (or can step inside on its move), it catches the pawn. If it is shut out and it is the pawn’s turn to advance, the pawn promotes. You don’t track squares one by one: you visualise the square and simply check whether the king is in or out.
One key point often decides the race: it is the side NOT to move that must already be in the square. If it is the king’s turn, it merely needs to be able to step inside; if it is the pawn’s turn to advance, the pawn shrinks its own square by one rank, and the king must have kept pace. Look at the diagram and trace the square with your eye before reading on.
Trace the square: one side rises from a2 to the a8 promotion square, the other reaches right, out to the g-file. The black king is left outside that square and can no longer step in fast enough: it will not catch the pawn, which will promote. Always ask the question before pushing or chasing a pawn: "is the king inside the square?"