Critical square in pawn endgames
Critical square
Definition
In pawn endings, a critical square is any square which, if occupied by the attacking king, guarantees that the pawn in question will reach the promotion square, regardless of whose turn it is. The exact group of critical squares depends on the pawn’s file and how far it has advanced:
- For a pawn on its 2nd, 3rd —or 4th rank, the three critical squares are found two ranks in front of the pawn and span the pawn’s file plus the two adjacent files.
- For a pawn that has reached its 5th rank (or farther), the critical squares shift to the next rank in front of the pawn, again covering three files.
- If the pawn is a rook pawn (a- or h-file), the flank restricts the set to only two or even one square, because the board edge chops off the normal trio.
Why the concept matters
The rule of the critical square is one of the fastest “calculator short-cuts” in chess: the moment you evaluate a king-and-pawn ending, you can see at a glance whether the pawn is already winning, already drawn, or whether everything hinges on a single tempo race.
Usage in practical play
- King placement planning. Endgame masters steer their king toward the closest critical square rather than directly escorting the pawn.
- Exchange decisions. Before simplifying into a pawn ending, players mentally paint the critical squares to make sure the resulting position favours them.
- Tempo counting. If both kings can reach a critical square, the side to move may win the tempo race unless technical tricks intervene.
Canonical position
White to move. The pawn on e5 has critical squares d6, e6, f6. 1. Ke4–d5! (or 1. Ke4–f5!) wins because the king marches onto a critical square in two moves, forcing the pawn through.
Historical & strategic significance
The term was popularised by German theoretician Johannes Zukertort in the 19th century, refined by Siegbert Tarrasch, and codified in modern manuals by Reuben Fine (“Basic Chess Endings”, 1941).
Some authors call the same idea the “key square” rule; the two terms are interchangeable, though “critical square” appears more often in English-language endgame books.
Illustrative game fragment
Peter Svidler – Viswanathan Anand, Wijk aan Zee 1999 (excerpt)
After 46…Rxd4 47. exd4 Kf6 the players liquidated to a pure king-and-pawn ending.
Svidler’s outside passed a-pawn had critical squares a6 & b6; his king was closer,
so Anand resigned a few moves later without forcing him to demonstrate the promotion.
Edge cases & curiosities
- Shouldering: Even if the defender cannot reach a critical square directly, he can sometimes block the attacking king with “body-checks,” a technique dubbed shouldering by GM Mark Dvoretsky.
- Rook pawns: A lone rook pawn may be hopelessly drawn because its critical squares are on the edge. The defending king needs to control only one corner square to build a stalemate fortress.
- Opposition games: Many endgame studies reduce to “Who reaches a critical square first while keeping the opposition?”—a duel that spices up seemingly “simple” positions.
Related terms
See also: Opposition, Shouldering, Passed pawn, Key square.