Rule of the Square
A quick visual method for determining whether a king can catch an enemy passed pawn before it promotes.
By drawing an imaginary square from the pawn to its promotion square, a player can instantly tell whether the defending king is inside that square and therefore able to catch the pawn in time.
Etymology
The phrase is purely descriptive: one imagines a square whose side runs from the passed pawn to its promotion square, and if the defending king can step inside that square it catches the pawn. No source consulted supplies an etymology, coiner, or first documented use for the phrase; the concept's positions are dated instead, citing Lolli's 1763 book and Reti's celebrated 1921 study.
First documented: 1763 — Earliest dated illustrative position cited: Lolli, 1763
Translations
Translations for this term haven't been added yet.