When chess teachers and chess authors begin talking about pawn endings — the most important kind of endgames to know — they start with “the rule of the square”, a handy device for determining whether one pawn can promote without the help of its king.
If you imagine drawing a diagonal line from the pawn to the eighth rank, that’s the hypotenuse of “the square”. We always draw a big square to demonstrate:
After drawing a3 -> f8 as the hypotenuse — that is, a3 and f8 are two corners of “the square” — we finish drawing its boundaries:
The “rule of the square” says: If the enemy king cannot enter the square with its move, the pawn can promote without assistance. In this position, the king cannot:
“The rule of the square” makes it easier to understand this vital position. If Black attacks either pawn, the other advances:
I don’t know if this is a composition (in which case, I apologize to the artist, no doubt an early-1700s Italian), or a position that arose in practice. Probably both.
Which way do you draw the square?