Key squares
Key squares are the target squares for the attacking king in a pawn ending: once it reaches one while its pawn is safe, the pawn promotes by force, no matter whose move it is.
Also called: critical squares
Endings with a single pawn often come down to a race between the kings for a handful of squares. Learn where those squares lie and you can judge many positions without calculating a single line.
For a pawn on the b- to g-file that has not crossed the middle of the board, the targets are the three squares two ranks above it: a pawn on d3 has c5, d5 and e5. Once the pawn stands on its fifth or sixth rank, the three squares directly above it are added, so the attacker has six targets. Rook pawns are the exception: only the two squares beside the promotion corner, such as g7 and g8 for an h-pawn, do the job, and even those are hard to reach.
The attacker's plan follows from this. Walk the king toward the nearest key square, using the opposition when the enemy king stands in the way. The pawn usually waits, because pushing it early moves the targets forward too.
The defender plays the mirror image, keeping the king in front of the pawn and on or beside those squares. A common error on both sides is to chase the pawn instead of the squares; another is to forget that a rook pawn plays by different rules.
It sits close to Distant opposition. Distant opposition is the long-range form of the kings' standoff: the kings share a line with an odd number of empty squares between them, and the side not on move can keep that count odd until the kings meet.
It sits close to King and pawn endgame. A king and pawn endgame is an ending in which only kings and pawns remain, so the result depends on promotion races, king placement, opposition, and exact counting of moves.
It sits close to Wrong rook pawn. A wrong rook pawn is an a-pawn or h-pawn whose promotion square is the opposite color to its side's bishop, so king, bishop and pawn cannot win once the defending king reaches the corner in front of it.
If "Key squares" has cost you half a point, a first lesson is a good place to find the pattern behind it: George Li goes through your games and builds a plan.
Related terms
Opposition is a standoff between the two kings on one file or rank with a single empty square between them; whoever does not have to move holds it, because the other king must give up ground.
A king and pawn endgame is an ending in which only kings and pawns remain, so the result depends on promotion races, king placement, opposition, and exact counting of moves.
A passed pawn has a clear road to promotion as far as enemy pawns are concerned: none stands ahead of it on its own file or the two neighboring files, so the opponent must spend a piece or the king to stop it.
The rule of the square is a shortcut for a lone pawn racing an enemy king: draw a square from the pawn's square up to its promotion square, and the king catches the pawn only if it stands inside or can step in.
Corresponding squares form a map for blocked pawn endings: each square the attacking king might use is paired with the square the defending king must occupy in reply, and missing a pair lets the attacker break through.
Guides that go further
What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid.
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A game review, a read on your level and a written study plan from George Li.
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A first lesson starts with your games: George reviews them and builds a study plan around what he finds.