Endgame 101 - Key Squares

Opposition
Outflanking
Key Squares (first four ranks)
Key Squares (last four ranks)
Key Squares (knight files)
Key Squares (rook files)
Test Problems

Once you understand the opposition and outflanking, it's time to learn about key squares. For this article, a key square is defined as a square in which once your king reaches that square, you can promote a pawn. If your opponent can prevent your king from reaching a key square, you will not be able to promote your pawn. We'll just be dealing with situations where one side has a king and pawn, and the other side has a king. If you have the pawn, your goal is to use the opposition and outflanking to reach a key square and then promote your pawn. If you do not have the pawn, your goal is to use the opposition to prevent your opponent's king from reaching a key square and thus salvage a draw.

Whenever you have the pawn, it is imperative to get your king in front of the pawn. We have two basic types of positions to consider for key squares. The first is when your pawn has not yet crossed the center of the board on its journey toward promotion. In this case you have three key squares, always located two ranks in front of your pawn:

The key squares for White are the three green squares. If White can get his king to one of those squares, he wins. Thus, White can only win in this position if Black is to move (since White would then have the opposition, and can then use outflanking to make forward progress and reach one of the key squares). If White is to move, then Black has the opposition and White can never make forward progress to reach a key square and the game is drawn. You should know how to play these positions in your sleep.

The second type of position is when your pawn has crossed the center of the board. In this case you have six key squares, always located one and two ranks in front of your pawn:

Since White's pawn has passed the fourth rank, he now has six key squares. His king is already on a key square, so White wins no matter whose turn it is to move. You should know these positions, too.

There are a couple of special cases you should know about. The first is when you have a knight-pawn.

White can still win this (his king is on a key square), but you must know the correct way to make progress.

And finally, rook pawns are notoriously difficult to promote. If the opposing side can get his king into the corner, there's no way you can force it out, and the game is drawn.

This position is drawn no matter who is to move. Notice that White really only has one key square, the b7-square. a7 is not a key square, since if White got his king there, Black can maintain a horizontal opposition (on the c-file) and prevent White from ever being able to get his king out of the way for the a-pawn to promote. You can play through a few moves and see how this is always drawn.

When you're comfortable with key squares, it's time to try out some test problems.