If the defending king is within the "square", then the pawn cannot queen without the help of its own king. The first concept that needs to be introduced is that of the
key square, also known as a
critical square. A key square is a square such that if White's king occupies it, White can force the pawn to promotion, regardless of where the black king is and regardless of which side is to move, and against any defense (assuming that the black king cannot capture the pawn). The key squares are relative to the position of the pawn. Whether or not the white king can reach a key square depends on the position of the pieces. Of course, even if the white king occupies a key square, accurate play is still required in order to promote the pawn. Note that the key square is in front of the pawn. Endgame expert
Yuri Averbakh said, just as a father leads his child across the road rather than pushing the child in front, the king should also lead the pawn to the queening square.
Rook pawn A (on the a- or h-file) has much less chance of promoting than other pawns. The reason is that if the opposing king can get to any square in front of the pawn, it cannot be driven away from the file, and the pawn cannot queen. Black can always draw if he can reach the c8-square for an a-pawn (pawn on the a-file), or the equivalent f8 for an h-pawn, except for the position in the next diagram, with White to move. Therefore, an advanced rook pawn generally has two key squares: b7 and b8 for an a-pawn, and g7 and g8 for an h-pawn. The key squares are indicated by the black dots in the position in the diagram. If White's king can reach either of the two key squares, he can keep Black's king away and the pawn will promote. If the black king can reach any of the squares marked with a dot or a cross, it stops the pawn. The pawn can also promote in the position on the right (if White is to move), after :
1. h7 In practice, however, most of the time the black king can stop a rook pawn because it is usually close enough that the white king cannot prevent it from getting in front of the pawn (or capturing it).
Examples from games The game
Oscar Panno–
Miguel Najdorf, Buenos Aires 1968, continued :
59. Kg4 Kc7 60. Kg5 and White won because the white king can reach the key square g7. Black
resigned in light of :
60... Kd7 61. Kg6 Ke7 If 61...Ke6, then 62.h4; not 62.Kg7 because 62...Kf5! wins the pawn. :
62. Kg7 Moving to a key square, the only move to win. :
62... Ke6 63. h4 Kf5 64. h5 The only move to win. The king protects the pawn as it promotes. If Black was to move in this position, he would draw by reaching the f8-square and preventing the white king from getting to a key square, and the pawn cannot promote. This position from a game between
Gedeon Barcza and future
world champion Bobby Fischer was a draw. (White's 96.Kd2 followed by 97.Kc1 draws.)
Pawns other than rook pawns Pawns other than rook pawns have a much better chance of promoting. If the pawn is on the second, third, or fourth , there are three key squares – the square two squares in front of the pawn and the squares to the left and right of that square. The key squares are indicated by the black dots (for example, see the left-most diagram). If the pawn is on the fifth or sixth rank, there are six key squares: the square in front of the pawn and the squares to the left and right, as well as the square two squares in front of the pawn, and the squares to the left and right of it (see the diagram in the middle). When the pawn is on the seventh rank, the key squares are the squares on the seventh and eighth rank that touch the pawn's square (see the right-most diagram). An easy way to remember the key squares is to note that if the pawn is not beyond the midpoint of the board, there are three key squares that are two ranks ahead. If the pawn is on the fifth or sixth rank there are six key squares on the two ranks in front of the pawn. If the pawn is on the seventh rank, the adjoining squares on the seventh and eighth ranks are key squares. Once White's king occupies a key square he can keep the opposing king from blocking the advance of the pawn, as will be shown below.
Knight pawn exception There is an exception to the key squares rule with a knight pawn, the black king in the corner, and Black to move. In the diagram, with the white king on either the square indicated or the square marked by a cross, the position is
stalemate if Black is to move. This is sometimes known as the
b- (or g-) pawn trap. In this position, the best move is 1.Kh6! If :
1. Kf6 Kh7 Now if 2.g6+ then 2...Kh8! draws, or :
2. Kf7 Kh8 does not work for White because 3.g6?? is stalemate. White must play :
3. Kg6 Kg8 getting back to the original position, followed by 4.Kh6. This position and sequence of moves came up in a game between
Harry Golombek and
Arturo Pomar. It is actually much older, having first appeared in
Giambattista Lolli's 1763 book.
Any key square by any route {{Chess diagram It is important that White wins if he gets his king to key square and the path to a key square is not always direct. For instance, in the diagram, the key squares for White are b5, c5, and d5; however, Black can prevent the white king from reaching a key square directly. For example: :
1. Kd2 Ke7 2. Kd3 Kd7 3. Kc4 Kc6 taking the
opposition (see
below). The white king can reach a key square (b5), however, by going on the other side of the pawn: :
1. Kc2! Ke7 2. Kb3 Kd6 3. Kb4 Kc6 4. Kc4 Opposition, and Black is in
zugzwang. :
4...Kd6 5. Kb5 or :
4... Kb6 5. Kd5 and the white king has occupied a key square and has a winning position. ==Opposition==