Why are chess pawns important?
The pawn (♙,♟) is the most numerous piece in the game of chess, and in most circumstances, also the weakest. It historically represents infantry, or more particularly, armed peasants or pikemen. Each player begins a game with eight pawns, one on each square of the rank immediately in front of the other pieces. (The white pawns start on a2, b2, c2, d2, e2, f2, g2, h2; the black pawns start on a7, b7, c7, d7, e7, f7, g7, h7.)
Individual pawns are referred to by the file on which they stand. For example, one speaks of “White’s f-pawn” or “Black’s b-pawn”. Alternatively, they can be referred to by the piece which stood on that file at the beginning of the game, e.g. “White’s king bishop’s pawn” or “Black’s queen knight’s pawn”. It is also common to refer to a rook’s pawn, meaning any pawn on the a- or h-files, a knight’s pawn (on the b- or g-files), a bishop’s pawn (on the c- or f-files), a queen’s pawn (on the d-file), a king’s pawn (on the e-file), and a central pawn (on the d- or e-files).
Placement and movement
Unlike the other pieces, pawns cannot move backwards. Normally a pawn moves by advancing a single square, but the first time a pawn moves, it has the option of advancing two squares. Pawns may not use the initial two-square advance to jump over an occupied square, or to capture. Any piece immediately in front of a pawn, friend or foe, blocks its advance. In the diagram, the pawn on c4 can move to c5; the pawn on e2 can move to either e3 or e4.
Unlike other pieces, the pawn does not capture in the same direction that it moves. A pawn captures diagonally forward one square to the left or right (see diagram).
Another unusual rule is the en passant capture. It can occur after a pawn advances two squares using its initial two-step move option, and the square passed over is attacked by an enemy pawn. The enemy pawn is entitled to capture the moved pawn “in passing” – as if it had advanced only one square. The capturing pawn moves to the square over which the moved pawn passed (see diagram), and the moved pawn is removed from the board. The option to capture the moved pawn en passant must be exercised on the move immediately following the double-step pawn advance, or it is lost for the remainder of the game.
Main article: Promotion (chess)
A pawn that advances all the way to the opposite side of the board (the opposing player’s first rank) is promoted to another piece of that player’s choice: a queen, rook, bishop, or knight of the same color. The pawn is immediately (before the opponent’s next move) replaced by the new piece. Since it is uncommon for a piece other than a queen to be chosen, promotion is often called “queening”. When some other piece is chosen it is known as underpromotion. The piece most often selected for underpromotion is a knight, used to execute a checkmate or a fork to gain a significant net increase in material. Underpromotion is also used in situations where promoting to a queen would give immediate stalemate. The choice of promotion is not limited to pieces that have been captured; thus a player could in theory have as many as ten knights, ten bishops, ten rooks or nine queens on the board simultaneously. While this extreme would almost never occur in practice, in game 11 of their 1927 world championship match, José Raúl Capablanca and Alexander Alekhine each had two queens in play from move 65 through move 66. While some finer sets do include an extra queen of each color, most standard chess sets do not come with additional pieces, so the physical piece used to replace a promoted pawn on the board is usually one that was previously captured. In informal games, when the correct piece is not available, a second queen is often indicated by inverting a previously captured rook, or placing two pawns on the same square. In tournament games however this is not acceptable, and may result in the arbiter ruling that the upturned piece is, in fact, a rook.
Main article: Pawn structure
The pawn structure, the configuration of pawns on the chessboard, mostly determines the strategic flavor of a game. While other pieces can usually be moved to more favorable positions if they are temporarily badly placed, a poorly positioned pawn is limited in its movement and often cannot be so relocated.
Because pawns capture diagonally and can be blocked from moving straight forward, opposing pawns can become locked in diagonal pawn chains of two or more pawns of each color, where each player controls squares of one color. In the diagram, Black and White have locked their d- and e-pawns.