Pawn (chess)
The pawn is the weakest and most numerous piece in the game of chess, representing infantry, or more particularly pikemen. Each player begins the game with eight pawns, one on each square of his second rank. In algebraic notation the white pawns start on a2, b2, c2, ..., h2, while the black pawns start on a7, b7, c7, ..., h7. Pawns are differentiated by the files in which they currently stand, for example one speaks of "white's f-pawn". Sometimes, however, pawns are still referred to using descriptive notation, e.g. "white's king's bishop's pawn".
| File:Cb pawn move.png |
| Pawn movement |
Pawns are unusual in movement and use. Unlike all the other pieces, pawns may not move backwards. Normally the pawn moves by advancing a single square, but the first time each pawn is moved from its initial position, it has the option to advance two squares. Pawns may not use the initial two-square advance to jump over an occupied square. In the diagram at left, the pawn on c4 may move to c5, while the pawn on e2 may move to either e3 or e4.
| File:Cb pawn capture.png |
| Pawn capture |
Unlike other pieces, the pawn does not capture in the same way as it moves. A pawn captures diagonally, one square forward and to the left or right. In the diagram to the right, the white pawn may capture either the black rook or the black knight. Any piece directly in front of a pawn, friend or foe, blocks its advance.
| File:Cb pawn ep.png |
| En passant capture |
An even more unusual move is the en passant capture. This arises when a pawn uses its initial-move option to advance two squares instead of one, and in so doing passes over a square that is attacked by an enemy pawn. That enemy pawn, which would have been able to capture the moving pawn had it advanced only one square, is entitled to capture the moving pawn "in passing" as if it had advanced only one square. The capturing pawn moves into the empty square over which the moving pawn moved, and the moving pawn is removed from the board. In the diagram at left, the black pawn has just moved c7 to c5, so the white pawn may capture it by moving from d5 to c6. The option to capture en passant must be exercised on the move immediately following the double-square pawn advance, or it is lost and may not be made later.
Finally, 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. The pawn is immediately (before the opposing player's next move) replaced by a queen, rook, bishop, or knight of the same color. Promotion is often called "queening", because the piece chosen is nearly always a queen.
In practice, a promoted pawn is often replaced with a piece previously captured, because standard chess sets do not come with additional pieces. The choice of promotion, however is not limited to captured pieces. It is perfectly acceptable to have, say, three knights, or two or more queens simultaneously in play. In fact, one notable world championship game went for many moves with four queens on the board. When extra pieces are not available, a second queen is often indicated by an inverted rook.
Strategy
Pawns are the source of nearly all of the strategic depth of chess. If pieces are temporarily badly placed, they can be regrouped more favorably. A poorly placed pawn, in contrast, cannot retreat to a more favorable position, it can only advance further.
| File:Chess pawn chain.png |
| Locked pawn chains |
Because pawns capture diagonally and can be blocked from moving straight forward, opposing pawns often become locked in diagonal chains of two or three, where each player controls squares of one color. In the diagram at left, black and white have locked their d- and e-pawns. Strategically black will attempt to gain some control over the dark squares with c7-c5 and perhaps f7-f6. In the mean time, his c8 bishop is a "bad bishop", i.e. hemmed in by friendly pawns.