en passant (from French, “in the act of passing”) The rule that allows a pawn that has just advanced two squares or more to be captured by an enemy pawn that is on an adjacent file. The pawn can be taken as if it had advanced to a square immediately diagonally in front of the capturing pawn. Capturing en passant is possible only on the next move.
CHEX follows the basic principle of en passant but it applies to all pawn advances of two or more squares or throughout the whole game. Any pawn that advances in such a way to deny an opposing pawn the opportunity to capture it can be taken en passent. This capture is only legal on the opponent’s next move immediately following the first pawn’s advance. The capturing pawn moves one square diagonally forward as if the attacked pawn were adjacent to it, even if that pawn is a number of squares past. The attacked pawn is removed from the board.
In the diagram, pawn g2 has advanced into the empty field g4/5 and has occupied the g5 square. This illustrates a pawn’s maximum move of three physical squares. By doing so it has denied the black h5 pawn the opportunity to attack it on g4. However, on black’s next move only, it can move the h5 pawn diagonally to g4 as if the white pawn were there and having ‘attacked’ it remove the pawn on g5 from the board.
En passant can occur at any time during a game. The white pawn on c5 has occupied the second square in the field c6/c7. The black pawn can still play en passant and capture the white pawn as if it were on c6.