In
chess parlance, the term
pure mate refers to a
checkmate (or occasionally a
stalemate) where each square adjacent to the checkmated
king is either occupied by one of his own pieces or attacked by exactly one enemy piece (but not both). A double checkmate, where in the final position two pieces attack the checkmated king, is usually considered impure. Here is an example of a
pure mate, derived from a 1929 problem by
Joseph Cumpe:
+---+---+---+---+
| | | |WK |
+---+---+---+---+
|BK |BB | |WR |
+---+---+---+---+
| |BP | |WB |
+---+---+---+---+
| | | | |
+---+---+---+---+
|WR | | | |
+---+---+---+---+
Note that this position disobeys the definition above, because the square to the king's right is both occupied by a black
bishop and attacked by a white
rook. However, this illustrates an exception to the usual rule, namely that if a friendly piece is
pinned to the king which could otherwise prevent mate (as this bishop could, by moving to block the other rook's attack on the king), then the mate is still termed pure. Note that if the white bishop were replaced with a
queen, the
mate would be
impure because the black pawn would then be under attack.
Pure mates occur most often in chess problems, where they are deliberately constructed for their aesthetic appeal; however they occasionally occur in real-world games. If a pure mate is also economical (as the position above is), it is termed a "model mate".