Part 6 of 6
VIII. Bishop Checks, Double Checks, Forks, Fork Checks, combined Fork Check
- moving his or her King out of check, and must do so if the Bishop is checking the King from an adjacent square on the diagonal line and the King cannot capture the Bishop, or
- interposing another piece or pawn between the Bishop and King on a square along the diagonal line; or
- capturing the bishop with:
- the King that is in check, but this requires the Bishop to be on one of the four diagonal squares adjacent to the square upon which the King in check is located because the King may only move one square at a time, and the Bishop must be unprotected; or
- with any of the player’s other pieces (other than the King) or pawns which are available to attack and capture the Bishop.
In addition, the Bishop in combination with another piece (other than the King) may engage in a Double Check on the opposing King. The Bishop like all the pieces (except the King) and pawns also may do forks and fork checks. A Bishop Fork is when a Bishop has two (single fork) or more pieces and/or pawns (multiple fork) under attack along the diagonal lines from the square upon which the Bishop is located, with the threat to capture either one on the next move. A Bishop fork may occur along a single diagonal line where the Bishop is located between the two pieces and/or pawns being attacked, or in a V-shape pattern based on triangulation along two converging diagonal lines. In a multiple Bishop fork situation, there must be a combination of these two because the Bishop can only attack a maximum of two pieces and/or pawns along a single diagonal line. Examples are shown below.
Single Bishop Fork
Multiple Bishop Fork
In the single Bishop Fork diagram, White’s Bishop and Queen also are in a battering ram lineup along the long diagonal from a1 to h8. Black has a competing Queen fork keeping White’s Rooks essentially pinned to the first rank. If White moves either Rook off the first rank in the current position, then Black will be able to capture the other Rook and have mate in one or two moves. Black’s competing Queen fork thus works to Black’s significant advantage negating the threat of White’s Bishop fork if it is Black’s move. Why? Take a look at the single Bishop Fork diagram. If it is Black’s move, Black has mate in two as follows: … Rxe1 followed by the forced 1…Rxe1 and Black mates with 2.Qxe1# (back rank mate). However, if it is White’s move, White has free capture of Black’s Rook at e8 [1.Bxe8] because Black’s Rook at a8 can not capture back White’s Bishop at e1 [1…Rxe1] without subjecting Black to checkmate on White’s next move 2.Rxe1#. However, Black’s Queen fork still comes into play even if it is White’s move because White could blunder and capture Black’s Rook at a8, leaving Black mate in two following the same line above.A Bishop Fork Check is when a Bishop has the opposing King in check along a diagonal line and also one or more opposing pieces and/or pawns under attack along another diagonal line or lines from the square upon which the Bishop is located with the threat to capture the other piece or pawn (or one of them if more than one under attack) on the next move. A Bishop also may combine with another piece to do a combined Fork Check & Double Check at the same time.
In a Bishop Fork Check & Double Check situation, the King either:
- must move out of check; or
- capture the Bishop or other piece or pawn involved in the Double Check & Fork Check if possible with any available piece or pawn, and if to be done with the King then this requires the piece or pawn to be captured to be on one of the squares that is adjacent along any line or touching diagonally the square upon which the King in check is located because the King may only move one square at a time, and it must be unprotected.