The Double Bishop Mate: Two Bishops on Neighboring Diagonals

Put the black king on h8 with its own pawn on h7. A white bishop on the long a1-h8 diagonal, say on f6, gives check and covers g7. A second white bishop on the neighboring b3-g8 diagonal covers g8. The king has three squares, g8, g7 and h7: the two bishops cover the first two, and its own pawn blocks the third.

The difference from Boden's mate is the geometry. In Boden's mate the bishops attack on crossing diagonals that meet in an X. In the double bishop mate they work on parallel, side-by-side diagonals, sweeping two adjacent lines through the king's area together.

The long diagonal is usually guarded by an enemy bishop, often a fianchettoed one on g7 or one that has come to f6. The attack starts by removing or deflecting that defender. A rook trade or sacrifice that forces the bishop to recapture somewhere else is a common way to do it, and once the diagonal is undefended, your bishop moves onto it with check.

The bishop covering g8 often does its work from very far away, from b3 or even a2, and it may have been sitting on that diagonal for many moves. When you have two bishops against an exposed king, look at both long diagonals and ask which defender is holding everything together.

Bishops placed far from the king do not look like attackers, so it is easy to miss that they already control the key squares. The defender is also often overloaded without anyone noticing, guarding both a back-rank rook and the long diagonal. The two-bishop mates you miss in your own games are good ones to go back and drill.