Black has a material advantage—a queen and a bishop against White’s two bishops. But having two bishops trained on the Black king’s vicinity is strong, too, and with Black’s queen behind his king White should be alert to any way of forcing an alignment between them. He begins his thinking in the customary way: by looking at any checks. He has Bg5, which loses a piece, and Bd4, which requires Black’s king to move. Where? The f5 and g6 squares are sealed off by White’s other bishop, so the Black king is driven to f7. Now the desired alignment is in place. White reaches for his next check, using the other bishop to play Bc4+. Black’s king moves to f8, from which square he will be able to recapture White’s bishop after it takes his queen on the next move.

A pair of coordinated bishops, like a pair of coordinated rooks, is stronger than the sum of its parts.