Basic checkmate
Bishop and Knight Checkmate
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Bishop and knight can force mate against a lone king, but only in a corner the bishop controls. The so-called W method is one way to organise the difficult edge-herding phase. Treat it as a map of controlled squares, not a knight-move recital: the defending king’s choices alter the order.
Which corner?
A bishop remains on one colour, so the final mate must be in one of the two corners on that colour. With a light-squared bishop those corners are a8 and h1; with a dark-squared bishop they are a1 and h8. The defender will normally head for a corner the bishop does not control. The attacking king, bishop and knight must then take away the edge squares that lead back there.
Three phases
- Centralise. Drive the lone king to an edge using king, bishop and knight together.
- The W method. Along the edge, the knight makes a series of moves whose path looks like a “W”, taking away escape squares while your king and bishop shepherd the defender toward the correct corner.
- Deliver mate. Box the king into the bishop’s-colour corner; the bishop checks while the king and knight cover the last two flight squares.
Watch the clock
Perfect play can require 33 moves from the least favourable legal starting positions. That fits inside the fifty-move rule, but an inaccurate route may not. Count from the last capture or pawn move under the applicable rules, and check every quiet move for stalemate.