Mate with Bishop and Knight: the hardest mate in chess

We’ve reached the Everest of basic mates. Mate with bishop, knight, and king against a lone king is, without question, the hardest mate in chess. So hard that even grandmasters have failed it in official games, letting victory slip away due to the 50-move rule.

The good news? It’s also the rarest mate. The odds you’ll need to execute it in a real game are minimal. But knowing it makes you a technically complete player, and the process of learning it improves your ability to coordinate pieces in a way no other exercise can match.

The fundamental restriction: the correct corner

Here’s the key difference from all other basic mates. With queen, rook, or two bishops, you can mate on any edge or corner. With bishop and knight, it only works in the corner matching the bishop’s color.

What does that mean? If your bishop moves on light squares, mate is only possible in the a8 and h1 corners (which are light squares). If your bishop moves on dark squares, only in a1 and h8.

Why? Because the bishop needs to give check or control the corner square, and it can only do that if that square matches its color.

The problem of the wrong corner

What if the rival king flees to the corner of the opposite color to the bishop? Then you can’t mate there. The rival knows this, and will try to reach that corner with everything they’ve got.

This is where the technique becomes truly difficult: you have to push the king from the wrong corner to the right one, traveling across the entire edge of the board. The king doesn’t want to go, and you have to convince it with perfect coordination of your three pieces.

The W technique (Deletang)

The best-known method for this transfer is called the W technique or Deletang technique. The name comes from the shape drawn by the knight in its maneuvers to create barriers.

The general idea is this:

1. Corner the rival king in any corner. Your king, bishop, and knight push it toward the edge.
2. If it’s in the correct corner, deliver mate with a pattern combining a bishop check on the diagonal and knight control of adjacent squares.
3. If it’s in the wrong corner, execute the W technique: the knight and bishop create a series of barriers along the edge that force the king to move rank by rank until it reaches the correct corner. Your king accompanies it, controlling the escape squares.

The W pattern consists of the knight jumping to key squares on the edge, creating “walls” that prevent the king from returning to the wrong corner. The bishop supports from afar, controlling diagonals. And your king closes the net.

Why is it so difficult?

Several reasons combine:

• Three pieces to coordinate, each with different movement. The bishop moves diagonally, the knight jumps in an L, the king moves to adjacent squares. Synchronizing the three requires calculation.
• The W technique is counterintuitive. Sometimes you have to move the knight away from the rival king to reposition it. It seems like you’re wasting time, but it’s necessary.
• The 50-move rule. You have a maximum of 50 moves without a capture or pawn move before the rival can claim a draw. With perfect technique, mate is achieved in about 33 moves. But with any imprecision, moves add up quickly.
• The rival king cooperates in its own defense. It heads toward the wrong corner and resists the transfer with every move.

Typical mating positions

The final mate usually has this structure: the rival king is in the corner (matching the bishop’s color), your king controls the escape squares on the edge, the knight controls a square adjacent to the corner, and the bishop gives check on the diagonal passing through the corner.

It’s a beautiful mate when executed correctly. The three pieces fit together like a perfect puzzle.

Is it worth learning?

It depends on your level and your goals:

• If you’re a beginner or intermediate player: it’s not a priority. Spend your time on the three essential mates (two rooks, queen, and rook) and on pawn endgames.
• If you’re an advanced player: learning it is an excellent piece-coordination exercise. It also gives you confidence in complex positions where bishop and knight have to work together.
• If you’re aiming for master level: it’s mandatory. You can’t afford to lose a point from not knowing a theoretical mate.

Practical advice

If you ever reach this position in a real game, remember two things:

1. Identify the correct corner before moving. Look at your bishop’s color and find the two corners of that color.
2. Bring the rival king to the edge first. Don’t attempt the W technique with the king in the center. First corner it on any edge, and only then worry about the corner.

Next steps

• Basic mates — back to the index of the five mates
• Mate with two bishops — the previous mate in difficulty
• Minor piece endgames — bishop and knight in endgames with pawns
• Endgames — general overview

The mate with bishop and knight is the ultimate test of piece coordination. Although you’ll rarely need it in a game, the process of learning it teaches you to think about the collaboration between different pieces, and that lesson is worth far more than the mate itself.