Mate with two bishops

The key idea

Bishops side by side: between the two they raise a four-square wall the enemy king can't cross. Your king pushes the wall; the corner does the rest.

Example 1 · The wall and the push

Bishops on d5 and e5, shoulder to shoulder. The black king is boxed in above and can't come down: watch its board run out.

1. Kf5 Before moving, look at the wall: the bishop on d5 controls c6 and e6, the one on e5 controls d6 and f6. Four squares in a row on the sixth rank forbidden to the black king. With the wall standing, the white king can stroll around freely — and that's what it does: it moves in from the flank.
2. Kd8 The black king pulls back. It has no alternative: trying to come down is impossible with the wall in place, so it moves along its upper strip.
3. Ke6 The white king enters the sixth rank, the one its bishops already control. This is the division of labor in this ending: the bishops hold, the king takes ground.
4. Kc8 Black shifts toward the queenside looking for the least bad corner.
5. Kf6 The white king keeps taking squares. No hurry at all: as long as the wall holds, the black king can't escape anywhere.
6. Kd7 Back to the center of its strip. It's the only thing it knows how to do.
7. Bf3 Now the white bishop readjusts. It changes squares within the same long diagonal: it keeps watching c6 and e6 from a distance, and picks up a waiting tempo along the way. In this ending, the waiting tempo is a weapon.
8. Kc8 The black king goes back to its favorite corner. It has less and less air left.
9. Bd6 The wall moves house to the seventh rank: the bishop on d6 controls c7 and e7. One floor higher, one less strip for the black king.
10. Kd7 It comes out to get in the bishop's way. It doesn't manage it: the bishop is defended by the king.
11. Bc5 The bishop reorders to make room for the other idea. Notice the two minor pieces are never left loose: either they defend each other or the king defends them.
12. Ke8 The black king approaches the edge. Every move of its own pushes it further toward the border.
13. Bd4 And the wall is set up again, now aiming at the top corner. From here on it's just repeating the maneuver: wall, king step, wall, king step. In the next example you'll see how it finishes once the enemy king is already pinned to the corner.

Example 2 · The finish in the corner (mate in 7)

Black king on b3 with the a1 corner two steps away. Here's the full mate, forced — with the stalemate trap in plain sight.

1. Kc1 The king first. In the two-bishop mate your king isn't a spectator: without it there's no mate, because the bishops alone don't cover the squares right next to the enemy king.
2. Ka3 The black king hugs the edge looking for air. It'll always do this: run toward the border and then toward the corner, because that's what we're leaving it.
3. Kc2 Another step. The white king places itself in opposition, taking away b3 and b2.
4. Ka4 It climbs up the a-file. It has no more board than that.
5. Bd3 The light-squared bishop comes into play: from d3 it controls b5 and c4. It's just put a ceiling over the black king from above.
6. Ka3 It comes back down, forced. The box has narrowed.
7. Bb5 And it narrows further: the bishop occupies b5 and takes away a4. Now the black king can only move between a3, a2 and a1. It's already on the shopping list.
8. Ka2 Toward the corner. Out of options.
9. Bc1 A waiting move with the dark-squared bishop, and a very fine one: it takes away b2 without giving check. And here's where you need to be careful — if you take away b1 and b2 from a king already stuck on a1 WITHOUT giving check, the game ends in stalemate and a draw. Since the black king is on a2, there's no stalemate: it can play Ka1.
10. Ka1 The corner. Right where we wanted it.
11. Bb2+ Check from b2, defended by the king on c2. The black king can't take it and can't stay put: it's only got a2 left.
12. Ka2 Only legal move: a1 is covered by the bishop on b2 and b1 is covered by your king. Black plays whatever we leave it.
13. Bc4# Mate. Look at the final picture: the bishop on c4 cuts the a2-b3 diagonal, the one on b2 covers a1 and a3, and the king on c2 covers b1 and b3. All three pieces, each with its job. That's the two-bishop mate: wall, push, corner and finish.

Practice

Black king on b3, your two bishops at home and your king ready to push. Deliver mate in seven moves: king first, then box it in with the bishops, and watch out for stalemate in the corner.

1. Good start: in this mate the king works just as much as the bishops. Before touching the bishops, bring your king closer: without it there's no mate.
2. Opposition taken: you take away b3 and b2 in one go. One more king step, placing yourself opposite theirs.
3. The light bishop puts a ceiling over it: b5 and c4, controlled. Bring in the light-squared bishop to take away the escape squares from above.
4. The box closes: the black king only has a3, a2 and a1 left. Narrow the box: with the light bishop, occupy the square that takes away a4.
5. A perfect waiting move, and no stalemate: you take away b2 while it can still go to a1. Time to wait with the dark bishop, taking away b2. Careful not to leave it with no legal moves: that would be stalemate.
6. Check, and the bishop defended by your king. Only one square left. Now it's time: check with the dark bishop, backed up by your king.
7. Mate! The two bishops and the king, each covering its part. Finish with the light bishop cutting off the diagonal it wants to escape through.

Two-bishop mate, delivered. What needs to stick isn't the seven moves: it's the picture of the bishops shoulder to shoulder raising the wall, and the king pushing it. With that you can drive the enemy king to any of the four corners. And the warning sign, also memorized: enemy king in the corner, no check and no squares, is stalemate and a half-point thrown away.