Figure 6.2.11.4[Black to move]

Start by examining White’s king and you see that it is hemmed in by the bishop on f5 (and by the White pieces on d1 and d2). It has no flight squares, so an attack against it from a3 would mate. The possibility of such an attack may seem remote, but notice that Black has his queen aimed at the pawn on c3; if that pawn gets taken, the b2 pawn will have to recapture and the diagonal leading toward the king from a3 will be open. The other problem is that Black’s dark-squared bishop is back on its original position—f8—with a pawn on d6 blocking its path to the White king’s territory. But this naturally suggests moving the pawn forward with 1. …d6-d5, attacking White’s bishop. White plays 2. Bxd5, apparently taking a pawn for nothing—and now Black lowers the boom with 2. …Qxc3+; 3. b2xQ, Ba3#. This was the climax of Schulder-Boden (1853), the game that gave Boden’s mate its name.

If it wasn’t clear at first, in retrospect you can see that two of the elements of the mate were in place from the outset, and that the Black pawn’s advance to d5 amounts to a discovered mate threat: Black suddenly is a short forced sequence away from winning if White does nothing to address the threat. White’s best option would have been Rd1-e1, creating a flight square for his king. This saves the game but of course enables Black to win a piece with d5xB.