Figure[White to move]

White has the power to play QxR, but to make it work he first has to loosen the rook. Its guard is the queen on d6. The (hopefully) obvious idea is c4-c5, attacking the queen with a pawn. The harder part is figuring out what happens next. Your first fantasy might be that Black’s queen will flee or play Qxc5; since it has no safe squares from which it can keep guarding the rook on f4, you will be able to play QxR safely next move. None of this is likely, though. You have to consider counterthreats Black might launch—moves he might make that will then allow him to retaliate rather than just recapture. Here Black has Rg4. Now the rook has protection from a new source, the pawn on h5. True, after the rook’s move the Black queen still is exposed to attack by the pawn now on c5. But now White’s queen is under attack, too, by the rook: the threatened retaliation. White’s simplest recourse now is to liquidate the queens with 2. QxQ, c7xQ, then play 3. BxR, h5xB, winning the exchange. A little stronger, however, is 2. QxR, h5xQ; 3. c5xQ, g4xB; 4. d6xc7+, Kxc7; 5. Nxh3—and now White has won a pawn as well as the exchange.

The position is most valuable as another reminder that when you try to chase off a guard by threatening it, you have to remember that your opponent may have a wide choice of replies. He can make a different threat of his own; if you carry through on yours, he carries through on his. To be effective, his counterthreat has to target something at least as valuable as your threat does. Thus a suitable counterthreat for Black when faced with 1. c4-c5 here was to attack White’s queen. The position then becomes a matter of comparing what happens if each side’s threats are carried out—not just what each side gains and loses from the execution, but what their next moves look like afterwards.