Figure 4.3.1.4[Black to move]

Now an example of how the pattern just viewed can emerge from a forcing sequence. This time the queens are faced off against each other. A natural question to ask is what it would take to enable you—Black—to play QxQ. White’s queen is guarded by the knight on f2. Black could simply take the knight with his bishop, but this wouldn’t get anywhere; White would reply QxQ, and then after Black recaptures White would have KxB and the sequence would be a wash. But the bishop aimed at White’s knight has another significance. There are ways of eliminating an obstacle besides capturing or chasing it; perhaps it can be pinned if its king can be brought into line with it. Or just inspect the consequences of any checks you give. Either train of thought leads you to Re1+. White’s reply is forced: KxR. Suddenly the knight on f2 is pinned, and therefore incapable of doing any defensive work. Black has QxQ.

Pins meant to capture the pinned piece—the sorts of pins studied before this section—can be brought into existence in many different ways, as we saw; often you can just slide your pinning piece into place to create the pin and then start throwing attackers at the target. But that method usually won't work if your goal instead is to take something the pinned piece protects. The reason is that once you impose the pin your opponent still remains free to move the target—i.e., the piece protected by the piece you have pinned. There are exceptions, but usually if you want to pin a piece to take something it guards you must bring the pin into existence with forcing moves that allow you to keep the initiative and don’t give your opponent time to move the target. The classic means of doing this is with a check—often a check sacrifice—that forces your opponent to move his king into line with one of its fellow pieces. In effect you have caused him to create the pin for you, and now it is your move again; anything the pinned piece used to protect suddenly is loose, and you can grab it. This case introduces the point.