Now a defensive study involving the same principles. Black finds himself in check. He has two choices: move his king or interpose his queen on f7. Which is preferable? Picture the interposition and ask what White’s next move would be. One way to answer the question is to ask what checks White could give, and with what consequences; another is to look for any patterns in the position Black would have created with his move. Either way you reach the same conclusion: Black’s queen will be under attack and protected only by its king. A standard flush check by White—Rxh7—will force Black to play KxR, then allowing QxQ+ by White and winning him a queen for a rook. So Qf7 isn't the answer for Black. The result illustrates a general danger in interpositions that block a check but cause the interposing piece—especially the queen—to be guarded only by its king.

For the sake of completeness let’s briefly consider what Black should play if he instead is to move his king. Kh8 causes Black to be mated on the spot, of course, with Qxh7. Kg8 results in Qxh7+, losing a pawn. Kf8 is better—but why? Because now if White plays Rxh7 or Qxh7, he doesn't give check; and this gives Black time to take White’s pawn on f2. Indeed, if White is really careless he can take the h7 pawn with his queen and then get mated; moving his queen into such poor defensive position leaves his king in jeopardy: 1 …Kf8, 2. Qxh7, Qxf2+—and now Black has seized initiative and never lets go: 3. Kh3, Qf5+, 4. g3-g4 (interposing), Ra3+; 5. Kh4, Qf6+; 6. g4-g5, Qf4#. Or 5. Kg2, Qc2+; 6. Kg1, Ra1#. So in reply to Black’s Kf8 White has no immediate way to win anything. (Of course Black must be careful to keep his king where it can’t be the subject of a fork that costs him the loose rook on a2.)