Now the fun part. We have seen that a check sometimes will force the king into line with one of its own pieces, allowing a skewer on the next move by the same piece that gave the first check or perhaps by a different one. The principle can be extended, of course; sometimes a first check has to be followed with a second or third or fourth that continues to push the king until at last it is forced against its will into a skewer. Those patterns will be our focus in this section.
The patterns considered here are reminiscent of the positions requiring multiple checks in the chapter on queen forks. The habit involved has immense value: examining not only any checks you can give, but every check you then would be able to give after your opponent’s response (and every check you then could give, etc.). But chasing out all of these possibilities can take a long time, so it is much more efficient if your pursuit of checks is guided by ideas. As you see what you can do to the enemy king—what is possible in the way of engineering—you also see a visual pattern coming into view—an idea. You play back and forth with the idea and the forcing moves until those checks are being used to try to achieve a clear goal. It might be a fork that becomes possible once the king is on a square that your queen can attack while also going after a loose piece; or it might, as in these positions, be a skewer that becomes possible once the king is lined up with its queen or with a loose piece.
There are subthemes that also help narrow the process of studying check after check. Focus first on checks that tightly control your opponent’s replies, and especially those that force the king to move. And keep in mind not only your piece that gives the first check but any other pieces or pawns in the king’s vicinity that might add checks of their own—or a skewer at the end.
In example to the left, White has a powerful battery on the a-file, so imagine the consequence of driving both pieces through to the back rank: 1. Qa8+ is answered with BxQ; and now follow through with more checks: 2. RxB+, Kc7—and Black’s king and queen are aligned on the seventh rank, making the skewer easy. 3. Ra7+, K moves; 4. RxQ. White has traded queens and won a piece.
The thought of a skewer probably wouldn't come to mind right away in this position. To see it you need to play with your checks, push through the discouragement of the big material loss on the first move, and notice the alignment of king and queen that results from Black’s second move. It is natural at first to think of a battery like the one White has on the a-file here as mostly a mating tool, and thus to turn attention away from it when you see that the enemy king escapes; but often the payoff of pressure against the king is the chance to unleash some other tactic made possible by its attempts to escape.