Moving along, then, there are three main issues to worry about if the Bxh7 sacrifice looks promising. The first and simplest is whether the squares you need—particularly g5, and then h7—are available for your pieces. The second is whether the king will be able to flee along the back rank. We have seen both of those complications; a third, to which we now turn, is the possibility that after taking your bishop (and being threatened by Ng5+) the enemy king will step forward to g6 rather than back to g8. This is the most complex variation on our current pattern, and it is hard to generalize about its consequences.
Sometimes you still can achieve mate quickly if you have other pieces available to help; sometimes you can use the king’s highly exposed position to create other tactical shots; and sometimes Black just gets away with it. You have to assess the facts on the board. Your goal in these next studies is to get a sense of the resources you have available against a king that ventures out to g6—the types of attacking ideas that become possible. The general ideas are these: (a) bringing your queen closer to the exposed king; (b) forcing the king into a discovered check unmasked by your knight on g5—and then possibly using your knight as a forking threat; and (c) advancing your h-pawn, g-pawn, or f-pawn to close off the king’s flight squares and support more mating threats.
The position diagrammed to the left started the same as another seen a few moments ago, then took a different turn. Assume play went 1. Bxh7+, KxB; 2. Ng5+, Kg6, bringing us to the current frame. White wants to get his queen into the picture; the combination of a queen and a protected knight will give him various ways to threaten mate in the sector where Black’s king has wandered. It’s best to introduce the queen with check to keep control over the position, so White plays Qd3+. Black now gets mated, but the tools White uses may seem a little surprising at first:
(a) If Black replies to Qd3+ with Kh6, White plays 2. Qh7#.
(b) If Black replies to Qd3+ with Kh5, White plays 2. g2-g4+—and will mate next move. For now (i) if Black moves his king to h6, White has Nxf7#—discovered mate. (ii) If Black plays Kxg4, White mates with Qh3. (iii) If Black plays Kh4, White has Qg3#. Notice the crucial work done by the bishop on c1. (After Black plays Kh5, White also can mate by playing his queen to h3 with check; then, after Black's Kg6, White has Qh7#.)
(c) Black’s best reply to Qd3+ is f7-f5, interposing a pawn in front of White’s queen. But since the f-pawn just jumped two squares alongside White’s pawn on e6, White can take Black’s pawn en passant: e5-f6+, discovering check. If Black then plays Kxf6, White mates with Rxe6. If Black moves his king to h5, White plays g2-g4 and mates as described a moment ago.
As you can see, the mating ideas here are a bit tricky. There are a half-dozen different ways White might finish the game depending on the choices Black makes, and they involve nets that all have different shapes. If White makes a false move, Black can escape—and a false move is a real danger, because the ideas just sketched aren't especially intuitive. Some involve using the queen on a square the knight protects; some involve combining those pieces with a pawn; one of them involves attacking with the rook on e1.
The general point is that once the king climbs to g6, it's in danger in lots of different ways. Sometimes its owner may be able to escape without being mated or suffering material losses, but careful play on the attacker's part generally will yield one of those outcomes—with emphasis on “generally.” Every position has to be considered on its merits. Study the attacking ideas presented here not because you necessarily will find them replicated in your games, but because they are the kinds of options that arise in this position. If you spend enough time with them now to make them familiar, you will have an easier time spotting related possibilities on the board.
This raises a final question: how much confidence must you have to play this pattern? Normally you don't want to sacrifice a piece unless you are certain where it will lead. But as you get better you sometimes may make sacrifices without being sure of the result because you know they produce strong positions where you feel sure you can make gains. These positions are examples: you may be able to see that you can flush the king to g6, and so play Bxh7 without being sure how the game will play out. After studying the position you might just know that with good play your chances of either mating or making material gains are strong; you might see a couple of ways that can happen, and no clear way for your opponent to extinguish the danger. But you nevertheless will be taking a risk, because you can't see every possibility and you know the sacrifice isn't a sure thing. It makes for an exciting game, anyway.