Here is a demanding position. A habitual scan for discovery kernels for Black makes the lineup on the d-file obvious, but nothing productive can be made of it because the target (the d4 knight) is secure. Less obviously, though, Black has a kernel of sorts in horizontal form on the sixth rank. There are no pieces blocking the path between queen and bishop, and the bishop has a check with Bxh2. The missing ingredient this time is a target: Black’s queen has nothing at all to attack once it is unmasked. How might Black somehow force or attract a White piece onto a6, b6, or c6? Consider Black’s other pieces and what moves they can make that might help. The rook can’t force anything useful, but now have a look at the bishop on c8. One way to attract an enemy piece onto a square is to put one of your pieces there in a manner sufficiently threatening to make your opponent capture it. Here Black can put the c8 bishop onto the sixth rank with Ba6, where it attacks White’s queen. What response could White make? Moving the queen seems out, because that would expose the rook on f1 to capture; and letting the queen be captured likewise is out. Another option would be Nb5, where White interposes a piece between his queen and Black’s bishop. But then Black has c7-c6, attacking the knight and winning a piece. (Once on b5 the knight is pinned to the queen.)
That leaves White with one other reply to Ba6: capturing the bishop with QxB. But this completes the three-piece kernel of a discovery on the sixth rank, setting up the board for Bxh2+—a discovered attack that takes White’s queen. Black ends up exchanging two bishops for a queen and a pawn. (Moving the queen, and enduring the loss of the exchange with BxR, would have been better after all for White.)
Seeing this idea will be easier after you have studied skewers, for then your attention would be attracted from the beginning by the alignment of White’s queen and f1 rook. You imagine running a piece through them with Ba6, see that this results in QxB, and then recognize the three-piece pattern for a discovery that would result on the sixth rank.
Notice what has been involved in each of the positions we recently have considered: (a) Identification of the basic kernel for a discovered attack by the bishop. (b) A precise grasp of the elements of a discovery that are in place and those that aren’t—a suitable target for the unmasking piece, a suitable target for the unmasked piece, and clear lines between all the relevant pieces. (c) Methodical thought about how any obstacle or missing element might be remedied. If the problem is that the unmasking piece lacks a good target, we consider ways of drawing the king into its range: checking the king with other pieces, sometimes repeatedly, or capturing something next to the king and thus forcing it to move to recapture. If the problem is that the unmasked piece lacks a good target, we consider ways of creating one: if there are unsuitable targets already in place, we might capture them with other pieces and invite recapture by more valuable enemy pieces; if there is no target in place, we think about putting our own pieces where we want an enemy piece to go and inviting capture of them there by making a threat. Or perhaps we can threaten an enemy piece that has limited movement and force it to jump onto the rank and file where the kernel for a discovery is in place.
Finally, if the problem is that there are pieces blocking the needed lines to make the discovery work, we have methods for dealing with that as well. If the obstructing pieces are our own, we look for ways to vacate them from their squares that are violent and time-consuming for our opponent: checks, captures, and threats. If the obstructing pieces belong to our opponent, we may be able to capture them and cause them to be replaced by the targets themselves. Or we may be able to draw them out of the way by capturing pieces they protect, or by making threats from squares they protect.
That is not a complete catalogue of problems that arise in creating discoveries and options for dealing with them, but it is a summary of the most common types. You want the thought processes involved in those sorts of sequences to become second nature so that you see them right away and can spend your tactical time thinking about more complicated things: how these ideas might be combined, or combined with other tactics; and how they might come into view after a series of preliminary threats or exchanges. We will return to all of these patterns, and explore and reinforce them further, when we examine discoveries by other pieces in the following chapters.