The Discovered Attack.
Introduction to Discovered Attacks Generally.
(took from www.chesstactics.org Ward Farnsworth's PREDATOR AT THE CHESSBOARD)
In a discovered attack, or “discovery,” one of your pieces moves out of the way of another, unleashing attacks on two enemy pieces at the same time—one by the unmasking piece and one by the piece unmasked. The enemy only has time to protect one of the threatened pieces. You take the other one. The diagram on the left shows the idea in skeletal form. If White plays his knight to f6, it gives check while unmasking an attack by his queen against Black's queen. Black only has one move to respond to these two threats, and he has to spend it moving his king to safety. Then White plays QxQ. This at least is one of the patterns (a knight discovery) in its classic form; there are many variations on the theme that we will consider in due course. Discovered attacks always involve two offensive pieces: an unmasked piece and an unmasking piece. Every piece has the power to unmask attacks by others by moving off of lines that it occupies. Not every piece has the power to be unmasked, though; a knight, for example, can't be unmasked because it can't be masked in the first place: it jumps rather than slides, so it doesn’t move along a line that can be temporarily blocked by a fellow piece. But the knight is a magnificent masker and unmasker of attacks by other pieces. Conversely, the queen is a great piece to unmask, but not a good masker of other pieces. It can’t hide an attack by a rook or bishop because a queen can make all the same moves that either of those other pieces can; if a queen masks a threat by a rook, it already makes the same threat the rook would. The essence of a classic discovered attack is that before it is executed, neither piece directly threatens anything. After it is executed, both of them do. The plan of this section will be to take each of the major unmasking pieces—the bishop, the rook, the knight, and the pawn—and study one by one how they can unveil attacks by other pieces: what the unmasking piece looks like when it is poised to do this, how the germ of such an opportunity can be created, and how such ideas can be perfected and executed once they come into view. We will identify the visual patterns that signify the possibility of a discovered attack and practice identifying them until it becomes habitual. Mastering discoveries means learning new ways to think about the pieces and the relationships between them. You may be accustomed to thinking of bishops as pieces that attack diagonally and to regarding rooks as pieces that attack back and forth and from side to side. That’s not wrong, but it’s incomplete. Bishops attack diagonally and unmask vertical and horizontal attacks by rooks and queens. Rooks attack vertically and horizontally and unmask diagonal attacks by bishops and queens. Make it one of your goals to think of your pieces not just as individuals but as partners—as parts of a team whose efforts need to be coordinated. Discovered attacks are an example of coordination, as each partner makes the other more powerful; a bishop and rook on the same file, with the former masking the latter, often has far more destructive power than either piece by itself. Every discovered attack starts with a kernel consisting of two pieces: the piece to be unmasked and the piece that will unmask it. Once found, a kernel can serve to organize the rest of your thinking about what to do: you start looking for targets for each piece or ways to clear the lines between the pieces and their targets. We will be studying discovered attacks one kernel at a time: first the one where the bishop masks a rook or queen on the same file or rank; then the kernel where the rook masks a bishop or queen on the same diagonal; and so forth. We will emphasize spotting the kernel of a discovery because the practical importance of training your eyes in this way is so great. If you don’t see the basic pattern when it's there, all the skill in the world at perfecting it won't be of much use.
Introduction to Bishop Discoveries.
We begin with discoveries where the bishop unmasks an attack by a queen or rook running up the board or from side to side. The position on the left is a skeletal illustration. If White moves his bishop to c4, it checks Black’s king; the bishop’s move also unmasks, or “discovers,” an attack by the White rook on Black’s queen, which White will win next move. The job of the piece in front is to give check and thus keep your opponent busy; the piece in the rear then has its chance to carry out a capture. This is the typical pattern, though there are others we will study later. Before a discovered attack is unleashed there always are three pieces in a line on a rank, file, or diagonal: the masked piece, the piece about to unmask it, and the target. When the bishop is doing the unmasking, the three pieces always are on a file or a rank. That is the kernel to look for in the positions that follow: a bishop blocking the path of a rook or queen. Then we'll follow up with standard questions: whether the two pieces in the kernel both have good targets, or whether targets might be created for them; whether the needed lines are clear or can be cleared; etc. We also can work toward discovered attacks by thinking about the suitable targets for them. Bishop discoveries always unmask attacks by queens and rooks. It follows that the target of the unmasked piece usually needs to be a queen or a loose piece for the attack to turn a profit. Unmasking an attack by your rook against a protected bishop, for example, isn't going to scare your opponent; the rook's target needs to be an unguarded bishop or else a protected piece that is more valuable, such as the enemy queen (whether it's guarded or not). But now we're getting a little ahead of our story. Let’s start by studying some positions involving discoveries by the bishop in simplest form.
The Classic Pattern.
We start with simple positions where a discovered attack is ready to be executed: one piece masks another, and both have good targets. Visually most of these positions will take a common form: a bishop moves from the middle of the board to the edge near the enemy king, where it gives check or makes a capture; in the process it unmasks an attack up the board by a rook or queen, usually made from the back rank. In the diagram to the left, notice the position of White’s rook and bishop on the d-file—a classic kernel of a discovered attack. The bishop masks the rook; if it can vacate the file in a forceful enough manner—e.g., with a check—White will have the capture RxQ a move later. So White plays Bxh7+; Black is forced to spend a move protecting his king with KxB; and now White takes Black's queen with his rook. After Black recaptures with RxR, White has traded a bishop and rook for a queen and a pawn.
Find the kernel of a discovery for Black. His bishop on d6 masks the Black queen’s path up the d-file. Meanwhile White’s queen is loose on d3. If Black can use the bishop to give check, he will be able to play QxQ afterwards. Black thus finds and plays Bxh2+. White is forced to play KxB (or NxB), and now Black takes White’s queen. There were lots of ways to see this move: the three pieces aligned on the d-file were a tipoff; or you might have set out to examine every check, found only Bxh2, and noticed that as a consequence of that move the d-file would be opened—and also seen that White’s queen is loose. Above all, however, study the relationship of the Black bishop and queen here. The most important thing about the bishop in this position is what it masks
An almost identical pattern seen from White’s side. You notice that the bishop masks the queen on d1; the queen otherwise would be able to take Black’s queen, which is loose. So White clears the bishop from the d-file and creates a distraction at the same time with Bg6+. Black has to address the check; after he takes White’s bishop, Black’s queen is lost. The more common checking move in this sort of position has the bishop taking the pawn on h2 or h7 and thus giving check to the castled king as we saw in the previous cases; but as this position shows, you want to look for every possible check you may be able to give with the unmasking piece.
The relationship between White’s bishop and rook on the b-file should jump out at you: never fail to notice when pieces are paired like this, as it signals a possible discovery. Here White has a good target in Black’s loose queen, so he looks for a check he can give with his bishop and finds Bxf7+. Of course the move is useless as a serious threat to Black’s king, but its purpose is just to create a distraction. Black has to capture the bishop or move his king, and now White plays RxQ.