As you do your scanning you will discover certain additional laws of knight moves that will become part of your visual vocabulary. An important example is that two pieces can't be forked if they are on the same diagonal with one square between them. Thus the Black king and queen in the diagram to the left are on squares of the same color, but there is no square from which a knight would be able to attack them both. This is a familiar pattern, and when you see it you will not need to pause to think about whether a knight fork is in the immediate offing; the sight of it will be self-explanatory, and you will move on.
Similarly, if your knight is on the same diagonal as an enemy piece and separated from it by one square, the knight is three moves away from being able to attack the piece. Thus in the diagram the White knight is three moves from being able to attack the Black king; it must move, say, to e4, then to g5, then to e6.
Another useful thing to know is that a knight may be able to attack an enemy target two different ways—but never more than two. In the diagram, for example, White's knight can attack the Black rook by moving to e4 or d5 (and only the latter move creates a fork). This is useful to remember because the first attacking idea you see with your knight may turn out not to be the best one—even against the same enemy piece.
Practice broad-mindedness when you scan for forking prospects. It is especially important not to dismiss a possible fork automatically, perhaps half-consciously, when you notice that the square your knight needs is protected by a pawn, or when you see that the fork would involve your opponent’s king on the one hand but a knight or protected pawn on the other. In the latter case you might quickly imagine that if you tried the fork the enemy would move his king and the pawn would not be worth taking, and so write off the forking prospect without taking it seriously. But that train of thought is premature; great combinations often look just that way at first. You want to separate the creative process of seeing that the geometry is there for a fork from the editing process of analyzing whether the fork can be made profitable. Much of the rest of this chapter is devoted to the editing process: how to take potential forks that look defective and turn them into tactical shots that work. But all along you also want to build the visual habit of noticing every time your knight can attack two sensitive points at once, no matter how implausible the attack looks at first.