The difficulty in fashioning a fork, of course, is that no matter where your knight sits you rarely will find a fork lying one move away against a decent player. Leaving two pieces to be forked by a knight on the next move is a blunder almost as bad as leaving a piece hanging outright. Forks have to be manufactured; the challenge is to see when one lies a few steps away. Fortunately knight forks a few steps away come in a finite number of types that you can learn to search for systematically and, with practice, recognize quickly. Such situations can be sorted into two general types.
First, sometimes two of your opponent’s pieces sit on squares that can be forked with one move of your knight, but there is some obstacle to your taking advantage of this; most commonly, the square your knight needs to reach—call it the “forking square”—is defended by your opponent (the diagram to the left shows such a case, again in skeletal form; White would like to play the fork Nf6+, but he can't; the f6 square is defended by a pawn). We will refer to these as cases where you have a potential fork—a move that amounts to a fork on its face, but that needs to be perfected by overcoming some defensive measure that your opponent has in place. In a moment we will catalogue those defensive measures and how to deal with them.