There are a couple of other variables to think about as you study the bishop. The most important involve the geometries involved when the bishop inflicts a fork and the visual patterns that result from them. We didn't emphasize this as much in studying queen forks because they can occur in so many ways that have little in common visually. But double attacks by bishops require certain conditions that often have a distinctive look.
A bishop fork most often occurs when your opponent has two pieces on the same diagonal with nothing between them; when the bishop moves into position, the three pieces all are in a line (the position diagrammed in skeletal form in the previous frame). It therefore is important to train your eyes to spot any two enemy pieces on the same diagonal—especially if there isn’t anything between them, but even if there is. This is a good habit for other reasons as well: pieces on the same diagonal may also be subject to a fork by your queen, or may be prey to a pin or skewer (possibilities considered elsewhere). The same goes for enemy pieces lined up on the same rank or file: they may be forked by one of your rooks, as we will see in another chapter; sometimes they may be forked by a bishop, as we will see in a moment; and they may also be subject to a pin or skewer. Diagonals will receive a lot of attention in this chapter because that is where bishops travel, but the general point is that pieces on a line of any type are important to spot.
There is another type of bishop fork that looks different and can occur when your opponent has two pieces on intersecting diagonals. When the fork is executed the pieces are arranged not on a line but in a triangle. A fork of this kind almost always results from a capture by the bishop on the square that forms its corner of the triangle; before the capture, the bishop was aimed at one of the pieces targeted by the fork, but an enemy piece blocked the bishop’s path to the target (it might be a pawn, as in the diagram to the left where White is about to play the fork Bxd6). Another way to say this is that before the bishop captures, there are three enemy pieces in a triangle, all on squares of the same color; the bishop captures one of them and forks the other two. (Again, see the diagram.) These patterns are important to study because to the untrained eye they don't look like the makings of a fork by a bishop. But they are; they are poised to be forked in triangular fashion.