And if someone says that the single whole produced by the two causes together cannot be produced by either alone, there is no dispute about this. Someone who regards this whole as multiple rulings does not contradict someone who regards it as one, provided the latter means unity of type within a single locus. The point, then, is that a ruling of one type may have two individual instances in two different loci; this is clear. At other times, two instances of it coexist in a single locus: they are two types when considered in themselves, but a single instance when considered in relation to their locus.

Thus, if someone says that the ruling produced by two causes is a single ruling, he is correct if he means a single type within a single entity. Someone who means two instances of one type within a single entity is also correct.

Section

It has thus become clear that two causes cannot each independently establish a single ruling when they occur together. This is self-evident once the matter is grasped, for independence is incompatible with joint participation: that which is independent has no partner. Hence, when two causes combine to produce a single effect, neither independently produces it.

It is also clear that the ruling established by two causes—whether described as multiple rulings or as a single, reinforced ruling—is not independently established by either of them. Rather, each is part of its cause, not a cause of it in its own right.