An example is wine, which exists actually (1) once it has fermented and become intoxicating. At another time, however, it may exist potentially, when (2) the moisture in which it is generated is still within the vine itself and its fruit pulp. What is generated may sometimes exist actually and sometimes potentially in the elements from which it is generated. When we speak of potentiality or actuality, we mean nothing other than form and matter. By “form” we mean that which can be separated (3) from the composite of form and matter. Examples of separable forms are light and darkness, since they can be separated from air; an example of what is composed of form and matter is the healthy body [and the body] that is sick (4). By “matter” I mean something capable of bearing both states, such as the body, which is sometimes healthy and sometimes sick.
Thus, the distinction between what exists actually and what exists potentially is found not only in the constituents of things composed of the two—that is, form and matter (5)—but also in things external to such composites, whose matter is not the matter of the things generated from them, and whose form is not their form but another form.
You must keep this point in mind when you set out to investigate the First Cause: some moving causes share the form of the thing moved (6) and are proximate to it, while others are more remote. As for the proximate cause (7), it is like the father,