Chapter 1 — Act and potency

Note that some things can be, although they are not, and some things now are. Those which can be and are not are said to be in potency, but those which already exist are said to be in act. But existence is twofold: one is the essential or substantial existence of a thing (for example, man exists). And this is existence simply speaking. The other is accidental existence, (for example, man is white): and this is existence in a certain respect.

Moreover, for each existence there is something in potency. Something is in potency to be man, as sperm or the menstrual blood, and something is in potency to be white, as man. Both that which is in potency to substantial existence and that which is in potency to accidental existence can be called matter: for example sperm is the matter of man and man is the matter of whiteness. But these differ, because that which is in potency to substantial existence is called the matter from which, but that which is in potency to accidental existence is called the matter in which.

Again, properly speaking, that which is in potency to substantial existence is called ‘prime matter,’ but that which is in potency to accidental existence is called ‘the subject.’ Thus we say that accidents are in a subject; but we do not say that the substantial form is in a subject. In this way matter differs from subject because the subject is that which does not have existence by reason of something which comes to it; rather, it has complete existence of itself, just as man does not have existence through whiteness. But matter has existence by reason of what comes to it because, of itself, it has incomplete existence. Hence, simply speaking, the form gives existence to matter. The accident, however, does not give existence to the subject; rather, the subject gives existence to the accident, although sometimes the one is used for the other (namely, matter for subject, and conversely).

But, just as everything which is in potency can be called matter, so also everything from which something has existence (whether that existence be substantial or accidental) can be called form; for example, man, since he is white in potency, becomes actually white through whiteness, and sperm, since it is man in potency, becomes actually man through the soul. Also, because form causes existence in act, we say that the form is the act. However, that which causes substantial existence in act is called substantial form, and that which causes accidental existence in act is called accidental form.

Because generation is a motion to form, there is a twofold generation corresponding to this twofold form. Generation simply speaking corresponds to the substantial form, and generation in a certain respect corresponds to the accidental form. When a substantial form is introduced, we say that something comes into being simply speaking: for example, we say that man comes into being or man is generated. But when an accidental form is introduced, we do not say that something comes into being simply speaking, but that it comes into being as this. For example, when man comes into being as white, we do not say simply that man comes into being or is generated, but that he comes into being or is generated as white. There is a twofold corruption opposed to this twofold generation: simply speaking, and in a certain respect. Generation and corruption simply speaking are only in the genus of substance, but generation and corruption in a certain respect are in all the other genera.

Also, because generation is a change from non-existence to existence, contrarily, corruption should be from existence to nonexistence. However, generation does not take place from just any non-being, but from the non-being which is being in potency. For example, a statue comes to be from bronze, which is a statue in potency and not in act.

In order that there be generation three things are required: being in potency, which is matter; non-existence in act, which is privation; and that through which something comes to be in act, which is form. For example, when a statue is made from bronze, the bronze which is in potency to the form of the statue is the matter; the shapeless or undisposed something is the privation; and the shape because of which it is called a statue is the form. But it is not a substantial form because the bronze, before it receives the shape, has existence in act, and its existence does not depend upon that shape. Rather, it is an accidental form, because all artificial forms are accidental. Art operates only on that which is already constituted in existence by nature.