We have further to remark that the act and the term, even when they are complete physical entities, in their manner of principiating the compound nature always behave towards one another as incomplete entities, inasmuch as their principiation is always of a metaphysical, and never of a physical, character. To speak first of those compound essences whose form is _composition_, we observe that the physical components of such essences are indeed _in act_, absolutely speaking, but, with regard to the composition, they are simply _in potency_: and since it is in this last capacity that they enter into the constitution of the compound nature, it is evident that they contribute to its constitution only inasmuch as they have a claim to further actuation. For to be potential respecting any kind of composition means not only that the parts _might_ be duly disposed to undergo such a composition, but moreover that they are already disposed and related to each other in that manner which _imperatively calls_ for such a composition. Consequently, the components, when thus disposed, constitute a potency which needs actuation, and stands, with respect to the form of composition, in the same relation in which any term stands with respect to its essential act. It is, therefore, manifest that the said components, though they are physical entities, behave as metaphysical principles in their material principiation of a compound essence. As for the composition itself, we have already seen that it is always a metaphysical constituent. In the same manner, the soul and the body are indeed physical beings, absolutely speaking, and, therefore, independent of one another so far as their existence is concerned; but the body is informed and vivified, not inasmuch as it exists in its absolute actuality, but inasmuch as it is potential respecting animal life—that is, inasmuch as its organic composition imperatively claims a soul. And similarly the soul is a vivifying form, not inasmuch as it is something absolute in nature, but inasmuch as it naturally requires completion in the body for which it is created and to which it is actually terminated. It therefore appears that the soul and the body, in their principiation of the animal, behave towards one another as metaphysical principles. Hence all composition of act and potency is, properly speaking, a _metaphysical_ composition; though, when the compound is resolvable into physical parts, the same composition may also, from the physical nature of the components, be rightly styled _physical_. The difference between a metaphysical and a physical compound does not, therefore, consist in the character of the composition itself, which is always metaphysical, but in this: that the latter can be resolved into physical parts which may and will exist after their separation, whereas the former can be resolved only into metaphysical constituents which are utterly incapable of separate existence.