Proposition 27

191. Every destructible substance either is not sempiternal or is composite or is supported by another thing.

192. This is because [destructible] substance is either lacking things from which it is made up and is composed of them, or it is lacking in its constancy and its supporting essence. Thus when that which supports it is separated, it is corrupted and destroyed.

193. Because if substance is not composite nor supported, it is simple and forever, it is not destroyed nor diminished in the least.

417. After he has shown what the condition of an incorruptible substance, here (191) he shows the condition of a corruptible substance, positing this proposition: every destructible, non-sempiternal substance is either composed or supported by another thing. And this same proposition is posited in Proclus' book in proposition 48.

418. The proof of this proposition (192) is: because if everything which is standing through itself is incorruptible, as has been proved (188 [414]), it is necessary that everything that is corrupted not be standing through itself, but need something sustaining. Which indeed happens in two ways: in one way, just as a whole needs parts for its constitution, whence, when the parts come apart from each other, corruption follows; in the other way, because the form is not subsisting, but needs for its fixedness a subject supporting it and on that account when the supporting subject be made indisposed to such a form, it is necessary that a separation of the form from the subject, and thus corruption follows.

419. Whence it is manifest that every corruptible substance either is composed out of different parts through whose dissolution the corruption of the whole follows, as appears in mixed bodies; or the form needs matter or subject for its sustenance and thus, by the transmutation of the subject, corruption follows, just as appears in simple bodies and accidents.

420. And on that account we can accept this corollary (193) that if any substance is not composite, but simple, and is not superimposed over a subject as if needing it for its being, but is standing in itself, this in every way is incorruptible: just as appears in the intelligence and in the intellectual soul, about which it is manifest that it is not a form superimposed over matter to which it gives being, so that, to be precise, it is supported by it totally, because it follows that none of its operations be without the communication of corporal matter. Which appears to be false from these which are proved in On the Soul, 3.