Elements of Theology, Proposition 16

Every thing which is able to return to itself has an essence separate from every body.

For unless it was separate from every body whatso­ever, it would not have a certain activity or act apart from body: since it is impossible that, the essence being inseparable from body, an activity (act) proceeding from essence (body) should be separate. For in this case its activity would be better than its essence, because the latter indeed would be indigent of bodies, but the former unindigent and self-sufficient. If therefore any thing is inseparable in essence from body, it is similarly insepar­able in activity (act), — or, rather, it is much more insep­arable. But if this be so, it will not return to itself: for that which returns to itself, being something other than body, has an activity separate from body, and which is not either through or with body, since the activity, and that to which the activity is directed, are not at all in­digent of body: hence that which returns to itself is wholly separate from bodies.

COMMENTARY

Proclus continues to challenge, and so again I'm going to work through this one line at a time.

We're still talking about "things which are able to return to themselves." We learned last time that such things are, by their nature, incorporeal. Bodies are necessarily composed of parts, and it is impossible for the parts to become one, that is, to return or convert to one another. And so this proposition seems to be an extension of the previous one.

Proclus continues, "unless it was separate from every body whatso­ever, it would not have a certain activity or act apart from body." Thomas Taylor translates this as "if it was inseparable from any body whatever, it would not have a certain energy separate from body." We can assume, then, that "act or activity" translates the Greek "energeia." Energeia is a term coined by Aristotle. Energeia or energy refers to activity. Something which was not separate from bodies would not act in a way that was separate from bodies. Or...

If it did, "in this case its activity would be better than its essence." The incorporeal being prior to the corporeal, an incorporeal act or energy would proceed from a bodily essence, which is impossible. 

Anything which acts on the physical plane is physical; anything which acts incorporeally must have an essence which is incorporeal and separate from bodies (corpora).