We’re blogging through St. Thomas Aquinas’ Compendium Theologiae, sometimes called his Shorter Summa. Find the previous posts here.
Now Thomas moves on to one of the fundamental notions of classic theism: the divine simplicity.
A similar course of reasoning clearly shows that the first mover must be simple. For any composite being must contain two factors that are related to each other as potency to act. But in the first mover, which is altogether immobile, all combination of potency and act is impossible, because whatever is in potency is, by that very fact, movable. Accordingly the first mover cannot be composite.
In normal English usage, a thing is a composite if it is made up of other things, as Lawry’s Seasoned Salt is made up of table salt and other seasonings. But then, table salt is generally iodized these days, so table salt isn’t really just one kind of thing; and even if it weren’t iodized, salt is a composite at the molecular level, made up of the two elements sodium and chloride. And then, each sodium atom is made up of protons and electrons and so forth.
That’s dividing up a composite into its components physically. But a thing can also be divided up into its components metaphysically, into form and matter. A rubber ball is the metaphysical composite of the form “spherical” and the matter, rubber, that has the potency of taking on different shapes.
According to Thomas, all composite beings are composite in this sense: there’s something in them that gives actuality to something else that would only exist potentially otherwise. For physical objects, the form gives existence to the matter. For immaterial substances, such as angels (as we will see later on), God gives existence (actuality) to form (which has the potency to receive it). But I digress.
The essential point here is that the components of a composite are metaphysically prior to it; something had to bring the components together. But we’ve established that there is nothing prior to God, and that God is unchanging; so God can’t be a composite, and hence has to be absolutely simple.
And that’s what simple means in this case: not having any separate parts.
The implications of divine simplicity are vast, and not to be grasped in a few moments (or, possibly, ever).
Moreover, something has to exist prior to any composite, since composing elements are by their very nature antecedent to a composite. Hence the first of all beings cannot be composite. Even within the order of composite beings we observe that the simpler things have priority. Thus elements are naturally prior to mixed bodies. Likewise, among the elements themselves, the first is fire, which is the simplest of all. Prior to all elements is the heavenly body, which has a simpler construction, since it is free from all contrariety. Hence the truth remains that the first of beings must be absolutely simple.
Here Thomas is running through the kinds of examples I discussed above, showing that as you take something to pieces, the pieces turn out to be simpler than the whole. His examples are based on the science of his day; but as usual, this is an illustration of the basic principle rather than an evidence-based argument. Don’t get hung up on it.