We’re blogging through St. Thomas Aquinas’ Compendium Theologiae, sometimes called his Shorter Summa. Find the previous posts here.
Now we begin to see the payoff from the dry metaphysics of the previous three chapters as Thomas proves that there is only one God.
The conclusion is evident that there can be but one God. If there were many gods, they would be called by this name either equivocally or univocally.
To use a word equivocally is simply to use it with multiple unrelated meanings. The word light can mean the photons by which I see, it can mean the quality of a room that’s well lit, and it can mean the weight of a pencil on my desk. To use a word univocally is to use it with a single meaning. So if there are many “gods”, either we mean different kinds of thing, each of which we call a “god”, or we mean many things of exactly the same kind.
If they are called gods equivocally, further discussion is fruitless; there is nothing to prevent other peoples from applying the name “god” to what we call a stone.
Words carry meaning; but the word is not the meaning. To have a fruitful conversation, you have to make sure you’re using words the same way.
If they are called gods univocally, they must agree either in genus or in species.
Recall from the previous chapters that genera and species are ways to classify essences. I am a human being, a rational animal; my dog is also an animal, though not rational. We are the same, in that we are both animals; we differ, in that we belong to different species. So for two “god”’s to be the same kind of thing, they need to share the same essence in whole (species) or in part (genus).
But we have just shown that God can be neither a genus nor a species comprising many individuals under Himself. Accordingly a multiplicity of gods is impossible.
Again, that whereby a common essence is individuated cannot pertain to many. Although there can be many men, it is impossible for this particular man to be more than one only.
You and I are distinct individuals, though sharing the same essence (humanity), because we are made of different matter. We need something over and above our essence to distinguish us and make us individuals. And the corollary is that the matter I’m made of is only me; it could only become someone else if I were to die.
So if an essence defines an individual all by itself, then it’s already an individual. You can’t add anything to it to get another individual. And this is the case for God; so He’s unique.
So if an essence is individuated by itself, and not by something else, it cannot pertain to many. But the divine essence is individuated by itself, since God’s essence is not distinct from His existence; for we have shown that God is His essence. Hence God cannot be more than one only.
Thomas usually gives two arguments; this topic is so important he’s giving a third.
Another consideration is the following. A form can be multiplied in two ways: first, by specific differences, as in the case of a generic form; in this way color is differentiated into the various species of color; secondly, by the subjects in which it inheres, for example, whiteness.
A generic form is the form that belonging to a genus gives to something. Because a dog is an animal, it has the form of an animal: it can take in nourishment and it can move by itself. Such a form can be “multiplied”, made many, by dividing into multiple species by applying specific differences. Similarly, the form “color” can be divided into all of the colors of the color wheel.
Another way a form can be multiplied is by existing in many things. There are many dogs; and for any color there are many things that have that color.
But note what these two cases have in common: there has to be multiple things—subjects—to which the form applies.
Therefore any form incapable of being multiplied by specific differences cannot be multiplied at all, if it is a form that does not exist in a subject. Thus whiteness, if it were to subsist without a subject, would not be more than one.
Now, the Godhead, we’ve seen, is not a genus; it isn’t multiplied by specific differences. And the Godhead, we’ve seen, isn’t a species predicated of individuals; if the Godhead is a form, then, it doesn’t subsist in individual subjects:
But the divine essence is very existence, ipsum esse, which does not admit of specific differences, as we have shown. Since, therefore, the divine existence is a quasi-form subsisting by itself, seeing that God is His existence, the divine essence cannot be more than one.
Note that word quasi-form. God is like a form that might subsist in a subject; but the Godhead is also distinct from all of the other forms we know of. He’s not quite like anything else, and our terms and definitions fail to capture Him.
So, metaphysically, there’s no way left to get multiple Gods, not in the sense of the First Cause whose essence is His Existence; and Thomas concludes with satisfaction:
Accordingly a plurality of gods is impossible.