We’re blogging through St. Thomas Aquinas’ Compendium Theologiae, sometimes called his Shorter Summa. Find the previous posts here.
Now that Thomas has established that God exists, is eternal and everlasting, and is utterly simple (in the sense of not being composed of distinct, separable parts) he begins to get seriously metaphysical. That is, he’s going to look at the metaphysical notions we apply to the objects of daily experience, and determine the extent to which those notions apply to God. I came almost to a full stop the first time I read this chapter, because there are so many important concepts that Thomas is taking for granted that I was unfamiliar with. Consequently, I’m going to take it slowly over the next couple of weeks, explaining the background in detail.
The further conclusion follows that God is His own essence.
For the objects around us, the essence of a thing is what you’d answer if someone asked you what it was. That’s a chair. This is an apple. That’s a man. You might think of essence as “is-ness”, what a thing is.Let’s consider an apple. It is an apple. We say it has the essence of an apple. Apples are not identical. This one is bruised and that one isn’t; this one is ripe, and that one isn’t; this one was a worm and that one doesn’t. All are apples, all share the same essence.
Metaphysically, we say that an apple is a substance. It has the substantial form of an apple; this is what remains the same as the apple changes, as it ripens or is bruised. (Something has to remain the same across these kinds of changes or we wouldn’t still have an apple.) Saying that this object has the substantial form of an apple, and that it has the essence of an apple, are more or less equivalent statements; but we can talk about the essence of apples apart from any particular substance with that form—as we do when we put apples on the grocery list.
So all apples have the same essence. They also have accidents: the things that differ about them, the bruises, the ripeness, the worminess. Thomas uses the words per se and per accidens to discuss what belongs to a thing according to its essence or according to its accidents.
Next week, we’ll begin to look at Thomas’ argument.