DE&E: Chapter 2:1

Thomas has established that the word being most truly and properly applies to substances, that is, to things that exist of themselves, like you and me and your dog, and further that composite substances, those composed of form and matter (again, like me and you and your dog), are easier to understand than simple substances. In Chapter 2, he begins to analyze the essence of such substances.

In composite substances we find form and matter, as in man there are soul and body.

So in man, the soul is the form, and the body is the matter.

We cannot say, however, that either of these is the essence of the thing. That matter alone is not the essence of the thing is clear, for it is through its essence that a thing is knowable and is placed in a species or genus. But matter is not a principle of cognition; nor is anything determined to a genus or species according to its matter but rather according to what something is in act.

Matter is potency, and not really knowable, so a thing’s matter can’t be its essence. Note that the term “matter” means something different in this context than in contemporary English; I’ve not worked out what the relation is between the metaphysical and physical senses of the word. But suppose you could directly apprehend the matter in your spouse: the amount of carbon, hydrogen, oxygen, calcium, etc., etc. Would any of that knowledge get at the essence of your spouse? Clearly not. (I’ve no idea whether this is a valid move in this context; I might just be confusing the issue. But it makes sense to me.)

Form makes a thing what it is, so you can’t take about a thing’s essence apart from its form. But…

Nor is form alone the essence of a composite thing, however much certain people may try to assert this. From what has been said, it is clear that the essence is that which is signified by the definition of the thing. The definition of a natural substance, however, contains not only form but also matter; otherwise, the definitions of natural things and mathematical ones would not differ.

If it has the form of a dog, but no matter, it’s not a dog. Consequently, it must be part of the essence of a dog, and any other composite thing, that it *is* a composite thing.

Nor can it be said that matter is placed in the definition of a natural substance as something added to the essence or as some being beyond the essence of the thing, for that type of definition is more proper to accidents, which do not have a perfect essence and which include in their definitions a subject beyond their own genus. Therefore, the essence clearly comprises both matter and form.

As I say, if there’s no matter, there’s no dog. Dogs can be black, white, brown, or beige, big or small, friendly or fierce, noisy or quiet; four-legged, three-legged, or even (as one dog I saw a video of on YouTube was) two-legged; all without ceasing to be a dog. All of these things are accidents. But the presence of matter isn’t an accident, something added on to the essence of a dog. Why? Because a dog that can’t be petted is no dog at all.

So “essence clearly comprises both matter and form.”

That’s clear enough–in fact, it’s plain as plain, once it’s pointed it. But I didn’t know it a few days ago.

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