CT 82: Man’s Need of Sense Faculties for Understanding

It’s been a while, so let’s recap. We understand with our intellect; we sense with our senses. All that know comes from our senses…but based on what we sense, our intellect apprehends the intelligible species of that which we sense.

Or, in other words, I see a brown furry object with a particular configuration of features, and I say, “That’s a dog!”

So, Thomas says:

However, we must realize that forms in corporeal things are particular, and have a material existence. But in the intellect they are universal and immaterial.

Here is a dog that I see and pet. I sense the form dog as this particular material dog, but I apprehend it as a universal, immaterial species.

Our manner of understanding brings this out. That is, we apprehend things universally and immaterially. This way of understanding must conform to the intelligible species whereby we understand.


Consequently, since it is impossible to pass from one extreme to another without traversing what lies between, forms reaching the intellect from corporeal objects must pass through certain media.

Material dog Spot there in the room, immaterial species Dog here in my head. The form dog has to get in here from out there. So what’s in the middle?

These are the sense faculties, which receive the forms of material things without their matter; what lodges in the eye is the species of the stone, but not its matter.

In other words, seeing a stone and having a stone in my eye are two very different things. The latter hurts, the former doesn’t.

However, the forms of things received into the sense faculties are particular; for we know only particular objects with our sense faculties.

I don’t see the species Dog; I see this particular dog. Iperceive its color and shape with my eyes, the texture of its fur with my touch, and its need for a bath with my nose. (Come to think of it, I problem sense that through the texture of its fur as well.) These forms are all particular, and apply to this particular dog. They are all accidental forms: I do not sense the dog’s substance, but only its accidents. Then, my intellect somehow operates on those accidental forms to perceive a substance, a body, an animal, a dog.

Hence man must be endowed with senses as a prerequisite to understanding. A proof of this is the fact that if a man is lacking in one of the senses, he has no knowledge of sensible objects that are apprehended by that sense. Thus a person born blind can have no knowledge of colors.

And if I lack a particular sense, I don’t perceive the related forms.

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