In the Commentary on the Metaphysics Aquinas drops another thought grenade, saying
“For the intelligible object and the intellect must be proportionate to each other and must belong to one and the same genus since the intellect and the intelligible object are one in actuality.”
The intelligible object, that is, the universal, is not a material thing. Think of your knowledge of the Pythagorean Theorem: is it a physical thing? Does it have atoms? Molecules? What is it made of? Certainly not anything material. And yet the mind, which, it is argued, is merely the brain, can know it.
What does “know” mean in this context? It means, according to Brother Thomas, that the mind and its object become unified. “One in actuality,” as he says it. The mind has to make real contact with the object, or there is no real knowledge.
The medievals and Aristotle thought that the mind was immaterial because it had to be for the possibility of knowledge.
Materialist objections: there isn’t anything that exists beyond the material world. Ok, fine, but this forecloses the possibility of knowledge in the sense that we used to understand it.
- If there is knowledge, then the mind is not immaterial.
- If the mind is material (aka just the brain), then there isn’t such a thing as knowledge.
I’m with Aristotle on this one. Yes, the soul is the form of the body, and it doesn’t make a great deal of sense to think of it apart from the body. “We are our bodies” as Gabriel Marcel says. And yet, there is some power of the soul which is not bodily, and this is required because we can actually know things. How can this be? I don’t know. See On the Soul and tell me what you think.