there would be no actual elements, like fire and earth, in the human body, because, if there were, the substantial forms of fire and earth would be present. And that would undermine the unity of the human substance. While the claim is a bold one, it isn’t quite as crazy as it may first seem. Though Aquinas does not want to admit that there are any further full-blown substances within each person, he is happy to admit that the human has parts like blood, bones, heart, and brain.
