Section 2. Our souls aren’t physical things.
Aristotle tries to prove that our souls aren’t physical things in several places in his book. Two of them are in Book 2 Part 5 and in Book 3 Part 3.
Book 2 Part 5 discusses the differences between an animal’s soul and a person’s soul. He says that an animal’s soul can only operate its physical organs, such as its eyes and ears, and it can only use those organs to sense physical things. A person’s soul can operate a mind and can take ideas into the mind. Here’s how Aristotle puts it: “The ground of this difference is that what [animal] sensation apprehends is [physical things], while what knowledge apprehends is [ideas], and these are in a sense within the soul.” (De Anima Book 2 Part 5)
The point of the above paragraph is that a person’s soul can sense ideas, and an animal’s can’t. Aristotle will use that ability to argue that a person’s soul isn’t a physical thing. His argument can be summarized this way:
(A) If our souls can sense nonphysical things, then our souls aren’t physical.
(B) Our souls can sense nonphysical things, because they can sense ideas.
© Therefore, our souls aren’t physical.
Note: I don’t think most atheists would admit to this argument, at least not right off the bat. They would probably object to both A and B, especially the part that says the soul can sense stuff. If our atheist friend from the previous section had a hard time agreeing to use the word “soul” as a name for whatever causes life, they probably aren’t going to admit right away that it senses things and does other stuff too. I think you can win them to that position by examining what the soul does from a logical perspective.
If I use a bat to hit a ball, then I can logically say that I hit the ball. If my cat knocks over a broomstick and that broomstick knocks a picture off the wall, then I can logically say that my cat knocked down the picture. From this we can learn an important concept: when you make one thing happen by doing another thing, you are the cause of both things. Ask your atheist friend if they think that’s reasonable. I think they will, if they are a reasonable person. Now use that concept to make a logical deduction:
(D) When you make one thing happen by doing another thing, you are the cause of both things.
(E) Our soul, the thing that causes life, makes one thing happen, it makes our organs to sense physical things, by doing another thing, it gives life to our organs.
(F) Therefore, our soul is the cause of both things: our physical life and our physical senses.
Aristotle puts this very simply: “[E]ach art must use its tools, each soul its body.” (De Anima Book 1 Part 3) The soul uses the body, and its organs, like a tool: it makes them function by giving them life, and they sense things because that’s what they do. The same thing is true about our mind: our soul gives it life, and it can sense ideas. Therefore, our soul can sense ideas by using our mind as a tool.
Because of the principle in Statement D, everything we do, physical and mental, is something our souls do. Aristotle puts it this way: “[K]nowing, perceiving, opining, and further desiring, wishing, and generally all other modes of appetition…and the local movements of animals, and growth, maturity, and decay…are [all] produced by the soul.” (Book 1 Part 5)
Using the logical deduction in Statement F, we’ve proven part of Statement B: our souls can sense things. Now we need to prove the other part of Statement B: ideas are nonphysical. Aristotle helps by giving some examples of ideas, which he calls concepts: “rightness and wrongness—rightness in prudence, knowledge, true opinion, [and] wrongness in their opposites.” (Book 3 Part 3)
According to Aristotle, concepts include rightness, wrongness, truth, and falsehood. But how can we prove that those things are nonphysical? Well, first of all, you can ask your atheist friend: what is “true” made of? Or what is “wrong” made of? If they admit that truth exists, and that right and wrong are real things, then they are either made of something physical or they aren’t. But they aren’t made of something physical. You can’t put truth in a test tube or examine wrongness under a microscope. Put that in a logical syllogism:
(G) Ideas are either made of something physical or they aren’t physical.
(H) Ideas are not made of something physical.
(I) Therefore ideas aren’t physical.
By combining the two logical arguments above, DEF and GHI, you can prove the truth of Statement B from earlier. Our souls can sense ideas because they can operate our minds and Those can sense ideas. And ideas are not physical because they aren’t made of anything physical. Put them together and you get Statement B: Our souls can sense nonphysical things, because they can sense ideas. It’s all about logic: keep adding up enough true statements, and stick to logic, because a reasonable atheist has to follow the truth wherever it leads.
Okay so Statement B can be proven using logic. What about Statement A? It says: If our souls can sense nonphysical things, then our souls aren’t physical.
This is another way of saying that a physical thing can’t sense something nonphysical. If you managed to put truth in a laboratory, a scientist couldn’t examine it using lab tools. I almost want to say that physical things pass right through nonphysical things, but that’s not quite true, physical things don’t even come close to ideas. If I’m thinking about an idea, and I am soaked with water until every part of me is filled up, the water hasn’t touched my idea, though I’ve probably stopped thinking about it. The idea doesn’t interact with the water, but it does interact with my mind. That’s another way of proving that my mind isn’t physical.