Aristotle's Arguments in Modern English: The Soul / The Afterlife / Immortality

The philosopher Aristotle wrote a book about the soul and the afterlife called “De Anima.” This book is important for several reasons. One of them is that Aristotle lived his whole life before the Catholic Church even existed, but he still believed “in advance” in several Catholic beliefs. For example, he believed that people have souls and that our souls live on after our deaths. His arguments are still used today to prove that there is an afterlife. This post is meant to summarize his arguments.

A big reason why I want to summarize Aristotle’s arguments re the soul is this: Aristotle did not know about the Bible (at least I don’t think he did), so his arguments are based on reason alone. That is one reason why I think it is important to study him: his arguments can be persuasive for atheists and other non-Christians.

Aristotle’s Basic Argument re the Soul and the Afterlife

Aristotle’s argument has several parts that each have proofs for them, but I don’t think I can put all of his proofs in this post by itself. The basic structure looks like this:

  1. People have souls.
  2. But our souls aren’t physical things.
  3. Therefore, they must be spiritual souls.
  4. Spiritual things don’t have parts.
  5. Therefore, our souls don’t have parts.
  6. The usual cause of death is when something’s parts stop working.
  7. Since human souls don’t have parts, the usual cause of death doesn’t work on them.
  8. Therefore, human souls don’t die, at least not in the usual way.
  9. Since human souls don’t die, they are immortal.
  10. Since human souls don’t die, there is an afterlife.

Note: there are statements in Aristotle’s argument, maybe all of them, that some atheists won’t agree with. To prove that there is an afterlife, we can’t just identify the parts of Aristotle’s argument, we need to prove that each statement in his argument is true. One thing that can help us do that is this: we can find the parts of his book where he tries to prove each part of his argument, and see if his proofs hold water. So keep reading.

Also, there’s an important leap in my summary above between #8 and #9. The argument says that human souls don’t die “in the usual way” and then assumes that they don’t die in any other way. A keen reader might notice a few problems with that: is Aristotle ignoring the other ways things can die? What if somebody’s soul ran out of energy? Or why can’t some super-powerful being erase somebody’s soul and make it die that way? I think the answer is this: Aristotle does not ignore the other ways that things can die, but discusses them in #6. Look there for more info.

Section 1. People have souls.

The word Soul is the name Aristotle uses for whatever causes living things to live, move, and act. His words are: “[T]he soul is in some sense the principle of animal life.” (Book 1 Part 1) Also of plant life: “[T]he principle found in plants is also a kind of soul; for [growth] is the only principle which is common to both animals and plants.” (Book 1 Part 5)

Notice that: plants and animals grow organically, therefore they are alive, therefore they have souls, at least if we use Aristotle’s definition of the term. Some people think that classic philosophy denies that animals have souls. Nope. The question people should be asking is not, “Do animals have souls,” but, “Does an animal’s soul die when its body dies?” We know that Aristotle believed that plants and animals have souls, because he said that’s what he believes. But it also makes sense if we know his assumptions, because he defined a soul as the thing that causes something to live.

I sometimes hear people explain Aristotle this way: the soul is the life-force inside a plant or animal or person. Or: the soul is a substance that gives things life. Or: the soul is just the life inside something. I think those statements are all basically accurate because I think they are all an attempt to say the same thing. If you see something alive, it’s got a soul, that’s just the name Aristotle gives to whatever is making it alive. With that definition, proving that people have a soul is pretty simple:

(A) “Soul” is just a name for whatever makes things alive.
(B) Therefore, whatever is alive has a soul.
© People are alive (at least for a while).
(D) Therefore, people have souls (at least for a while).

Note: Most atheists who I’ve talked to about this subject won’t admit (B) right off the bat. They might admit to it If you’ve clearly defined soul as a simple name for whatever makes living things alive. But some won’t, because they think that definition of soul is fishy. I think I’ve found a solution to this difficulty, at least for the atheists who I usually encounter.

The atheists who I usually talk to seem to believe in a mechanical cause of life: tiny chemicals interact in the cells of animals, plants, and people, and when these chemicals react with each other they transfer energy between cell parts. This energy moves the parts of each cell. Natural selection has organized these parts into relatively large structures. Thus, when the cell parts move, the cell structures move, and therefore the cells move. Natural selection has organized the cells into tissues and organs. When the cells in those tissues and organs move, it activates the tissues and organs. When the organs of the animal or plant are acting, it’s alive. If you are talking to an atheist who believes that, he or she might wonder why we should agree to call that process a soul.

Their objection might look like this: We know the process that causes life. Science has revealed it to us. If I agreed to call a soul the thing that causes life, that would bring religious ideas into the discussion and it would help you build your case. So why should I call it that?

Here’s how I would answer that objection: The definition of “soul” I gave doesn’t use any ideas you don’t already believe in. It just says the soul is whatever causes life. At this point, your mechanical theory fits that definition. In the next section I’ll try to prove that the soul isn’t something physical, and we can discuss your mechanical theory there. I’ll try to prove that the life principle is a soul in the Catholic sense later. So how about for now we’ll just use the word “life”? Does that seem reasonable?

Your atheist friend will probably think that’s reasonable. If they don’t, that probably means they are unwilling to meet you half-way by putting their mechanical theory and your soul-theory to the test. If that’s what’s happening, you can just directly challenge their mechanical theory using the information in the next section, and change the word “soul” to “cause of life” to fit both your definitions.

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.

Section 3. Therefore, they must be spiritual souls.

This statement is easy to prove because spiritual is almost exactly what nonphysical means. Actually, I snuck this statement into Aristotle’s argument: Aristotle never uses the word spiritual. But all it means is something that exists that isn’t physical.

In my experience, atheists tend not to like the concept of spiritual reality. But they do believe in ideas, and ideas are spiritual. One time an atheist asked me about spirits: “What is God made of?” he asked. I wanted to say Nothing, but that would have validated his atheism. I think the best response is: “The same stuff that ideas are made of.”

Since souls exist, as proven in Section 1, and since they aren’t physical, as proven in Section 2, it follows that they are spiritual. You can put it into logical form:

Either souls exist, or they do not. If they do exist, they are either physical, or they are nonphysical. That simple argument gives us three options for understanding the soul’s existence: (A) souls do not exist, (B) souls exist as physical things, or © souls exist as nonphysical things.

Section 1 disproved A and Section 2 disproved B. All that remains is C: souls exist as nonphysical things, and “spiritual” is a name we give to nonphysical things that really exist.


I haven’t completed Section 4.


Section 5. Therefore, our souls don’t have parts.

This statement follows directly from the two parts above it:

(A) Spiritual things don’t have parts.
(B) Our souls are spiritual things.
© Therefore, our souls don’t have parts.

Statement C follows logically from Statements A and B, and those statements have already been proven. So we actually don’t need to go any further to prove that our souls don’t have parts: it’s a simple deduction of logic. But Aristotle uses another argument to prove that the soul doesn’t have parts. He shows that the soul can’t have parts because if it did, something absurd would result. Basically, if the soul has parts, something must hold it together. But the soul is the name we give to the thing that holds living things together. Thus a soul that had parts would need a second soul to hold the first soul together, and then that soul will need a third soul, and so on forever.

As Aristotle puts it: “[If] there is something else which makes the soul one, this unifying agency would have the best right to the name of soul.” “[In that case,] we shall have to repeat for it the question: [Does it have parts]? If it is one, why not at once admit that ‘the soul’ is one? If it has parts, once more the question must be put: What holds its parts together, and so ad infinitum.” (De Anima Book 1 Part 5)

Thus, another argument can be used to prove that souls don’t have parts:

(1) Either the soul has parts or it does not have parts.
(2) If the soul has parts, an absurdity results: the soul must have a soul, and so on.
(3) The absurd is false.
(4) Therefore, the soul does not have parts.


I haven’t completed the other sections.


I am pretty sure Aristotle denied the immortality of the soul. At least that is my memory of him, and everyone says so in commentaries

De Anima Book 3 Part 6: “When mind is set free from its present conditions it appears as just what it is and nothing more: this alone is immortal and eternal.”

One might argue that this says the mind is eternal, not the soul, but I think that would be a false rebuttal. The mind needs the soul to live.

I don’t understand when people in the Church say that animals and plants have a “soul”–however defined. It seems like a bit of ancient philosophical residue that has crept into theology. It seems like now science has a lot more to say about what makes something alive.

Animals are said to have souls born from matter. They are not the form of their body.

I think Aristotle was ambiguous on whether consciousness continues after death, and whether God has consciousness

A little article I read says “When it comes to the intellect being separate from the body, however, Aristotle waffles. See DA III.4”

My question is: are all translations of Aristotle basically the same?

I don’t own Aristotles works anymore, but I sometimes read them from the local library (reading that on the internet it tedious). Anyway, I will need to read De Anima iii. 4 when I get the chance. Someone on the internet wrote that Aristotle defines God as ‘thought of thought’, or ‘thinking about thinking’. If true, then I guess Aristotle DID believe in a personal God

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