What is a Soul?

John Guerrero
4 min readJun 19, 2022
Photo by Jeremy Bishop on Unsplash

What is a soul? I’ve taken this word for granted all my life. I come from a Catholic upbringing and I have always believed the body and the soul to be two separate beings. The body is a vessel through which the soul can operate. Aristotle has his own ideas about the body and the soul. He has his own ideas about form and matter.

On the Soul consists of three books that are divided further into short chapters. Don’t mistake brevity for clarity. I don’t think Aristotle makes this stuff difficult intentionally. Rather, he is making a difficult subject accessible to the layperson. These fundamental and philosophical questions are tough. He offers a logical perspective on understanding it. Spiritual perspectives assume some things when it comes to these tough questions. The bottom line is that the deep philosophical questions that have faced humanity just cannot be explained easily.

Aristotle was not the first thinker to ponder the soul. Nor will he be the last. As brilliant as Aristotle was, humanity is not satisfied with his definition of the soul. What exactly is his definition of the soul?

Book I

Like all good researchers, Aristotle pays homage to his predecessors. He does a literature review of the existing thinking on “the soul.” Does a soul move the body in which it inhabits? That is, is the ​​soul a self-moving thing? Is it an originator of movement? Is it the first mover? Or are there other factors at play when movement is realized?

Book II

The book starts with Aristotle describing the soul. A soul is a thing’s essence. A thing’s essence is its function. Soul = essence = function. An eye’s function is its soul, for example. Aristotle also talks about the different types of soul in this book. Soul manifests through bodies, matter. But there is also a soul that manifests through an intangible- knowledge and reflection. Form defines the soul. The soul, although not a first mover, does move the body because of the body’s need for nutrition. The soul is the source of the living body. Therefore, it is responsible for the body’s nutrition.

The soul is able to accomplish nutrition because of sensation. Sensation is of two categories and involves three things. The two categories are sense potential and sense actual. Sensation involves: the sense organ, the object of sensation, and the medium through which the organ can sense the object.

Aristotle finishes the book discussing specific senses. All senses, except touch, require a medium. Sight requires the medium of light to view the object of sensation. Hearing requires the medium of air through which the object of sensation can be heard. Touch requires no such medium. The body can touch an object without a medium.

Sense is the act of abstracting form from a sensible thing. Sight offers an example. When you see a tree, you are not seeing the actual tree. The tree does not need to touch your eye for you to realize it is a tree. You can abstract the matter of a tree from its form.

Book III

This book analyzes thought. The thinking brain is itself a sensory organ. Just like typical sense organs, the brain has a fundamental function- perceiving. The brain perceives external stimuli. This sensation is never false. Judgment on the perceived object, however, can be true or false. This “thinking” is the object of thought. It is meta-thinking, thinking about how you are thinking. It is thinking (realizing) that you are thinking.

Truths and falsehoods have one thing in common, they are thoughts. The product of sense perception in thinking is actual knowledge. Actual knowledge is identical with its object. Thought is judgment. It is of a higher order of thinking than simply perceiving. Humans are rational animals. We possess the ability to abstract forms from matter. That is, we don’t need the actual deer in front of us to “see” the deer in our heads. We have abstracted the essence and the form of a deer from the many examples of deers we’ve seen in our lives. There is no requirement to see an actual, in-person, deer for us to abstract its “deerness.” We can abstract that from what we know about deers. Aristotle calls this ability “the calculative faculty of imagination.” The other faculty, sensitive, is common to all beings.

Aristotle ends the treatise talking about movement. In a human, what compels us to move? Is it the soul? And if the soul is not the first (prime) mover, what compels movement? The urge to live according to nature is what compels movement. Nutrition allows beings to fulfill their natural potential. In pursuit of that, they must move.

Finally, Aristotle discusses the sense of touch. Touch is fundamental to all beings. Without touch, a being could not live life according to nature. Touch enables all other senses.


This was not an easy read for me. But I take solace in knowing that it took Saint Thomas Aquinas over fifty reads to even understand some of Aristotle’s work (Metaphysics). I’m not in bad company.



John Guerrero

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