What Is a Human Being?

Start here: what are you?

Here are three common answers to the question “What is a human being?”

1. “You are your brain.” You are a very complex arrangement of matter, and thinking is just chemistry.
2. “You are a soul trapped in a body.” The real you is a spirit; the body is a vehicle you happen to be driving.
3. Something else.

Aquinas takes the third option. To see why, we need to go back to Lesson 4.

The soul is the form of the body

In Lesson 4 we met matter and form: what something is made of, and what makes it the kind of thing it is. For a living thing, the form is called its soul.

So a soul isn’t a ghost. It is simply what makes a living body alive and makes it this kind of living thing. A dead body has the same matter as a moment before death, but something is gone: the principle that organised that matter into a living whole.

Aquinas, following Aristotle, describes three grades of soul:

Each higher grade includes the powers of the ones below. You grow like a plant and see like an animal, but you also understand and choose.

One substance, not two things

Because the soul is the form of the body, body and soul are not two separate things glued together. They make one substance: one human person. Think of a statue: its shape isn’t a second object sitting inside the bronze; shape and bronze together are the statue.

This is why Aquinas rejects the “ghost in a machine” picture. Your body is not a container or a car. When someone hurts your body, they hurt you.

The intellect is not an organ

Here is the most important step. What kind of thing does your intellect understand?

• Your eye sees this colour, here and now.
• Your intellect understands justice, the number 7, what a triangle is, as such: universal, unchanging and not made of matter.

You can point to the part of the brain that is active when you see red. But where in the brain is justice itself? Where is the number 7? The brain is certainly involved when we think, as a tool. But the act of understanding universal, immaterial natures cannot be simply the act of a material organ, because matter always receives things in a particular, limited way.

So the human soul has at least one activity, understanding, that is not the act of any bodily organ. And the will, which follows the intellect, is a spiritual power too. That is why we can genuinely choose, rather than just react.

Why the soul survives death

Aquinas reasons like this:

1. A thing acts according to the way it exists.
2. The human soul has an activity (understanding) that does not depend on a bodily organ.
3. So the human soul has an existence that does not depend on the body.
4. So when the body dies, the human soul does not cease to exist.

An animal’s soul, whose every activity depends on the body, ends when the body dies. The human soul does not.

Yet because the soul is made to be the form of a body, a soul without its body is incomplete. This fits closely with the Christian hope in the resurrection of the body, though that hope itself is known through revelation.

Why this matters

If human beings were only matter, it would be hard to say why each person has a unique dignity, or why we are really free and responsible for what we do. If a person is a rational soul united to a body, then every human being, whether strong or weak, young or old, healthy or sick, has a dignity that does not depend on what they can do or how useful they are.

Read the texts

Read Summa Theologica I, q.75, a.2 and a.6, then q.76, a.1. As you read, ask:

1. What reason does Aquinas give for saying the intellect does not use a bodily organ?
2. Why does Aquinas insist that the soul is the form of the body, rather than a separate being that moves it?