Body and soul
What a human being is, with Thomas Aquinas.
What is a human being? An advanced machine, one animal among others, or a spirit living in a body? Thomas Aquinas gives an answer that takes both body and soul seriously: a human being is one single being, and the soul is what makes the body a living human being.
Read the argument in short first. Then walk through it step by step, and at each step pick the most common objection to see how to answer it.
The argument in short
The argument in five sentences, to learn by heart.
- What makes the body alive is not the body itself. We call it the soul.
- The soul is the form of the body. It is the same human being who thinks and who senses with the body.
- Reason can understand all bodily things and so does not act through a bodily organ. The soul is spiritual.
- Whoever has reason can weigh reasons and choose. Human beings have free will.
- Through reason the human being is made in the image of God, and the soul does not cease when the body dies.
Concepts you needAct and potency
Act and potency actus, potentiaPotency is the capacity to become or receive something. Act is its actually being so. What receives something is in potency to it, and what is received is its act.
Example
A seed is a tree in potency, a grown tree is a tree in act. Cold water is hot in potency, until someone heats it.
In Thomas
Thomas applies the concepts to existence: what receives its existence is related to it as potency to act (De ente et essentia, ch. 3). In God there is no potency, and so his essence and his being are one (Summa theologiae I q.3 a.4).
Step by step
or tap a box in the map to see the texts behind it.
Test yourself
Think of your answer first. Nothing is saved.
Why can't the soul be a body?
If a body lived because it is a body, every body would live. What makes the body alive is something else: the soul.
What does it mean that the soul is the form of the body?
That the soul does not live in the body like a house, but makes it a living human body. A human being is one single being of body and soul.
How do you answer someone who says the soul is just the brain?
Thinking needs the brain as long as we live, but reason can understand all bodily things and so is not itself an organ.
Why do human beings have free will?
Because they have reason. They weigh reasons against each other and are not bound to a single choice, as animals are to their instinct.
What happens to the soul when the body dies?
It does not cease, since it has its existence of itself. But a human being is made to be whole, and the faith confesses that the body will rise.