The Nature of the Soul

1.) Unity in a Living Being

Unity means that all the parts of a body — hands, legs, neck, organs (heart, brain, lungs), and internal substances (blood, bones, tissues) — work together as one living whole.

The heart works for the whole body.
The lungs work for the whole body.
The brain coordinates the whole body.

A living organism is not merely a collection of parts, but a unified being.

2.) A Principle of Unity Is Required

For many parts to become one living being, there must be something that unifies and organizes them into one whole. This is called a principle of unity.

3.) This Principle Is Called “Form”

👉 The principle that makes a body one living being is called its form.

In living beings, this form is called the soul.

Plants possess a vegetative soul (growth, nutrition, reproduction).
Animals possess a sensitive soul (sensation, movement, appetite).
Humans possess a rational soul (intellect and rational will).

Different living beings therefore possess different levels and kinds of intrinsic activities.

4.) Artificial Unity vs Living Unity

Machines can also possess a kind of unity, but this unity is externally imposed by designers, engineers, or programmers. This kind of unity is sometimes called an artificial or accidental form.

The parts of a machine work together because they are arranged externally for the purpose of an external agent.

5.) Living Beings Possess Intrinsic Unity

A living being possesses intrinsic unity — unity from within. The soul is also called the substantial form because it is the principle that makes a living being a unified substance from within itself.

6.) What Intrinsic Unity Means

Self-motion (acting toward goals from within).
Self-nutrition (growth and metabolism).
Internal causation (cells repairing tissues, immune regulation, healing).
Self-preservation from within.

A living organism actively maintains itself as a unified whole.

A machine, by contrast, does not possess genuine self-maintenance, genuine self-repair, intrinsic self-generated unity, or immanent activity directed toward preserving itself as a living organism. Its unity continuously depends on external agents such as engineers, programmers, or operators.

7.) The Question of Future Robots

Suppose a future robot possessed self-maintenance, self-repair, internal regulation, autonomous adaptation, perhaps even self-reproduction. A Thomist would still ask whether this unity is truly intrinsic or merely the execution of externally derived programming and design.

A modern phone can already regulate temperature, manage battery usage, and optimize processes. Yet its unity is still considered mechanical rather than substantial.

The debate then becomes metaphysical: Is the robot merely executing externally derived functions, or does it possess a genuine intrinsic principle of being and activity?

8.) Instincts, Biology, and Evolution

Thomas Aquinas would agree that humans possess instincts, genetics, biological drives, and natural tendencies.

Cells use DNA. Brains use neurons. Humans possess survival instincts.

The confusion often comes from modern language when we say: 👉 “DNA contains instructions.” 👉 “The brain is programmed by evolution.”

A mechanist may conclude: “The body is merely a highly complex biochemical machine shaped by nature through evolution.”

Someone may then argue: 👉 “Even living beings are simply programmed by an external agent called nature.”

However, from a Thomistic or substantialist perspective, nature is not viewed as an external programmer or separate entity imposing unity from outside.

“Mutations, recombination, and genetic inheritance occur at the material level through physical processes. The form is the intrinsic principle that makes these processes belong to a single living organism and constitute one unified biological individual. Matter cannot organize itself into a unified living substance without form.

Form makes matter exist as one living organism at all, rather than as merely many interacting physical parts. Form is the first principle of life.

A Materialist say: “If matter is organized correctly, life emerges. Materialists treat unity as emergent from interactions. ”