St. Thomas Aquinas on Human Nature and Divine Existence

Anthropology and Knowledge

Anthropology

Man is a substance composed of body and soul. The body is mortal, the soul is immortal. In this sense, Aquinas is closer to Plato, who speaks of the immortality of the soul and not the body. Aristotle's hylemorphic theory (where body is the subject, and soul is the form) is also influential, although there are Aristotelian elements.

The doctrine of creation points to the relation between God and the rest of us; these beings are contingent. They exist, but they could not exist. This leads St. Thomas to affirm the distinction between essence and existence. The essence is what a thing is, and existence is that it is. The only being in which essence and existence are identical is God.

The assertion that all created beings are contingent, composed of essence and existence, fits and explains the reality of beings.

Knowledge

Man is composed of soul and body (form and matter). What determines his behavior is the understanding, which is linked to the senses. The understanding, which develops concepts from data supplied by the senses, distinguishes between two forms of knowledge:

• Sensitive Knowledge: obtained through the senses.
• Intellectual Knowledge: obtained through understanding.

To move from individual representations to universal concepts, Santo Tomás posited the existence of abstraction. Through the abstractive ability (the agent intellect), individual representations (matter and form) are stripped of their individual elements (matter) and retain the essential characteristics (form), forming universal concepts (in the possible intellect).

Natural Theology: Proofs for God's Existence

That God exists is a primary datum of revelation, but this does not mean that it is immediately known to us or that it is captured by the senses. Santo Tomás affirms the need to demonstrate rationally the existence of God. To do this, he starts from creatures, using the principle of causality (everything has a cause) and admitting the impossibility of an infinite regress.

Ways of demonstration:

1. Via of Movement: This is constituted by the so-called cosmological proof, which follows from the physics and metaphysics of Aristotle: that everything that moves is moved by something else; nothing can move itself. Since we cannot regress infinitely in the series of movers, this proclaims the existence of a First Mover.
2. Via of Efficient Causality: This way also attempts to demonstrate rationally the existence of God. Each way is presented starting from an observable fact, applying a metaphysical principle, demonstrating the inability to regress infinitely, and concluding with the existence of God. The observable fact for this second way is the existence of an order of efficient causes in the sensible world; that is, something requires an efficient cause (which makes or produces it), and this in turn has another efficient cause.