Aquinas' Proofs: The Existence of God Through Five Ways

Aquinas on the Existence of God

The Summa Theologica is a highly influential work in theology and Christian doctrine. It is divided into three parts: the first part, "On God"; the second, covering ethical and moral issues; and the third, dedicated to the study of Christ.

The Problem of God's Existence

The question of God's existence is framed within the structure of reality. God is real, as are creatures, but God's being and existence are not derived from anything or anyone. Creatures, however, derive their being and existence from God. Created beings are contingent; they exist, but their existence is not necessary. God, on the other hand, necessarily exists.

This distinction highlights the difference between essence and existence. Created things are composed of both essence and existence, while in God, there is no such distinction. God is existence; God cannot not exist. God's essence includes existence.

Essence relates to potential, as essences are likely to exist. When they are actualized, they achieve existence.

Aquinas' Five Ways

The existence of God, while clear in itself, is not immediately clear to us. It is demonstrable through five arguments, which are a posteriori, meaning they start from experience. Aquinas believes that all knowledge begins with the senses. Therefore, to demonstrate God's existence, we must start with creatures, the effects perceived by the senses, and move to their causes. This is based on the principle of causality, which states that every effect has a cause, and it is impossible for the series of causes to be infinite. The first cause is God.

These five arguments share a common structure: they begin with an observable fact, apply the principle of causality, affirm that there cannot be an infinite causal series, and conclude that there is an original being, the cause of all, which is God.

The Five Proofs

1. Unmoved Mover: Everything that moves is moved by another. The first unmoved mover is God.
2. First Cause: Everything that exists has a cause. The first cause of all existence is God.
3. Necessary Being: Contingent beings need a cause to exist. There must be a necessary being that exists in and of itself, which is God.
4. Infinite Perfection: No created being is perfect. There must be an infinite perfection that encompasses all perfections, which is God.
5. Final Cause: Every agent acts with a purpose. There must be an absolute final cause towards which all things are directed, which is God.