Aquinas' Five Ways: Demonstrating God's Existence

Structure of the Ways

The tracks are five formulations with a common scheme in four steps: a fact of experience, the application of the principle of causality, the impossibility of an infinite causal process, and the term of the causal process.

1st: Starting from a fact of experience, movement, understood as the passage from potency to act, the application of the principle of causality leads to the conclusion that nothing can be both mobile and motor simultaneously. "Everything that is moved is moved by another."

2nd: In the world of the senses, there are efficient causes, which are subordinate to each other to produce effects (for the birth of a tree requires land, water, electricity, etc.). Nothing can be its own cause; it would then be anterior to itself, since the cause is always prior to the effect produced.

3rd: In nature, there are beings who no longer exist or which did not exist; they are contingent, that is, not necessary. If all beings were contingent, we could not explain actual existence since before creation there was nothing. We need one necessary being to cause the existence of others, "to which all call God."

4th: Experience teaches us that things have different degrees of perfection, for example, goodness, beauty, and so on. There must exist a being who has full perfection and that is the cause of being, goodness, and perfection of all beings, "and this we call God."

The Way to Reach God's Existence

The only valid procedure is based on the effects that manifest to the senses. From here, we reach the first origin that explains them. It is a demonstration a posteriori, the testimony of the senses confirms effects that require a corresponding cause to explain them. Aquinas offers five tracks with a common point, which presents various aspects of reality. This starting point requires the application of the principle of causality, which seeks to explain the effect because if there are subordinate causes, there must be a first cause. The existence of God is analyzed by Aquinas in the second question of the Summa Theologica:

a) Is it obvious to us?

If it were obvious, there would be no sense of faith, because the obvious is not necessarily accepted, but is it clear that God exists? Aquinas replies that something may be evident in two ways: 1) in itself and not for us and 2) in itself and for us.

b) Must it be demonstrated?

For the things God has done, we can prove the existence of God. Now there are two kinds of demonstration: 1) "propter quid," which starts from the cause, which is pre-effect, and 2) "quia," which starts from the effects we perceive through the senses, and from these effects proves its case.

5th: Things do not act at random, but they do so according to their nature and seeking an end. To bring about the means that lead to an end requires knowledge of that order, but many people do not know, view, and reach it. Then there must be a supreme chief cause of the universe, "and this we call God."