Thomas Aquinas: 5 Ways to Prove God's Existence

Thomas Aquinas and the Existence of God

Thomas Aquinas sought to integrate Christian faith with common sense and empirical observation (confidence in the senses). This approach influenced his quest for a rational demonstration of the existence of God. For Thomas, God's existence lies outside the scope of the obvious and, therefore, necessitates a rational demonstration. He believed that all human knowledge begins with the senses, so the existence of God can only be inferred from sensible objects. God, he argued, must have left significant clues in the world He created that lead us to prove His existence.

Thomas Aquinas' Five Ways

Thomas produced five ways to prove the existence of God. In these five ways, he argues similarly, following the same script, which can be summarized as follows:

1. It starts with empirical data from the sensible world, captured by the five senses.
2. It applies the Aristotelian causal principle: everything that happens depends on an external cause that produces it.
3. Following Aristotelian theory, it rejects an infinite series of causes and concludes that there must be an ultimate cause.
4. It reaches God as the ultimate cause of the empirical data from the five senses.

First Way: The Argument from Motion

In the created world, there is movement. Aristotle stated that everything that moves is moved by another. However, if something moves and, in turn, is moved, it must also be moved by another, and so on in an infinite sequence. But Thomas says this infinite sequence of movers is impossible; there must be a being who moves others without being moved. Thus, we arrive at God as the unmoved mover that moves the world.

Second Way: The Argument from First Cause

For Thomas, some things are efficient causes. There must be a first and uncaused cause, which would be God.

Third Way: The Argument from Necessary Being

There are things that exist but might never have existed and may cease to exist. It is impossible that things subject to that possibility always exist because what has in itself the possibility of non-existence at some time did not exist. If nothing is impossible, something comes into existence because nothing can come from nothing. Therefore, there must necessarily be something that will be necessary in itself, a reality that has in itself the reason for its existence and not in another, a being that cannot not exist, that is the cause of the necessity of others, and that all call God.

Fourth Way: The Argument from Degrees of Perfection

In the sensible world, there are things that are more or less true and good. Therefore, there must be a maximum degree of these perfections that will cause the lesser degrees, and that perfect being is God.

Fifth Way: The Argument from Intelligent Design

We see things in the sensible world devoid of reason acting toward a certain purpose. Their behavior seems to have an objective, namely, that there is a teleology of nature or purpose. These trends toward certain purposes in humans of limited capabilities have been revealed by an intelligent being, the director of the universe: God.