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The Five Ways of St. Thomas Aquinas, Part I

June 11, AD2017 8 Comments

Thomas Aquinas’ Ways

But on one particular day, she grabbed my full, locked-on attention. She was talking about St. Thomas Aquinas’ famous Five Logical Proofs of God’s Existence, or five ways to demonstrate God’s existence. Up until that moment, I’d pretty much taken the Catholic Church’s teachings for granted. But this was new! These five proofs just blew me away.

I’d always had an interest in philosophy, world religions, theology, and mythology, so this was as much entertainment as it was education. St. Thomas Aquinas is one of the most prominent doctors of the Catholic Church. His writings formed the basis of many subsequent Catholic writings by others. To this day, I credit St. Thomas Aquinas with cementing my belief in God, and starting my active Catholic journey in understanding “Why Catholic?”

If you’ve never heard of these proofs, know little about them, or have forgotten them, the following is the first of a series describing each of these proofs. There’s a link to these five proofs at the end of this article. Note that St. Thomas used/defined words differently from how we do today. So, you may have to stretch your mind.

The First Way: Movement, or the Argument from Change

The First Way is about what causes movement or change.

By “change” St. Thomas refers to the change from potentiality to actuality. A pile of wood is potentially hot. When someone lights it, he moves it from potentially hot to actually hot. While the wood is hot it can no longer be simultaneously potentially hot, rather, it is potentially cold.

In St. Thomas words:

It is certain, and evident to our senses, that in the world some things are in motion [i.e., changing]. Now whatever is in motion is put in motion by another, for nothing can be in motion except it is in potentiality to that towards which it is in motion; whereas a thing moves inasmuch as it is in act. For motion is nothing else than the reduction of something from potentiality to actuality (emphasis mine).

For a thing to be in motion (changing,) it must have been put in motion (changed) by something else, something that is itself in motion. And the thing that put it in motion must have been put in motion by something else. It cannot put itself in motion.

Tracing each change and its move backward to the first thing put in motion, the first change must have been placed in motion by an unmoved mover or a prime mover. While the universe may well have been set in motion by the Big Bang, what Mover set the Big Bang in motion?

… But this cannot go on to infinity, because then there would be no first mover, and, consequently, no other mover; seeing that subsequent movers move only inasmuch as they are put in motion by the first mover; as the staff moves only because it is put in motion by the hand.

Mathematics is a world of ideas, so mathematicians can use infinite series anyway they please. But not every mathematical idea is useful in the real world. In the real, concrete world, you can’t count backward along a series without eventually arriving at one. Father Andrew Younan, in his book Thoughtful Theism: Redeeming Reason in an Irrational Age (see Anthony S. Layne’s review), sums up the problem best: “If ‘infinite’ doesn’t mean ‘no firsts’, then it means nothing at all and is therefore impossible to think about ….” (Op cit., p. 30)

The Prime Mover, which is never in potentiality but is pure Actuality (that is, it changes without being changed), is not an arbitrary barricade against an infinite regress but rather a necessity demanded by the very meaning of infinite. Saint Thomas concludes:

… Therefore, it is necessary to arrive at a first mover, put in motion by no other; and this everyone understands to be God.

Next month I’ll talk about The Second Way: The Argument from Efficient Cause. You can find St. Thomas’ Five Ways to Prove the Existence of God at New Advent:

Hat tip to Anthony S. Layne for his help with this article series.

Photography: See our Photographers page.

About the Author:

Michele is retired, happily married, the mother of two adult daughters and has one granddaughter. As a lifelong Catholic and writer, she has managed to find a way to write in most of her career positions. She spent 35 years as a registered respiratory therapist, during which time she was given opportunities to write for the hospitals where she worked. She earned her Certificate in Healthcare Quality in 1994, which led to more writing opportunities. Some of this writing included grant proposals, educational materials, brochures, patient home care materials, policies and procedures. Later, she wrote articles and blogs for websites on legal, medical, genealogy, and RVing/camping topics. Noting that Truth, Jesus, and God have been increasingly disregarded, she hoped for an opportunity to write about the Church, Truth, and the wonderful things she's learned, with God's guidance, from a Catholic point of view.

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