The Five Ways of St. Thomas Aquinas, Part I

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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.

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9 thoughts on “The Five Ways of St. Thomas Aquinas, Part I”

  1. Pingback: MONDAY CATHOLICA EXTRA | Big Pulpit

  2. Laurence Charles Ringo

    Here’s a question I have, Michele: Seeing as how you’re a big fan of Aquinas, perhaps you can explain why he endorsed the ecclesiastical murder of so-called heretics in his magnum opus “Summa Theologica”. I myself was a fan of Aquinas until I read that particular section of this work; now I have very little regard for this man. I await your reply.

    1. The Declaration of Independence is an excellent statement of principles. I would be a fool to nay say it because I have one criticism of it and judge its author to be a knave. The truths it lists as self-evident are not self-evident. Jefferson, as a slave owner, was not only a knave, but a hypocrite in stating that all men are created equal.
      I highly admire St. Thomas Aquinas, whose charity is evident in his thousands of excellent philosophical and theological arguments. In the instance you cite, St. Thomas’ statement is conditional. If the state imposes the death penalty on those found guilty of forgery, it would be reasonable to impose it on those found guilty of heresy. Note also that this refers to the juris prudence of the political state at that time and not to a matter of principle.

    2. Laurence Charles Ringo

      Sorry Mr.Drury,but no. Listen to yourself here: “If the state imposes the death penalty on those found guilty of forgery,it would be reasonable to impose it on those found guilty of heresy”…I sincerely hope that you don’t believe that, and wouldn’t have believed it then. When the Roman Catholic Church tosses around the word”heresy”, even in the 21st century it’s a fearful and hateful perjorative; it makes me think that even now, Roman Catholics wish that what you term” heretics” access to YOUR definition could be rounded up and murdered by the State. When RomanCatholics utter the words”heresy” and ” heretics”, that’s when I trust your institution the LEAST.

    3. The word, if, introduces a condition. ‘If offense A deserves punishment X, then offense B, which is worse than offense A, deserves at least as severe a punishment as X’, is a conditional statement. It does not justify punishment X in either case.

    4. What bearing does your opinion of the man have on the force of his rational argument for the existence of God?

    5. Laurence Charles Ringo

      Didn’t want you to think that I had forgotten you, Mr.Aldrich…So, let me get this straight: In YOUR mind, support theological brilliance somehow trumps moral rectitude? In other words, as long as Aquinas was correct in his doctrine, it doesn’t really matter that he was indifferent to the suffering and murder of human beings by the coercive power of the State. Got it. Thanks for the clarification. Thank Almighty God for separation of Church and State. PEACE. ?.

    6. If I can translate your comment into plain ignorance, are you saying, “Go to blazes and have a nice day”?

      In logic you are committing the fallacy of an ad hominem attack. I don’t agree at all with you that Thomas was a bad man. In fact, I think he was a very holy one. Be that as it may, truth is truth no matter who speaks it.

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