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Does God Exist - Proof #1 (The Unmoved Mover)

Introduction to the blog series:

St. Thomas Aquinas, the great 13th century Dominican priest, set out to illustrate five rational arguments for the existence of God; five ways of coming to know that God exists based solely on evidence readily observable by anyone and everyone in the natural world.

In these five proofs, he is essentially telling us is that we are living in God’s universe, and God left His fingerprints all over it for us to find. God gave us the gift of reason so that we could contemplate creation and, seeing the nature of things, and the beauty, power, order, and harmony of what God had made, we could then reason our way from creation to the existence of a divine Creator.

In this series of five blog posts, I will first outline each of these five arguments, then explain and illustrate them briefly.

I hope you will find these posts helpful, both for your own understanding of the reasons we Catholics believe firmly in God’s existence, and also as a means by which you can make the case for His existence to others.

Here is St. Thomas Aquinas’ first proof for the existence of God – the proof from motion, or change.

Proof # 1: From Motion to the Unmoved Mover

  • We see that everything in the universe moves, or changes. This includes the most fundamental motion or change: the move from non-existence to existence.
  • But for anything to move or change, it has to be put in motion, or changed by something outside itself.
  • As we investigate, in turn, the things that give motion or change to other things, we see that they, too, were put in motion or changed by something outside themselves.
  • This chain of changed changers, of motion-receiving motion-givers, can’t go on forever.
  • Behind all things that move and change, and move and change each other, there must be an ultimate unmoved source of all motion, an unchanged source of all change.
  • This Unmoved mover, says Aquinas, we call God.

The world around us is constantly in motion. Birds fly through the air, clouds form and shift in the sky, waves crash on a beach, and a soft summer breeze ruffles your hair and is gone.

If we pay attention to the things around us we notice an interesting fact: None of these things is the cause of its own motion or change. As the Law of Inertia states, “A body at rest will stay at rest unless acted upon by an outside force.”

It is those “outside forces” on which Aquinas focuses our attention in this first proof. Put another way, the outside forces moving and changing the things we observe around us are the causes of that motion and change.

If we investigate further, we notice another fact: all of these “outside forces,” or causes of motion and change, are also moved and changed by still other outside forces, which, in turn, are moved and changed by still more outside forces.

To illustrate what I mean, let’s consider the waves crashing on the seashore. They are set in motion, and therefore change shape and location as they come in to the shore, by a variety of causes – wind, ocean currents, the tidal pull of the moon, etc. It takes all these causes to explain the motion of an ocean wave.

But each of these causes is, itself, set in motion, moved, changed by other, prior causes, which are themselves moved by still other causes.

For example, the wind moving waves across the surface of the sea is caused by changes in air pressure, which are caused by the heating (expansion) and cooling (contraction) of air, which is caused by the penetration of sunlight and solar radiation arriving from the sun, and the thermal effect of clouds forming or dissipating over various areas of the earth’s surface, etc., etc., etc. The same is true of the ocean currents and the tidal pull of the moon, and of any other causes moving the waves.

The point Aquinas wants us to see here is that each of the causes at play in the motion of the waves, is itself receiving its motion from another cause, from another “outside force”.

Having observed this fact, Aquinas thinks logically about the ultimate reason anything moves or changes at all. If all motion is received from another, but all givers-of-motion that we observe are first, themselves, receivers-of-motion, simply passing along the motion they have received, then what we are observing is a massive, interwoven chain of motion and change, being passed along from one receiver-of-motion to the next receiver-of-motion.

But this would mean that, if only these receivers-of-motion exist there is no ultimate originating explanation for the motion we observe in things. This is impossible.

Then where, Aquinas asks, did motion come from in the first place? What gave motion to all the receivers-of-motion, since none of them could set themselves in motion (let alone the whole chain of motion in the universe) and all of them are dependent on some prior cause to give them the motion they are passing on?

The only logical explanation, the only possible explanation, is that, behind all the motion we observe in this great chain, there exists a giver of all motion; the source of all motion, a being which does not receive motion, but which imparts motion to all things which move.

Aquinas joins Aristotle in referring to this unmoved source of all motion as The Unmoved Mover. This Unmoved Mover, the source of all motion and change in the universe, says Aquinas, we call God.

To sum up: if the Unmoved Mover (God) did not exist there would be no source of the motion received by all the receiver/movers in the chain of motion, and therefore there could be no motion, or chain of movers. Since there are receivers-of-motion and a chain of movers, and we can observe that they are, in fact, in motion, it is demonstrated that God (The Unmoved Mover) does exist.

Got it? Great! Stay tuned for the next blog post in this series, on Proof #2, the Proof from Cause.

And thanks for reading this post!