I have a hard time understanding Thomas Aquinas' 1st way


I know this is a bit weird, but for some reason amongst the 5 ways or 5 proofs for God’s existence, the first one is the most difficult one for me to understand. I have a few questions that come to mind when reading about the argument.

  1. Why is it that a hierarchical series of “movers” can’t be infinite? I feel like an infinite number of hierarchical movers could be possible similar to how linear movers can also be infinite. Why exactly do we need pure actuality for this?
  2. How could God be pure actuality? If Christianity believes that God became man, then wouldn’t that mean that God went from potentially man to actually man, thus making him NOT pure actuality?
  3. What about God creating? Wouldn’t God be going from potentially creating to actually creating?

PS: I am NOT an expert in philosophy. If I had made an error in reasoning, please tell me. Thanks in advanced!


The infinite regression is a logical impossibility. It defies logic in other words.
For something to change state you require a cause, the change is the effect.
And you cannot go backward ad infinitum since eventually you will stop at the primary cause that started the chain of events to our present.
Also we are now fairly sure that the Universe will also come to an end. When all the energy within it has expended itself it will die.
Thomas did not have the luxury of modern physics but his mind understood the logic and impossibility of an infinite regression.


In the first way, Aquinas introduces the metaphysical principles of potency and act which are fundamental to his metaphysics. Indeed, the first of the 24 Thomistic theses states:

“Potency and Act so divide being that whatsoever exists either is a Pure Act, or is necessarily composed of Potency and Act, as to its primordial and intrinsic principles”.

Whatever changes is in potency to change and is an admixture or composite of potency and act. The very definition of change or motion which Aquinas adheres to is taken from Aristotle, namely, the act of a being in potency in so far as it is in potency.

Potency cannot raise itself to actuality so Aquinas says that whatever moves or changes is moved by something in act other than itself or what is in potentiality. Aquinas goes on to say that we cannot regress to an infinite series or numbers of movers each moving or changing something and themselves changed by some other thing.

So, movement or change is a passage from potential being to actual being such as water which is actually cold but potentially hot to becoming actually hot. Something in potency does not actually exist but it potentially exist. Something that only potentially exists cannot bring itself to actual being or existence but only that which is in act or is actually existing can cause that which is only in potency to be actual. For example, water which is actually cold but potentially hot is changed to being actually hot by something other than itself which is either itself hot such as fire or capable of heating or producing heat such as light rays from the sun. Now, if this thing or mover itself is in potentiality to being hot or causing heat in some way and so changed by a prior mover and so on to an infinite regress of ordered movers moving and themselves being moved since potency cannot raise itself to act, which member of this infinite series causes the water to become actually hot at the end of the series when every single member of this infinite series taken individually is only in potentiality to being hot or capable of producing heat? There isn’t one with the end result that the water at the end of the series never becomes hot but this is contrary to observation.

Accordingly, we must go outside this series of infinite regress, and admit a first mover or being outside the series who is either essential hotness or heat itself and/or capable of producing heat in the series and the same reasoning applies to any other kind of change we observe in the visible universe with the end result being that the first mover must be essential Being or Being itself, Being in act, pure actuality.


The two natures in Christ, namely, the divine and human are not mixed so as to form a third nature but they retain what is proper to each nature. The two natures are united in the one person of the eternal Son of God. Christ’s divine nature is unchangeable even as the Godhead is. But, Christ’s human nature is a creation of God just as ours is. So, what changed in the incarnation of Christ was not his divinity or the eternal person of the Son of God in the human nature but the creation of the human nature of Christ which is not eternal but began to be or exist at the incarnation of Christ a couple thousand years ago.

  1. What about God creating? Wouldn’t God be going from potentially creating to actually creating?

Creation is not a change from potentiality to actuality because in the act of creation by God there was nothing pre-existing to change. God created the universe of creatures out of nothing. What changed so to speak and as in the incarnation of Christ and his human nature was not God, but the newness of the universe itself which before its creation did not exist but began to be when God created it. Nor was there a change in God when He created the universe which he brought about through his intellect and will because God willed to create the universe from all eternity at that ‘time’ he chose and willed to do so from all eternity.


The point is that every “non-prime” mover only uses causal power given by the previous mover. If “non-prime” movers are all that are there, no causal power is going to be there to be used.

There are some analogies that might help one to see it.

One standard analogy uses train cars. Can you get a movement using just an infinite series of cars and no locomotive? No.

Or, perhaps, it will be useful to think about currency. If you have a currency backed by gold, it is worth (approximately) as much, as (some amount) gold, you have gold standard. If you have currency backed by currency backed by gold, you still get some weakened version of gold standard. But if you have an infinite series of currencies backed by one another, and no gold, it is not any version of gold standard.


Actually, for a train, not moving isn’t possible. And this holds true for everything, everything is in a constant state of change. Thus it would seem that to exist, is to change, and not to change, is not to exist.


Analogies always have flaws, GOD exists and yet does not change. In the material universe everything is constantly changing since the beginning of the Universe. Change was initiated when from Nothing, everything was created.


But as they say, from nothing comes nothing. Therefore to change from not existing, to existing is impossible.


Again, that is incorrect. Before the Universe was created it did not exist.
The Universe and all the matter and energy that is within it was created from NOTHING and that has been pretty much proven with math and physics.
Human beings did not exist before GOD created their souls.
But GOD does not change, HIS existence does not have beginning or end.


The form of things change, always has, always will, but the existence of things never has. For from nothing comes nothing.

Sorry, but this simply isn’t true, physics has neither proven any such thing, nor even theorized any such thing.

Pure speculation.

That something exists is self-evident, that God exists…not so much.


First, there was a second analogy, in case the first one didn’t make the right impression.

Second, in this analogy the “movement” is the local movement of the train car as a whole in respect of the ground. In that sense the train car is often not moving. For example, when it is in the station and people are going into or out of it.

Third, “everything” makes this a pretty strong claim. Maybe you should actually argue in favour of such a claim (hopefully, clarifying it in the process of doing so), instead of merely proclaiming it? What makes you think that “everything” (and not merely “everything you could think of at the moment”) changes and does so “constantly” (is that meant to indicate “always”, or some constant rate of change?)?

There is a sense in which that is definitely true. Something that is only potential can’t just start existing spontaneously, on its own.

A cause is required for that. Having actual existence.

That, by the way, is one of the steps of the First Way.

I am happy to see that you accept it so enthusiastically. :slight_smile:


Yes, but the second analogy isn’t relevant to Aquinas’ First Way which has to do with change.

Exactly, all movement is relative. Nothing ever, ever, ever stands still. And that’s true, not just for movement, but for any change. Standing still is something that things simply cannot do.

Well the First Way does rest upon what our senses, through observation, tells us is true. And observation tells us that at their most fundamental level things are always in a state of indeterminancy, until observed. Only then do they possess a fixed state. This means that things are constantly fluctuating between an indeterminant state, and a determinant one. If this wasn’t true then Zeno’s Paradox would make change impossible. This means that things are constantly changing.

Me thinks that you may be conflating your Ways a bit, but be that as it may, existence itself cannot have a cause, that much is self-evident. But where the First Way oversteps its bounds is in presuming that change isn’t a necessary and irreducible property of existence itself. It may be that existence, without change, is impossible. To not change, is to not exist.


It does illustrate why “delegation” of power cannot be done in infinite series, just like the first one. Which is the very point.

First, by “movement” Aquinas means “change”, not merely local movement (the one that is changing the coordinates).

Second, I’m afraid you got close to self-contradiction here. The train car is forever standing still in the coordinate system associated with itself. If “all movement is relative”, you can’t rule out this case.

Third, “everything” means everything, unless you qualify it. So, I offer the proposition “Nothing ever, ever, ever stands still.” as an example of “something”. Or your whole post. Or Pythagorean theorem. Or number “5”. So, how do they move?

No, observations do not tell us anything like that.

That sounds like something vaguely inspired by some popular description of quantum mechanics…

“Constantly fluctuating”? In that case, what is the frequency? How many hertz? Or, if there is no frequency, in what way can one say anything is “constantly fluctuating”?

Be precise. It is easy for nonsense to hide, when you speak vaguely.

Did you investigate how Aristotle dealt with that paradox?


You should study what a singularity is.
Science has not only proven they exist they have also found them all over the Universe.
The Universe was created precisely from a singularity.


Being as being cannot be other than being. The only possible alternative or contrary to Being is not-being or nothing but not-being or nothing doesn’t exist.


I don’t understand why infinite regression is logically impossible. You have infinite sequences and infinite series many of which are convergent in mathematics and it is completely logical.


Can you kindly give us the mathematical proof that the universe was created from nothing.


That might be true - maybe you do not.

Unfortunately, you do not claim that you were trying to understand.

But we are not looking for the sum of causes. Whatever that would mean.

Instead, take the two analogies I have offered:

Looking at those two examples, can you see why infinite series in those cases does not work?


First of all you have used sequences, not series in those examples. Secondly, the fact that the theory of infinite sequences does not work in a particular case, does not mean that infinite regression is a logical impossibility.

Thirdly, infinite series and infinite sequences are used all the time in mathematics and they are perfectly logical. Mathematics does not defy logic, although it can be argued that some of the various interpretations of quantum mechanics have problems.
Fourthly, as far as currency and the gold standard goes, we are currently in the age of cryptocurrency, which depends on a network based public ledger constantly being verified by computers. This shifts the value of money away from gold and ;puts it in the hands of people. Bitcoin enables you to do commercial transactions using an open source protocol. Once again, it depends on computers which in turn depend on mathematics which does not find any problem of logic in using infinite series and infinite sequences.


Unfortunately the example you are using does not apply to this particular case.
In mathematics you can have an infinite series (numerical, integer, etc).

Instead here we are talking about a series of “EVENTS” or effects, not a numerical series.

An “event” requires a “cause”, or there is cause and effect. That is what cannot regress at infinitum. There was 1 cause that put in motion the Universe. Time, Space, Energy, Matter all came forth from a singularity.

DISCLAIMER: The views and opinions expressed in these forums do not necessarily reflect those of Catholic Answers. For official apologetics resources please visit www.catholic.com.