Philosophy

That’s their account of how change is possible. But what makes it ever actually happen? To answer that question, in their view, is to begin a line of inquiry which ends in nothing less than an argument for the existence of God. In particular, in their view it leads to the conclusion that nothing could change or move at all unless there was something which changed or moved other things without itself being changed or moved at all – a first Unmoved Mover (or Unchanging Changer) of the world. And on analysis, this Unmoved Mover would have the attributes or characteristics definitive of God – of being a single all-powerful, all-knowing, etc. cause of things. God thus functions as the apex of reality as Aristotle and Aquinas understand it – the ultimate explanation of how the natural order works.

This is, of course, an idea often associated with religions like Judaism, Christianity, and Islam, but it is important to note that Aristotle and Aquinas think it can be established by purely philosophical arguments. Indeed, though Aquinas was a Christian thinker, Aristotle was a pagan philosopher writing three hundred years before Christianity got started, and who had no awareness of the Bible. He was just giving philosophical arguments, and later Jewish, Christian, and Islamic thinkers saw him as having arrived through pure reason at a conclusion similar to the one they derived from what they took to be divine revelation.

God as Unmoved Mover

Aristotle presents his argument for the Unmoved Mover in Book VIII of his Physics, and in Book XII of his Metaphysics. Later followers of Aristotle present their own versions of the argument. For example, it is the first of the famous Five Ways that Aquinas develops for proving the existence of God. We’ll look at Aquinas’s version. I’ve posted a “Handout on Aquinas’s First Way” which sets the argument out in a step-by-step form, and summarizes some other ideas that are important for properly understanding it. Take a look at it either before or after reading the rest of this lecture – I’ll be referring to it in what follows.

The First Way

Again, the handout gives a step-by-step statement of Aquinas’s argument, but here is a way to understand the basic idea, using a simple example. Suppose that as I sit here at my desk, I use a pen to write something down. The pen moves, and of course, that is because I am moving it. And again, for Aristotle and Aquinas, what that means is that I am making the pen go from potentially moving to actually moving.

Now, my fingers can do that only because they are themselves going from potentially holding and moving the pen to actually doing so. And what is making that happen is the firing of certain motor neurons. Those neurons are in turn firing only because certain further neurons are causing them to do so. So, the movement of the pen is actualized by the flexing of the finger muscles, which is actualized by the firing of the motor neurons, which is actualized by the firing of further neurons… and so on.

What makes this possible?

Now, notice three things about this series. First, it is simultaneous. The pen is moved here and now because the fingers are flexing here and now because the motor neurons are firing here and now, and so on.

Second, the members of the series are dependent on other members for their ability to do anything. The pen has no power to move on its own. Left to itself it will just sit there. Its power to move is derivative or borrowed from the fingers. But the fingers, left to themselves, will just lie there limp. Their power to move things (like the pen) is borrowed from the firing of the neurons. And so forth.

Third, all of this happens here and now only because all of the members of the series exist here and now. For example, the neurons can fire here and now only because they exist here and now. And they exist here and now only because their molecular structure is holding together here and now – which is happening only because the atomic structure is holding together here and now.

You might say that the atomic structure is here and now actualizing the molecular structure, which is here and now actualizing the neurons, which are here and now actualizing the flexing of the fingers, which are here and now actualizing the movement of the pen. Z is being actualized by Y which is being actualized by X which is being actualized by… and so on.

How far down can it go?

Can this go down forever? Aquinas says that it cannot. The reason is that each member is, we might say, borrowing its actuality from other members, which are in turn borrowing their actuality from yet others. And there can’t be borrowing without something to borrow from.

What they are “borrowing” from can only be something that has its actuality in a “built-in” way rather than in a borrowed way. It can only be something which can actualize other things without having to be actualized itself. And that would be something that is always already fully actual, without having any potentiality at all that is waiting to be actualized. It would be a “purely actual actualizer ” – what Aquinas calls an Unmoved Mover or Uncaused Cause.

The reason it is uncaused is that to be caused, you need potential waiting to be actualized – and this cause, again, has no potential waiting to be actualized. It just is, always and already, fully actual. So, not only does it not need a cause, it couldn’t have one. Remember Aristotle’s idea that though there could not be something that is purely potential, there could be something that is purely actual. This is what he meant. He had in mind God as the Unmoved Mover of the universe, and Aquinas is borrowing and building on that idea.

What Aquinas is not saying

There is a lot more to Aquinas’s argument, such as the reasons he gives for concluding that this Unmoved Mover would be all-powerful, all-knowing, etc. We’ll get to that later on. For the moment, it is important to warn against some common misunderstandings of Aquinas’s argument.

First, you might think that what Aquinas is doing is saying that “Everything has a cause, so the universe has a cause.” And then you might think that there is an obvious response to this: If everything has a cause, then what caused God?

But that is NOT what he is saying. This objection is often flung at Aquinas, but it is aimed at a “straw man” or caricature of his argument. Aquinas does not say that “everything has a cause,” and in fact he rejects that idea. What he says is only that what goes from potential to actual has a cause. That’s a much more limited claim.

Second, you might think that Aquinas is tracing the series of causes back to the Big Bang, and then asking “What caused the Big Bang?” But that too is NOT what he is saying. He is not trying to argue about whether the universe had a beginning. He isn’t even getting into that question.

Not what Aquinas has in mind

Rather, he is asking: What keeps the universe going here and now? And he is arguing that the world could not keep going here and now unless the Unmoved Mover were actualizing it here and now. That would be true, he thinks, even if the universe had no beginning – even if it had never started existing, but had always existed. It would still always need God to keep it existing.

Here’s an analogy: Suppose you’re watching a puppet show. How are the arms and legs of the puppet moving? They’re moved by the strings, which are in turn moved by the puppeteer. Without the puppeteer’s action, the puppet would be motionless. Now, notice that this has nothing to do with how long the puppeteer has been moving the puppet. Suppose the puppet show has always been going on, with no beginning. It would still be true that the puppet has only been moving (even if forever in the past) because the puppeteer has always been moving it (forever in the past).

In the same way, Aquinas is saying that, even if the world had had no beginning, that wouldn’t matter to the question of whether God is causing it. What matters, for Aquinas, is that the world could not exist here and now, or at any moment, unless the “purely actual actualizer” or Unmoved Mover was here and now actualizing it -- keeping the world in existence from moment to moment to moment. That is, in his view, the deepest sense in which the world depends on God as First Cause.

Two kinds of cause and effect

The technical way of putting this is to say that Aquinas is not talking about an “accidentally ordered (or linear) series ” of causes and effects – the kind that extends forward and backward in time. Instead, he is talking about an “ essentially ordered (or hierarchical) series ” of causes and effects – the kind where all the members of the series exist simultaneously.

The reason that this second kind of series needs a first cause is, again, that the members have only borrowed causal power, and there must be something for them to borrow it from. If the puppeteer were not moving the strings, then the puppet’s arms and legs could not move. For they have no power to move on their own, and the strings also have no power to move them unless they derive it from the puppeteer.

In the same way, the flexing of my muscles as I move the pen, the firing of the neurons as they cause the muscles to flex, the holding together of the molecular structure of the neurons as they fire, and so on… all of that involves one level of reality here and now actualizing another level, only because it is in turn here and now being actualized by another. Each level is borrowing its actuality from some deeper level, and this regress cannot stop except at a level which can give actuality without having to borrow it – and only something that is already purely actual, without potentiality, can do that.

What would such a thing be like? That brings us to Aquinas’s reasons for thinking that a purely actual actualizer or Unmoved Mover would have the attributes characteristic of God. We’ll get to that in the next lecture. Meanwhile, here are some optional YouTube videos on our topic:

Thomas Aquinas and the Argument from Motion: