Aquinas Explainer: The First Way

Moving on from our last instalment, which covered the Fifth Way, today let’s explore the First Way.

The first three of the Five Ways are cosmological arguments: in other words, they argue for the existence of God as a First Cause, but despite that they are nothing like the typical First Cause argument that people are used to. Instead of positing God as kickstarting the universe eons ago, Aquinas wants to prove that God is causing everything here and now. To find out how this works, and why “what caused God” is not a good response, read on.

The First Way is about change. Aquinas bases his metaphysics on that of Aristotle, which was primarily concerned with explaining change philosophically. It works like this: every substance has “actualities” that describes what it is like now and “potentialities” that describe what it has the potential to become but is not yet. Change is when one or more of these potentialities becomes actual.

According to Aquinas, it is not possible for anything to change itself; its potentialities must be made actual by something else. Note that this is about simultaneous “here and now” change. So if your hand changes, it is being changed by the muscles within your hand. But your muscles are also changing, so they are being changed by your cells, which are being changed by atoms, which are being changed by quarks and so on.

Aquinas argues that there cannot possibly be an infinite number of layers of physical stuff with potentialities doing the changing. That would be like an infinite number of train carriages without an engine. Thus at the very bottom there must be something driving it all – a First Cause that has no potentialities whatsoever, and can change others without itself changing.

What makes this interesting (at least to me) is what Aquinas says about the physical world. We assume the bottom layer of the world we live in – be it quarks or strings or whatever – can carry on on its own without anything propping it up. It’s buried so deep in our thinking we don’t even realise it is an assumption. But this is odd when you think about it. We know that all the other layers are dependent on the one beneath. Why would the bottom one be any different? Shouldn’t it be the same as the others? Unless it has some specific property that allows it to cause itself, on what basis can you assume that the bottom layer “just is” and doesn’t depend on anything?

What would a First Cause be like? Since all physical things have potentialities, the First Cause cannot be physical. Since potentialities are required to explain change, the First Cause must be unchangeable. Aquinas goes on to argue that the First Cause must be eternal, conscious and all-powerful. In any case, it’s not hard to see how to get from the First Cause to God.

Okay, so what caused God? If Aquinas’ metaphysics is correct, most things need causes but not all. God, being unchangeable, does not need a cause on that basis. Anything that is changeable or has a beginning needs a cause, as does anything that is divisible into parts or could possibly not exist. Because of this, Aquinas argues elsewhere that the First Cause must not have a beginning, could not possibly not have existed and must be simple – and therefore not only does not have a cause, but could not possibly have one.

The last point there – that God must be simple (in the sense of not divisible into parts) is deeply strange and hard to comprehend. It deserves a post of its own. Nevertheless I think the above shows that Aquinas’ arguments for God’s existence have more to them than most people realise and that they deserve consideration.

That’s all for Aquinas Explainer. There’s a lot more that could be said here, but I think you get the idea. For more on Aquinas, I recommend Aquinas by Edward Feser.

Further reading

A Defense Of Aquinas’s First Way by David Haines


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