Reflections on Thomas' Arguments for the Existence of God

Part 1, The First Three "Proofs"

I've been reading Thomas Aquinas' Summa Theologica. The Summa has many famous parts, but perhaps the most famous part comes early in Part 1 of the Summa where Thomas presents his five "proofs" for the existence of God. 

I expect you've heard of a few of these "proofs." For example, everything must have a cause. But an infinite chain of causes is impossible. So, at the start, there must have been an Uncaused Cause who is God. God is, as we say, the "Unmoved Mover." 

Again, you've likely heard this argument before. And yet, many scholars would argue that the summary of the argument I made above is actually a misunderstanding of Thomas' argument. It also misunderstands how steeped in apophatic mystery are Thomas' "proofs," which is why I'm putting the word "proof" in scare-quotes. Basically, there's a whole lot of confusion, among both Christians and atheists, about what Thomas is doing with this five "proofs" for the existence of God. Because of this, I'd like to share some clarifying thoughts in this series. 

But before I do that, let's today review Thomas' five arguments. The ones I want to focus on in this series are the first three arguments, two of which famously appeal to "infinite regress." Here's ChatGPT's summary of the those first three arguments:

The Argument from Motion: Aquinas observed that objects in the world are in a state of motion. He argued that for something to be in motion, it must have been set in motion by something else. However, this chain of motion cannot go on infinitely because there must be a "First Mover" that initiated the motion. Aquinas identified this First Mover as God.

The Argument from Efficient Causes: Aquinas considered the cause-and-effect relationships that exist in the world. He claimed that every effect has a cause, and this chain of causation cannot go on infinitely. There must be an ultimate "Uncaused Cause" that set everything into motion. Aquinas identified this Uncaused Cause as God.

The Argument from Contingency: Aquinas argued that everything in the world is contingent, meaning they depend on something else for their existence. He reasoned that if everything were contingent, then at some point, nothing would exist because there would be nothing to bring contingent things into existence. Therefore, there must be a necessary being—an entity that exists by its own nature and does not depend on anything else. Aquinas identified this necessary being as God.

I've highlighted the contentious issues among these arguments. The first is the premise that "a causal chain (or chain of motion) cannot be infinite." You can go online to find a lot of YouTube videos where atheists dispute this claim, or make the obvious point that the question of "infinite regress" just shifts the mystery onto God, replacing one impossibility for another. So pick your poison.

The second contentious issue is from the argument from contingency, where Thomas argues that if everything in the world is contingent (i.e., doesn't have to exist) then, at some point, nothing would exist. The way Thomas frames this argument is a bit odd. He doesn't describe contingency in a temporal sequence as with the first two arguments, that at some point in the past contingent existence came into being. So you'll note the missing "infinite regress" premise in the Argument from Contingency. Thomas' premise is that, if all things are contingent, then "at some point" nothing would exist. Most of us would assume that this "at some point" would be "at the beginning" (like a "Big Bang" event). But that's not exactly what Thomas says. It's possible that, given an infinite amount of time, the "at some point" is in the future, like the "Big Chill," the final heat death of the cosmos. But even that idea raises the question, as we'll discuss, about if a quantum vacuum, at either the Big Bang or the Big Chill, really qualifies as being "nothing."

To wrap this up today, this is just a sketch of the three "proofs" to get everyone on the same page, with a gloss about their disputed elements. Tomorrow I'll turn to comment on some of the misunderstandings about these arguments.