Thomas Aquinas’ Argument From Contingency: A Socratic Dialogue

St. Thomas Aquinas
St. Thomas Aquinas

In today’s dialogue Brad and Sarah discuss the third of Thomas Aquinas’ proofs for the existence of God, the argument from contingency. You can read their first dialogue in which they discus the first two proofs of Aquinas here.

Brad: Hey Sarah. Coffee?

Sarah: Good to see you. I’m okay, just got one.

Brad: K, give me one sec.

. . .

Brad: How are you?

Sarah: I’m good, I’m good, thanks. Did you get a chance to read Answering Atheism?

Brad: I read the first few chapters. It was okay. You’ll be proud of me, I looked up Aquinas’ third way for our discussion today.

Sarah: I hope you don’t mean that you “looked it up” in The God Delusion.

Brad: No, no, online. Are you ready?

Sarah: Sure, I actually have what St. Thomas wrote in the Summa here. Do you mind if I read it first?

Brad: Sounds like a good idea.


Thomas’ Third Way


Sarah:The third way is taken from possibility and necessity, and runs thus.We find in nature things that are possible to be and not to be, since they are found to be generated, and to corrupt, and consequently, they are possible to be and not to be.

But it is impossible for these always to exist, for that which is possible not to be at some time is not.Therefore, if everything is possible not to be, then at one time there could have been nothing in existence.

Now if this were true, even now there would be nothing in existence, because that which does not exist only begins to exist by something already existing.

Therefore, if at one time nothing was in existence, it would have been impossible for anything to have begun to exist; and thus even now nothing would be in existence—which is absurd.

Therefore, not all beings are merely possible, but there must exist something the existence of which is necessary. But every necessary thing either has its necessity caused by another, or not. Now it is impossible to go on to infinity in necessary things which have their

necessity caused by another, as has been already proved in regard to efficient causes.

Therefore we cannot but postulate the existence of some being having of itself its own necessity, and not receiving it from another, but rather causing in others their necessity.

This all men speak of as God.”

Sarah: Alright. Can we agree there are things that don’t have to exist, like rocks or planets, or people—contingent things. And could we agree, in theory, there could be things which have to exist or can’t not exist—necessary things.

Has to and doesn’t have to exist seem pretty exhaustive, don’t you think?

Brad: Yeah, okay. You’re saying when we consider a particular thing, that it either does not have to exist or that it does, and that these are the only options for any given thing. Yes, I grant that.

Sarah: Okay. Is there anything we observe that has to exist? Or could what we observe have been different, even at the molecular level; strings instead of quarks, or six basic quarks instead of nine basic quarks?

Brad: As a theist I know you’re committed to saying that at least God has to exist, right? I on the other hand, I don’t know. Either everything that exist doesn’t have to exist or else there might be something that has to—which I don’t think we have any reason to call “God” by the way. I just don’t know.

Sarah: Okay. Let’s go back to the universe. If the past is infinite then an infinite number of things will happen. Or every possibility will be actualized. Isn’t it possible then for everything to not exist?

Brad: I suppose so.

Sarah: Okay, and if the past is infinite, then it seems to me that it must have happened at least once. But if there was ever a state of nothing in the past then why isn’t there a state of nothing now? Thomas says that the only resolution to this dilemma is to posit a begin that is necessary, or must exist, and this is the classical description of God, the necessary being.


Define “Nothing”


Brad: First of all, nothing is a tricky concept. We actually know—Laurence Krauss talks about it in his book A Universe From Nothing—that things can come into existence out of nothing. So even if it’s true that there was once a state of nothingness, if my only options are: 1. God made it, or 2. it came out of nothing—and since we’ve got good reasons from modern physics to think this can happen—I’d choose option two.

Sarah: Krauss does a bait and switch with nothing. By nothing I mean the complete absence of anything while Krauss means a vacuum that has not matter in it but only unstable quantum energy. That’s not nothing. My point is it’s possible for there to be pure nothing and if there was pure nothing, then why is there something now. If you just say “something can come from nothing because I can imagine it, then we’re back to unfalsifiable atheism. Booming voices or angels proclaiming God could just be something from nothing too.

Brad: Maybe everything in the universe could and has failed to exist at one point but the universe itself necessary.

Sarah: I don’t understand what you mean. What is the difference between “everything in the universe” and “the universe.” The term “universe” just means all spatio-temporal realities, or “everything.” You basically said, “Maybe everything in the everything failed to exist but everything is necessary! That seems incoherent.

Brad: What if nothing, in the way you’re using the word, can’t exist? What if the only “nothing” there is is what Krauss refers to? Why think your “nothing” has to exist.

Sarah: What if we live in the Matrix? What if we never landed on the moon? We can do “what if” all day. When we reason about the world we have to use our intuitions to see what’s possible and what isn’t. If we can imagine a world without one kind of thing (say couches) or many kinds of things (animals) or even more kinds of things (no complex molecules) then why couldn’t there be a world without anything? It’s not logically impossible and indeed, the question “Why is there something rather than nothing?” has been debate by philosophers for centuries which shows that absolute nothing is an intellectually worthy possibility.

Also, I could ask you the question, what makes something that doesn’t exist right now possible or impossible in the logical sense of the world? How do you know a universe with only Krauss’ nothing is possible (since that universe doesn’t currently exist) but a universe with pure nothingness is not, or we can’t know it’s possible?

Brad: Yes, we can ask “what if” all day, and honestly, I think this is one of the major differences between you and me. I’m okay not knowing. I’m okay with mystery. You—and try not to take this too offensively—need a Bible and a God to make your world neat, ordered, and, well, unmysterious.

For the sake of argument, however, I’ll grant your point. Let’s say Krauss is doing a bait and switch like you say and things can’t come into existence out of nothing and that nothing is, as you say, the complete absence of anything. Okay. So things can possibly fail to exist or not possibly fail to exist. And I’ll even admit that you’ve stumped me on what I said about the universe, you’re right, the universe simply is all of spatio-temporal reality. Now what.

Sarah: Well I’m in danger of repeating myself. Contingent things can go out of and come into existence. Since it’s possible that every contingent thing could not exist simultaneously, given an infinite amount of time that possibility would eventually be realized. But if it were realized there would be nothing that existed now, since, “out of nothing, nothing comes.”  We can debate whether that cause is God, but right off the bat I can tell you that contingent things like aliens or physical forces won’t work so the window of candidates is extremely small.


Why Only One Efficient Cause?


Brad: Even if you’re right and there is a necessary being, how do you know this necessary being is one? You talk about him being the first mover, or the first efficient cause, or the necessary being. Why can’t there be multiple first movers, first causes, and necessary beings? Why does it all have to trace back to one God?

Sarah: The biggest reason is that this God is pure act, something that has no potential since it activates the potential of all other things. If there were two gods, one would lack what the other had. After all, how could we distinguish between them unless there was something different about them. Therefore, that which is pure act cannot be divided, which is why Christians believe God is one.

Brad: Why can’t there be two things that are pure act? I’m not trying to be argumentative, I’m just trying to understand.

Sarah: If there were two, what would these beings be like? How could you tell there were two of them?

Brad: I don’t know, you think God is just an immaterial mind right? So maybe there’s two immaterial minds with two different agendas.

Sarah: God isn’t just an immaterial mind, those are angels. Instead God is being or existence itself. He just IS and exists without limit. If there was another God like him, both would limit each other (hence different agendas) and so they could not be pure act, which is what God is.

Brad: We’ll have to continue this discussion next week, Sarah. My friends and I are going out tonight and I have to run home to get ready.

Sarah: Sounds good, Brad. Nice seeing you again.


5 thoughts on “Thomas Aquinas’ Argument From Contingency: A Socratic Dialogue

  1. I guess I’m not understanding this, as it seems essentially a retread of the first proof, really another way of saying that you can’t have infinite regress – Newton’s first law if you like. It seems again to devolve into God of the Gaps: we don’t understand how the universe began, so it must have been God. We don’t know where the universe came from, or if it started at all, or even understand the nature of time itself – can there be time without physical objects? Calling whatever created the universe “God” is insufficient as clearly the Christian concept of God is much more than that.

    I can certainly understand the idea that God is the essence of the physical universe, that from which it came and through which it continues to exist. God is existence itself. But it’s a great leap from that to the idea that God is a transcendent, sentient being that takes a personal interest in each of us and with which it’s possible to have a personal relationship. And an even greater leap to the dogma of the Christian Church.

    1. Thanks for commenting Patrick. This argument does not depend on the universe being finite. So Thomas certainly isn’t arguing, “we don’t understand how the universe began, so it must have been God.” In fact, Thomas didn’t believe that the finitude of the universe could be demonstrated philosophically, so none of his arguments for the existence of God make that assumption.

      And yes, leaping to Christianity from a necessary being is a giant leap. But you can’t accuse Aquinas (or me. Or Sarah) of doing that since he does not make that leap in this argument. Christianity is not what this argument is trying to prove. Here’s an argument for Christianity, albeit short:

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