Here is my most concise summary of the contingency argument for God’s existence: Things that don’t have to exist, but do, can only be explained by something that does have to exist.
Here is a version that is more fleshed out:
Things that did not have to exist, but do exist (contingent beings), require an explanation for why they exist, and that explanation must be found in some external cause. If everything that exists had an external cause, however, then there would have to be an infinite number of beings and an infinite regress of causes, and ultimately there would be no explanation for why anything that exists, exists. To explain why things that did not have to exist do exist, there must be at least one being that must exist and cannot not exist. This necessary being has being in Himself, and gives being to all other contingent beings.
And finally, here is a way of cashing out the argument in terms of explaining why everything that exists, exists:
What caused everything to exist? Only things that already exist can cause other things to exist, so the thing that caused everything to exist must be part of the group of all existing things that we are seeking to explain. If every individual thing in the group of all existing things were a contingent being, however, this would lead to an infinite regress of explanation and require that there be an infinite number of existents – none of which have an ultimate explanation. Since an infinite number of things cannot exist and an infinite regress is impossible, not every existent in the group of all existing things can be a contingent being. At least one existent must be a necessary being who has being in himself, and gives being to all other existents.
Thinking to Believe 
April 26, 2024 at 6:06 pm
“Things that don’t have to exist, but do, can only be explained by something that does have to exist.”
I think Aquinas’ argument from Possibility and Necessity is especially noteworthy here. Primarily, his argument extensively attempts to demonstrate the impossibility of an infinite logical regress. It can be summarized as thus:
1. “We find in nature things that are possible to be and not to be:” contingent beings.
2. Everything is either necessary or contingent.
3. Assume that everything is contingent.
4. “It is impossible for [contingent beings] always to exist, for that which can not-be at some time is not.”
5. Therefore, by (3) and (4), at one time there was nothing.
6. “That which does not exist begins to exist only through something already existing.”
7. Therefore, by (5) and (6), there is nothing now.
8. But there is something now!
9. Therefore (3) is false.
10. Therefore, by (2), there is a necessary being: God.
His treatment of this argument especially emphasizes the physical observation of contingency rather than the metaphysical abstraction of the concept you may see articulated by Avicenna and Leibniz.
In A-T metaphysics, we allow for a infinite temporal regress, but not an infinite logical regress. The reasoning for this is deep-rooted in the fact that through nature, we can distinguish between two things: essence and accident. Essences are the definable natures of those things that exist. In finite beings, essences are composite with existence to constitute a substance. A substance is properly basic, and everything else is predicated either of or in them. Accidents are what accrue to and modify substances. They are dependent on substances, and cannot exist on their own.
With that explanation out of the way, Aquinas intentionally allows for “accidentally ordered” causes of universe in his first 3 of the 5 Ways. That is to say: it is temporally possible for an infinite series of causes for the origin of the universe (or things in the universe). This in our modern analytic philosophy climate would actually work quite convincingly since there is a constant back and forth of A-Theory vs. B-Theory of Time discussion regarding the Kalam.
Anyhow, what I would argue from Aquinas’ thought, in addition to yours, is that the existence of contingent things (or the universe) cannot be “essentially ordered,” That is to say: the definable nature of contingent things does not allow for an infinite logical regress, for they are by definition not able to have an infinite series of causes per se.
I hope that little nugget of Thomistic thinking could help elucidate to you the value that Aquinas has on some of these issues.
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April 27, 2024 at 9:27 pm
Very good observations, Bro. Andrew. As I’ve pointed out several times now, the weakness in Jason’s approach is his failure to argue why a necessary being, on his account, has all the attributes of God. Why couldn’t a being be necessary as to existence without everything else we associate with God. If God’s attributes can be itemized A thru Z, and if A is existence, why does that entail B thru Z? Or, if the being in question has attributes A thru G, why does that necessitate H thru Z? His metaphysics don’t answer that question, but classical theism does.
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