Looks like I've got to tell you now what I think about the Cosmological Argument. I believe that Cosmological Arguments can give us a good reason to believe in some type of fundamental entity which causes the universe to exist. In Theism that fundamental entity is taken to be God. However, I think that the Cosmological Argument by itself, apart from other considerations, does not necessarily imply either Theism or Supernaturalism. That is because there are also candidates within Naturalism for what that entity might be. But there are related considerations, having to do with consciousness and ethics, which in my view tip the scales towards Theism, and I will try to also explain what these are.
Before I begin, let me tell you right away that this isn't my preferred approach for doing Apologetics. I generally prefer a more empirical approach based on examining historical records for things like, oh, people being raised from the dead. That's not just because that type of data can potentially get you to Christianity instead of just Theism. It's also because, as a scientist, I've been trained to prefer the data to purely theoretical reasoning. Also, as someone who has studied the history of Philosophy, I'm well aware of just how far astray one can be led by so-called “armchair reasoning”, where you try to figure out how it makes sense for the universe to work, based only on broad aspects of reality.
There's way too many examples of philosophers (I'm looking at you, Kant) who say that things logically follow necessarily from premises, when in fact they don't. They're sneaking in extra assumptions on the side: relying on intuitions and then calling it Reason. It's not irrational to have intuitions—without them reasoning would never get off the ground—but not everyone necessarily shares those intuitions. That's just how it is in Philosophy. Any strictly deductive arguments for the existence of God necessarily rest on premises that not everyone is going to accept.
So I'm not going to even try to make deductive claims for most of what I'm going to say, but instead I'll try to tell you why I find Theism plausible, from an armchair reasoning point of view. There are plenty of places where you'll be able to dissent from me. I will argue that Theism makes better sense out of the world than any rival view, but not that all other views are inconsistent or absurd.
The English idealist F.H. Bradley said that “Metaphysics is the finding of bad reasons for what we believe upon instinct; but to find these reasons is no less an instinct.” Well, I'm going to indulge that instinct here. I'm well aware that what I say isn't going to convince everyone.
I've been told that the perfect philosophical argument would be one where if the hearer understood the argument but failed to accept the conclusion, they would just die. The struggle to accept the incoherence would just be too much, and their brain would shut down. Well, there aren't any arguments like that, but I think Metaphysics is still worth doing anyway.
In fact, we must do Metaphysics. Even if you decide to focus on empirical evidence such as miracle claims, you still have to decide how much empirical evidence you actually need to accept a conclusion that may seem weird to you. But just how weird is God's existence? Bayes' Theorem says that the assignment of prior probabilities is a necessary step in evaluating any claim.
So that means, when deciding whether something exists or not, we always need to have some set of plausibility heuristics in our mind which say how likely that thing is to be. In cases where we are talking about the fundamental nature of existence, that means we've got to do Metaphysics. Even if there are no strictly deductive arguments (from indisputable premises), there are still going to be plausibility arguments pointing in various directions. It's irrational to put too much faith in plausibility arguments, but it's also irrational to be completely insensible to them. We must assess the plausibility of propositions in order to evaluate them properly.
If at any point you think I am handling things badly and going beyond my evidence, I ask only to be judged by fair standards. It's easy enough to just take a negative point of view, and criticize unwarranted assumptions in other people's arguments. But suppose that someone asked you to stand up and defend your own metaphysical beliefs (say, materialism) with arguments capable of persuading others. Not just something offhand like “This makes sense to me, and I've never seen any good reason to believe otherwise”, but some robust intellectual argument for certain types of existence or nonexistence claims. You'll quickly find that it's a hard thing to do. Yet some particular specific set of metaphysical statements must in fact be true, even if it is hard to see which ones.
So if you disagree, please do not just say, “There's a hole in your reasoning at line 278, therefore you are being illogical and religion is irrational.” Instead tell me what metaphysical view you find more plausible and why.
From this perspective, I find it interesting that it is possible to argue for the existence of God as well as we can. There are no compelling armchair arguments for the existence of quarks, jaguars, and so on, yet these exist and are observationally measurable. Only in the case of the most fundamental being, God, can we make any kind of purely philosophical argument for his existence. And that is precisely because he is so fundamental, that he is part of the background for everything else that we can or do experience.
I hasten to repeat that this type of considerations I'm about to present are not the primary reasons why I believe in God. God has shown himself through explicit divine revelations, recorded in the Bible and elsewhere. So it is not necessary to approach him through purely philosophical means. And there are many important things about God which we cannot hope to learn without revelation. Nevertheless, there are some people who have argued themselves into Theism for reasons similar to those I am going to describe. I also think it gives some helpful background motivations for Christian theology, even though it is not the primary source of it.
But I don't think Cosmological Argument type reasoning should be exclusively thought of as an argument for Theism, as though it had no other applicability except as a religious tool. I think there are several different types of Cosmological considerations, and that anyone trying to think through Metaphysics seriously, will have to do some type of reasoning not completely unlike what I am going to say. Indeed, quite a bit of what I am going to say should be acceptable even to atheists, and I would continue to accept several of the arguments even if I ceased to be religious.
None of what follows is intended to be particularly original, except for the presentation, and perhaps also the modesty with which I wish to assert the following claims as plausibility arguments, rather than any kind of strict deductions. Broadly speaking, the types of arguments being considered have been around for a long time (longer than Christianity has been around), although I'm going to present them in the form I find most plausible even at the cost of a bit of originality.
One might worry that such arguments are a post hoc attempt to justify, through specious reasoning, conclusions which really came from certain religious texts. But historically speaking, this is not at all what happened. The arguments were developed primarily by Greek philosophers such as Plato, Aristotle, and the Stoics. These arguments tended to support a monotheistic view of the world, which was actually in conflict with the polytheistic view of their surrounding culture. (Other Greek philosophers developed something more akin to Naturalism, which was of course also in conflict with popular Greek religion.) It is therefore quite interesting that the Greek arguments supported something much closer to the Hebrew conception of divinity, which the Hebrews had received by Revelation rather than Reason. Western culture as we know it is really the synthesis of the Greek mind with the Jewish heart, without which there is no theo-logy.
But that combination is also not the origin of Christianity. Rather, it is the cultural milieu in which Christianity started. The compatibility of these two sets of ideas was just starting to be appreciated, when something far stranger than either of them came into the world to save it.
Next: Causes and Explanations.
(Update: edited the sentence about the perfect philosophical argument.)