There’s a lot of philosophy and argument that go into any proof for God, but if you only have five minutes, here’s Karlo Broussard’s quick summary of one of Thomas Aquinas’ Five Ways on Catholic Answers Live.
Transcript:
Caller: Hi, I’m just wondering what your favorite argument for the existence of God is.
Karlo Broussard: There are many different types of arguments that theists employ or use in order to argue that God exists. So you got some arguments, Jonathan, you may be familiar with what is known as the Kalam cosmological argument, where philosophers will argue that past time cannot be infinite, that there must be an absolute beginning of time and physical reality; these philosophers will use contemporary science to justify that claim. Some philosophers will try to argue philosophically that an infinite past time involves a contradiction and cannot be, and thus if a beginning, then it would require a cause. If the universe had a beginning, it would require a cause outside of itself, and that cause would have to be pretty powerful in order to bring the universe into existence. So it’s the contingency of the universe, in other words, that the universe didn’t have to be, it began to exist, and it would need a cause or a creator.
You also have arguments from contemporary science such as the fine-tuning. You may have looked into some of those. For these types of arguments, I would highly recommend you check out a philosopher and Christian apologist by the name of Dr. William Lane Craig. In his resources, he deals a lot with these sorts of arguments.
Now Jonathan, there are other types of arguments for God’s existence that try and prove that claim to demonstrate—not just provide probable knowledge that God likely exists, but to demonstrate—that God exists, and these are known as metaphysical or philosophical demonstrations. And the arguments that sort of embody this sort of approach are famously St. Thomas Aquinas’ five ways; and there are other philosophical demonstrations that sort of are related to Aquinas’ five ways from the Summa Theologiae, and a resource that you can check out for those kinds of arguments, Jonathan, is Dr. Edward Feser, F-E-S-E-R, in his book Five Proofs of the Existence of God.
And one of those proofs in that book, which is coming and inspired from St. Thomas Aquinas—and basically, Jonathan, we start with things of our experience that exist, but they don’t have to exist. Now this is just a sketch, we can’t defend all the premises here in this reasoning, but here’s the sketch.
The things I experience, like the tree outside, do not have to exist. The tree outside, there was a time when it did not exist, there’s going to be a time in the future when it won’t exist; and from that, Jonathan, we get an insight that the principle and virtue of which it is something rather than nothing—namely its existence, the fact that it has existence—the tree does not have existence in virtue of its own essence, or nature. It doesn’t have it in virtue of just what it is, otherwise it would always exist. But since it hasn’t always existed, it can’t have existence in virtue of its own nature.
And consequently, as St. Thomas Aquinas reasons, Jonathan, if it doesn’t have existence in virtue of its own essence, then it must receive that existence from something outside of itself, and that leads us in a reasoning process to conclude that there has to be some cause, Jonathan, that unlike the tree does not have to receive its existence from something outside of itself, but has existence in virtue of its own essence or nature. And the reason why that is necessary, Jonathan, is because without such a cause from which the tree and everything like it could receive their existence, you would have no existence, because everything would be like the tree: not having existence in virtue of its own essence or nature, in which case you would have a bunch of existential zeros. In other words, you would have a bunch of things with no existence, and you would have nothing. But there is something, and so therefore there must be some cause that has existence in virtue of just what it is, and has the power to give that existence to things like the tree.
And this sort of cause is what St. Thomas Aquinas, Jonathan, calls the first cause or the uncaused cause. It does not have to be caused by another to exist, because it just simply has existence in virtue of what it is. Dr. Edward Feser articulates this kind of proof in his book Five Proofs of the Existence of God, known as the Thomistic Proof.