One Way We Can Know That God Exists

How do we know God exists? A lot of us have never even thought to ask that question, but in our increasingly secular and even anti-Christian world, we have to be able to answer it. In an age when the majority of people already live as if there is no God, and the prevailing wisdom seems to move closer and closer to genuine atheism every day, we cannot just assume that God exists and expect people to take our faith seriously.

No, if we want to show people the truth and beauty of Catholicism, if we want to re-evangelize our culture and spread God’s kingdom on earth, we need to know how to explain our faith in an intellectually appealing way. We need to know how to show people that it makes sense to believe, and a big part of that involves knowing how to prove that God really does exist. Now, there are numerous ways we can do that, but we obviously can’t go over every one of them in a single article. Instead, let’s just take a brief look at one of my favorites, and we will see how reasonable it truly is to believe in God.

The Basic Idea

The argument we are going to be looking at here is called the kalam cosmological argument, and if that name sounds intimidating, don’t worry. It is actually based on a very simple syllogism, so all we need to do is discuss the reasonableness of its premises:

  • 1) Everything that begins to exist has a cause.
  • 2) The universe began to exist.
  • 3) Therefore, the universe has a cause.

The first premise is pretty easy. If a kid walked into his house with mud all over his new, expensive clothes, his parents wouldn’t believe him if he said that the mud just appeared there for absolutely no reason and without any cause. That would be ridiculous, and it is no different here. It is ludicrous to say that something can just pop into existence with absolutely no cause, so this first part of the argument isn’t all that controversial.

The Infinity Problem

The controversy really starts when we get to the second premise, that the universe began to exist. Is that really true? How do we know that the universe hasn’t just existed forever? Well, consider this. If the universe has always existed, then the past must be infinite, but that cannot be. See, an actual infinite quantity of anything, including time, gives rise to a bunch of absurdities that make its existence impossible.

For instance, imagine that there is a library with an infinite number of books, each with a number written on its spine. Let’s also imagine that all the odd-numbered books are painted red, and all the even-numbered books are painted black. In this scenario, we are dealing with three infinite sets (the set of odd-numbered books, the set of even-numbered books, and the set of all the books), and right away we already have an absurdity. All three sets are equal (they are all infinite), but the set of all the books must also be larger than either subset (the odd- and even-numbered books) because it includes both of them. In other words, the set of all books is both equal to and larger than either subset, which is absurd.

Even More Problems

But the problems don’t stop there. If we take away all the even-numbered books, we are still left with an infinite amount (the odd-numbered books), so infinity minus infinity gives us infinity. That is absurd enough, but it is just the beginning. If we take away all the books except for one of them, we are still subtracting infinity from itself, but this time we are left with only one book. Or if we take away all the books except for two of them, we are left with two.

And we can do this with any number we like. We can take away all the books except for three of them, or four of them, or five of them, etc., and we can be left with whatever number we want. These are all instances of infinity minus infinity, so when we subtract infinity from itself, we can get any number of results (an infinite number, in fact) even though we’re dealing with the same quantities every time. And that is absurd.

What We Call “God”

So while the idea of infinity works in pure mathematics, it doesn’t work in the real world. An infinite set of anything (including past time) simply cannot exist, so the past cannot be infinite. As a result, the universe must have begun to exist at some point, and if it began to exist, it must also have a cause.

And that cause is what we call “God.” Now, at this point, we might be tempted to pat ourselves on the back and marvel at our great philosophical acumen, but our job isn’t done yet. As always, there are counterarguments to refute and questions to answer, so we still have a bit of work to do. Granted, we do not have space to go over every objection an atheist or agnostic might raise against this argument, so let’s just look at one of the most obvious.

Does This Argument Disprove God?

At first glance, it seems that we may have proved too much. See, God is supposed to be infinite, so according to the logic of this argument, he can’t exist. As a result, we are back at square one, and all we have done is run around in a big logical circle.

So how can we respond to this challenging objection? The key, I would suggest, is that the kalam cosmological argument only proves the impossibility of a quantitatively infinite set. It is impossible for an infinite quantity of anything to exist, but God is not infinite in that way. He is not infinitely big, nor is he composed of an infinite number of parts.

Rather, he is what we call qualitatively infinite. His qualities (like his goodness and his power) are infinite in the sense that they have no limits, but they are not composed of an infinite number of “power units” or “goodness units.”

God Exists

Admittedly, we’ve only scratched the surface of the kalam cosmological argument in this article. There are many more questions we could answer, and there are many more subtle nuances we could clarify, but that is the basic gist of it. The argument shows pretty conclusively that the universe must have been created by God a finite amount of time ago, so we can be confident that the ultimate bedrock of our Catholic faith is as solid as ever.

Photo by Maxim Abramov on Unsplash


JP Nunez has been a theology nerd since high school. He has master's degrees in both theology and philosophy (with a concentration in bioethics) from Franciscan University of Steubenville, and he spent three years in Catholic University of America's doctoral program in biblical studies before realizing that academia isn't where he wants to be. During his time in Steubenville, he worked for two years as an intern at the St. Paul Center for Biblical Theology, where his responsibilities included answering theological questions and helping to format and edit their Journey Through Scripture Bible studies. He blogs at JP Nunez: Understanding the Faith Through Scripture.

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