While belief in God is often assumed to be a matter of personal faith – of hope for things not yet seen – the Catholic tradition has long held that God’s existence can be affirmed through rational argument. This tradition is known as natural theology, whereby a person discovers a simple principle of existence – for example, that things change – and reasons deductively from there to some ultimate cause of things.

To help us understand how these arguments work, I elicited the help of a Dominican priest, Fr. Gregory Pine, who studies in the tradition of St. Thomas Aquinas, famous for presenting his Five Ways as “proofs” for the existence of God. But what exactly do these proofs show? And, more importantly, do they hold up today? Let’s find out.

Pat: As a priest, much of your work is built upon the assumption that God exists. But what do you say to people who are skeptical of this? More particularly, what do you say to people who don’t take the Bible as a valid starting point?

Fr. Gregory: All of my eggs are in the “God exists” basket. If God doesn’t exist, I am a man most of all to be pitied. Fortunately, I think there’s warrant for believing that God is. Now, admittedly, the reason I believe—the reason that most people believe—is that someone else chose for us. My parents chose to have me baptized and catechized in the faith. And so, by the light of faith, I assented from a young age to the fact of God’s existence. Over time, that assent has become something more personal, but it was an assent that went before me. It was the atmosphere of my home, before it was ever a conscious choice. But, that’s not the only way to come to a knowledge of God.

St. Thomas Aquinas taught that the existence of God is a preamble of the faith: it is both revealed by God and discoverable by reason. So, regardless of whether or not you have received revelation of any sort, you can work it out for yourself that God exists. St. Thomas is willing to concede that such an effort is difficult, takes a long time, and admits the possibility of error, but he thinks that people who stick with it, can come to “prove” the existence of God.

Pat: OK, I’ll bite. Say I’m willing to entertain the idea that God’s existence can be rationally gotten at.  Where do we start?

Fr. Gregory: In St. Thomas’s arguments—which are most famously laid out in the Summa Theologiae as the five ways—he begins first with observations about the world around us. He starts close to his experience. So, for instance, things move, or things tend to an end. And then from these observations, he reasons back to a source for the coherence of what he observes. Basically, he’s making a judgment that reality can’t explain itself causally. As a result, there is a need for something or Someone which transcends the limitations of created being as a way by which to account for all that is.

So, for instance, St. Thomas observes (in the third way), that everything that is, could not have been or could have been otherwise. So, you or I could not have been born. I could step off the curb in front of a bus. You could get spirited away by space aliens. Anything could happen. Our existence is contingent, it’s not necessary. That I am is a separate consideration from what I am. There is nothing about what I am that demands that I am.

But, St. Thomas continues, how then do we account for the fact that these things are—that we are? Or, as the argument is sometimes formulated, why is there something rather than nothing? It’s these types of questions and this type of inquiry that leads St. Thomas back to God as the source of created reality.

Pat: So, God is the cause of everything? But if that’s the case, couldn’t the skeptic simply ask the question of who – or what – caused God? Are we caught in an unresolvable dilemma here, Fr. Gregory?

Fr. Gregory: St. Thomas would respond that everything that is moved must have a mover, and everything that is caused must have a cause. But in order for the whole chain of movements or causes to work, there must be some unmoved mover or uncaused cause—a principle which imparts to the whole order the very capacity to move or to cause. God is not a mover or a cause in the way that creatures are. He is unmoved and uncaused, and so to ask what moves or causes him is to miss what is distinct about God in the order of being.

Pat: Fine and fair. Say we admit of an uncaused cause.  But why assume this uncaused cause is God? Couldn’t it be, like, a meatball, or an electron, or something else?

Fr. Gregory: St. Thomas arrives at certain conclusions from the five ways, and—admittedly—they don’t sound like the God of Abraham, Isaac, and Jacob. What he discovers is an unmoved mover, a transcendent first cause, an ultimate necessary being, an utmost perfection, and the end of all creation. But, St. Thomas is able to reason from what he has picked up along the way to prove further points about God. So, for instance, a big yield of the five ways is the recognition that God is in no way coming to be, he just is. In fact, it is his very nature to be. So, there is none of what St. Thomas calls potency in God . . . no possibility of further realization. He is fully realized. In fact, he is pure realization, what St. Thomas calls pure act.

From that conclusion, there’s a lot that follows. God is not limited or circumscribed in the way that creatures are. By virtue of the fact that we’re human beings, it follows that we’re not Chick-fil-A Spicy Chicken Deluxe sandwiches or Kiwi birds. So, what we are is just a limited and fairly well-circumscribed expression of what it means “to be.” God transcends this limitation. He literally exhausts all that there is of being. There is nothing of is-ness that falls outside of his whole and simultaneous embrace of endless life. And so, he cannot be reduced to a Higgs boson or a Flying Spaghetti Monster . . . for to suppose such a thing is to miss the point about God.

Charming side note: I work for the Thomistic Institute. We just launched a program called Aquinas 101, which introduces the interested viewer to the thought of St. Thomas Aquinas. It’ll be super helpful to anyone who has even a little interest in these types of questions. It’s a series of short videos coming out over the course of this year that walk you through an introduction to St. Thomas Aquinas, his philosophy, and his Summa Theologiae. . . all with accompanying readings, podcasts, and further resources. It’s awesome. Enrollment is highly advisable : ) Oh yeah, it’s free too.

Pat: Funny, I was just going to bring up the Flying Spaghetti Monster. So, kudos. You got me there. Just one more objection, before we move on. Couldn’t it be the case that God just is the universe? What’s wrong with praying to the universe?

Fr. Gregory: So, here again, we have to consider these things in light of being. God just is. All creatures, by comparison, are in this, that, or the other way. And each creature’s individual expression of being is a matter of its particular, limited sharing in the being of God.

It follows that God transcends his creation. Creation is made by God, made for God, and patterned on God, but it does not add anything to God nor is it in any way necessary for God. It is but an expression of his infinite majesty. Why express his majesty? Well, because he thought we might like it and love him in turn.

Pat: These arguments seem well thought out. But here’s one final question: What does all this get you? What’s the practical significance, here? In other words, what’s to stop a person from going through this line of reasoning and concluding, “OK, God exists, so what? What does that have to do with me?”

Fr. Gregory: Basically, if God is, then that has a claim on my life. St. Thomas reasons from God’s existence to his simplicity, goodness, and beyond. He arrives fairly quickly at God’s omnipresence. Sounds fancy, but basically it means that God is present to all that is. Why? Because he is giving us being as a participation in his existence and giving us agency as a participation in his act. We literally live and move and have our being in God.

St. Augustine teaches that God is more interior to me than I am to myself. I think many people experience a lot of existential angst because their lives don’t correspond with reality. If we spend our lives as if God weren’t present to us—with the offer of friendship and the promise of communion—that can wreak havoc in the human heart. But, if through prayer, sacrament, study, mortification, and friendship we are gradually reconciled to the truth of our lives, then we can hope for a life that—though probably still filled with difficulty and sadness—is possible to live and even worth living. That has everything to do with you.