Why do we need to bring in an uncaused cause to explain the existence of things? Why could there not simply be an infinite series of things mutually keeping one another in existence, thus, eliminating the idea of a first cause?

“My existence is caused by my parents.” In the Quinquae Viae, St. Thomas Aquinas offers us the second way from the nature of efficient cause. This way claims that any thing in existence is caused by something. And, Aquinas further suggests that this something is God. He is the first and primary cause.

In the question posted above, the uncaused cause here pertains to God, of course. So, we can rephrase the question in simpler terms. Why do we need to bring the idea of God to explain the existence of things? Aquinas, himself, answered this question in The Five Ways, and I agree with him. “There is no case known (neither is it, indeed possible) in which a thing is found to be the efficient cause of itself. Nothing is responsible for its own existence. Something has brought something into existence, into what it is.” Now, let us make sense on all of these. Say, an object caused its own existence; then, that is tantamount to saying that the object existed before itself. How bizarre! In the concept of logic, this idea is definitely nonsense. Before I even existed, I'm already existing. How is that possible? Before any thing can exist, something must cause that thing to exist. This idea is similar to Aquinas' and Newton's idea of motion. In the absence of force, an object at rest will remain at rest, and an object in motion will remain in motion. But, when force is present, a thing at rest may come into motion, and a thing in motion may come at rest. In this concept, force is the cause why things are in motion or at rest. Thus, it is absolutely beyond possibility that an object will simply exist without a cause.

Now, we can apply the same idea in answering the concept that an infinite series of things mutually keeps one another in existence. We are faced here with the idea of infinity. However, how can this infinite series of things lead to its infinity without existing first? Thus, we go back to the argument that something must have caused this infinite series of things to come into existence before it can infinitely exist by mutually keeping one another. We are then led to the idea of a first cause.

Let me end this discussion with an illustration. In a game of bowling, when the bowling ball is thrown by a person, the ball rolls and eventually hits the ten pins, causing a series of movements. The bowling ball rolled because it was thrown by the person. It then hits the pins because it rolled. The pins topple because they were hit by the bowling ball. In these series of movements, the force exerted by the person is the primary cause. The other movements would not have happened without the first cause. In other words, there would be no intermediate cause if there is no first cause.