Aquinas' Ways to God

Can we demonstrate with our reason that God exists? Saint Thomas Aquinas, following in the footsteps of Plato and Aristotle, thought so. In his Summa Theologica he gives five ways, five logical demonstrations, for believing that God exists. I'm going to look at three of those ways here, beginning first (and going into a little more detail) with the argument from efficient causality.

In the material world we see that everything that exists has a cause. A rock, a tree, a person - these things do not exist on their own; rather, something, in fact a great number of things, caused them to be. But if everything in the material universe requires a cause, how could anything in the material universe exist? For the material universe to exist, there has to be something that does not require a cause, something that is powerful enough to cause (directly or indirectly) all the things in the material universe to come into existence. The only appropriate name for this powerful Uncaused Cause, Aquinas argues, would be God.

It can be tempting to see this argument as a linear string of causes and effects stretching far back into time, almost like a massive set-up of dominoes, with God as the first cause knocking the first domino over and getting the whole thing started. But that's oversimplifying the argument a bit. Skeptics argue that a linear string of causes and effects could stretch back infinitely, and St. Thomas agreed with them. His argument from efficient causality doesn't actually depend on time at all. Think about it: your existence is dependent on, is being caused by, many factors at this particular moment. Sunlight, oxygen, gravity, and many other things are working together to cause your existence right now. And other things are causing sunlight and oxygen and gravity to exist right now. The whole universe is comprised of a vast myriad of causes and effects at every given moment. None of these could exist right now without the Uncaused Cause. Nothing in the universe is sufficient to exist right now on its own.

Two of Aquinas' other ways to God are variations on, and reinforcements of, the argument from efficient causality. The argument from motion - and by motion Aquinas means change - says that material objects cannot change on their own. An acorn cannot become an oak tree on its own, and an infant cannot become an adult on its own. This necessitates an Unmoved Mover who does not change but can activate change in others. We call this Unmoved Mover God.

The argument from contingency states that material things are dependent and perishable. It is not necessary for any individual material thing to exist. But if all material things are contingent, if they need not exist, how can any of them exist? There must be a Necessary Being who cannot not exist and who is capable of giving being to all other material beings. This Necessary Being said His name is I AM (Exodus 3:14); we call Him God.

Aquinas did not consider his ways to God to be proofs strictly speaking; as Scripture tells us, "we walk by faith and not by sight" (2 Corinthians 5:7). However, Aquinas' ways show us that it is reasonable to believe in God; indeed, it is much more unreasonable to believe there is no God.

Pray the Divine Mercy Chaplet every day for the salvation of souls.