Discussion Starter - Summa Theologiae, Aquinas

In the Summa of Theology, Aquinas sets out to answer the question “Does God Exist?” He begins by stating two objections. The first is that if God, meaning something infinitely good, did exist, then it would have obliterated all evil in the world. Since evil is observable in the world, then God must not exist. The second is that since all natural things can be explained by natural causes, then everything else must be an invention of man (Q2, page 30). 

“On the contrary,” Aquinas tells us, “God says in the Scripture, ‘I am who am.’”

Aquinas says he can prove the existence of God in five ways:
1. Motion
Aquinas tells us that the act of movement is a process that converts potentiality (the potential to be in some state) to actuality (actually being in that state). The only agents who can affect this transformation are those who are already in motion, but “everything that moves must be moved by something else … and that by something else again” until we week a so-called “first mover,” the source of all motion, “and this everyone understands as God” (31). 

2. The nature of an efficient cause
In a similar vein as his argument about motion, Aquinas says that if we trace back all cause and effect relationships, we must find that there is a first efficient cause that preceded all other causes because nothing is capable of causing itself (“because it would precede itself—which is impossible”). Therefore, the first cause is that “which all men call God” (31). 

3. Possibility and necessity
Aquinas says that God is a necessary being, because without God nothing else would exist. The reason is that certain things can come into existence and then cease to exist (by being corrupted). If something can be corrupted, then at some point it must not have existed. Therefore, “if it is possible for everything not to exist, at one time nothing was in existence,” which is impossible for the same reasons outlined above—there has to be a first cause and first mover. This is why God exists as a necessary being, one that “does not owe its existence to anything else” (31). 

4. Gradations
Since we can evaluate things with relative terms such as “more” or “less,” there must be something that is the most and the best of [any quality] that we are trying to evaluate. For hotness, fire is the hottest and the cause of all hot things. For being and goodness and perfection, there is God. 

5. Order in the universe
There are things in the universe that lack consciousness. However, even lacking consciousness, they function purposefully and consistently. Therefore, they must have been designed and directed to reach whatever function they serve. Thus the being who intelligently designed and directed all things is God. 

Aquinas ends his argument by replying to the two objections stated at the beginning to this section. About evil, he cites Augustine who said that God “permits evils to exist so that he can bring good from them” (32). About natural causes, Aquinas says that they too find their source in God’s design. The same goes for the inventions of man, because the reason and will of man can be changed and can cease to exist, unlike those of God.