Aquinas's Five Arguments for God's Existence
Aquinas thought that reflection on familiar features of the physical world affords evidence of God's existence. So he attempted five proofs to demonstrate the existence of God. Recall that Anselm had begun his ontological proof with the idea of a “greatest conceivable being,” from which he inferred the existence of that being. By contrast, Aquinas said that all knowledge must begin with the experience of sense objects.
Before addressing Aquinas's five arguments for the existence of God, one thing is worth noting. The question of God's existence is a metaphysical and epistemological concern, since it raises the question of what kind of reality God is and if you can know — and how you can know — whether that reality exists.
Like Aristotle, Aquinas was an empiricist, claiming that knowledge comes from experience. By contrast, Anselm was a rationalist. For Aquinas, sense experience tells you that this universe is a system of causes and effects and lawlike behavior. This world system, this cosmos, requires a
Aquinas rejected Anselm's ontological argument. “Even if it be granted that everyone understands this name ‘God' to signify what is said, viz., ‘that which a greater cannot be thought,' it does not follow that what is signified by the name exists in the nature of things, but only that it exists in the apprehension of the understanding” (
In the first way, Aquinas writes that “it is certain, and it is clear from sense-experience, that some things in this world are moved.” Aquinas, like Aristotle, understood the term
From the first argument one can observe a feature that appears in all five. Aquinas ends each of the arguments with the conclusion that God is the cause of some reality, since without God the reality would not be explainable.
Aquinas had a fresh understanding of the problem of evil. He said evil denotes the “absence of good” but it is not every absence of good that is called “evil.” For instance, evil in the negative sense — as when a man cannot run like a cougar — is not evil. Rather, it is absence of good in the privative sense that is called evil, as with privation of sight, which is called blindness.
“The second way is from the nature of efficient cause,” Aquinas begins. “There is no case known (neither is it, indeed, possible) in which a thing is found to be the efficient cause of itself; for so it would be prior to itself, which is impossible.” Imagine that you look outside your window and see a tree branch moving. That branch is being moved by the wind. That wind has its causes, and so on. But as with motions, you cannot go on to infinity in a series of causes. If there is no first cause, there will no be intermediate causes, like the wind and the swaying tree branches. “Therefore it is necessary to admit a first efficient cause, to which everyone else gives the name of God,” Aquinas concludes.
These first two arguments are cosmological, since they show features of the world order, like motions and causes, and claim that these realities require an explanation from a divine reality outside the world order.
Aquinas's fifth way, or argument, is a teleological argument for God's existence. It is sometimes referred to as his “design argument,” and it is his most renowned one. Stated in its entirety, it reads:
Here Aquinas, an empiricist, shows his “teleological” understanding of nature (the word
If you came into a classroom where the chairs were all in neat rows, would you assume that their “order” came about accidentally or designedly? If you conclude that some “intelligent designer” — like a custodian or teacher — must have ordered the rows neatly, then you are thinking right along with Thomas Aquinas.
Aquinas designed the five proofs not to satisfy the critical minds of mature philosophers, but as introductory material for “novices” in the study of theology. Still, one finds in his
The proofs remind one of Aquinas's position on faith and reason. The realm of human knowledge can be divided into two areas:
Truths known to us in revelation and known by faith
Truths revealed in nature and known by reasoning from experience
His proofs of God's existence fit this last category. In so doing, he shows his allegiance to the empiricism of Aristotle. In