Fixed Ideas and Mutable Rules
The product of one's labor depends on what one starts with. Ideas concerning the world, for instance, are influenced by observation. Observations are regarded as true; they become the premise from which people derive conclusions regarding the nature of things. It is emphasized that this process relies on the validity of the initial assumption (i.e., the premise). A proof that concludes with a confirmation of the premise could only be valid if the original assumption is true and the logic faultless. This proof, however, relies on the start as accurate; it does not really prove it so.
According to Copleston in his Commentary, St. Aquinas' five arguments for the existence of a god are meant to be causal, "proceeding from the affirmation of some empirical fact...to the affirmation of a transcendent cause". The whole enterprise rides on the assumption that there is a primary cause from which everything else is engendered. These arguments are, afterall, metaphysical. Conviction in an ultimate cause fails to prove its existence though.
...a full understanding of the empirical facts which are selected
for the consideration in the five ways involves seeing the
dependence of these facts on a transcendent cause.
The word 'selected' is underscored to stress Aquinas' choice of facts. If people are allowed to choose which facts are examined to prove a premise and which are to be ignored, they can prove anything. Noting the motion of the sun as an isolated fact, it is not difficult to conclude the sun revolves around the earth. While avoiding "sweeping generalizations", he equally leaves the possibility of there not being a god. If there is a god, an ultimate cause/mover of all things, then it is unnecessary for Aquinas to be so restrained. Everything would be "moved" (save the god). Why does he not say so?
The fourth argument is an example of circular logic. Seeing the gradation of qualities in things, Aquinas declares there must be something which is the quintessence of these qualities. Things are judged "...as they resemble...something which is the maximum...". Since the maximum is the "cause of all [that possess the given quality]", there "must also be something which is to all beings the cause of their being, goodness, and every other perfection; and this we call God." Using the assumed necessity of an absolute, he "proves" the existence of an absolute. Actually, such a confirmation leaves the question begging.
Aquinas' belief in perfection can be examined in another light. Consider what it means for something to be perfect. The perfect fruit is faultless in terms of its final function, but is this function to be eaten, to form another fruit bearing plant, to give philosophers something to write about, or something else? A cherry with a sound pit is perfect for the genesis of another cherry tree, but it is not perfect for eating. Also, the status of excellence is retained only so long as this fruit is judged by the set of values that deems it complete in the first place. Which value system should be used? When Aquinas states in the fifth argument that material things designedly "achieve their end", he is not saying the world acts out of convenience for humans. He implies there is an order and design in the world to which humans are subordinate. Hence, it seems unlikely that the esteem people place on certain things has any bearing on how the world is governed; on a universal scale, human values are unimportant. Which value system should be used, then, if not human? Aquinas' arguments do not produce convincing evidence of a god. How can people adopt the values of a being which is not shown to exist?
Attempts to defend Aquinas on the grounds of changes in meaning of words fall short. His replies to the objections of a god's existence are refutations; they present evidence and argument running counter to the arguments and the evidence the objections present. Copleston state Aquinas' proofs are not proofs as understood by modern folk.
Aquinas was not confusing causal relations...with logical
entailments: he was asserting a unique relation between
finite things and the...transcendent cause on which they depend.
These assertions, these "illustrations to elucidate a point", depend on a person's already accepting the existence of a god whose being Aquinas tries to clarify. They cannot persuade anyone who raises the objections in disbelief; they cannot make more lucid what has to be clear for the illustrations to be accepted anyway. Disputing what this process should be called becomes moot.
Even if the five arguments are "introductory material for a 'novice' in...theology" and not "to satisfy the critical minds of mature philosophers", they should not pose as proofs (regardless of the word's definition) when they are not. The major difficulty in these attempts to show God's existence is that they are metaphysical. Metaphysics deals with finding the ultimate causes and the underlying nature of things, but this attempt assumes there is an ultimate cause and underlying nature to be found. The evidence is a rationalization of what Aquinas already believes. It fails to demonstrate that his belief is true.