Aquinas did not, of course, deny that people can come to know that God exists by other ways than by philosophic reflection. Nor did he ever assert that the belief of most people who accept the proposition that God exists is the result of their having elaborated metaphysical arguments for themselves or of their having thought through the metaphysical arguments developed by others. Nor did he confuse a purely intellectual assent to the conclusion of such a metaphysical argument with a living Christian faith in, and love of, God. But, he did think that reflection on quite familiar features of the world affords ample evidence of God’s existence. The reflection itself, sustained and developed at the metaphysical level, is difficult, and he explicitly recognized and acknowledged its difficulty: he certainly did not consider that everyone is capable of sustained metaphysical reflection. At the same time, the empirical facts on which this reflection is based were, for him, quite familiar facts. In order to see the relation of finite things to the being on which they depend, we are not required to pursue scientific research, discovering hitherto unknown empirical facts. Nor does the metaphysician discover God in a manner analogous to the explorer who suddenly comes upon a hitherto unknown island or flower. It is attention and reflection which are required, rather than research or exploration.
What, then, are the familiar facts which, for Aquinas, imply the existence of God? Mention of them can be found in the famous “five ways” of proving God’s existence, which are outlined in the Summa theologica (1a, 2, 3). In the first way, Aquinas begins by saying that “it is certain, and it is clear from sense-experience, that some things in this world are moved.” It must be remembered that he, like Aristotle, understands the term “motion” in the broad sense of change, reduction from a state of potentiality to one of act; he does not refer exclusively to local motion. In the second way, he starts with the remark that “we find, in material things, an order of efficient causes.” In other words, in our experience of things and of their relations to one another, we are aware of efficient causality. Thus, while, in the first way, he begins with the fact that some things are in motion or in a state of change, the second way is based upon the fact that some things act upon other things, as efficient causes. In the third way, he starts by stating that “we find, among things, some which are capable of existing or not existing, since we find that some things come into being and pass away.” In other words, we perceive that some things are corruptible or perishable. In the fourth proof, he observes that “we find, in things, that some are more or less good and true and noble and so on (than others).” Finally, in the fifth way, he says, “we see that some things which lack knowledge, namely, natural bodies, act for an end, which is clear from the fact that they always or, in most cases, act in the same way in order to attain what is best.”
From: Aquinas by F. C. Copleston (Harmondsworth: Penguin Books, 1955), pp. 114-115.
Frederick Charles Copleston (1907-1994) was a British Roman Catholic (Jesuit) philosopher. He is best known for his 9-volume History of Philosophy (1946-1975).
