THE TRADITIONAL APPROACH
WE now pass on to consider what can be learnt as to the existence of God by the exercise of the human reason. As we have already seen, even in the discussion of religious experience and of revelation the rational element cannot be altogether excluded. But it was there involved in a different way from that with which we are now concerned. There it came in simply in order to decide whether the claims which were made for religious experience and for revelation were justified; here, in contrast, it is itself the instrument by the use of which the problem of God's existence is to be investigated.
St. Thomas Aquinas divides his discussion of the existence of God in the Summa Theologica1 into three articles: Whether the existence of God is self-evident? Whether it is demonstrable? And, lastly, whether in fact God exists? And he discusses the same three points in greater detail in chapters x to xiii of the First Book of the Summa contra Gentiles.
Under the first heading he first of all explains what is meant by self-evidence. "Those things," he tells us, "are said to be self- evident which are known as soon as the terms are known,"2 and he gives as an example the truth that the whole is greater than the part, which, he says, is known immediately as soon as it is known what is meant by whole and part. This would seem at first sight to exclude any possibility of argument whatsoever. If the existence of God was self-evident in this sense, we should only have to make certain that we understood what was meant by the definition of God in order to see immediately that he existed. And, indeed, M. Gilson has suggested that St. Thomas's great Franciscan contemporary, St. Bonaventure, actually held this position. "For St. Anselm," he writes, "the definition of God implied a content which our thought had to unfold in order to get at the conclusion involved in it," but "for St. Bonaventure, the same definition becomes an immediate evidence, because it participates in the____________________