It was the greatness and glory of Plato to have seen this, and thereby to have become the founder of all true philosophy. For to say that the Absolute is concepts is the same as saying it is reason. It might seem, then, that Plato has satisfied the second canon of criticism. He takes as first principle a self-explanatory reality. But we cannot quite so quickly jump to this conclusion. After all, the mere word reason is not a key which will unlock to us the doors of the universe. Something more is necessary than the mere word. We must, in fact, be told what reason is. Now there are two senses in which we might ask the question, what reason is, one of which is legitimate, the other illegitimate. It is illegitimate to ask what reason is, in the sense of asking that it shall be explained to us in terms of something else, which is not reason. This would be {242} to give up our belief that reason is its own reason. It would be to seek the reason of reason in something which is not reason. It would be to admit that reason, in itself, is not rational. And this is absurd. But it is legitimate to ask, what reason is, meaning thereby, what is the _content_ of reason. The content of reason, we have seen, is concepts. But what concepts? How are we to know whether any particular concept is part of the system of reason or not? Only, it is evident, by ascertaining whether it is a rational concept. If a concept is wholly rational, then it is a part of reason. If not, not. What we need, then, is a detailed account of all the concepts which reason contains, and a proof that each of these concepts is really rational. It is obvious that only in this way can we make a satisfactory beginning in philosophy. Before we can show that reason explains, that is, rationalizes the world, we must surely first show that reason itself is rational, or rather, to be more accurate, that _our conception_ of reason is rational. There must not be any mere inexplicable facts, any mysteries, any dark places, in our notion of reason. It must be penetrated through and through by the light of reason. It must be absolutely transparent, crystalline. How can we hope to explain the world, if our very first principle itself contains irrationalities?