There are many possible ways of approach to philosophy, and there is also an impossible one, though one that has often been tried. That the philosopher can somehow spin his philosophy out of what he finds inside himself; that he has some private internal source of information in virtue of which he can decide what the Universe must be, without needing to take the trouble to look at it, is a belief that dies hard. But it is now dying, if not dead, so that it is hardly necessary to refute it in detail. It should suffice to say that anybody who cherishes the belief will not find anything to interest him in what follows. I shall simply assume that the philosopher is, what we all are to some extent, a spectator of the world and of man's life in it and a commentator on what he sees. Where the philosopher differs from others is in the kind of interest he takes in the facts, not in the kind of facts that are there to be interested in.