According to Plato, it is the aim of Philosophy to furnish us with a certain vision of all time and all existence. This must always have seemed a large and difficult undertaking; but the opening years of the present century have already introduced considerable changes in our estimation of magnitudes. We are learning to think of modes of existence that are much more minute and of others that are much larger than any that had previously been conceived with any definiteness. Analysis now leads us to entities and processes that are almost inconceivably small; and synthesis points to a totality that is almost inconceivably great, and that may be even greater than we know. Our interests naturally begin with our human lives on earth ; and we are rapidly discovering that even these have to be thought of in ways that were hardly possible for any previous generation. In a sense, it may be said that our human world has been becoming much smaller. Distances within it are beginning to seem, in many respects, almost negligible ; and great hopes may be based upon this contraction.