Since the days of Locke modern philosophy has been almost entirely dominated by the assumption that one must study the process of knowing before one can find out the nature of things known; in other words, that psychology is _the_ central philosophic science. The result of this has been an almost complete identification of philosophy with mental science. Nor did the influence of biologic studies of the middle of the nineteenth century shake the belief in that banal dictum of philosophic mediocrity: “The proper study of mankind is man.” The recent renaissance of logical studies, and the remarkable progress of physics in our own day bid fair to remind us that while the Lockian way has brought some gains to philosophy, the more ancient way of philosophy is by no means exhausted of promise. Man cannot lose his interest in the great cosmic play. Those who have faith in the ancient and fruitful approach to philosophy through the doors of mathematics and physics will find the writings of Charles S. Peirce full of suggestions. That such an approach can also throw light on the vexed problem of knowledge needs no assurance to those acquainted with Plato and Aristotle. But I may conclude by referring to Peirce’s doctrine of ideal as opposed to sensible experiment,[23] and to his treatment of the question how it is that in spite of an infinity of possible hypotheses, mankind has managed to make so many successful inductions.[24] And for the bearing of mathematical studies on the wisdom of life, the following is certainly worth serious reflection: “All human affairs rest upon probabilities. If man were immortal [on earth] he could be perfectly sure of seeing the day when everything in which he had trusted should betray his trust. He would break down, at last, as every great fortune, as every dynasty, as every civilization does. In place of this we have death.” The recognition that the death of the individual does not destroy the logical meaning of his utterances, that this meaning involves the ideal of an unlimited community, carries us into the heart of pure religion. Footnote 1: See Plantamour’s “_Recherches Experimentales sur le mouvement simultané d’un pendule et de ses supports_,” Geneva, 1878, pp. 3-4. Footnote 2: P. 190. Footnote 3: Pp. 162-163. Footnote 4: Pp. 249 ff. Footnote 5: James, _Pluralistic Universe_, pp. 398-400. Footnote 6: Royce, _Studies in Good and Evil_, and _The Problem of Christianity_, esp. Vol. 2. Baldwin (_Mental Development_) is heavily indebted to Royce in this respect. Footnote 7: