Many of the problems of philosophy are of such broad relevance to human concerns, and so complex in their ramifications, that they are, in one form or another, perennially present. Though in the course of time, they yield in part to philosophical inquiry, they may need to be rethought by each age in the light of its broader scientific knowledge and deepened ethical and religious experience. Better solutions are found by more refined and rigorous methods. Thus, one who approaches the study of philosophy in the hope of understanding the best of what it affords will look both for fundamental issues and contemporary achievements. Written by a group of distinguished philosophers, the Foundations of Philosophy Series aims to exhibit some of the main problems in the various fields of philosophy as they stand at the present stage of philosophical history.