From later antiquity down to the close of the eighteenth century, most philosophers and men of science and, indeed, most educated men, accepted without question a traditional view of the plan and structure of the world. In this volume, which embodies the William James lectures for 1933, Arthur O. Lovejoy points out the three principles--plenitude, continuity, and graduation--which were combined in this conception; analyzes their origins in the philosophies of Plato, Aristotle, and the Neoplatonists; traces the most important of their diverse samifications in subsequent religious thought, in metaphysics, in ethics and aesthetics, and in astronomical and biological theories; and copiously illustrates the influence of the conception as a whole, and of the ideas out of which it was compounded, upon the imagination and feelings as expressed in literature.