Max Planck, the physicist who originated the quantum theory, turns in this volume to a definition of the philosophy of physics, analyzing the task of that science and scrutinizing its achievements in the light of its goals. He deals most exhaustively with a basic problem common to both physics and philosophy, the problem of causality in nature--not because he hopes to solve it at last, but because he feels he cannot avoid it: "Placed at birth in the middle of life, and in order to find our way through this live which is ours whether we want it or not, we try to introduce order into our experience." He discusses the characteristics of a "scientific" idea, its origin and effect, and in closing makes some extremely shrewd remarks on the familiar subject of science versus faith.