This book traces the development during the 20th century of four central themes in the philosophy of science: inductivism, conventionalism, the nature of observation, and the demarcation between science and metaphysics. The movement of ideas is placed against the background of the lives of the philosophers and of contemporary developments in science. The four themes have been chosen because of their central importance, and are expounded in such a way which does not presuppose any previous knowledge of philosophy or science. The book thus constitutes an excellent introduction to the philosophy of science.--