A top flight philosopher's historical study, posthumously published, of the problems of knowledge in the fields of contemporary (1932-1932) mathematics, theoretical physics, biology and history. This is the fourth and final volume, and deals with the ""methods"" in each of the disciplines and the conception of the knowledge sought for in each. Describing ideas and trends of thought in their origins and in historical order, the author also explains the general purport of ideas and their significance as systems. Part I deals with the exact sciences; Part II is concerned with the never science of biology; Part III, with the discipline of history. A learned, scholarly inspection of the principles of the separate sciences and an attempt to explain how they handle primary principles.