A major purpose for the philosophy of science is to explain, and hence to justify, what science is and why its theories should be accepted as true. Another aim of philosophy of science was to prescribe what "good" science is. Contemporary philosophy of science, however, has largely abandoned this prescriptive task and has instead concentrated on a descriptive mode of operation. This role is not an unimportant one. In an age of skepticism about science and acceptance of mystical and occult sources of knowledge it is important that the basis of scientific truth be fully understood. Dr. Oberdan is examining one of the founders of modern philosophy of science, Moritz Schlick, the leader of the Vienna Circle of Logical Positivists. Dr. Oberdan aims to provide a biographical as well as intellectual background to Schlick's work. Under this grant, he is examining Schlick's early life and career, especially the development of his philosophical views of relativity theory and the initial stage of his Positivist thought. The importance of this study is directly related to two central issues in the philosophy of science: the nature of causality and the positivism- realism dispute. Given the rise of quantum theory with its probabilistic foundations, uncertainty principle, and wave/particle duality, the questions of causality and the "real" existence of theoretical entities have become even more contentious in contemporary physics. The positions that Schlick offered are important for our understanding of how philosophy and science have addressed these questions. Dr. Oberdan's study promises to make significant contributions to our understanding of the foundations of these debates.