What does cognitive science have to tell us about the role of evidence and argumentation in science? Over the past twenty or more years, cognitive science has been analyzing belief and persuasion. Dr. Margolis has taken what he has learned in cognitive science and applied it to an analysis of belief change -- i.e. "scientific revolutions" -- in science. He is specifically applying his understanding of cognitive science to the paradigm case of change in belief in science: the Scientific Revolution of the sixteenth and seventeenth centuries. Such analyses of these well-studied areas promise to have important and provocative implications for history and philosophy of science as well as for cognitive science. Under this grant, Dr. Margolis will examine three different aspects of the Scientific Revolution: 1) how persuasive was the status of the Copernican argument as it stood in 1633; 2) why astronomers were unlikely to accept the authority of non- astronomers on cosmology; and 3) how other kinds of evidence such as the discovery of America affected arguments for Copernicanism. These points go directly to the level of evidence needed for scientists to become persuaded of the accuracy of a new theory. According to Dr. Margolis, this level of evidence is much less than we have earlier supposed. If his research bears out his theory, our understanding of the processes of persuasion, using both qualitative and quantitative evidence, and theory change in science should be greatly improved.