Relativism emerged as a significant issue in the philosophy of science as a result of the historical turn that took place in the field in the 1960s. Influenced by historical studies of science, philosophers came to see the process of scientific theory change as crucial to the understanding of science itself. Rather than focus on static relations between theory and evidence, proponents of the historical turn emphasized the profound transformations which accompany theory change. The transformations are not restricted to mere change in what theories say about the world. They extend to the method and practice of science, alter the conceptual and semantic apparatus of theories, and affect the content of scientists' perceptual experience. But in the absence of fixed elements capable of playing a neutral role in the context of theory change, it is unclear how choice between competing theories may be made on an objective basis. Because of this a relativistic account of scientific theory choice may seem to be the inevitable consequence of the historical turn in the philosophy of science. Among the most influential advocates of the historical approach to the philosophy of science were Paul Feyerabend and Thomas Kuhn, both of whom emphasized the far-reaching implications of scientific theory change. In separate publications originally published in 1962, Feyerabend and Kuhn independently proposed the thesis that successive or competing theories may be