In recent times it has become fashionable to emphasize the role of conceptual change in the history of science. To judge from recent writers, every significant theoretical change in science is first and foremost a revolution in scientific concepts—a conceptual revolution. According to this view, every level of experience is affected by each fundamental theoretical change: physical theory, experimental practice and even perceptual experience. The Aristotelian patrician who watched the sun sink beneath the horizon not only had different beliefs about (...) the phenomenon but actually saw something different from the Newtonian gentleman who saw the horizon rise above his eye-sun line, and the Einsteinian professional who saw the sun's varying geometrical relations to the world light-geodesics on which successive temporal stages of his eye world-line lay. Moreover, such is the completeness of the conceptual-experiential shifts undergone in a fundamental scientific change that it is impossible to meaningfully discuss the one theory within the confines of the other or, indeed, to provide any systematic, cumulative comparison of successive theories. (shrink)