| I asked him, “If paradigms are really incommensurable, how is history of science possible? Wouldn’t we be merely interpreting the past in the light of the present? Wouldn’t the past be inaccessible to us? Wouldn’t it be ‘incommensurable?’ ” If two theories are incommensurable, it means they lack equivalence in terms. Mass in one theory will not mean mass in another theory. If they meant the same thing, you might be able to derive one theory from another. Instead, you have to interpret or translate between terms. Add to this the idea that for a particular time, a particular world view will shape the way we understand and perceive things. For scientists, these world views will be scientific theories. Kuhn's big idea was that because theories were incommensurate, theory change could not be rational. That is to say, scientists did not pick up this theory, then that one, and make an objective judgment. Instead, scientists grew up within the context of one theory, which provided a domain of scientific exploration, or paradigm, bounded by its assumptions. Regular science involves poking around in the concepts provided by the paradigm. Revolutionary science breaks the paradigm and offers something else. But when a new paradigm appears on the scene, the old guard have no access to it and its new concepts. New scientific theories rarely convince the old guard. Instead, the young pick it up as their paradigm, and start working from there. But surely the experiments will prove one or the other is true, right? Not according to Kuhn. The problem is that each world view assumes different things to exist, along with different forces, different mathematics, and so on. Furthermore, you can't do experiments except from within a particular paradigm. Finally, even if you could judge one theory superior on one point over another, who is to say that the losing theory would not be superior in the long run? In other words, how resilient should we be in the face of contrary evidence, when every theory faces contrary evidence? There is no hard and fast rule. That gives you a rough outline of Kuhn's philosophy of science. If you are interested in the philosophy of science, try the nice introductory reader Philosophy of Science: The Central Issues, Curd & Cover eds. W.W. Norton & Company, New York. From this book, I'll make a few quotations from Laudan's "Dissecting the Holistic Picture." Laudan attacks the idea of the paradigm as a holistic unit of scientific understanding, with a take-it-or-leave-it hard core that cannot be revised without "rejecting the entire world view." | ...we solve the problem of consensus [of the scientific community] once we realize that the various components of a world view are individually negotiable and individually replaceable in a piecemeal fashion. (144) He goes on to prove that it is conceivable, but then asks why theory change often appears so abrupt. | ...only because our characterizations of such historical revolutions make us compress or telescope a number of gradual changes... in to what, at our distance in time, can easily appear as an abrupt and monumental shift. (146) Laudan proposes a gradualist understanding of theory change, concluding that | sociologists and philosophers of science who predicate their theories of scientific change and cognition on the presumed ubiquity of irresolvable standoffs between monolithic world views (of the sort that Kuhn describes in The Structure of Scientific Revolutions) run the clear risk of failing to recognize the complex ways in which rival theories typically share important background assumptions in common. (155) These shared background assumptions would act as | enough common ground between rivals to engender hope of finding an "Archimedian standpoint" which can rationally mediate the choice. That, my friends, is a critique of Kuhn. But you'd have to do some reading to decide whether it works. Philosophy of Science: The Central Issues, Curd & Cover eds. W.W. Norton & Company, New York.