 There are good reasons to believe that these admittedly cryptic remarks directly inspired Feyerabend’s use and development of the idea of incommensurability. Although Feyerabend did not cite from Einstein (1949) in his (1962), he does cite from Bohr’s paper in that very same edited volume (Schilpp 1949). Moreover, there are striking similarities between Feyerabend and Einstein’s uses of the term. First, both make a distinction between universal theories and theories that do not apply to the totality of all physical appearances, and then use this distinction to limit the application of incommensurability in the same way; i.e., the problem of weighing incommensurable qualities in selecting and evaluating theories is explicitly only meant to apply to such universal physical theories, and not just any pair of scientific theories (cf. Feyerabend 1962a, 28 and Einstein 1949a, 23). Second, Einstein’s theoretical attitude is explicitly a form of neo-Kantianism very much like that of Feyerabend and Kuhn’s. According to Einstein, his theoretical attitude “is distinct from that of Kant only by the fact that we do not conceive of the ‘categories’ as unalterable (conditioned by the nature of the understanding) but as (in the logical sense) free conventions. They appear to be a priori only insofar as thinking without the positing of categories and of concepts in general would be as impossible as is breathing in a vacuum” (Einstein 1949b, 374). This is the same basic perspective that both Kuhn and Feyerabend delineated when they developed their ideas of incommensurability. For example, Kuhn says, “I go around explaining my own position saying I am a Kantian with moveable categories” (Kuhn 2000 [1995], 264), an idea developed in detail by Hoyningen-Huene (1993). As for Feyerabend, he set out such a ‘Kant on wheels’ approach – to use Peter Lipton’s apt expression (Lipton 2001) – at the beginning of ‘Explanation, Reduction and Empiricism’ (1962a). Feyerabend overtly adopted such a neo-Kantian metaphysical perspective with changing categories in order to pursue the question: If universal theories determine all of our experiences of the world, how can experience be used to test such theories? Third, the main example Feyerabend used to illustrate that and how incommensurable theories can indeed be compared on the basis of a ‘crucial experiment’ was Einstein’s quantitative prediction, and Perrin’s subsequent confirmation, of Brownian motion, which served as a crucial experiment between classical and statistical thermodynamics – one of only three examples of incommensurable scientific theories in Feyerabend (1962a) (cf. Oberheim 2006, 253ff.; Sirtes and Oberheim 2006). Feyerabend argued that although Brownian motion was already a well-known phenomenon, it became evidence for statistical thermodynamics and against classical thermodynamics only after the development of the kinetic theory, which was needed to interpret it as such. Even though there was a crucial experiment between these two universal theories, the theories have no common measure as the observations of Brownian motion that confirmed statistical thermodynamics were not couched in a neutral observation language. The observations only became evidence after they were interpreted according to statistical theory. Einstein discussed exactly this episode at length in his ‘Autobiographical notes’, where he used the term ‘incommensurable’ to apply to difficulties in judging the merits of universal physical theories. Fourth, later Feyerabend often defended his view that there is no fixed scientific method (e.g. 1975, 10–11) by citing Einstein: “The external conditions which are set for [the scientist] by the facts of experience do not permit him to let himself be too much restricted, in the construction of his conceptual world, by the adherence to an epistemological system. He therefore must appear to the systematic epistemologist as a type of unscrupulous opportunist” (Einstein1949b, 683ff.). Although Feyerabend’s development of the idea of incommensurability of scientific theories was received by the philosophic and scientific communities as propagating radical, irrationalist ideas about science, he was actually trying to develop something he found in Einstein. In the preface to the German version of Against Method, Feyerabend wrote, “I want to emphasize yet again that the views in this book are not new – for physicist like Mach, Boltzmann, Einstein and Bohr they were a triviality. But the ideas of these great thinkers have been distorted [by positivist philosophers] beyond recognition” (1983, 12, our translation).