 With respect to the range of theories that are subject to incommensurability, Feyerabend’s concept is again much more restricted than Kuhn’s. For Feyerabend, only universal, fundamental, non-instantial theories that are interpreted realistically can be incommensurable (Feyerabend 1962, 44; 1965b, 216; 1975, 114, 271, 284; 1975, 221–222; 1987, 272). Feyerabend was interested in fundamental, universal theories that apply to everything, because he believed that only “such comprehensive structures of thought” have ontological implications that are capable of sustaining entire worldviews (Feyerabend 1962, 28; cf. Feyerabend 1954 and Oberheim 2006, 157ff.). He restricted incommensurability to non-instantial theories, which he distinguished from empirical generalizations, on the basis of the differences in their test procedures. Generalizations of the form ‘All As are Bs’ (regardless of whether the As or Bs are observable) are tested by inspecting instances. So for example, Kepler’s first law makes claims about the planets, which can be tested directly by inspecting their motion. In order to test non-instantial theories, such as Newton’s theory of gravitation, first empirical generalizations must be derived from them with the help of auxiliary hypothesis, and only thereafter can they be tested by inspection (Feyerabend 1962, 28). Due to these restrictions (only universal, fundamental, non-instantial theories), for Feyerabend, incommensurability of scientific theories occurs comparatively rarely (1987, 272). Kuhn included a wider range of theories as candidates for incommensurability. For him, even smaller episodes, like unexpected discoveries, might be incommensurable with the earlier tradition (cf. Hoyningen-Huene 1993, 197-201). This difference in the range of incommensurability between Kuhn and Feyerabend’s versions finds its most striking expression in the way they regard the transition from the Ptolemaic to the Copernican theory. For Kuhn, the differences between these two theories comprise an exemplary illustration of incommensurability. For Feyerabend, however, because planetary theory lacks the quality of universality, there is no incommensurability (1975, 114). Furthermore, in his later writings Kuhn insisted that the version of incommensurability he championed had always been “local incommensurability,” a notion that restricts conceptual change to a few, typically interconnected concepts (cf. Hoyningen-Huene 1993, 213, 219). Thus, there may be empirical consequences of incommensurable theory pairs that can be immediately compared. For instance, the geocentric and heliocentric planetary theories are incommensurable in Kuhn’s sense, while predictions of the planetary positions of both theories are fully commensurable, and can be immediately compared regarding their empirical accuracy. By contrast, Feyerabend always thought of his concept more globally, as affecting all statements derivable from two fundamental theories (1962, 93; 1965c, 117; 1965b, 216; 1975, 275–276; 1981a, xi). 