 Paul Feyerabend first used the term incommensurable in 1962 in “Explanation, Reduction and Empiricism” to describe the lack of logical relations between the concepts of fundamental theories in his critique of logical empiricists models of explanation and reduction. He argued that in the course of scientific advance, when fundamental theories change, meanings change, which can result in a new conception of the nature of reality. By calling two fundamental theories incommensurable, Feyerabend meant that they were conceptually incompatible: The main concepts of one could neither be defined on the basis of the primitive descriptive terms of the other, nor related to them via a correct empirical statement (Feyerabend 1962, 74, 90). For example, Feyerabend claimed that the concepts of temperature and entropy in kinetic theory are incommensurable with those of phenomenological thermodynamics (1962, 78); whereas the Newtonian concepts of mass, length and time are incommensurable with those of relativistic mechanics (1962, 80). Feyerabend repeatedly used the idea of incommensurability to challenge a wide range of forms of conceptual conservativism, arguing that they unjustifiably favor successful, entrenched concepts over potential improvements, and overlook the possibility of developing incommensurable alternatives (Oberheim 2005, 2006).