 The notion of incommensurability applies to (inter alia) a comparison of theories operative during different periods of normal science. Kuhn held that if two theories are incommensurable, they are not comparable in a way that would permit the judgment that one is epistemically superior to the other, because different periods of normal science are characterized by different “paradigms” (commitments to symbolic representations of the phenomena, metaphysical beliefs, values, and problem solving techniques). As a consequence, scientists in different periods of normal science generally employ different methods and standards, experience the world differently via “theory laden” perceptions, and most importantly for Kuhn (1983), differ with respect to the very meanings of their terms. This is a version of meaning holism or contextualism, according to which the meaning of a term or concept is exhausted by its connections to others within a paradigm. A change in any part of this network entails a change in meanings throughout—the term “mass”, for instance, has different meanings in the contexts of classical physics and relativistic physics. Thus, any judgment to the effect that the latter’s characterization of mass is closer to the truth, or even that the relevant theories describe the same property, is importantly confused: it equivocates between two different concepts which can only be understood in an appropriately historicized manner, from the perspectives of the paradigms in which they occur.