 Kuhn compared the function of such lexical taxonomies to Kant’s a priori when taken in a relativized sense. Each lexicon makes a corresponding form of life possible within which the truth or falsity of propositions may be both claimed and rationally justified. For example, with the Aristotelian lexicon, one can speak of the truth or falsity of Aristotelian assertions, but these truth values have no bearing on the truth of apparently similar assertions made with the Newtonian lexicon (Kuhn 2000 [1993], 244). A lexicon is thus constitutive of the objects of knowledge (Kuhn 2000 [1993], 245); and consequently, Kuhn rejected characterizations of scientific progress according to which science zeros in on the truth: “no shared metric is available to compare our assertions … and thus to provide a basis for a claim that our (or, for that matter, his) are closer to the truth” (2000 [1993], 244). Instead, the logical status of a lexical structure, like that of word-meanings in general, is that of convention, and the justification of a lexicon or of lexical change can only be pragmatic (2000 [1993], 244). Kuhn thus reaffirmed his earlier claim that the notion of a match or correspondence between the ontology of a theory and its real counterpart in nature is illusive in principle (1970, 206; 2000 [1993], 244). The implications that incommensurability has for scientific realism have been widely discussed and continue to be controversial (cf. Devitt 2001, Oberheim and Hoyningen-Huene 1997, Sankey 2009).