 Kuhn continued to emphasize the difference between normal, cumulative growth that does not change existing concepts; such as the discovery of Boyle’s law, which left the concepts of gas, pressure and volume and the instruments used to measure them unchanged, from revolutionary discoveries that could not have been made on the basis of antecedently available concepts; such as the discovery of Newton’s theory (Kuhn 2000 [1981], 14). Such developments require replacing existing concepts with new concepts that are incompatible with the older ideas. To help explain the nature of this conceptual incompatibility, Kuhn adopted the notion of a ‘lexical taxonomy’ or ‘lexicon‘ from linguistics (2000 [1989]). A lexical taxonomy stores and structures the vocabulary used to state laws and theories; or more specifically, the kinds of things that they describe. It is the “mental module” in which members of a speech community store the kind terms prerequisite to generalization and description (2000 [1991], 92–97; 2000 [1993], 229, 233, 238–239, 242, 244). To communicate, the terms that speakers use do not have to have the same meanings, nor do speakers need to use the same criteria for identifying something as a member of a particular kind (one ornithologist might identify ducks by their beaks, another by their tails) (cf. Hoyningen-Huene 1993, 99). Speakers need only share homologous lexical structures; that is, vocabularies incorporating the same system of taxonomic classification. This suffices to ensure that they refer to the same objects with the same kind terms. If two theories do not share the same taxonomic lexical structure, then they are incommensurable (2000 [1989], 63; 2000 [1991]; cf. Sankey 1997 and Wolf 2007).