 Another, more general, unifying element of this kind is Holton’s notion of themata. Themata are conceptual values that are a priori yet contingent (both individual and social), informing and organizing presuppositions that factor centrally in the evolution of the science: continuity/discontinuity, harmony, quantification, symmetry, conservation, mechanicism, hierarchy, etc. (Holton 1973). Unity of some kind is itself a thematic element. A more complex and comprehensive unit of organized scientific practice is the notion of the various styles of reasoning, such as statistical, analogical modeling, taxonomical, genetic/genealogical or laboratory styles; each is a cluster of epistemic standards, questions, tools, ontology, and self-authenticating or stabilizing protocols (Hacking 1996; see below for the relevance of this account of a priori elements to claims of global disunity; the account shares distinctive features of Kuhn’s notion of paradigm).