 Additional categories and distinctions include the following: vertical unity or inter-level unity is unity of elements attached to levels of analysis, composition or organization on a hierarchy, whether for a single science or more, whereas horizontal unity or intra-level unity applies to one single level and to its corresponding kind of system (Wimsatt 2007). Global unity is unity of any other variety with a universal quantifier of all kinds of elements, aspects or descriptions associated with individual sciences as a kind of monism, for instance, taxonomical monism about natural kinds, while local unity applies to a subset (Cartwright has distinguished this same-level global form of reduction, or "imperialism", in Cartwright 1999; see also Mitchell 2003). Obviously, vertical and horizontal accounts of unity can be either global or local. Finally, the rejection of global unity has been associated with isolationism, keeping independent competing alternative representations of the same phenomena or systems, as well as local integration, the local connective unity of the alternative perspectives. A distinction of methodological nature contrasts internal and external perspectives, according to whether the accounts are based naturalistically, on the local contingent practices of certain scientific communities at a given time, or based on universal metaphysical assumptions broadly motivated (Ruphy 2017). (Ruphy has criticized Cartwright and Dupré for having adopted external metaphysical positions and defended the internal perspective, also present in the program of the so-called Minnesota School, i.e., Kellert et al. 2006.) 