Abstract
In this paper I offer a unified causal account of natural kinds. Using as a starting point the widely held view that natural kind terms or predicates are projectible, I argue that the ontological bases of their projectibility are the causal properties and relations associated with the natural kinds themselves. Natural kinds are not just concatenations of properties but ordered hierarchies of properties, whose instances are related to one another as causes and effects in recurrent causal processes. The resulting account of natural kinds as clusters of core causal properties that give rise to clusters of derivative properties enables us to distinguish genuine natural kinds from non-natural kinds. For instance, it enables us to say why some of the purely conventional categories derived from the social domain do not correspond to natural kinds, though other social categories may.
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Notes
But for a recent dissenting opinion, see Ereshefsky and Reydon (2014), who argue that some scientific kind terms are not projectible.
Quine (1969, p. 115) puts it in terms of confirmation rather than inductive inference: “projectible predicates are predicates \(\upzeta \) and \(\upeta \) whose shared instances all do count, for whatever reason, toward confirmation of \(\ulcorner \) All \(\upzeta \) are \(\upeta \) \(\urcorner \).” I prefer my formulation partly because I think that universal generalizations are vanishingly rare in the sciences.
Examples have been put forward of projectible terms that are not natural kind terms. For example, Godfrey-Smith (2011) has argued that certain types of statistical projections do not involve an assumption of “naturalness”. I only claim that projectibility is a necessary condition on natural kind terms, not that it is a sufficient condition.
I don’t think that Peirce’s talk of “defining character” requires a commitment to analytic truth. We can think of the defining characters of a natural kind as those properties used to identify the kind in the first place (see Sect. 3 for more on this).
Moreover, the condition of modal necessity is trivial and can be satisfied by natural kinds and non-natural kinds alike. See Khalidi (2013) for criticisms of essentialism about natural kinds.
One of the main sources for this criticism is Ereshefsky and Matthen (2005), and one of the principal responses is Wilson et al. (2009). For other examples of natural kinds that do not conform to Boyd’s template, see Khalidi (2013). But it should be noted that Boyd (1989, p. 16) sometimes indicates that the homeostatic mechanism may be metaphorical rather than literal. The account I am proposing is very similar to Boyd’s when one drops the mechanism and homeostasis.
Roughly speaking, X is a “direct cause” of Y when there is a possible intervention on X that will change Y when all other variables are held fixed by some intervention, relative to some level of analysis (Woodward 2003, p. 55).
Is it obvious that the link between the core and derivative properties is always causal? On this account, it follows directly from the fact that I have characterized the relationship between core and derivative properties in terms of causal priority. Others (e.g. Hawley and Bird 2011) seem to characterize it in terms of natural law, but I would argue that laws concerning natural kinds are causal laws. Yet others may do so in terms of metaphysical necessity (e.g. Oderberg 2011) but this presupposes an essentialist view that I reject.
It is interesting that some social kinds appear to be copied (e.g. parliament, confederation, trade union, corporation), while others may not be (e.g. marriage, government, ritual, money). The latter seem to have arisen independently in different human societies.
The existence of causal feedback loops means that the directed causal graphs described in the previous section will need to be modified to represent the fact that an effect can sometimes causally produce an iteration of the cause.
For a detailed treatment of a case of this kind, see Magnus (2012) on the anglerfish, though his handling of the case is a little different from mine.
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Acknowledgments
This paper is based on a presentation given at a symposium on Causation and Natural Kinds hosted by the Institute for History and Philosophy of Science and Technology (IHPST), Université Paris 1, in March 2014. I am grateful to the organizers, particularly Andrew McFarland, for inviting me, and to all participants for very helpful feedback.
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Khalidi, M.A. Natural kinds as nodes in causal networks. Synthese 195, 1379–1396 (2018). https://doi.org/10.1007/s11229-015-0841-y
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DOI: https://doi.org/10.1007/s11229-015-0841-y