Author’s Introduction (Section 1. Two Questions)
- Distinguish two questions about natural kinds.
- First, the naturalness question: what, if anything, makes a natural kind natural? Perhaps the members of a natural kind, unlike the members of an arbitrary group, stand in some natural similarity relation to one another. Perhaps they share an essence or some other natural feature. Or perhaps, as conventionalists argue, the boundaries of natural kinds do not correspond to distinctions in nature.
- Second, the kindhood question: what, if anything, makes a natural kind a kind? The distinction between natural kinds and other natural groupings was noted by Mill (1843: 122–3), who remarked that horses formed a natural kind but white things do not. Mill’s point is that, natural similarity among white things notwithstanding, leukocytes, chalks, white vans, clouds, comets, and degenerate (white) dwarf stars are too diverse a group to form a natural kind. If Mill is right, then investigating the difference between grue and green, for example, will not fully illuminate natural kinds, for neither green things nor grue things form a natural kind.
- The naturalness question has dominated debate about natural kinds, at the expense of the kindhood question. One consequence of this dominance is that certain questions concerning the ontology of natural kinds have been obscured. Richard Boyd, for example, explicitly understands questions of the form ‘is such-and-such a kind real?’ to be questions concerning naturalness and integration with inductive practices (‘accommodation’).
- But there are two tasks:
In this paper, we take the kindhood question seriously, and we examine how best to develop a realist view of natural kinds. In particular, we will articulate a view of natural kinds as complex universals1. We do not attempt to argue for the existence of universals2. Instead, we will argue that, given the existence of universals3, and of natural kinds, the latter can be understood in terms of the former, and that this provides a rich, flexible framework within which to discuss issues of indeterminacy, essentialism, induction, and reduction.
- to distinguish natural from unnatural similarities – which will help explain ‘accommodation’ – and also
- to understand the metaphysical status of natural kinds, distinguishing the natural similarities that underpin natural kinds from the natural similarities that do not.
- Two Questions
- The Kindhood4 Question
- 1) Natural kinds are universals5.
- 2) Natural kinds are particulars.
- 3) Natural kinds are sui generis entities, neither universals6 nor particulars.
- What are Complex Universals7?
- Natural Kinds as Complex Universals8
… 4.1 Precise Structural Kinds
… 4.2 Precise Conjunctive Kinds
… 4.3 Indeterminate Kinds
… 4.4 Exception-permitting Kinds?
- Complex Universals9 and Homeostasis
- Essences of Natural Kinds
- Conclusion: We have not done enough to persuade the determined sceptic about natural kinds, or about universals10 to come over to our point of view. However, we have begun to explore the potential rewards of identifying natural kinds with mereologically complex universals11, and thereby drawing upon a range of better-understood ideas about mereologically complex ordinary objects. Incorporating kinds into our ontology this way enables us to recognise their significance without having to posit an entirely new category of being.
Footnote 4: The authors reject out of hand the nominalist assertion that there are no such things as Natural kinds.
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