Abstract
Scientific essentialism holds that: (1) each scientific kind is associated with the same set of properties in every possible world; and (2) every individual member of a scientific kind belongs to that kind in every possible world in which it exists. Recently, Ellis (Scientific essentialism, 2001; The philosophy of nature 2002) has provided the most sustained defense of scientific essentialism, though he does not clearly distinguish these two claims. In this paper, I argue that both claims face a number of formidable difficulties. The necessities of scientific essentialism are not adequately distinguished from semantic necessities, they have not been shown to be necessities in the strictest sense, they must be relativized to context, and they must either be confined to a subset of scientific properties without warrant or their connection to causal powers must be revoked. Moreover, upon closer examination (1) turns out to be a trivial thesis that can be satisfied by non-kinds, and (2) is inapplicable to some of the most fundamental kinds in the basic sciences.
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Notes
Does this also apply to essentialism about kind membership (EM)? Since individual scientific entities are rarely given proper names, it seems harder to assess this claim when it comes to EM than to EK.
Consider Mackie (1974, p. 560) on necessities involving individual persons and natural kinds: “Though these necessities apply to individual things and natural kinds (‘This man could not have…,’ ‘Gold could not have…,’ etc.), that they so apply is primarily a feature of the way we think and speak, of how we handle identity in association with counterfactual possibility.”
Here, we need to be careful not to confuse essentialism about kinds (EK) with essentialism about kind membership (EM). It may be accidental of some figure that it is rectangular; in some other possible world it may have been square. But it is surely not accidental to the kind rectangle that it is associated with the property of being a four-sided plane figure. That is presumably true in every possible world in which the kind rectangle is exemplified.
See Nozick (2001, p. 133) for a catalogue of alleged metaphysical necessities that have been abandoned in light of further empirical investigation.
Needless to say, essentialists do not rule out the possibility that we might come to discover, for example that the mass of the electron is larger or smaller than we thought, but that is an epistemic rather than a metaphysical possibility. Given that it actually has the mass me, it does so necessarily.
A referee points out that this is in keeping with the premise of Putnam’s original Twin Earth thought experiment. On Twin Earth, there is no water (i.e. substance with microstructure H2O), but rather a substance sharing many of water’s macroproperties.
This is suggested, for example, by Fine (2002/2005, p. 239), when he writes: “However, ever since Kripke (1980), we have learnt to be suspicious of such considerations (e.g. that bodies should attract one another according to an inverse cube law). For can we be sure that the hypothetical situation in which an inverse cube law is envisaged to hold is one in which the bodies genuinely have mass? Perhaps they have some other property somewhat like mass, call it schmass, which conforms to an inverse cube law.” But Fine’s view, unlike Ellis’, distinguishes natural necessity from metaphysical necessity; he regards some but not all natural laws as being metaphysically necessary.
Concerning the connection between universals and natural kinds, Ellis (2001, p. 19) writes: “All universals are natural kinds, even property universals can be considered natural kinds, instances of which are tropes.”
I owe this reply to an anonymous referee for this journal.
For a critique of the strict hierarchy thesis as applied to science, see Khalidi (1998).
At least this is suggested by Ellis when he says that universals range “from the most general category-wide universals (which the members of any given category of things must all instantiate)…” (2001, p. 19).
In Khalidi (1998), I have argued that it is just as well that natural kind theorists not embrace the stricter hierarchy requirement, since there are plenty of natural kinds that crosscut one another. But I will argue here that Ellis’ endorsement of a weaker hierarchy requirement also poses problems for his essentialist view.
The atom of chlorine-37 has 17 protons and 20 neutrons in its nucleus, while the atom of argon-37 has 18 protons and 19 neutrons in its nucleus.
For related reasons, some proponents of rigidity have abandoned the project of extending rigidity to general terms, since virtually any general term can be considered rigid. For example, Soames (2000, pp. 250–251) writes: “Nor will it do to say that a predicate is rigid iff there is a unique property which it stands for that determines its extension at each possible world.” He notes that this is not only true for natural kind predicates like cow and animal, since “the same could be said for any predicate: for any predicate F, and any world w, the extension of F with respect to w is the set of things that have, in w, property expressed by being an F. But there is no point in defining a notion of rigidity for predicates according to which all predicates turn out, trivially, to be rigid.” Similar points have been made by Schwartz (1980) and Donnellan (1983). Cook (1980) defends rigidity about natural kind terms, but he does so on the grounds that natural kinds satisfy EM rather than EK.
The argument in this paragraph draws on the debate concerning the rigidity of natural kind terms mentioned in the previous footnote, but that debate pertains to the semantics of kind terms rather than the metaphysics of kinds.
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Khalidi, M.A. How Scientific Is Scientific Essentialism?. J Gen Philos Sci 40, 85–101 (2009). https://doi.org/10.1007/s10838-009-9074-4
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DOI: https://doi.org/10.1007/s10838-009-9074-4