Using semantic deference to test an extension of indexical externalism beyond natural-kind terms

Since Kripke and Putnam, there is a widespread assumption that natural-kind terms function just like proper names: they designate their referents directly and they are rigid designators: their reference is unchanged even in worlds in which the referent lacks some or all the properties associated with it in the actual world. There have, however, been heated debates about what should be taken as a natural-kind term. These often take on a strong epistemological or metaphysical dimension.
We think the issues can be clarified within the limits of the philosophy of language: by looking into what ranges of general terms are perceived by speakers as rigid designators of natural kinds. The first step to take is to ground the various kinds of semantic externalism in distinct brands of semantic deference. Our focus is on spotting the words for which speakers would defer not (just) to the current usage of the word in the linguistic community, nor to the current experts of the field to which the word pertains, but ultimately to the very nature of the referent of the term. When speakers’ deference conforms to that pattern, we argue, that is evidence that indexical externalism (à la Kripke or Putnam) provides the right metasemantic account of how the meaning of the word is determined; the word is treated like a natural-kind term.
But how can patterns of deference be measured? In an ongoing survey, we confront participants with conditions that may prompt them to revise certain classificatory statements. Each condition makes salient one of the targets we have identified for deference: the community usage, the experts, the ‘world as it is’. In the condition that seeks to tap into the latter kind of deference, participants are presented with a scenario in which future scientific discoveries result in excluding from the extension of a term certain members currently thought to fall under that extension Our reasoning is that, if participants significantly modify their statements in the light of that scenario, they can be taken to ‘defer’ to the nature of the referent, thus vindicating indexical externalism. We test if words not normally assumed to be natural-kind terms exhibit patterns of deference similar to those for natural-kind terms. If so, speakers have something like realist intuitions with respect to words whose meaning is usually taken to be purely conventional or polemical, and there’s therefore a case for an extension of indexical externalism beyond the usual set of terms.
We believe our results will enrich the conclusions from previous empirical studies (Braisby et
al. 1996, Jylkkä et al. 2009, Genone & Lombrozo 2012). Braisby, N., Franks, B. & Hampton, J. 1996. Essentialism, word use, and concepts. Cognition 59, 247-74./Genone, J. & Lombrozo, T. 2012. Concept possession, experimental semantics, and hybrid theories of reference. Philosophical Psychology 25, 717-742./Jylkkä, J., Railo, H. & Haukioja, J. 2009. Psychological essentialism and semantic externalism: Evidence for externalism in lay speakers’ language use. Philosophical Psychology 22, 37-60