Some experimental studies have recently claimed to undermine semantic externalism about natural kind terms. However, it is unclear how philosophical accounts of reference can be experimentally tested. We present two externalistic adaptations of psychological placeholder essentialism, a strict externalist and a hybrid externalist view, which are experimentally testable. We examine Braisby, Franks, and Hampton's (1996) study which claims to undermine externalism, and argue that the study fails in its aims. We conducted two experiments, the results of which undermine internalism and the hybrid theory, and support strict externalism. Our conclusion is that lay speakers' natural kind concepts involve a belief in an external category essence, which determines reference.

Following the influential thought experiments by Hilary Putnam and others, philosophers of language have for the most part adopted semantic externalism concerning natural kind terms. In this article, we present results from three experiments on the reference of natural kind terms. Our results confirm some standard externalist assumptions, but are in conflict with others: Ordinary speakers take both appearance and underlying nature to be central in their categorization judgments. Moreover, our results indicate that speakers’ categorization judgments are gradual, and proportional to the degree of similarity between new samples and familiar, “standard” samples. These findings pose problems for traditional theories, both externalist and internalist.

We distinguish and discuss two different accounts of the subject matter of theories of reference, meta-externalism and meta-internalism. We argue that a form of the metainternalist view, "moderate meta-internalism", is the most plausible account of the subject matter of theories of reference. In the second part of the paper we explain how this account also helps to answer the questions of what kind of concept reference is, and what role intuitions have in the study of the reference relation.

We argue that the term "intuition", as it is used in metaphilosophy, is ambiguous between at least four different senses. In philosophy of language, the relevant "intuitions" are either the outputs of our competence to interpret and produce linguistic expressions, or the speakers' or hearers' own reports of these outputs. The semantic facts that philosophers of language are interested in are determined by the outputs of our competence. Hence, philosophers of language should be interested in investigating these, and they do this by testing what we would say or understand in hypothetical communication situations. In the final section of the paper we suggest methods to investigate these outputs that are independent of the subject's reporting them, and hence might be used as an alternative to the standard use of hypothetical cases.

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