Variation in Natural Kind Concepts

Since Kripke’s and Putnam’s work in the 1970s, most philosophers have assumed that our natural kind concepts are externally individuated. However, both psychologists and philosophers have questioned this assumption, partly on empirical grounds. There is some evidence of systematic variation in how subjects apply natural kind terms; it has been argued that this shows that natural kind concepts are not as universally shared, or temporally stable, as many philosophers have been assuming. Yet, it is not clear exactly what kind of variation in subjects’ application of natural kind terms would seriously cast doubt on the view that natural kind concepts are externally individuated. Here, we take a detailed look at this question, and argue that the existing studies do not call for dramatic revisions to the externalist mainstream, and conclude by exploring some possible new directions for the experimental study of natural kind terms and concepts.