Abstract

We need to distinguish two sorts of natural kinds, scientific and common NKs, because the notion of NK, which has to satisfy demands at three different levels—ontological, semantic and epistemological—, is subject to two incompatible sets of constraints. In order to prove this, I focus on the much-discussed case of jade. In the first part of the paper, I show that the current accounts are unsatisfactory because they are inconsistent. In the process, I explain why LaPorte’s analysis of “jade” as a vernacular NK-term with an open-texture meaning does not offer a way out. Using a reductio ad absurdum argument, I conclude that according to the main tenets of NK-term theories, today’s “jade” has to be an NK-term, and jade thereby an NK. In the second part of the paper, I argue for this conclusion in a positive manner. First, I present a series of thought experiments demonstrating that today’s “jade” has the specific features of an NK-term. Then, I show that the kind that we presently call “jade” exhibits the typical ontological and epistemological features of an NK. More generally, I expound on why common NKs are more than mere classes, and why categories such as “jade” are useful in many inferences and explanations.