In his more mature years, Kuhn became increasingly interested in the conceptual structure of conceptual taxonomies and in the meaning of kind terms. Contrary to those who claim that such an interest is evidence of a ‘linguistic turn’ he underwent to be accepted by the philosophy community of his time, in this chapter I examine the philosophical reasons that drove Kuhn to the problem of meaning, and how he attempted to solve such problems by focussing on taxonomies. Then, I analyse Kuhn’s crucial shift from the ‘principle of similarities’ to the ‘principle of differentiae’, and how the latter sheds a new light on other parts of his philosophy. Finally, I discuss the problems that Kuhn’s concept of taxonomy faces.