I discuss Edouard Machery’s claim that philosophers and psychologists when using the term ‘concept’ are really theorizing about different things. This view is not new, but it has never been developed or defended in detail. Once spelled out, we can see that Machery is right that the psychological literature uses a different notion of concept. However, Machery fails to acknowledge that the two notions are not only compatible but complementary. This fits more with the traditional view according to which philosophers (...) and psychologists are merely interested in different aspects of the same kind. The main aim of this paper is then to show how precisely the two notions of ‘concept’ relate. Distinguishing them resolves the long-standing debate on whether concepts can be prototypes and allows me to formulate success conditions of a theory of categorization that are independent of the success conditions of a theory of concepts. (shrink)