Concepts Are Not a Natural Kind*

In cognitive psychology, concepts are those data structures that are stored in long-term memory and are used by default in human beings’ higher cognitive processes (categorization, inductive and deductive reasoning...). Most psychologists of concepts assume that these mental representations share many scientifically important properties, and the psychology of concepts is expected to describe those properties. Psychologists assume thereby that concepts constitute a natural kind. I call this assumption the Natural Kind Assumption. This article challenges the Natural Kind Assumption. It is argued that a growing body of evidence suggests that concepts do not constitute a natural kind. Hence, the notion of concept is inappropriate to carve human beings’ mental representations at their joints, if one aims at formulating scientifically relevant inductive generalizations about the human mind.