Abstract : Concept is the mental entity that allows the cognitive agent who possesses it to think about his environment. It is characterized by two dimensions : its application (objects it refers to) and its use (relationships it bears with other mental states). The contemporary theories of concept fail to explain both these features of concept, due to the confusion made between a theory of concept and a theory of classification and of a fuzzy distinction between conceptual and nonconceptual. The main difference between conceptual and nonconceptual is that the former is representational whereas the latter is not. Being a representation means being corrigible. The theory of concept proposed here is normative. Principles are offered for characterizing the concept. A cognitive agent possesses a concept if he is able to assign a content to it at first person (cognitive content) and at third person (canonical content). This entails a theory of mind. Moreover, the agent must be able to explain his use of the concept, for himself (cognitive derivation) and for other minds (canonical derivation). The holism implied by this theory enables us to explain the change and the evolution of concept which are different from concept replacement.