In her lectures and seminars at the Collège de France, Claudine Tiercelin has examined a number of fundamental metaphysical problems : the status of " natural species " and contemporary essentialism, the nature and reality of dispositions, or what authentic metaphysical knowledge of nature can consist of. In the philosophy of knowledge, she has proposed a new definition of knowledge itself, clarified the meaning of the concept of practical knowledge, underlined the importance of epistemic virtues, and recalled the close links between knowledge and democracy understood as a space of truth and reason. His most recent lectures examine the complex historical relationships between ontology and semiotics, and demonstrate the relevance of a project aimed at developing an ontology that is simultaneously semiotic and realist. His forthcoming lectures will return to the classic question of the articulations of reality and the place that the mind must take if we are to be able to access a metaphysical knowledge that is able to reconcile " philosophy of nature " and " philosophy of the intellect ".