This paper is devoted to a fundamental aspect of Diderot’s materialist philosophy: the fact that psychological identity does not exactly correspond with the material individuals we are because the memories on which psychological identity relies are always partial. This is complicated by the fact that even the material individual is denied reality since, as is stated in the Rêve de d’Alembert, the only individual is the «whole». By relating these two approaches, I try to show how one can develop a theory of the individual that takes into account the gap between individuation as a physical process and the constitution of a psychological individual.