This paper aims to analyze Pierre Janet’s interpretation of Maine de Biran’s notion of the “unconscious” through a comparative study between L’automatisme psychologique (1889) and some Biranian writings devoted to the problem of pure affections. The objective is to question whether Janet’s psychological reading of this very notion had been faithful to Biran’s intentions, and to understand what kind of Biranism Janet is referring to when dealing with the problem of the unconscious.