The exchange between the philosopher Pierre Maine de Biran and the psychiatrist Antoine-Athanase Royer-Collard has been read either as an exemplary case of the influence of philosophy on medicine or as a dialogue of the deaf. However, these two readings imply a clear distribution of roles between the philosopher and the doctor. This article, instead, examines the metaphysical nature of the discussion between the two spiritualists in their aim to establish a "true spiritualism" from a common problem: the nature of madness. Based on a constellation analysis of Biran's Nouvelles considérations sur les rapports du Physique et du Moral and Royer-Collard's 1821 lecture on this manuscript, the article shows that both thinkers are concerned with the most appropriate form of dualism, and with how it is possible to establish a relationship between the two fundamental aspects of man-the physical and moral-without denaturing each of them. Paradoxically, the analysis makes manifest a reversal of roles: whereas Biran has a static conception of dualism leading to an organic conception of madness, Royer-Collard demands a dynamic dualism that makes it possible to conceive a causal role for the mind in madness.