This paper considers how certain ideas elaborated by the Montpellier vitalists influenced the rise of French alienism, and how those ideas framed the changing view of passions during the eighteenth century. Various kinds of evidence attest that the passions progressively became the focus of medical attention, rather than a theme specific to moralists and philosophers. Vitalism conceived of organisms as animal economies understandable through the transformations of the various modes of their sensibility. This allowed some physicians to define a kind of anthropological program, which viewed human beings as a whole, with no distinction between le physique and le moral. The passions in this context became a specific alteration of the animal economy. Such an anthropological program was the framework within which Pinel understood the various classes of madness as disease – those troubles being general disturbances of the animal economy, which presupposed a knowledge of the latter, to be addressed and cured. In this view, and departing from the vitalist writers with regard to the specificity of mental illness as such, Pinel proposed another conception of the relations between passions and madness, and elaborated a general view of their status in etiology and therapeutics; those views were taken up and systematized by Esquirol, who finally defined a new kind of continuity between passion and madness, demonstrated by the idea that some kinds of madness that he called “monomania” had as a principle a “ruling passion” that the alienist, this novel medical specialist, had to unveil and address.