Abstract
Leibniz is one of the philosophers who is most present in the philosophy of Maine de Biran, particularly from 1813 onwards. His influence is decisive in the reform of metaphysics (or First Philosophy) that he carries out from that moment on, reviving the notion of substance. Leibniz allows him to reconcile it with the idea of force, and thus to link it to the primitive fact of consciousness. This move has often been emphasized by commentators, but what has been less studied is the way in which this reform takes place in Biran’s intellectual trajectory from the time when he claimed to be an Ideologist inspired by Condillac’s philosophy, to the last texts written in 1824, when he eventually adopted a spiritualist monism that owed much to Leibniz, abandoning the Cartesian-inspired metaphysical dualism to which he had been committed until then.