One of the most pressing philosophical problems in early modern Europe concerned how the soul and body could form a unity, or, as many understood it, how these two substances could work together. It was widely believed that there were three (and only three) hypotheses regarding the union of soul and body: (1) physical influence, (2) occasionalism, and (3) pre-established harmony. However, in 1763, a fourth hypothesis was put forward by the French thinker André-Pierre Le Guay de Prémontval (1716–1764). Prémontval’s (...) hypothesis, given the grand name of “psychocracy” (i.e., the dominion or the rule of the soul), held that there was a real influence between soul and body, but that this was an immaterial kind of influence as opposed to the physical kind that had been entertained heretofore. Prémontval’s hypothesis is the focus of this paper. I shall begin by sketching out the details of Prémontval’s hypothesis (Section 1), then proceed to consider its claims to constitute a true fourth hypothesis distinct from the other three (Section 2), before closing by briefly considering two objections and the responses either that Prémontval himself made or that may be made on his behalf (Section 3). (shrink)