In this paper I aim to identify, disentangle, and relate physical, medical, and moral perspectives on the role of the passions in human life. In one of the prefatory letters to the The Passions of the Soul, Descartes’ “physics” (which includes the study of plants, animals, and humans) is presented as especially relevant to medicine—one of the three principal “branches” of philosophy that sprout from its “trunk” (physics), to employ Descartes’ image of the Tree of Philosophy (also referenced in the prefatory letters of Passions