According to the standard Aristotelian doctrine of the identity of passion and action (Ipa), a passion and the action with which it is identified are distinguished through a distinction of reason, and both passion and action are located in the patient. Descartes has recently been interpreted by some scholars to be rejecting Ipa in favor of a view that throws into contention a dualistic interpretation of his philosophy of mind. This article contends that Descartes did hold Ipa, albeit expressed in (...) his own metaphysical vocabulary of substance and mode. On this interpretation, (1) a passion and the action with which it is identified are distinguished through a conceptual distinction or distinction of reason and (2) the passion and the action constitute one and the same mode which is locatedin the patient. This result is significant first, because it shows Descartes's retention of a fundamentally Aristotelian understanding of the metaphysical categories of passion and action and second, because it removes some of the support for recent interpretations on which Descartes is seen in the Passions of the Soul to diverge from a dualistic view of mind and body. (shrink)