Descartes employs the term “passion” in three ways. In physics, a passion is anything that “takes place or occurs” as the result of “that which makes it happen” (AT XI 328, CSM I 328). In physiology, a passion is a corporeal impulse of the animal body (AT V 278, CSMK 366). In psychophysics, “passions of the soul” are modes of the soul that “depend absolutely” on actions of the body (AT XI 359, CSM I 343). The following entry considers only this last category of passions, focusing on their relationship to actions in the body, their definition, their functions, and their relationship to virtue.

1.Action and Passion: Unam et eadem rem

As Descartes writes to Hyperaspistes, it is “contradictory that there should be a passivity without an activity for even a single moment” (AT III 428, CSMK 193). Indeed, actions and passions are “one and the same thing” (unam et eadem rem), called an “action” when referred to the agent and a “passion” when referred to the patient (AT III 428, CSMK 192–93). This identification between actions and passions is repeated at the beginning of the Passions of the Soul. Even though the agent and patient are often quite different, action and passion are always one and the same thing (une meme chose) (Passions, I.2). In the letter to Hyperaspistes, Descartes allows that a thing (e.g., a top) may act on itself, but in the case of passions of the soul, the agent is one thing (the body), the patient another (the mind).

Paul Hoffman (1990, 317) points to a problem here: if the agent and patient are really distinct, then, given Descartes’ theory of distinctions (AT VIIIA 28–30, CSM I 213–15), actions and passions should also be really distinct. But given the identification of actions and passions (Passions, I.1), they cannot be. Nor can they be modally distinct either, since that presupposes separability as well. This leaves only the distinction of reason, but the question then is how a mode of an immaterial substance could be identical with a mode of extension? What sort of nature could a mode of mind share with a mode of body?