This chapter analyzes Freud's debt to, and impact on, philosophy. It begins by distinguishing between the many influences on the young Freud and the formal debt he owed to transcendental philosophy. It then examines two important ways in which Freud challenged Kant's epistemology: the first in terms of the explanatory and diagnostic resources of Freud's model of the mind; the second in light of Freud's contribution to the structure of mental temporality. Finally, it turns to his case of male hysteria to argue that, while owing philosophy a complicated and unacknowledged debt, Freud delivered a blow to the Aristotelian-Kantian conception of affectivity and passions. By psychologizing hysteria, Freud made it impossible to hold to simple divisions of the passions into educable versus ineducable, masculine versus feminine ones—or even to argue that affectivity should be reduced to physiological events and changes in the body.