Philosophy since its Platonic inception has situated itself at the juncture in which a given meaning, assumption, or opinion falters. To philosophize entails coming to grips with an essential blockage, encountering something over which one trips, and that can only be thought through a kind of twisting of language. Plato referred to this stumbling block as an aporia, an impasse. An impasse names something that refuses assimilation, which cannot be incorporated and whose stubborn presence can only be acknowledged at the cost of abandoning one’s pious certainties. Such a conception of what it means to think suggests that the activity of thinking is inseparable from a fundamental upheaval of the soul. In this seminar, we will look at three ways of posing this problem of the stumbling block, of thought’s encounter with the inassimilable. Tracing an aberrant line that begins with Plato and then leaps to Nietzsche, specifically Klossowski’s Nietzsche and the Vicious Circle, and concludes with Freud, taking up Lyotard’s treatment of Freud in Discourse, Figure, we will explore the notion that thought must be situated at that point at which the subject stumbles over itself.