While originally Lacan seconds Heidegger's contention that 'anxiety has no object', in the early 1960s, he dismisses his own earlier position as a childish reassurance and argues, to the contrary, that 'anxiety is not without an object'. With particular attention to his use of the double negative, 'not without', this essay examines this turning point in Lacan's thinking in order to explain the opposition between his psychoanalytic critical theory and Derrida's deconstruction. The arguments that Lacan brings to bear on his work of the 1950s closely approximate those that Derrida levels against Heidegger in the formulation of his own concept of 'the aporia of the impossible'. Indeed, as commentators often emphasise, the formal logic of Lacan's later thinking is strictly isomorphic with Derrida's philosophy; and their respective concepts of anxiety and aporia are frequently misconstrued, accordingly, as simply identical. However, insofar as Lacan discerns a content in this formal negativity, contesting the idealism of his earlier theory and reasserting the materialist objectivity of the Freudian 'lost object,' as intractably Real, the two do not coincide. On the contrary, Lacan's repudiation of Heidegger's concept of anxiety extends equally to Derrida's aporia, as if, for Derrida, Heidegger's existential phenomenology were not reassuring enough.