Descartes is not as major a figure for Nancy as he is for Merleau-Ponty. Indeed, even though Descartes is mentioned in shorter texts on the body and the soul, such as Corpus, ‘On the Soul’ or ‘The Extension of the Soul’, the only in-depth treatment of Descartes is found in the 1979 book Ego Sum. On the other hand, the meditations on the body Nancy undertakes in Corpus are made possible by the thinking of ego as unum quid and as the union of the soul and the body undertaken in Ego Sum. Indeed, it is in the earlier text, in a meditation on the mouth, that we encounter Freud's famous posthumous note ‘Psyche is extended, knows nothing about it’ for the first time, a statement to which Nancy returns in almost all his writings on the body. Developing Nancy's understanding of the body then requires a detour through the earlier text on Descartes. We will see how Nancy proposes a circular reading of Descartes's Meditations not unlike Merleau-Ponty’s, but also how he radicalises further Merleau-Ponty's later reading of the cogito as vertical, operative cogito. The passage through Ego Sum also helps in warding off certain misinterpretations concerning Nancy's concept of body, namely the overemphasis on ‘exposition’ or ‘exposure’ at the expense of a certain ‘distinction’ or ‘withdrawal’, as well as the exclusive focus on the spacing between bodies (or parts of bodies) at the expense of the spacing or differance at the heart of the body.

1. Nancy's reading of Descartes: The unum quid against the modern subject

The issue at the core of Nancy's reflection on Descartes is the problematic return of the Subject Nancy diagnoses in the philosophical situation at the time, one in which the ‘deconstruction’ of the Subject was in full swing. It had become commonplace at the time to speak of the Subject as an effect – of the text, of history, of power, and so forth – and believe that one had in so doing overcome the metaphysics of the Subject and left Descartes behind.

If we follow the Heideggerian interpretation and see the Cartesian cogito as the inaugural moment of modern metaphysics, then we can see how such a Cartesian conception of the Subject is already disrupted, ‘deconstructed’, by the discourse of psychoanalysis, and especially Lacanian psychoanalysis.