Sartre's attitude to Freud is, from the outset, ambivalent: while recognizing the debt of existential to Freudian psychoanalysis, he is anxious to stress the differences of principle and methods. While agreeing with Freud that all human behaviour is ‘significant’, Sartre rejects totally both the suggestion that its source is the unconscious and the ensuing psychic determinism of Freudian theory.

But after 1943 Sartre moved increasingly closer to Freud, without always acknowledging this evolution. The reasons for this change appear to be threefold. In the first place, his own notion of human liberty underwent a considerable transformation, to the point where he could admit: ‘D'une certaine façon nous naissons tous prédestinés’ (Sit X, 98). Secondly, he significantly modified his early view of human consciousness. Thirdly, his knowledge of Lacan led him to interpret Freudian theory in a new light. L'Idiot de la famille provides clear evidence of this rapprochement with Freud.

Sartre lays out the aims and principles of existential psychoanalysis in L'Etre et le Néant. Existential analysis is based on the principle that man is a totality and each of his acts is therefore révélateur (EN, 656); its aim is to decipher and conceptualize the meaning of his behaviour; and it is supported, Sartre claims, by man's intuitive understanding of himself.