Here we discuss, in the name of psychoanalysis, the conception of alterity in the work of Emmanuel Lévinas and highlight what is definitive in it. We situate ourselves not with regard to psychoanalysis, but with regard to philosophy when it takes up the fundamental hypothesis (the unconscious). We show how, for alterity itself, the affirmation of philosophical knowledge, but of a knowledge that heralds the unconscious, and its reality, sex, becomes essential. It then appears that any truth contained in three revelations – Christian, Jewish and Moslem – must come from this knowledge.