Lacan summons reason and the letter together in the title of his 9 May 1957 lecture at the Sorbonne, ‘The Agency of the Letter in the Unconscious or Reason since Freud’. This joint convocation, made before the Philosophy Group of the Fédération des Etudiants ès Lettres, seems to imply that the epoch of Freud has effected some historical shift in the ancient relation of logic and language, philosophy and poetry, metaphysics and metaphor. Whether the connective word ‘or’ signifies a conjunction of the two terms, in the sense that western philosophy has always considered language to be the instrument, or even the essence, of reason, or a disjunction, along the lines of Plato's primordial quarrel between mythos and logos, the title does not specify.