<p>This book is a close reading of Jacques Lacan's seminal essay The Agency of the Letter in the Unconscious or Reason Since Freud selected for the particular light it casts on Lacan's complex relation to linguistics psychoanalysis and philosophy. It clarifies the way Lacan renews or transforms the psychoanalytic field through his diversion of Saussure's theory of the sign his radicalization of Freud's fundamental concepts and his subversion of dominant philosophical values. The authors argue however that Lacan's discourse is marked by a deep ambiguity: while he invents a new language he nonetheless maintains the traditional metaphysical motifs of systemacity foundation and truth.</p>