The "Seminar on the "Purloined Letter"" is a "mythical" text that was not randomly placed by Lacan at the forefront of his writings. It constitutes the written monument of the most important metapsychological revolution in psychoanalysis. In it, Lacan processes the protocol of an unheard-of axiom that establishes the Symbolic at the level of the letter and shapes the terms of the famous "Return to Freud". Liberated from its romantic, psychological, and neurological versions, the structure of the unconscious is specialized as metabiological memory and falls under the jurisdiction of the letter and its combinatory, while at the same time complemented by a heterogeneous and antimonic element: the concept of the subject, defined in a way that has no precedent in the history of Western thought.

The text is also distinguished not only because it establishes the classic motif of the superiority of the Symbolic over the Imaginary, but mainly because with a precursory, albeit indistinct, theoretical gesture it privileges the entanglement of the Symbolic with the Real, S-R, axis of Lacan's later teaching.

As Lacan himself emphasizes, "the mnemonic inscription that befits the unconscious - the Freudian, of course - is not of the same order as the regime we assume in memory, conceived as a property of the living. [...] While it is obvious that [...] we can find, in the ordered chains of a typical language, all the aspects of a mnemonic inscription: especially the one required by the discovery of Freud. [...] The program outlined for us henceforth concerns the way in which a typical language determines the subject.
But the interest of such a program is not simple: assuming that a subject will fulfill it only by presenting its specificity."