Jaques Lacan (1901-1981) was a French psychoanalyst/psychiatrist. He describes the 3 stages of identity called RSI (Real, Symbolic, Imaginary) which make up part of every psychic function.
Lacan is associated with the idea that the unconscious and conscious are structured like a language but that it is not the same structure. Further that the subject cannot necessarily be equated with the speaker.
The central concern in Lacanian psychoanalysis is desire, not of the conscious but of the unconscious. This can only be articulated in speech.
He introduced the variable session with the understanding that the unconscious (which psychoanalysis is only interested in) has no concept of time and therefore had no need for the more conventional 50 min time frame for analytic sessions.
The cut in the sessions which is based on the material that emerges in the sessions acts as a form of comma in the signifying chain of the unconscious.
The introduction of the variable session was partly responsible for Lacan and his followers being expelled from the International Psychoanalytic Association in France. He went on to establish new psychoanalytic institutions to further develop and promote his thinking.