Lacan's Theory

Lacan's Theory is based around 'The order of the Real', 'The order of the Imaginary', 'The order of the Symbolic' and 'The Symptom'. These four orders intertwine 'The Real', 'The Imaginary' and 'The Symbolic' are the three outside orders that overlap to create 'The System' in the middle. 

Lacanianism is the study of, and development of, the ideas and theories of the dissident French psychoanalyst Jacques Lacan. Beginning as a commentary on the writings of Freud, Lacanianism developed into a new psychoanalytic theory of humankind, and spawned a worldwide movement of its own.

Development of Lacan's Theory:
Early Lacan:

• Lacan's early psychoanalytic contributions centered on the questions of image, identification and unconscious fantasy. Developing Henri Wallon's concept of infant mirroring, he used the idea of the mirror stage to demonstrate the imaginary nature of the ego, in opposition to the views of ego psychology.

Structuralist Lacan:

• In the fifties, the focus of Lacan's interest shifted to the symbolic order of kinship, culture, social structure and roles all mediated by the acquisition of language into which each one of us is born and with which we all have to come to terms. The focus of therapy became that of dealing with disruptions on the part of the Imaginary of the structuring role played by the signifier/Other/Symbolic Order.

The Real: Poststructuralism

• The sixties saw Lacan's attention increasingly focused on what he termed the Real not external consensual reality, but rather that unconscious element in the personality, linked to trauma, dream and the drive, which resists signification. The Real was what was lacking or absent from every totalising structural theory; and in the form of jouissance, and the persistence of the symptom or synthome, marked Lacan's shifting of psychoanalysis from modernity to postmodernity.

{website reference: https://en.wikipedia.org/wiki/Lacanianism#Development_of_Lacan's_thought}