In the sense given to these terms by Jacques Lacan, the three essential orders of the psycho-analytic field are the Imaginary, the Symbolic, and the Real. The concept of the "imaginary" can be grasped through initially through Lacan's theme of the " mirror stage." Lacan proposed that the ego of the infant -- as a result of its biological prematurity -- is constituted on the basis of the image of the counterpart (specular ego). Following from this primordial experience, the Imaginary defines the basically narcissistic relations of the subject to his ego, the intersubjective relations of a counterpart -- an other who is me, a type of apprehension characterized by resemblance and homeomorphism -- a sort of coalescence of the signifier and signified. (from Laplanche and Pontalis) While Lacan's use of the term "Imaginary" is highly idiosyncratic, he insists that all imaginary behavior and relationships are fundamentally deceptive, and that the intersubjective realm of the symbolic must be separated out from the Imaginary in analytic treatment.
Didier Anzieu uses the distinction between imaginary and symbolic in his discussion of Freud's dream of "Irma's Injection," which can be described as the foundation of psychoanalysis. Anzieu differentiates the imaginary and symbolic aspects of this dream, by which the secret of dreams was revealed in a dream. The imaginary structure is related to latent wishes, while the symbolic structure is related to formal processes.
Symbols must be part of a closed group of transformation that links them. (This is often referred to as a combinatoire, or combinatory group.) The systematic relationships of the symbol system enable its referential functions. (see language)
Gottlob Frege distinguished between the sense of a term (Sinn ) and its reference, or meaning (Bedeutung ). Sense can be thought of as "something in the head", the idea one has in mind, while reference is "something in the world" which corresponds with the term and its sense. Frege illustrated the distinction through the expressions "the morning star" and "the evening star" whose sense is different but whose reference (the planet Venus) is the same. In this case, the different senses trace back to a historical context when the common reference was not recognised.
Symbolic systems make a new kind of generalization possible: logical or categorical generalization.