"Is unconscious a thing, a place, the unconscious, or is it a mode, an adjective, unconscious ?" (Francoise Meltzer, in Critical Terms for LIterary Study.) "The unconsious does not have a rhetoric, but is a rhetoric." (Gorgio Agamben, Stanzas, p.150 n.) 

How can the unconsious be known? (in German, it is the Unbewusste, the unknown ) Can it only be diagnosed, inferred through its symptoms in parapraxis? Can ideas and memories be effective yet unavailable to consciousness

Freud approached the unconsious from a number of points of view. In his first important paper on the subject, "A Note on the Unconscious in Psycho-Analysis" (1912), Freud adopted a descriptive viewpoint and divided the psyche into conscious and unconscious. The descriptive model was the source of Freud's "topographic " or spatial geography of the mind, which divided the psychic apparatus into three systems: Ucs., Pcs., Cs. (unconscious, preconscious, conscious) (see "The Unconscious," 1915) 
(see topos ) 

Later Freud developed a dynamic model, called "hydraulic" by critics, which described energy flows that build up and seek release. In this model, tension is displeasure and will always seek an avenue for release. For Freud, these interplays of forces are of organic origin. They are represented as images or ideas with an affective charge.The dynamic model lead Freud to consider the unconscious from an economic viewpoint, that is, to attempt to quantify the relative magnitudes of the forces of excititation. "From the economic standpoint, psycho-analysis supposses that the mental representatives of the instincts (instinctual drives) have a charge (cathexis) of definite quantities of energy. In his later publications, Freud referred to two instinctual drives: libido and agression. In the 1930's Freud replaced the topographical viewpoint with the structural one, dividing the mental apparatus into his famous "tripartite" model of agencyid, ego, and superego

Throughout his analyses, Freud adopted a genetic viewpoint, holding that any psychological phenomenon, in addition to its contemporary and experiential aspects, can be traced back through its ontogenesis to its psychological origin. Throughout his life, Freud remained faithful to the idea of an intrication of ontogeny and phylogeny. He was quite prepared to see the relationship between consciousness and the unconscious in terms of an evolutive, integrative emergence of the latter from the former, and to see neurotic symptomology as a regression and freeing of early or repressed mental processes and contents. (Anzieu, Freud's Self-Analysis, p. 38) 

From the beginning, the notions of the unconscious and repression (or resistance) were closely linked for Freud. The repression barrier divided consciousness from unconsciousness. The first thing that happens in repression is that idea and affect are severed. The affect can be inhibited; it can remain in consciousness but attached to another idea, or it can undergo transformation, notably into anxiety. For Freud, it was through repression that ideas, especially ones that were threatening, painful, or unpleasant, found their way into the unconscious, just as, through the lowering of resistance, in dreams or therapy, they found their way out. (What is the relation of repression to forgetting?) 

Freud's investigations into traumatic hysteria clearly revealed cases where a patient's behaviour could not be explained or even identified without reference to operative but unconscious ideas. The fact that the same behaviour could be artificially induced by hypnosis, by the insertion of ideas into the subject's mind, strongly suggested that ideas were operative, even though the subject knew nothing of them. Freud's preferred explanation of inner conflict was in term of the incompatibility between certain ideas and a mental agency, identified as the ego which exerted repression. 

For Freud, the residue of the "prehistoric stage of life", from the age of one year to three, is the source of the unconscious and contains the aetiology (the medical word for cause) of all the psychoneuroses. It is a stage normally obscured by an amnesia similar to hysteria. (see screen memories for a mode of persistence to infantile memories.) Thus Freud could conclude that because small children do not truly understand the meaning of death, in our unconsious we know nothing about death in general and our own death in particular. 

For Freud, the unconscious system was characterized by exemption from mutual contradiction, by primary process, which is indifferent to logical, spatial, or temporal order, by timelessness, and by the replacement of external by internal reality. Displacement and condensation are two forms of primary process that Freud describes in The Interpretation of Dreams.

Gerald Edelman describes primary process as a consciousness that arises from perceptual organization, memory, learning and self/non-self discrimination. Identitymemory, and space compose primary consciousness. From this primary consciousness, a higher-order consciousness evolves in man, with the powers of language, conception, and thought. 

What are unconscious memories? In 1897, Freud abandoned the seduction theory, whereby hysteria (primarily in women) was a result of actual abuse. (Whatever else may be true about hysteria, it is a thoroughly gender-laden diagnosis, description, or discourse.) One reason for this shift was that for Freud there were no criteria in the unconscious to distinguish between an actual event and a fantasy, an issue which paved the way for the idea of narrativetruth. Through his own self-analysis, Freud came to the conclusion that "neurosis" was caused not by an actual sexual trauma, but by incestuous fantasies. Recent critics of Freud, especially Jeffrey Masson, have claimed that Freud chose to ignore evidence of real abuse in some of his female patients, notably in the case of Emma Eckstein, who was also negligently treated when Fliess left gauze up her nose after operating on her. 

For Freud "somatic conversion" was a link between repressed ideas and the body. It was an indication of the body's powers of symbolic expression. (see body thinking )

what is relation between unconscious and automatic behaviour? 
A contrary current of interpretation of the unconscious views it as enabling instead of custodial. Efficiency rather than repression accounts for unconscious mental work. Automatic mental processes "unconscious cerebration" do not require comprehensive awareness, and free up consciousness to the physiological tasks for which it is best fitted. Many nineteenth-century psychologists saw the unconsious as "actively generating the processes which are integral to memory, perception and behavior. Its contents are inaccessible, not because, as in psychoanalytic theory, they are held in strenuously preventive detention, but, more interestingly, because the effective implementation of cognition and conduct does not actually require comprehensive awareness. On the contrary, if consciousness is to implement the psychological tasks for which it is best fitted, it is expedient to assign a large proportion of psychic activity to automatic control; if the situation calls for a high level management decision, the unconscious will freely deliver the necessary information to awareness." (see Jonathan Miller, "Going Unconscious" in Hidden Histories of Science, pp 1-35. This passage quoted in Crary, Suspensions of Perception, p. 40) 

This is also the neurolgical tradition. Gestalt psychologists, like Kurt Goldstein, rejected the notion of the unconscious. For Goldstein, "What appears as the unconscious is nothing but the entering of a former reaction pattern of the organism into a present response, when the situation is suitable." (p258) 

The unconscious can be thought of as a step away from a unified, centralized mind towards a decentralized one. (D+G: " molar" versus "molecular") Rather, it is everything that is left behind in a contraction of selection or sensation than moves from one level of organization to another. The only things the unconsious are not are present perception and reflection. (Massumi. p.83) 

What is the relationship between the unconscious and the "plane of consistency of desire" which Deleuze and Guattari call the Body without Organs ? For Deleuze "the unconscious is not a deep container of yet-unknown sources, but rather the marking of the structural non-coincidence of the subject with his / her consciousness." Rejecting the "anthropomorphic representation of sex", Deleuze and Guattari describe the workings of the unconscious and of the sexual drives as the actions of desiring machines .

"Thinking...is to a very large extent unconscious, in that it expresses the desire to know, and this desire is that which cannot be adequately expressed in language, simply because it is that which sustains language." (Braidotti, "Toward a New Nomadism")

"Within the Freudian notion of the unconscious the involution of the strange in the pysche loses its pathological aspect and integrates within the assumed unity of human beings an otherness that is both biological and symbolic and becomes an integral part of the same." "Uncanny, (unheimlich ) foreigness is within us: we are our own foreigners." (Julia Kristeva, Strangers to Ourselves, p. 181) 

"We are in a system where there is no more soul, no more metaphor of the body -- the fable of the unconscious has lost most of its resonance" (Baudrillard, The Ecstasy of Communication New York, Semiotext(e), 1988, 50-51)

to read: Ellenberger, The Discovery of the Unconsious