“Nosce te ipsum” (“Know Thyself”) 
“There are in the mind processes and purposes of which one knows nothing at all, has known nothing for a long time, and has even perhaps known anything.” 
- Sigmund Freud
To understand the unconscious it is necessary to first consider the conscious. The word “conscious” comes from the Latin “conscientia”, whose etymology is comprised of two morphemes: the Latin “con” meaning (“with” or “together”), and “sci” meaning “knowing” (from “scire”, to notion of the know).  Etymologically, then, the term conscious/consciousness denotes an idea of shared knowledge, knowing together, or communal priviness. This usage of the term has become obsolete, as we normally consider “consciousness” to be a quality that one arrives at individually. The OED supplies the contemporary definition of consciousness as “The state or fact of being mentally conscious or aware of anything” particularly “oneself” and includes in its definition “the recognition by the thinking subject of its own acts or affections” (a quoted extracted from the words of Sir W. Hamilton).  The unconscious, then, in the most primary sense, can be understood as a lack or absence of the quality of consciousness, of shared knowledge, and of one’s own recognition of one’s acts and affections. The notion of the unconscious is thus intrinsically connected to the notion of knowledge, and a state of unconsciousness can be understood as a state of “Nosce non te ipsem”—not knowing thyself.
Our modern understanding of the term unconscious is highly influenced by Freud’s seminal psychoanalytic work, in which this notion played a central role. Freud’s focus on the activity of the unconscious in human psychical life expanded the meaning of the term from the description of a state of being to an actual mechanism within the human psyche or mind. Freud was the first to take up serious disputation with the prevalent understanding that “what is mental is conscious.”  He believed that consciousness made up only part of mental processes, and that “…the hypothesis of there being unconscious mental processes” would “pave the way to a decisive new orientation in the world and in science.”  Freud considered that “There are in the mind processes and purposes of which one knows nothing at all, has known nothing for a long time, and has even perhaps never known anything,”  those very processes serving as the body, or stuff, of unconscious mental life, or simply, the unconscious.
Freud considered the unconscious to exist as one facet of a tripartite system of consciousness, the other two facets being the preconscious and the conscious. Freud employed a spatial analogy to describe the relationships within this system; he describes the unconscious as a large entrance hall where different mental impulses fly around in autonomy, leading into a second, narrower room in which consciousness resides. “But on this threshold between the two rooms a watchman performs his function: he examines the different mental impulses, acts as a censor, and will not admit these into the drawing-room if they displease him…If they [the impulses] have already pushed their way forward to the threshold and have been turned back by the watchman, then they are inadmissible to the consciousness; we speak of them as repressed”  he wrote in his Introductory Lectures. This threshold, or interface, where the watchman stands guard, is the preconscious level of consciousness. It is perhaps the most important site of mediation within the entire system, as it is at the preconscious level that impulses are either censored and sent back to the unconscious (repressed), or admitted to pass on to consciousness.
This schema allows for a better understanding of Freud’s unconscious as it relates to media. Freud’s characterization of the unconscious in this analogy highlights its function not as a medium itself, but as a storage apparatus for other media, namely, mental impulses. The unconscious is not outside the body, but within the psyche, and as such, it does not serve to extend the body as much as it acts to store and even withhold its impulses. The unconscious can be said to be the environment in which the medium of mental impulses are nested. If we consider McLuhan’s description of the function of media as configuring “awareness and experience of each one of us,”  then it is not the unconscious which directly engages with this process, but the preconscious. As the watchman at the interface between the unconscious and conscious realms, the preconscious literally determines how or if we are aware of what we experience. So while the unconscious (as distinguished from the preconscious and conscious) cannot be considered a medium per se, than the unconscious with its correlative systems of the preconscious and conscious can, as a greater network, be considered an environment for the medium of mental impulses, thoughts and desires, in which the preconscious ultimately plays the greatest role as mediator. It is the interaction of these three systems which determines our understanding and awareness of phenomenological experience, which allows us to either know, or not know, ourselves.
If we take Marshall McLuhan’s assertion that “The medium is the message,”  then the mental impulses of Freud’s system of consciousness can be literally understood as messages to the self which are either consciously or unconsciously realized. The mental impulse, in all its instability and abstractness, is quick to be taken up by other media once it enters into the conscious realm, additionally impacting the form of the message. As polymorphous entities, impulses cannot exist outside the body without further mediation, but must assume the forms of such media as: thought, speech, words, drawing, painting, or any other sort of semiotic code or form of visualization (even dreams). The impulse (often nested in memory), once expelled from the unconscious, needs some sort of agent which in most cases is a type of medium, and with Freud’s methods, was words. Freud-scholar Norman O. Brown paraphrases Freud’s thinking on this matter as "…he [Freud] says that the unconscious becomes conscious by getting connected with words—“the verbal images which correspond to it”; these verbal images are memory-residues of external perceptions; the work of analysis supplies verbal images of this kind which act as connecting links between the unconscious and the conscious.”  Freud considered psychoanalysis, which relied highly on the mediation of unconscious impulses by verbal utterance, a successful method of helping patients to expose the repressed material which he believed played a part in their manifest symptoms of hysteria and neuroses. He sought, essentially, to expose the messages behind his patient’s internal psychical media. But Freud’s emphasis on the possibilities of psychoanalysis in accessing and revealing the unconscious was quickly appropriated by thinkers from other fields and disciplines, who adapted Freud’s findings to cultivate psychological theory to fit their own media of interest.
Many artists and literary figures contemporary to Freud explored both how their work might mediate the unconscious and how the unconscious might mediate their work. The most notable instantiations of the unconscious within the visual arts took place during the first half of the twentieth century, as avant-garde movements such as Dada and later Surrealism and Art Brut, relied on the role of the unconscious as a guiding source for aesthetic production. The release of Dr. Hans Prinzhorn’s publication Artistry of the Mentally Ill in 1922, a compilation of over 5,000 artworks by schizophrenic patients, inspired many artists to consider the way in which visual media could express unconscious impulses and even instabilities. While the relationship of the 20th century avant-garde with notions of modernity is highly complex, freeing the stuff of the unconscious seemed to be viewed by many as an anecdote the stifling aspects of modernity which were considered to have repressed this “stuff” in the first place. The mentally insane played a similar role for the early 20th century avant-garde as did the primitive and the infantile: all of these “other”-types were considered to exist with free, unmediated states of consciousness, and represented, then, the ideal source for a way out of modern, repressive straits.
Max Ernst, a key figure in the Surrealist movement wrote of its artists, “…these artists move freely, boldly and confidently at the borderline between the inner and the outer world, a borderline that is physically and psychologically entirely real (‘surreal’) even if it has not yet been adequately defined and determined…”  Ernst describes the Surrealist artist as one who could inhabit the liminal interstices of unconscious and conscious realms, and even traverse and translate these borders through the medium of painting. Jean Dubuffet, the major figure in Art Brut or “Crude Art”, wrote that art should renounce its reliance on ideas and seek alternative, anti-academic sources for inspiration: “When it is mixed with ideas, art becomes oxidized and worthless. Let there be as few ideas as possible! Ideas do not nourish art!”  Dubuffet considered Art Brut a new way of accessing the pure, and he explained that “the artists take everything (subjects, choice of materials, modes of transposition, rhythms, writing styles) from their own inner being, not from the canons of classical or fashionable art. We engage on artistic enterprise that is completely pure, basic; totally guided in all its phases solely by the creator’s own impulses.”  These two key figures of very different movements attest to the way in which the unconscious was capitalized as both a source of new aesthetic inquiry, and a means of rejecting of traditional, academic aesthetics.
While Surrealism and Art Brut were the two avant-garde movements which most explicitly affiliated themselves with notions of psychoanalysis and “freeing” the unconscious, many other modernist movements including Post-Impressionism, Fauvism and Expressionism could be said to have intricate ties with notions of the unconscious. These fascinations lead many to denounce modernist art as “degenerate,” (which has its own psychoanalytical resonance) or, as Adolf Hitler most starkly articulated “That flood of slime and ordure which the year 1918 belched forth into our lives.”  But while some took issue with the modernist portrayal of grotesque dream imagery, illogical and uncouth mental associations, or anti-traditional “subject matter” in general, other critiques of the avant-garde were more analytical and less reactionary. Freud himself was suspicious of the modernist artistic activities purported to be associated with the unconscious, as any attempts at “freeing the unconscious” inevitably landed right back in the realm unfree mental as well as material mediation. As the Oktober group suggests in their collective work Art in 1900, “…to propose an art free of repression, or at least of convention, was to risk psychopathology… (This is why Freud once called the Surrealists “absolute cranks”).” 
Artistic engagement with theories of the unconscious reverberate far beyond the Modernist avant-garde. The marked revolutionary attachment to the unconscious in the 60s encouraged further consideration of mediation of the unconscious, and even the social role of the unconscious through different media (the Jungian notion of “collective consciousness” became increasingly popular). Artists such as Jackson Pollock and other Abstract Expressionists revived certain methods of mediation of the unconscious as witnessed with the avant-garde, involving automatism and unguided impulse into their creative methods. However, new theories of psychoanalytic radicalism re-interpreted the unconscious not only through cultural production (artistic mediation), but in terms of culture—as Norman O. Brown articulated, “The psychoanalytic theory of therapy has to be theory of culture… because becoming conscious of the unconscious is a cultural phenomenon.”  Taking the thinking of the 20th century artistic avant-garde a step further (not only in extremity, but in technicality), Brown writes, “Human culture is a set of projections of the repressed unconscious.”  The notion of the unconscious in the later half of the 20th century came to be considered less as a source to be culturally mediated (through words, speech, paint) and more as a part or affect of culture itself. Historicizing the notion of the unconscious reveals how significantly inscribed the term is in both its social, as well as technological context. If Freud provided a notion of the unconscious as a technical model, many others seized this model and compared or adapted it to actual technological means. In “The Work of Art in the Age of Mechanical Reproduction”, Walter Benjamin writes that “The camera introduces us to unconscious optics as does psychoanalysis with unconscious impulses.”  This implication of a technological device, the camera, as engaging in a sort of unconscious exposure is not dissimilar to Marshall McLuhan’s later assertion that the preponderance of electric over mechanical media is working to guide humanity toward a single consciousness.  These two theorists show the way in which the notion of the unconscious became wholly integrated into notions of technology and their integral media. Both Benjamin and McLuhan are concerned with how different media organize and determine modes of perception, how media convey reality, or, convert it into a specific “message”. For Benjamin, photography’s exposure of unconscious optics allows mankind to become an object of contemplation for itself.  While with McLuhan, electric media is “strikingly the age of consciousness of the unconscious” where man strategically employs “numbness” and “apathy” and relegates consciousness to his psychical life, as a tactic of accepting technology “as an extension of his physical body.”  The notion of the unconscious with Benjamin is revelatory, even revolutionary, whereas McLuhan’s unconscious is markedly artificial, as it is consciously employed.
Advertising is one of the foremost activities to exploit McLuhan’s notion of the unconscious, the unconscious as a form of strategy. Contemporary cultural theorist Stuart Ewen writes, concerning marketing strategies: “…strategic thinking, however, went beyond making rational appeals to the consumer’s desire for pleasure. Styling, it was increasingly argued, must speak to the unconscious, to those primal urges and sensations that are repressed in the everyday confines of civilization.”  Ewen writes that the work of Freud, Jung, Alfred Adler, Pavlov and others provided “business with tools that could be used to its ‘active advantage.’”  This engagement with the unconscious marks a historical shift in the media/unconscious relationship, as the media employed to engage with the unconscious in advertising does so not with the primary attempt to promote self-understanding, but rather, to encourage consumptive action. However, like many of the aforementioned attempts at mediating the unconscious (e.g., psychoanalysis, art,) advertising too employs different media to transverse the liminal boundaries between the unconscious and conscious, and bring hidden impulses to light. But what advertising seeks to accomplish is to specifically access unconscious desire and translate it into conscious, active desire which relates to actual consumer products.
The word “unconscious” is particularly interesting in its relation to media theory in that whether considered as a metaphysical state of not knowing, the psychological apparatus in Freud’s theory of consciousness, or any combination of these metaphysical/psychological resonances, the unconscious is something without physical grounding. Further, those media nested within the unconscious—thoughts, impulses, memories, dreams, images—are equally weightless in terms of their absence[link] of physical form.  This uncanny ontology of the unconscious seems to lend itself to a fruitful occupation in the field of media theory, because the only way to consider the stuff of the unconscious is, precisely, to consider it as “stuff,” or through certain facets of mediation. In order to pass into the conscious realm, the thoughts, impulses, memories and dreams of the unconscious need to undergo some sort of metaphysical, but maybe even physical conversion. While there exist conscious thoughts, impulses, memories and dreams, these perceptual media cannot be acknowledged or understood without the representative and semiotic secondary media which organize and make them socially, but even individually comprehensible. Hence, the verbal/linguistic utterance, written word, drawn image and painted scene, seem like, if not logical, at least intuitive next steps in the effort to grasp the unconscious. And while the innate ambiguousness and ungroundedness of the unconscious as a concept does not entirely account for the diverse ways in which it has been evoked and formulated in relation to different media, there is something inherent to the unconscious which, like a call to arms, screams for mediated intervention and participation.