Unconscious mind
Various observers throughout history have argued that there are influences on consciousness from other parts of the mind. These observers differ in the use of related terms, including: unconsciousness as a personal habit; being unaware and intuition. Terms related to semi-consciousness include: awakening, implicit memory, the subconscious, subliminal messages, trance, and hypnosis. Whilst sleep, sleep walking, delirium and coma may signal the presence of unconscious processes, that is different from an unconscious mind. Science is also in its infancy in exploring the limits of consciousness.

# Historical overview
The idea of an unconscious mind originated in antiquity  and has been explored across cultures. It was recorded between 2500 and 600 B.C in the Hindu texts known as the Vedas, found today in Ayurvedic medicine   . In the Vedic worldview, consciousness is the basis of physiology   and pure consciousness is "an abstract, silent, completely unified field of consciousness"  within "an architecture of increasingly abstract, functionally integrated faculties or levels of mind" .
Shakespeare explored the role of the unconscious  in many of his plays, without naming it as such   . Western philosophers such as Spinoza, Leibniz, Schopenhauer, and Nietzsche, developed a western view of mind which foreshadowed those of Freud though Schopenhauer was also influenced by his reading of the Vedas and the Jewish mysticism of the Kabbalah. Freud drew on his own Jewish roots to develop an interpersonal examination of the unconscious mind    into an apparently new therapeutic intervention and its associated rationale, known as psychoanalysis.
Articulating the idea of something not conscious or actively denied to awareness with the symbolic constructs of language has been a process of human thought and interpersonal influence for millennia. Freud and his followers popularized unconscious motivation in a culture of the individual, of a self viewed as both separate and sufficient, which is a uniquely western world view akin to the survival of the fittest.
The resultant status of the unconscious mind may be viewed as a social construction - that the unconscious exists because people agree to behave as if it exists . Symbolic interactionism goes further and argues that people's selves (conscious and unconscious) though purposeful and creative are nevertheless social products .

# Unconscious process and unconscious mind
Neuroscience is an unlikely place to find support for a proposition as adaptable as the unconscious mind . For example, "Researchers at Columbia University Medical Center have found that fleeting images of fearful faces - images that appear and disappear so quickly that they escape conscious awareness - produce unconscious anxiety that can be detected in the brain with the latest neuroimaging machines." The conscious mind is hundreds of milliseconds behind those unconscious processes.
To understand that research a distinction has to be drawn between unconscious processes and the unconscious mind. They are not the same. Neuroscience is more likely to examine the former than the latter. The unconscious mind and its expected psychoanalytic contents       are also different from unconsciousness, coma and a minimally conscious state. The differences in the uses of the term can be explained, to a degree, by different narratives about what we know.  This is called epistemology - the study of knowledge - of how we know what we know. Science is as much a narrative as psychoanalysis and both rely on their own paradigm. One such paradigm is psychoanalytic theory 

# The psychoanalytic unconscious
Probably the most detailed and precise of the various notions of 'unconscious mind'  and the one which most people will immediately think of upon hearing the term  is that developed by Sigmund Freud and his followers. It lies at the heart of psychoanalysis.
Consciousness, in Freud's topographical view (which was his first of several psychological models of the mind) was a relatively thin perceptual aspect of the mind, whereas the subconscious was that merely autonomic function of the brain. The unconscious was considered by Freud throughout the evolution of his psychoanalytic theory a sentient force of will influenced by human drive and yet operating well below the perceptual conscious mind. For Freud, the unconscious is the storehouse of instinctual desires, needs, and psychic actions. While past thoughts and memories may be deleted from immediate consciousness, they direct the thoughts and feelings of the individual from the realm of the unconscious.
Freud divided mind into the conscious mind or Ego and two parts of the Unconscious: the Id or instincts and the Superego. He used the idea of the unconscious in order to explain certain kinds of neurotic behavior.
In this theory, the unconscious refers to that part of mental functioning of which subjects make themselves unaware .
Freud proposed a vertical and hierarchical architecture of human consciousness: the conscious mind, the preconscious, and the unconscious mind - each lying beneath the other. He believed that significant psychic events take place "below the surface" in the unconscious mind., like hidden messages from the unconscious - a form of intrapersonal communication out of awareness. He interpreted these events as having both symbolic and actual significance.
For psychoanalysis, the unconscious does not include all that is not conscious, rather only what is actively repressed from conscious thought or what the person is averse to knowing consciously. In a sense this view places the self in relationship to their unconscious as an adversary, warring with itself to keep what is unconscious hidden. The therapist is then a mediator trying to allow the unspoken or unspeakable to reveal itself using the tools of psychoanalysis. Messages arising from a conflict between conscious and unconscious are likely to be cryptic. The psychoanalyst is presented as an expert in interpreting those messages.
For Freud, the unconscious was a repository for socially unacceptable ideas, wishes or desires, traumatic memories, and painful emotions put out of mind by the mechanism of psychological repression. However, the contents did not necessarily have to be solely negative. In the psychoanalytic view, the unconscious is a force that can only be recognized by its effects  it expresses itself in the symptom.
Unconscious thoughts are not directly accessible to ordinary introspection, but are supposed to be capable of being "tapped" and "interpreted" by special methods and techniques such as random association, dream analysis, and verbal slips (commonly known as a Freudian slip), examined and conducted during psychoanalysis.
Freud's theory of the unconscious was substantially transformed by some of his followers, among them Carl Jung and Jacques Lacan.

## Jung's collective unconscious
Carl Jung developed the concept further. He divided the unconscious into two parts: the personal unconscious and the collective unconscious. The personal unconscious is a reservoir of material that was once conscious but has been forgotten or suppressed.
The collective unconscious is the deepest level of the psyche containing the accumulation of inherited experiences. There is a considerable two way traffic between the ego and the personal unconscious. For example, our attention can wander from this printed page to a memory of something we did yesterday.

## Lacan's linguistic unconscious
Jacques Lacan's psychoanalytic theory contends that the unconscious is structured like a language.
The unconscious, Lacan argued, was not a more primitive or archetypal part of the mind separate from the conscious, linguistic ego, but rather, a formation every bit as complex and linguistically sophisticated as consciousness itself.
If the unconscious is structured like a language, Lacan argues, then the self is denied any point of reference to which to be 'restored' following trauma or 'identity crisis'. In this way, Lacan's thesis of the structurally dynamic unconscious is also a challenge to the ego psychology of Anna Freud and her American followers.
Lacan's idea of how language is structured is largely taken from the structural linguistics of Ferdinand de Saussure and Roman Jakobson, based on the function of the signifier and signified in signifying chains.  This may leave Lacan's entire model of mental functioning open to severe critique, since in mainstream linguistics, Saussurean models have largely been replaced.
The starting point for the linguistic theory of the unconscious was a re-reading of Freud's The Interpretation of Dreams.  There, Freud identifies two mechanisms at work in the formation of unconscious fantasies: condensation and displacement.  Under Lacan's linguistic reading, condensation is identified with the linguistic trope of metonymy, and displacement with metaphor.
Lacan applied the ideas of de Saussure and Jakobson to psychoanalytic practice. For example, while de Saussure described the linguistic sign as a relationship between a signified and an arbitrary signifier, Lacan inverted the relationship, putting in first place the signifier as determining the signified, and so being closer to Freud's position that human beings know what they say only as a result of a chain of signifiers, a-posteriori. Lacan began this work with the case of Emma (1895) from Freud, whose symptoms were disenchained in a two-phase temporal processTemplate:Clarifyme. Lacan allowed many young people, by this bias, to begin re-reading Freud as more akin to modernity than cognitive psychology. For Lacan, modernity is the era when humans begin to grasp their essential dependence on language.

## Controversy
Today, there are still fundamental disagreements within psychology about the nature of the unconscious mind. It may simply stand as a metaphor that ought not to be reified. Outside formal psychology, a whole world of pop-psychological speculation has grown up in which the unconscious mind is held to have any number of properties and abilities, from animalistic and innocent, child-like aspects to savant-like, all-perceiving, mystical and occultic properties.
There is a great controversy over the concept of an unconscious in regard to its scientific or rational validity and whether the unconscious mind exists at all. Among philosophers, Karl Popper was one of Freud's most notable contemporary opponents. Popper argued that Freud's theory of the unconscious was not falsifiable, and therefore not scientific. He objected not so much to the idea that things happened in our minds that we are unconscious of; he objected to investigations of mind that were not falsifiable. If one could connect every imaginable experimental outcome with Freud's theory of the unconscious mind, then no experiment could refute the theory.
In the social sciences, John Watson, considered to be the first American behaviourist, criticizes the idea of an "unconscious mind," for similar line of reasoning, and instead focused on observable behaviors rather than on introspection.
Unlike Popper, the epistemologist Adolf Grunbaum argues that psychoanalysis could be falsifiable, but its evidence has serious epistemological problems. David Holmes  examined sixty years of research about the Freudian concept of repression, and concluded that there is no positive evidence for this concept. Given the lack of evidence of many Freudian hypotheses, some scientific researchers proposed the existence of unconscious mechanisms that are very different from the Freudian ones. They speak of a cognitive unconscious John Kihlstrom  , an adaptive unconscious Timothy Wilson , or a dumb unconscious Loftus & Klinger , which executes automatic processes but lacks the complex mechanisms of repression and symbolic return of the repressed.
Ludwig Wittgenstein and Jacques Bouveresse argued that Freudian thought exhibits a systemic confusion between reasons and causes: the method of interpretation can give reasons for new meanings, but are useless to find causal relations (which require experimental research). Wittgenstein gave the following example (in his Conversations with Rush Rhees): if we throw objects on a table, and we give free associations and interpretations about those objects, well find a meaning for each object and its place, but we wont find the causes.
Other critics of Freudian unconscious were Hans Eysenck, Jacques Van Rillaer, Frank Cioffi, Marshal Edelson, Edward Erwin.
Some stress, however, that these critics did not grasp the real importance of Freud conceptions, and rather tried to criticize Freud on the basis of other fields. The first who really grasped this was Bertrand Russell (see for example: "The impact of science in society, 1952). But in modern times, many other thinkers, as for example Althusser, and Bernard-Henri-Levy, managed to grasp the "falsification theory" from Popper, and the critics from Eysenck, as another expression of Master's discourse: the aspiration to a so-called scientific society leaded by evaluation. For this side of the controversy, cf the works of Jean Claude Milner in France.
In modern cognitive psychology, many researchers have sought to strip the notion of the unconscious from its Freudian heritage, and alternative terms such as 'implicit' or 'automatic' have come into currency.  These traditions emphasize the degree to which cognitive processing happens outside the scope of cognitive awareness, and show that things we are unaware of can nonetheless influence other cognitive processes as well as behavior     .  Active research traditions related to the unconscious include implicit memory (see priming, implicit attitudes), and nonconscious acquisition of knowledge (see Lewicki, see also the section on cognitive perspective, below.

# Unconscious mind in contemporary cognitive psychology

## Research
While, historically, the psychoanalytic research tradition was the first to focus on the phenomenon of unconscious mental activity (and still the term "unconsciousness" or "the subconscious", for many, appears to be not only deeply rooted in, but almost synonymous with psychoanalytic tradition), there is an extensive body of conclusive research and knowledge in the contemporary cognitive psychology devoted to the mental activity that is not mediated by conscious awareness.
Most of that (cognitive) research on unconscious processes has been done in the mainstream, academic tradition of the information processing paradigm. As opposed to the psychoanalytic tradition, driven by the relatively speculative (in the sense of being hard to empirically verify), theoretical concepts such as Oedipus complex or Electra complex, the cognitive tradition of research on unconscious processes is based on relatively few theoretical assumptions and is very empirically oriented (i.e., it is mostly data driven). Cognitive research has revealed that automatically, and clearly outside of conscious awareness, individuals register and acquire more information than what they can experience through their conscious thoughts.

## Unconscious processing of information about frequency
For example, an extensive line of research conducted by Hasher and Zacks has demonstrated that automatically (i.e., outside of conscious awareness and without engaging conscious information processing resources), individuals register information about the frequency of events.  Moreover, that research demonstrates that perceivers do that unintentionally, truly "automatically," regardless of the instructions they receive, and regardless the information processing goals they have.  Interestingly, their ability to unconsciously, and relatively accurately tally frequency of events appear to have little or no relation to the individual's age, education, intelligence, or personality, thus it may represent one of the fundamental building blocks of human orientation in the environment and possibly the acquisition of procedural knowledge and experience, in general.

## Artificial grammars
Another line of (non-psychoanalytic) early research on unconscious processes was initiated by Arthur Reber, using so-called "artificial grammar" methodology.  That research revealed that individuals exposed to novel words created by complex set of artificial, synthetic "grammatical" rules (e.g., GKHAH, KHABT...), quickly develop some sort of a "feel" for that grammar and subsequent working knowledge of that grammar, as demonstrated by their ability to differentiate between, new grammatically "correct" (i.e., consistent with the rules) and "incorrect" (inconsistent) words.  Interestingly, that ability does not appear to be mediated, or even accompanied by the declarative knowledge of the rules (i.e., individuals' ability to articulate how they  distinguish between the correct and incorrect words). Thus causing the overall out view of the world.

## Unconscious acquisition of procedural knowledge
The gist of these early findings (from the seventies) has been significantly extended in the eighties and nineties by further research showing that outside of conscious awareness individuals not only acquire information about frequencies (i.e., "occurrences" of features or events) but also co-occurrences (i.e., correlations or, technically speaking, covariations) between features or events.  Extensive research on nonconscious acquisition of information about covariations was conducted by Pawel Lewicki, followed by research of D. L. Schachter (who is known for introducing the concept of implicit memory, L. R. Squire, and others.
In the learning phase of a typical study, participants were exposed to a stream of stimuli (trials or events, such as strings of letters, digits, pictures, or descriptions of stimulus persons) containing some consistent but non-salient (hidden) covariation between features or events.  For example, every stimulus person presented as "fair" would also have a slightly elongated face.  It turned out that even if the manipulated covariations were non-salient and inaccessible to subjects' conscious awareness, the perceivers would still acquire a nonconscious working knowledge about those covariations.  For example, if in the testing phase of the study, participants were asked to make intuitive judgments about the personalities of new stimulus persons presented only as pictures (with no personality descriptions), and judge the "fairness" of the depicted individuals, they tend to follow the rules nonconsciously acquired in the learning phase and if the stimulus person had a slightly elongated face, they would report an intuitive feeling that this person was "fair."
Nonconscious acquisition of information about covariations appears to be one of the fundamental and ubiquitous processes involved in the acquisition of knowledge (skills, experience) or even preferences or personality dispositions, including disorders or symptoms of disorders.

## A note on terminology: "unconscious" vs. "nonconscious"
Unlike in the psychoanalytic research tradition that uses the terms "unconscious" or "subconscious," in the cognitive tradition, the processes that are not mediated by conscious awareness are sometimes referred to as "nonconscious." This term (rarely used in psychoanalysis) stresses the empirical and purely descriptive nature of that phenomenon (a qualification as simply "not being conscious") in the tradition of cognitive research.
Specifically, the process is non-conscious when even highly motivated individuals fail to report it, and few theoretical assumptions are made about the process (unlike in psychoanalysis where, for example, it is postulated that some of these processes are being repressed in order to achieve certain goals.