Freud and 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...