In psychoanalytic theory, knowledge, images, emotions, and other mental phenomena that are not present in immediate consciousness but are quickly accessible and can be brought into consciousness easily without the use of special techniques.
Sigmund Freud theorized that the human mind was divided into three parts: the conscious, preconscious, and unconscious. This schema first appeared in his earliest model of mental functioning, published in his classic work, The Interpretation of Dreams (1900). Freud believed that the preconscious functions as an intermediate or transitional level of the mind—between the unconscious and the conscious—through which repressed material passes.
Freud described this arrangement spatially, depicting the unconscious as a large room crowded with thoughts and the conscious area as a smaller reception room, with a doorkeeper between the two rooms selectively admitting thoughts from the unconscious to the consciousness. Those thoughts that are restricted to the unconscious area remain repressed, meaning that they are totally invisible to the conscious self, and can be recovered only by hypnosis, free association, or some other technique. Not all thoughts allowed into the "reception area" necessarily become conscious, however. Rather, they become available for consciousness, with one or another becoming conscious at a given time when attention is drawn to it in some way. Thus, the smaller room might more properly be thought of as a preconscious area, in which are gathered all of the thoughts that are not deliberately repressed. Because of their relative closeness to each other, Freud actually grouped the conscious and preconscious systems together in contrast to the unconscious, emphasizing that thoughts in the conscious and preconscious categories do not differ in any essential way and can be distinguished only functionally. A preconscious thought can quickly become conscious by receiving attention, and a conscious thought can slip into the preconscious when attention is withdrawn from it.
Firestone, Robert. Psychological Defenses in Everyday Life. New York: Human Sciences Press, 1989.
Goleman, Daniel. Vital Lies, Simple Truths: the Psychology of Self-Deception. New York: Simon and Schuster, 1985.