In the psychoanalysis of Sigmund Freud (1856–1939), a subsystem of the mental apparatus characterized by consciousness, receiving input from the outside world via the sensory receptors and from the preconscious via the activation of memories, and playing a dynamic role in avoidance of unacceptable thoughts or ideas and control of the pleasure principle. In An Outline of Psycho-Analysis (1938), Freud considered the existence of this system to be ‘a fact without parallel, which defies all explanation or description. … Nevertheless, if anyone speaks of consciousness we know immediately and from our most personal experience what is meant by it’ (Standard Edition, XXIII, pp. 144–207, at p. 157). ω or W or Pcpt-Cs abbrev.