The division of mental life into what is conscious and what is unconscious is the fundamental premise on which psycho-analysis is based; and this division alone makes it possible for it to understand pathological mental processes, which are as common as they are important, and to co-ordinate them scientifically. Stated once more in a different way: psycho-analysis cannot accept the view that consciousness is the essence of mental life, but is obliged to regard consciousness as one property of mental life, which may co-exist along with its other properties or may be absent.
