Freud's insight that mental processes are fundamentally unconscious is now an unquestioned assumption of neuroscience and cognitive psychology. Psychoanalysts are now faced with the question, What differentiated the psychoanalytic unconscious from that of other disciplines? Behind this question lies a more profound issue, the mind-body or mind-brain problem. It appears to be an insoluble paradox. Freud's concept of repression as a defense "mechanism" illustrates this paradox. To describe repression as a "mechanism" is to claim that it is analogous to a physiological process. Yet we know that repression is highly individualistic and subject to cultural values. In examining the Freudian concept of the primary process, the Noble prize-winning psychologist Daniel Kahneman has shown that the primary process is not wish fulfilling, as Freud claimed, but adaptive. The waking primary process is in the service of the reality principle. The growth of contemporary neuroscience has created challenging problems for psychoanalysis that did not exist in Freud's lifetime.