Freud, one of the most influential theorists in modern history, was the creator of psychoanalysis, his method for treating mental illness and neurosis through the dialogue between a patient and a psychoanalyst.  Over a hundred years later, Freud’s concepts and terminology—including words like Ego, Id, Superego, Oedipus Complex,  Libido, Penis Envy, Transference, Freudian Slip, and Denial—remain the currency of modern life, integral to the way most people, in therapy or not,  decipher human behavior. Central to his method of analyzing his patients was the interpretation of dreams as sources of insight into unconscious desires. Freud began with the idea that mental illness derives from repressed experiences—when these things are thwarted from expression, they result in neurosis.  Eventually he postulated the "Seduction Theory," the idea that the only cause of neurosis was an episode of sexual abuse that occurred in childhood.  Freud’s conviction that sexuality was the underlying basis for all repression and its subsequent illness remained paramount in his thinking throughout his life.