In speaking of the "unconscious" I purposely left out from consideration the way in which the sum total of its content was separated from the conscious mental life of the individual, in order to bring it in alignment with the discussion of the principles of resistance and repression. The content of the unconscious, broadly speaking, is brought about through the activity of these two principles. If one endeavors to unearth by means of psychoanalysis the pathogenic unconscious mental impulses, or if one endeavors to bring to consciousness some instinctive biologic craving which may be responsible for the individual's conscious behavior, one regularly encounters a very strong resistance on the part of the patient, a force is regularly betrayed whose object it seems to be to prevent them from becoming conscious and to compel them to remain in the unconscious. This is Freud's conception of the principle of resistance and from its constant coming to the fore whenever an endeavor is made to penetrate into the unconscious, Freud deducts that the same forces which today oppose as resistance the becoming conscious of the unconscious purposely forgotten, must at one time have accomplished this forgetting and forced the offending pathogenic experience out of consciousness. This mechanism he terms repression. We spoke of an offending pathogenic experience, or in other words what has been termed a psychic trauma. But the same principle holds true of certain instincts which because of their peculiar nature become engaged in a kind of struggle for existence with the ethical, moral and esthetic attributes of the personality and are thrust out of the conscious mental structure as one might say by an act of the will. We are especially concerned here with these inacceptable instincts, for the elucidation of which a brief review of Freud's theories on sexual instinct is essential.