In this paper I have first briefly traced three historical stages in the development of Freud's views on the classification of instincts, leading to the present view most widely held by psycho-analysts that there are two basic classes of instincts or drives, the sexual or erotic instincts and the aggressive-destructive instincts.

Next I have proposed a revision of this basic classfication, based upon three lines of reasoning, adding explicitly defensive instincts or drives and classifying them with the aggressive-destructive drives as opposed to the erotic or libidinal instincts, so that the classification becomes (1) vital-libidinal instincts, and (2) defensive and aggressive instincts. I have tried to show why defensive instincts have not been explicitly recognized as such in psycho-analytic theory, although they were implicit in Freud's early writings on hysteria and on 'The Defence Neuro-Psychoses'.