Dyads and Dialectics - Note No. 4
It is more aptly characterized as a theory of psychic drives. For a full discussion of the renderings of Freud's term Trieb see "Instinct" entry in J. Laplance and J.-B Pontalis, The Language of Psycho-Analysis, Trans. Donald Nicholson-Smith (New York & London: W.W. Norton, 1973).