Psychoanalytic theory also attributed behaviour to powerful innate forces. Freud believed that behaviour was determined by two basic energies: The life instincts which found expression in sexual behaviour and the death instincts which underlie aggressive acts. These instincts though unconscious were powerful motivational forces.
Both psychoanalytic theory and instinct theory were influential in turning interest away from a rationalistic conception of people toward a motivational view that saw behaviour as the result of unconscious irrational forces within the individual.