According to the classical psycho-physiological theories, human and animal behaviour are dictated by inborn or acquired motivation. The sight of a serpent for example, is an inborn motivation for flight and fear in a dog, but the fear of a policeman, on the other hand, is an acquired motivation in humans. Acquired or derived motivations result from conditioning or associative procedures that come under the general heading of reflex theory. This does not take into account the notion of subjectivity, which subordinates the state to an act whose motive can always be traced back to the satisfaction of an inborn need of the species. But can we always talk about vital needs or acts that have been learnt when we see certain ways of behaving which cannot be explained or justified by any utility?