Not only do failures occur in the adjustment of action to circumstance, but when these failures occur, or when the conditions are such as would lead to failure if the reactions took their ordinary form, animal behaviour has been found to be capable of modification. Exact observation on animals has shown that their reactions to their surroundings have not the rigid and mechanical character which was once ascribed to them. On the one hand, it has been found that the behaviour of animals, even such animals as the insects which are regarded as pre-eminent patterns of the instinctive, shows many features, such as adaptability to unusual conditions, which can only be explained by qualities of the same order as those belonging to intelligence. All recent work in psychology 'has shown this distinction to be of little value. It is not long since it was regarded as a sufficient definition of instinct that it is the mode of mental activity proper to animals as distinguished from the intelligence which was believed to be the chief, or even the only, factor of any importance in regulating Man's behaviour. Classics in the History of Psychology - Rivers (1920) Chapter 6 Classics in the History of PsychologyĪ CONTRIBUTION TO A BIOLOGICAL THEORY OF THE PSYCHO-NEUROSES

All or none principle definition