Although Group Psychology is only in its infancy, it embraces an immense number of separate issues and offers to investigators countless problems which have hitherto not even been properly distinguished from one another. The mere classification of the different forms of group formation and the description of the mental phenomena produced by them require a great expenditure of observation and exposition, and have already given rise to a copious literature. Anyone who compares the narrow dimensions of this little book with the extent of Group Psychology will at once be able to guess that only a few points chosen from the whole material are to be dealt with here. And they will in fact only be a few questions with which the depth-psychology of psycho-analysis is specially concerned. II LE BON'S DESCRIPTION OF THE GROUP MIND Instead of starting from a definition, it seems more useful to begin with some indication of the range of the phenomena under review, and to select from among them a few specially striking and characteristic facts to which our inquiry can be attached. We can achieve both of these aims by means of quotation from Le Bon's deservedly famous work _Psychologie des foules_.[2] Let us make the matter clear once again. If a Psychology, concerned with exploring the predispositions, the instincts, the motives and the aims of an individual man down to his actions and his relations with those who are nearest to him, had completely achieved its task, and had cleared up the whole of these matters with their inter-connections, it would then suddenly find itself confronted by a new task which would lie before it unachieved. It would be obliged to explain the surprising fact that under a certain condition this individual whom it had come to understand thought, felt, and acted in quite a different way from what would have been expected. And this condition is his insertion into a collection of people which has acquired the characteristic of a 'psychological group'. What, then, is a 'group'? How does it acquire the capacity for exercising such a decisive influence over the mental life of the individual? And what is the nature of the mental change which it forces upon the individual? It is the task of a theoretical Group Psychology to answer these three questions. The best way of approaching them is evidently to start with the third. Observation of the changes in the individual's reactions is what provides Group Psychology with its material; for every attempt at an explanation must be preceded by a description of the thing that is to be explained.