We may take as a good example of the historical complexity of significant attitudes and actions in life, the process of falling in love—especially if it is not, or at least seems not to be, love at first sight. It is generally admitted that, in the development of this psychological phenomenon, onlookers see most of the game. In other words, the actions of the two persons who are gradually becoming more and more attracted to each other are partly determined by motives, which, unknown to them, are patent to their observant relations and friends. Further examples may be given to illustrate this important and oft-disputed point. Let us suppose that a musical critic, after hearing a new symphony by an unconventional composer, immediately writes a lengthy appreciation of the performance. It is clear that nobody would expect him to be able to give, off-hand, an account of his reasons for every sentence of the criticism. But it is obvious that a single phrase in this account may be but the apex of a whole pyramid of memories emanating from the critic’s technical training, his attitude towards the new departure, experiences highly coloured with emotion which a few notes of the music may have evoked, and his mental condition at the time he heard the performance. Nobody denies that these may have shaped or even determined his criticism. But who believes either that they were all conscious at the time of writing the article, or that he could resuscitate them without much time and trouble and perhaps the help of a cross-examiner? Again, there are occasions when society expects that a man shall be unconscious of the reasons for some of his actions. He is expected, for example, to behave politely, attentively and chivalrously to ladies, not because at the moment of taking the outside of the pavement he remembers why he does so, but simply because he has been brought up in this way. And conversely, too conscious politeness in a man arouses in others—and often rightly—the suspicion that it is a recent acquisition. We see then that it is rare for a man to be able to give a true account, even to himself, of the reasons underlying his important acts and beliefs, when his mental condition is relatively calm and his social relationships are normal. But when a case of mental disorder is in question it becomes quite obvious that the patient is frequently not in a position to give, either to himself or to another, anything like a complete or true enumeration and description of the antecedent experiences which have brought about his present condition. It therefore becomes necessary to admit that unconscious factors of great importance may play an influential part in the production of mental disorder and that, therefore, some way must be found of tapping these submerged streams.