=Applied psychology.=—Much has been discovered in recent years regarding the part played by subconscious processes in the production of normal and abnormal phenomena. But we do not as yet know the possibilities and limitations of these processes. We have as yet but an imperfect knowledge of what they can do, what they can’t do, and what they do do, and of the mechanisms by which they are called into play and provoke phenomena. _Many pathological phenomena_ have been shown to be due to subconscious processes; and it is quite probable that these play an important part in determining the mental processes of normal life, but this is still largely theory. In applied psychology and psychopathology the “subconscious” has been made use of to explain many phenomena with which we have practically to deal. Assumed as a concept the phenomena are explained by it with a greater or less degree of probability. In those _hysterical conditions_ where the subconscious processes have been shown to be split-off conscious processes, we can often recover memories of the latter and demonstrate their relation to the hysterical phenomena by the various technical methods already mentioned. But where this cannot be done, as is ordinarily the case, some conserved antecedent experience must be inferred as the causal factor and assumed to be the functioning subconscious process which determines the phenomenon. To a large extent, then, in applied psychology and psychopathology the postulation in specific cases of a subconscious process is theoretical and open to more or less doubt. In other words, although a principle may be established, its application, as in all applied sciences, is apt to meet with difficulties. Now the application of the principle of a subconscious process to the explanation of a given phenomenon is rendered peculiarly difficult because for practical purposes it is not so much the question of a subacting process that is at issue as it is of what particular antecedent experience is concerned in the process. The question is of the causal factor. For example, we may know from general experience in a large number of instances that a given hysterical phenomenon—a tic or a convulsive attack or an hallucination or a dream—must be in all probability determined by a subconscious process derived from some conserved experience, but what specific experience may be a matter of considerable uncertainty. _Hence the different theories and schools of interpretation_ that have arisen. The importance of clearly appreciating the nature of such problems and properly estimating the different theories at their true value is so great that I may be permitted a few words in further explanation.