For popular treatment I divide applied psychology into such various, separated books because they naturally address very different audiences. That which interests the lawyer does not concern the physician, and again the school-teacher has his own sphere of interests. Moreover the different subjects demand a different treatment. The problems of psychology and law were almost entirely neglected. I was anxious to draw wide attention to this promising field and therefore I chose the form of loose popular essays without any aim towards systematic presentation of the subject. As to psychology and medicine almost the opposite situation prevails. There is perhaps too much talk afloat about psychotherapy, the widest circles cultivate the discussion, the magazines overflow with it. The duty of the scientific psychologist is accordingly not to stir up interest in this topic but to help in bringing this interest from mere gossip, vague mysticism, and medical amateurishness to a clear understanding of principles. What is needed in this time of faith cures of a hundred types is to deal with the whole circle of problems in a serious, systematic way and to emphasize the aspect of scientific psychological theory. Hence the whole first part of this book is an abstract discussion and its first chapters have not even any direct relation to disease. I am convinced that both physicians and ministers and all who are in practical contact with these important questions ought to be brought to such painstaking and perhaps fatiguing inquiry into principles before the facts are reached. To those who seek a discussion of life facts alone, the whole first part will of course appear to be a tedious way around; they may turn directly to the second and third parts.