This book is the fruit of nearly twenty years of work in the field of practical psychology. It gradually arose intellectually, firstly from countless impressions and experiences in psychiatric and neurological practice as well as from dealing with people of all social classes, then from my personal confrontation with friend and foe, and finally from the criticism of the psychological peculiarity of myself I have resolved not to burden the reader with casuistry, but it was important to me to attach my abstracted thoughts from experience to the existing knowledge both historically and terminologically. I undertook this undertaking less out of a need for historical justice than to to bring the experience of the medical specialist from the narrow field into more general contexts; in contexts which also enable the educated layman to make use of the experience of a special field. I would never have attempted this inclusion, which might easily be misconstrued as an intrusion into other fields, unless I believed that the psychological points of view presented in this book are of general importance and applicability, and therefore better in a general context dealt with than left in the form of a scientific hypothesis. In accordance with my intention, I have limited myself to dealing with the ideas of individual processors of the problem at hand and have refrained from to mention everything that has already been said in relation to our question. Quite apart from the fact that it is far beyond my power to achieve even a near completeness of such an inventory of relevant materials and opinions, such a collection would contribute nothing thorough to the discussion and development of the problem. I have therefore left out much of what I have collected over the years without regret and have limited myself to the main points as far as possible. A valuable document that gave me a lot of help fell victim to this renunciation. This is an extensive correspondence with my friend, Dr. medical H. Schmid in Basel, whom I discussed with him about the type question. I owe a great deal of clarification to this exchange of views, and much of it has also been included in my book, albeit in a different and repeatedly revised form. Essentially, this exchange of letters is part of the preliminary work, the disclosure of which would create more confusion than clarity. But I owe it to my friend's efforts to express my thanks at this point.