On the other hand, I feel a very genuine regret that I have been unable to include some discussion of the problems connected with the _size_ of families. These problems are, I am convinced, of the greatest importance. At a moment like the present when large portions of the human race are suffering from a shortage of the very necessities of existence the question of family limitation, in particular, becomes one that is of enormous, one might almost say of paramount, urgency. Nevertheless, the treatment of this question from the psychological, as distinct from the ethical, sociological or economic standpoint, has as yet been so slight and fragmentary, as to make a full consideration of the question scarcely suitable to a volume of expository character; and I have thought it better to omit the subject almost altogether than to deal with it in a manner that would be either inadequate and superficial or else manifestly inappropriate[1]. I am of course aware that much with which we have here to deal makes far from pleasant reading. The unpleasantness arises mainly from the fact that, in the pursuit of our present purpose, we are chiefly brought into contact with the unconscious and more primitive aspects of the mind rather than with the more recently acquired and more morally edifying aspects. But those who realise the importance, for human welfare and progress, of a true understanding of our mental nature, should no more be deterred from the consideration of unpleasant aspects of the mind, than should the student of economics neglect to take account of poverty or the student of hygiene turn away from the contemplation of disease. From personal observation and experience, as well as from more theoretical considerations, I have acquired a deep conviction of the significance of those aspects of the human mind with which we are here concerned. It is principally because I am assured that a wider realisation and a deeper study of these aspects--both by the student of the mind and by the ordinary reading public--will contribute in very considerable measure to the solution of many of the most important moral and social problems with which humanity is faced, that I have ventured to embark upon the following, I fear very inadequate, presentation of our knowledge on the subject. It only remains for me to express my sincere thanks to those who have assisted me in one way or another; particularly to Dr. Ernest Jones who was the first to interest me in the work of Freud and his followers, and without whose personal help in more than one direction, the present pages could not have been written. I am also deeply indebted to Mr. Cyril Burt for many valuable criticisms and suggestions, to Mr. Edward de Maries for several interesting comments on the subject matter of the last few chapters, to Mr. Eric Hiller for assistance in seeing the work through the press, and to my wife for help in a variety of ways throughout the work. J. C. F.