The subject of every chapter in the present volume could easily form, and often has formed, the topic of a volume, and the literature of many of these subjects is already extremely voluminous.

It must therefore be our main object here not to accumulate details but to place each subject by turn, as clearly and succinctly as may be, in relation to those fundamental principles of sexual psychology which--so far as the data at present admit--have been set forth in the preceding volumes.
It may seem to some, indeed, that in this exposition I should have confined myself to the present, and not included so wide a sweep of the course of human history and the traditions of the race.

It may especially seem that I have laid too great a stress on the influence of Christianity in moulding sexual ideals and establishing sexual institutions.

That, I am convinced, is an error.

It is because it is so frequently made that the movements of progress among us--movements that can never at any period of social history cease--are by many so seriously misunderstood.