It would be evasive to shirk mention of the fact that many of the most devoted servants of health and morals object to public discussion of the facts of sex. They discard enlightenment about sex as relatively unimportant because a clean ancestry, decency in the family and neighborhood, and noble needs in friendship, love, and marriage must, in any case, be the main roots of healthy direction and ideal restraint of the sex-instinct. Or they fear enlightenment as a possible stimulus to undesirable imagination and experimentation. Or they dislike, even abhor, it as esthetically repulsive--shocking to an unreasoned but cherished craving for silence about these things--a craving which the customs of our land and time have made an unwritten law of society. Of the first of these three attitudes, it may be said briefly that the relative unimportance of enlightenment is a fact, but no argument against it. Modesty, austerity, and clean living on the part of parents will counterbalance much negligence in direct guidance or protection. But the former need be in no wise lessened by improving the latter. Of the second, I dare affirm that if the men and women in America should stop whatever they are doing for an evening and read this book, there would be less harmful imagination as a result than from the occupations which its reading would replace. Of all the causes of sexual disorder, the reading of scientific books by reputable men is surely the least! The third--that is, the esthetic--repulsion toward publicity in respect to the natural history of sex, I will not pretend to judge. Only we must not strain at gnats and swallow camels. It is no sign of true esthetic or moral sensitiveness for a person to be shocked by 'Ghosts,' 'Mrs. Warren's Profession,' or 'The Sexual Life of the Child,' who finds pleasant diversion in the treatment of sex-behavior in the ordinary novel, newspaper, or play. On the whole, the gain from giving earnest men and women the facts they need, seems likely to outweigh by much the harm done to such light minds as will be misled, or to such sentimental minds as will be wounded, by enlightenment about sex. No harm will be done to those men and women whose interest in the welfare of children makes them eager to face every problem that it involves, and whose faith in the ideal possibilities of love between the sexes is too well-grounded to be disturbed by the facts of its natural history. EDWARD L. THORNDIKE. MAY, 1912. PREFACE