The difficulty seems not so much to be that we have forgotten the incidents of our boyhood as that we have lost its feelings. So far as specific doings are concerned, we probably remember those crowded years more distinctly than any equal period of our entire lives. Most of us, too, remember them happily, as happily probably as any years we have lived. No, the trouble is not with the memory, but with the self. The experiences of life since we were boys have shifted our psychic centre of gravity, so that we realize the particular incident far more easily than we realize the being to whom it occurred. We do not completely feel that the boy that was is quite ourselves; and while the memory of the fact is sharp, the memory of the mental state that went with it has become dim. Therefore, it costs a distinct effort to put one’s self in the boy’s place. Any proper man will recite by the hour tales of the old swimming-hole in the summer. But if men actually felt toward the water as boys do, every club and half the private houses would have a swimming tank instead of a smoking room. But if we men fail to comprehend boys, what shall we say of the women! The experiences which we have forgotten, they have not even had; if there is a psychic fence which separates men from boys, there are at least knot-holes in the boards; but between boys and women there is a solid wall. There are parts of a boy’s soul which any woman may observe or imagine, but which no woman can ever feel. That women often do understand boys, understand them sometimes better than men do, is simply one of the marvels of feminine insight. This book is, then, addressed, first of all, to fathers, with the hope that it will, in some sort, serve to revive memories of boyhood days, not so much of specific acts of boyhood as of long-dead impulses and past ways of envisaging the world. Every man who sits down and thinks out for himself, not only what he did as a boy, but also how it feels to be a boy, and how the world and the people in it appear through a boy’s eyes, has taken a long step toward the understanding and the control of his own sons. A scientific account of certain aspects of boy psychology, such as this book aims to be, may aid this introspective process.