The word “love” is applicable to the sexual impulse of human beings only. Its use implies that in the case of man the purely animal feelings have acquired an =importance= far greater than that of subserving the purposes of mere reproduction, and aim at a =goal= transcending that of the preservation of the species. The nature of human love can be understood and explained only with reference to this intimate and inseparable union of its purposes in respect of the preservation of the species and its independent significance in the life of the loving individual himself. Herein is to be found the starting-point of the whole so-called “sexual problem,” and it is necessary that the matter should be clearly understood at the outset of this book. In earlier days human love was mainly concerned with the purposes of the species. Modern civilized man, conceiving history as progress in the consciousness of freedom, has also come to recognize the profound =individual= significance of love for his own inward growth, for the proper development of his free manhood. To quote a phrase from Georg Hirth, a cultured modern writer, the genuine experienced love of a civilized man of the present day is one of the “ways to freedom.” By love is made manifest, and through love is developed, his inmost individual nature. For this reason Schopenhauer’s “Metaphysik der Geschlechtsliebe” (“Metaphysic of Sexual Love”), which wholly ignores this individual factor, must be regarded, brilliant as it unquestionably is, as a quite inadequate explanation of the nature of love. Again, a recent writer, Arnold Lindwurm, greatly influenced by Schopenhauer’s teaching, in the introduction to his work entitled “Ueber die Geschlechtsliebe in sozial-ethische Beziehung” (“Sexual Love in its Socio-Ethical Relations”), writes: “The =fruit of love=, =children=, and =marriage= as a domestic institution indispensable for the upbringing of children--these constitute the author’s ethical criterion in the field of sexual research; these also form the socio-ethical goal of all sexual love, inasmuch as the =sole= standard by which sexual love can be judged is the procreation and upbringing of children.” We, however, at the very outset, contest the validity of such a standpoint, for we consider that it fails entirely to do justice to the nature of modern love. For the history of the human sexual impulse teaches us beyond dispute that, in the course of the development of the human species, that impulse, through its progressive association with intellectual and emotional elements to form the complex whole designated by the term “love,” has undergone a progressive individualization, and has attained a more defined significance for the unitary human being. At the present day sexual love constitutes a part of the very being of the civilized man; his sexual life clearly reflects his individual nature, and love influences his development in an enduring manner.