Although in recent times we have had revelations of the psychical life of half-women and three-quarter women, it is practically only about the male side of them that they have written. We have really only one clue; we have to rely upon the female element in men. The principle of sexually intermediate forms is the authority for what we know about women through men. I shall define and complete the application of this principle later on. In its indefinite form, the principle would seem to imply that the most womanish man would be best able to describe woman, and that the description might be completed by the real woman. This, however, is extremely doubtful. I must point out that a man can have a considerable proportion of femaleness in him without necessarily, to the same extent, being able to portray intermediate forms. It is the more remarkable that the male can give a faithful account of the nature of the female; since, indeed, it must be admitted from the extreme maleness of successful portrayers of women that we cannot dispute the existence of this capacity in the abstract male; this power of the male over the female is a most remarkable problem, and we shall have to consider it later. For the present we must take it as a fact, and proceed to inquire in what lies the actual psychological difference between male and female. It has been sought to attribute the fundamental difference of the sexes to the existence of a stronger sexual impulse in man, and to derive everything else from that. Apart from the question as to whether the phrase “sexual instinct” denotes a simple and real thing, it is to be doubted if there is proof of such a difference. It is not more probable than the ancient theories as to the influence of the “unsatisfied womb” in the female, or of the “semen retentum” in men, and we have to be on guard against the current tendency to refer nearly everything to sublimated sexual instinct. No systematic theory could be founded on a generalisation so vague. It is most improbable that the greater or lesser strength of the sexual impulse determines other qualities. As a matter of fact, the statements that men have stronger sexual impulses than women, or that women have them stronger than men, are false. The strength of the sexual impulse in a man does not depend upon the proportion of masculinity in his composition, and in the same way the degree of femininity of a woman does not determine her sexual impulse. These differences in mankind still await classification.