The possibility of applying the principle of correlated variation to psychology depends on differential psychology, the study of psychological variation. I believe, moreover, that a combination of study of the anatomical “habit,” and the mental characteristics will lead to a statical psycho-physics, a true science of physiognomy. The rule of investigation in all the three sciences will have to be that the question is posed as follows; given that two organisms are known to differ in one respect, in what other respects are they different? This will be the golden rule of discovery, and, following it, we shall no longer lose ourselves hopelessly in the dark maze that surrounds the answer to the question “Why?” As soon as we are informed as to one difference, we must diligently seek out the others, and the mere putting of the question in this form will directly bring about many discoveries. The conscious pursuit of this rule of investigation will be particularly valuable in dealing with problems of the mind. Mental actions are not co-existent in the sense of physical characters, and it has been only by accidental and fortunate chances, when the phenomena have presented themselves in rapid succession in an individual, that discoveries of correlation in mental phenomena have been noticed. The correlated mental phenomena may be very different in kind, and it is only when we know what we are after and deliberately seek for them that we shall be able to transcend the special difficulties of the kind of material we are investigating, and so secure for psychology what is comparatively simple in anatomy. CHAPTER VI EMANCIPATED WOMEN As an immediate application of the attempt to establish the principle of intermediate sexual forms by means of a differential psychology, we must now come to the question which it is the special object of this book to answer, theoretically and practically, I mean the woman question, theoretically so far as it is not a matter of ethnology and national economics, and practically in so far as it is not merely a matter of law and domestic economy, that is to say, of social science in the widest sense. The answer which this chapter is about to give must not be considered as final or as exhaustive. It is rather a necessary preliminary investigation, and does not go beyond deductions from the principles that I have established. It will deal with the exploration of individual cases and will not attempt to found on these any laws of general significance. The practical indications that it will give are not moral maxims that could or would guide the future; they are no more than technical rules abstracted from past cases. The idea of male and female types will not be discussed here; that is reserved for the second part of my book. This preliminary investigation will deal with only those charactero-logical conclusions from the principle of sexually intermediate forms that are of significance in the woman question.