The causes on which social phenomena are dependent fall within the domain of different sciences—Biology, Psychology, or Sociology. The reader will find that I put particular stress upon the psychological causes, which have often been deplorably overlooked, or only imperfectly touched upon. And more especially do I believe that the mere instincts have played a very important part in the origin of social institutions and rules. We could not, however, by following the method of investigation here set forth, form any idea of the earlier stages of human development, unless we had _some_ previous knowledge of the antiquity of mankind. Otherwise we should, of course, be quite ignorant whether the causes in question operated or not in the past. Fortunately, in this respect also, modern science has come to results which scarcely admit any longer of being considered as mere hypotheses. It teaches us, to quote Sir John Lubbock, “that man was at first a mere savage, and that the course of history has on the whole been a progress towards civilization, though at times—and at some times for centuries—some races have been stationary, or even have retrograded;”[7] that, however, all savage nations now existing are raised high above primitive men; and that the first beings worthy to be called men, were probably the gradually transformed descendants of some ape-like ancestor. We may, further, take for granted that all the physical and psychical qualities that man, in his present state, has in common with his nearest relatives among the lower animals, also occurred at the earlier stages of human civilization. These conclusions open to us a rich source of new knowledge. Finally, as to social survivals, I agree, certainly, with Mr. McLennan that they are of great importance to Sociology. But we must be extremely careful not to regard as rudiments customs which may be more satisfactorily explained otherwise. It is only by strictly keeping to these principles that we may hope to derive information touching the early history of man. In doing so, the student will be on his guard against rash conclusions. Considering that he has to make out the primary sources of social phenomena before writing their history, he will avoid assuming a custom to be primitive, only because, at the first glance, it appears so; he will avoid making rules of exceptions, and constructing the history of human development on the immediate ground of isolated facts. It is true that the critical sociologist, on account of the deficiency of our knowledge, very often has to be content with hypotheses and doubtful presumptions. At any rate, the interests of science are better looked to, if we readily acknowledge our ignorance, than if we pass off vague guesses as established truths. * * * * *