If, however, myth and science have the same origin, and start from a common fact, a fundamental principle is necessary, and an internal human act, which is at once the cause and genesis both of myth and science. And although the source is one, myth and science vary in their aspects and effects, and have different fields of historic activity, so that it is necessary to trace the cause of this diversity in their progress and results, to enable us to make a scientific definition of the nature of myth and science, their respective sources and objects. If on the one side we continually see the birth of fresh myths, which ramify into many fertile sources of superstitions, of religions, of poetry and aestheticism; on the other side we see almost simultaneously a more or less distinct and lively manifestation of the scientific faculty, although still in an empirical form. They are like two streams which issue from the same source and take a parallel course, sometimes mingling their waters, only to separate anew, and then again to become united as they fall by a wide mouth into the sea. In this manner we have ascertained the actual origin of science and of myth, and have entered on a field perhaps never before attempted nor contemplated; we have established a firm basis for such researches, and, which is perhaps still more important, have shown the continuity of the mythical faculty between man and the animal kingdom. We have ascertained this fact, in its cosmic necessities, both physiological and psychical, but without considering the faculty on which it depends; we have still to decompose the elements of which it consists, and to consider their nature and number. This inquiry forms the chief problem we have to solve, and it is precisely what we have endeavoured to state in this chapter. In the necessary order of things the fact has its physiological and cosmic conditions in man; it is therefore necessarily internal and psychical, and it is accomplished by the special and intrinsic exercise of the intelligence. We shall be convinced of this truth if we only consider that science and myth have a common origin. It is evident that there are great difficulties in such an inquiry; for, putting aside other extrinsic difficulties, we have to reduce to a single act or fact the origin of the two vast worlds of myth and science; it is needful to gauge the inmost psychical faculty of the intelligence, and to discover the continuous yet rapid and delicate process of its exercise. If we are able to attain our object and to tear away the veil which conceals this mysterious act, we shall have a noble recompense in the laborious path on which we have entered, inasmuch as we shall reveal one of the most important laws of life, of the exercise of reflex intelligence and of the genesis of science. Yet we are very sensible how far we are from being equal to the enormous difficulties of this inquiry. CHAPTER V.