In order to pursue this important inquiry into the first and final cause of the origin of myth, it is evidently not enough to make a laborious and varied collection of myths, and of the primitive superstitions of all peoples, so as to exhaust the immense field of modern ethnography. Nor is it enough to consider the various normal and abnormal conditions of psychical phenomena, nor to undertake the comparative study of languages, to ascertain how far their speech will reveal the primitive beliefs of various races, and the obscure metaphorical sayings which gave birth to many myths. It is also necessary to subject to careful examination the simplest elementary acts of the mind, in their physical and psychical complexity, in order to discover in their spontaneous action the transcendental fact which inevitably involves the genesis of the same myth, the primary source whence it is diffused by subsequent reflex efforts in various times and varying forms. In speaking of the transcendental fact, it must not be supposed that I allude to certain well-known _a priori_ speculations, which are opposed to my temper of mind and to my mode of teaching. I only use the term transcendental because this is actually the primitive condition of the fact in its inevitable beginning, whatever form the mythical representation may subsequently take. This fact is not peculiar to any individual, people, or race, but it is manifested as an essential organism of the human character, which is in all cases universal, permanent, and uniform. In order to give a clear explanation of my estimate of the _a priori_ idea, which also takes its place as the factor of experimental and positive teaching, I must observe that for those who belong to the historical and evolutionary school, _a priori_, so far as respects any organism, habit, and psychological constitution in the whole animal kingdom, in which man is also included, signifies whatever in them is fixed and permanently organized; whatever is perpetuated by the indefinite repetition of habits, organs, and functions, by means of the heredity of ages. The whole history of organisms abounds with positive and repeated proofs of this fact, which no one can doubt who is not absolutely ignorant of elementary science. Every day adds to the number of these proofs, demonstrating one of those truths which become the common property of nations.