Old and young, educated and uneducated, peasant and city-bred, testify to the actual existence of the Celtic Fairy-Faith; and the evidence from Roman Catholics stands beside that from Protestants, the evidence of priests supports that of scholars and scientists, peasant seers have testified to the same kind of visions as highly educated seers; and what poets have said agrees with what is told by business men, engineers, and lawyers. But the best of witnesses, like ourselves, are only human, and subject to the shortcomings of the ordinary man, and therefore no claim can be made in any case to infallibility of evidence: all the world over men interpret visions pragmatically and sociologically, or hold beliefs in accord with their own personal experiences; and are for ever unconsciously immersed in a sea of psychological influences which sometimes may be explainable through the methods of sociological inquiry, sometimes may be supernormal in origin and nature, and hence to be explained most adequately, if at all, through psychical research. Our study is a study of human nature itself, and, moreover, often of human nature in its most subtle aspects, which are called psychical; and the most difficult problem of all is for human nature to interpret and understand its own ultimate essence and psychological instincts. Our whole aim is to discover what reasonableness may or may not stand behind a belief so vast, so ancient, so common (contrary to popular non-Celtic opinion) to all classes of Celts, and so fundamental a shaping force in European history, religion, and social institutions. When we state our conviction that the Fairy-Faith is common to all classes of Celts, we do not state that it is common to all Celts. The materialization of the age has affected the Fairy-Faith as it has affected all religious beliefs the world over. This has been pointed out by Dr. Hyde, by Dr. Carmichael, and by Mr. Jenner in their respective introductions for Ireland, Scotland, and Cornwall. Nevertheless, the Fairy-Faith as the folk-religion of the Celtic peoples is still able to count its adherents by hundreds of thousands. Even in many cases where Christian theology has been partially or wholly discarded by educated Celts, in the country or in the city, as being to them in too many details out of harmony with accepted scientific truths, the belief in fairies has been jealously retained, and will, so it would seem, be retained in the future.