For the term animism we have to thank Dr. E. B. Tylor, whose _Primitive Culture_, in which the animistic theory is developed, may almost be said to mark the beginning of scientific anthropology. In this work, however, there is a decided tendency (which indeed displays itself in most of the leading anthropological works, as, for example, in those by Dr. Frazer) to regard men, or at any rate primitive men, as having a mind absolutely homogeneous, and therefore as thinking, feeling, and acting in the same way under all conditions alike. But a decided change is beginning to manifest itself in the interpretation of the customs and beliefs of the ruder races. It is assumed as a working principle that each ethnic group has or tends to have an individuality of its own, and, moreover, that the members of such a group think, feel, and act primarily as the representatives, so to speak, of that ethnic individuality in which they live, move, and have their being. That is to say, a social as contrasted with an individual psychology must, it is held, pronounce both the first and last word regarding all matters of mythology, religion, and art in its numerous forms. The reason is that these are social products, and as such are to be understood only in the light of the laws governing the workings of the collective mind of any particular ethnic group. Such a method is, for instance, employed in Mr. William McDougall's _Social Psychology_, in Mr. R. R. Marett's _Threshold of Religion_, and in many anthropological articles to be found in _L'Année Sociologique_. If, therefore, we hold by this new and fruitful method of social psychology we must be prepared to treat the Fairy-Faith of the Celtic peoples also in and for itself, as expressive of an individuality more or less unique. It might, indeed, be objected that these peoples are not a single social group, but rather a number of such groups, and this is, in a way, true. Nevertheless their folk-lore displays such remarkable homogeneity, from whatever quarter of the Celtic world it be derived, that it seems the soundest method to treat them as one people for all the purposes of the student of sociology, mythology, and religion. Granting, then, such a unity in the beliefs of the pan-Celtic race, we are finally obliged to distinguish as it were two aspects thereof.