As Mr. R. U. Sayee has well said: 'It should be clear a priori that fairy lore must have developed as a result of modifications and accretions received in different countries and at many periods, though we must not overlook the part played by tradition in providing a mould that to some extent determines the nature of later additions.' It must also be self-evident that a great deal of confusion has been caused by the assumption that some spirit-types were fairies which in a more definite sense are certainly not of elfin provenance. In some epochs, indeed, Faerie appears to have been regarded as a species of limbo to which all 'pagan' spirits - to say nothing of defeated gods, monsters, and demons - could be banished, along with the personnel of Olympus and the rout of witchcraft. Such types, however, are usually fairly easy of detection.
Lewis Spence, British Fairy Origins
fairies, fairy, monsters, mythology, pagan-gods, spirits