the idea of fairies being small creatures with wings is comparatively modern. in old mythology they varied in size, but were of generally human size, and did not have wings. it is not quite clear as to whether the original fairies of Celtic mythology were the Pictish aboriginal stone age people who were here before them, or the ghosts of those long passed. The Celts mixed hsitory with myth in a way that is confusing, and they often spoke in riddles and alegories. they often refered to Faieries as "the Little People" not because of their stature, but because they had little influence and were diminished as a race. it is quite likely that as they regarded them as magical anyway, the average Celt would not distiguish any difference between a living aboriginal tribe, or a gaggle of ghosts - one and the same to them.
as time moved on, the nature spirits the Celts worshipped as Gods were increasingly regarded by later civilisations as Fairies - so we now have three kinds of Fairy - a Pict, a ghost, and an ancient god / nature spirit. Celtic mythology was woven into Christian folklore. some Fairies were still believed to be quite large - as tall as 6 foot at least, whereas others were diminutive dwarvish creatures of about two or three feet tall.
the Fairies in Shakespeare's Midsummer Night's Dream were based on Celtic Gods and Godesses - though Puck actually predates the Celts as he is a varient of the Bucca or Poohka (Harvey to you).
in essence, the commonly held idea of a Fairy is a sprite - a smaller version of the Judaic angel.
and yes - i do believe in Faeries.
