Fairies are generally described as human in appearance and having magical powers. Their origins are less clear in the folklore, being variously dead, or some form of demon, or a species completely independent of humans or angels. Folklorists have suggested that their actual origin lies in a conquered race living in hiding, or in religious beliefs that lost currency with the advent of Christianity. These explanations are not necessarily incompatible, and they may be traceable to multiple sources.Much of the folklore about fairies revolves around protection from their malice, by such means as cold iron (iron is like poison to fairies, and they will not go near it) or charms of rowan and herbs, or avoiding offense by shunning locations known to be theirs. In particular, folklore describes how to prevent the fairies from stealing babies and substituting changelings, and abducting older people as well. Many folktales are told of fairies, and they appear as characters in stories from medieval tales of chivalry, to Victorian fairy tales, and up to the present day in modern literature.In his manuscript, The Secret Commonwealth of Elves, Fauns and Fairies, Reverend Robert Kirk, minister of the Parish of Aberfoyle, Stirling, Scotland, wrote in 1691:
"These Siths or Fairies they call Sleagh Maith or the Good People...are said to be of middle nature between Man and Angel, as were Daemons thought to be of old; of intelligent fluidous Spirits, and light changeable bodies (lyke those called Astral) somewhat of the nature of a condensed cloud, and best seen in twilight. These bodies be so pliable through the sublety of Spirits that agitate them, that they can make them appear or disappear at pleasure"
Although in modern culture they are often depicted as young, sometimes winged, humanoids of small stature, they originally were depicted much differently: tall, radiant, angelic beings or short, wizened trolls being two of the commonly mentioned forms. Diminutive fairies of one kind or another have been recorded for centuries, but occur alongside the human-sized beings; these have been depicted as ranging in size from very tiny up to the size of a human child. Even with these small fairies, however, their small size may be magically assumed rather than constant.Wings, while common in Victorian and later artwork of fairies, are very rare in the folklore; even very small fairies flew with magic, sometimes flying on ragwort stems or the backs of birds.Nowadays, fairies are often depicted with ordinary insect wings or butterfly wings. Various animals have also been described as fairies. Sometimes this is the result of shape shifting on part of the fairy, as in the case of the selkie (seal people); others, like the kelpie and various black dogs, appear to stay more constant in form.In some folklore fairies have green eyes and often bite. Though they can confuse one with their words, fairies cannot lie. They hate being told 'thank you', as they see it as a sign of one forgetting the good deed done, and want something that'll guarantee remembrance.