[OscarCunningham]

They're supernatural in terms of literary genre, but in terms of the actual content of the belief there's nothing supernatural about the idea that there could be people much smaller than us (unless you also claim they have magical powers).

[navaati]

Well no, a major characteristic of a fairy it that it flies, it has insect-like wings in the back.

And I believe that from a bio-mechanical (muscular, skeletal) point of view, insect-like wings capable on sustaining flight are not possible on a human back.

For an interesting take on this, see the Artemis Fowl series of books where fairies don't have actual wings but are much more advanced that us regular humans, and fly thanks to technological winged backpacks, and this is the origin of the human myth of fairies (they started hiding after middle age, thus why the myth stayed intact).

[OscarCunningham]

That seems to me like a natural argument against a natural hypothesis, rather than a proof that the hypothesis is supernatural.

I guess I'm using a definition of "supernatural" like Richard Carrier's: "mental things [that] cannot be reduced to nonmental things" (http://richardcarrier.blogspot.com/2007/01/defining-supernat...).

So under this definition wizards, psychics, ghosts and gods are all supernatural; but Bigfoot, UFO abductions and fairies aren't.

The Artemis Fowl series is great. Although in the context of this discussion I find it funny that the fairies do have magical powers, it's just that flying isn't one of them.