On Fairy-Stories is a lecture, later an essay, by J. R. R. Tolkien, which treated of literary criticism of the Fairy Tale and Fantasy, genres not entirely distinct in his day. He takes the "Color Fairy Book" collections of Andrew Lang as his starting point, and offers illuminating observations that served as significant Trope Codifiers both for the fantasy/fairy tale genres and for his own legendarium.
- All Just a Dream: According to Tolkien, this device automatically disqualifies any story that uses it from consideration as a Fairy Tale. Even an otherwise good story is like "a good picture in a disfiguring frame."
- Beast Fable: If there's no other magic involved, the mere presence of Talking Animals doesn't make a story a Fairy Tale either.
- Escapism: Tolkien spends much time defending the legitimacy of escapist fiction, as at the time this mode of storytelling was widely ridiculed and derided by critics.
- The Fair Folk: Discussed at length naturally and compared to "cute" fairies. One example given is the J.M. Barrie play Mary Rose in which humans are meddled with by Fair Folk who are never actually seen (see the play's entry at Wikipedia for a fuller description). Tolkien seems to have liked the play reasonably, but thought it uncommonly creepy—and he thought it was fun to write stories about Evil Overlords in hellish countries. He noted though that what made it work is that it was written in a way that did not require special effects.
- Heinz Hybrid: He mentions this, and notes that it can lead to unimpressive results if overdone.
- Immortality Seeker: Discussed with an interesting Perspective Flip:"And lastly there is the oldest and deepest desire, the Great Escape: the Escape from Death. Fairy-stories provide many examples and modes of this ... Fairy-stories are made by men not by fairies. The Human-stories of the elves are doubtless full of the Escape from Deathlessness."
- Land of Faerie: Tolkien draws a significant distinction between tales about the Land of Faerie (what he means by "Fairy-stories") and stories about the cute little "fairies" of pop culture (of which he takes a very dim view).
- Mythopoeia: Described by Tolkien as "sub-creation."
- Special Effect Failure: One problem with the dramatic presentation of fantasy. Part of his definition of Elves as idealized artists ("sub-creators") involves pointing out that this doesn't happen in the art they are rumored to produce.
- What Do You Mean, It's Not for Kids?: Discussed with particular vigor.