I take this thread's title from Tolkien's phrase in his essay, "On Fairy-Stories" because it is that essay I wish to use to provide a way to consider his fictional tales.
Tolkien's essay offers some very specific characteristics of "genuine fairy-story". He goes to some length to distinquish his meaning from a variety of "lesser" (his term) forms of fantasy. Would his fiction fit his definition and the characteristics he provides?
To what extent do
The Hobbit,
Lord of the Rings and
The Silmarillion satisfy those qualities? We can throw the Minor Works in, too, for good measure, for those who wish. We might even consider if some of his favourite books satisfy his meaning, such as
Beowulf and
Sir Gawain and the Green Knight, if anyone has read those.
So, does Tokien take his own advice?