Wow, this has been a great thread!
I'd feel better if JD and Cel would shake hands and say sorry for calling each other names at times, but we're all still standing, it looks like. Phew.
I keep going back and forth on all this. And I think I know why.
Because different genre definitions serve different purposes.
You CAN define genres based on "trappings". Which is, broadly what JD is doing. It looks like SF, it sounds like SF, it's SF. Whether you describe the trappings as "mechanical" or "plausible" or "derived from a theoretical framework", you're deciding which texts fit into which genres according to the trappings of the text, as opposed to the themes or "meanings" (can we just pretend those terms aren't problematic, for a second?) of the STORY (and once more, thanks).
That's a perfectly valid way to divide books into groups. It's the most commonly-used method, in fact, as any quick trip to a bookstore will show. That's because it's the EASIEST. You don't have to read the book to know which section it belongs in. Open to random page and scan.
"drive", "reactor", "plastic", "hyper-*", metric measure units -- SF
"dragon", "eldritch", "mystical", "cloak", ancient measure units -- Fantasy
That works for 90% of the books out there, so people use it. It's starting to break down a little now as assorted "-punk" genres start to evolve (my favourite being JD's very own "Lovecraftian Ringwaldpunk"), but it still works most of the time, and it's easy to use, so it's the most commonly-employed.
I don't happen to like it, but I'll agree it's useful for the purpose of deciding where to stack a given book so that people will find the books they expect to find.
Now, I don't work in a bookstore. And I don't organize my shelves by genre. So such a definition is frankly useless to me, so I have no interest in it.
I am, however, a writer. And a person who likes comparmentalizing things according to their "fundamental natures" (let us maintain our cordial willingness to let problematic terms lie, shall we?) just for the fun of it, so I'm looking for a way to distinguish fantasy from SF (assuming of course that they CAN be distinguished, which it's interesting nobody yet has asked about) that relies on, let us say, story considerations.
My question is, is there a TYPE OF STORY that all (or a reasonable subset of) fantasy stories make use of? Is there some quality to the stories that we generally call fantasy (as opposed to the settings, or the prose style or what have you) that distinguishes them from other stories? And if so, is that quality universally found in all stories we generally call fantasy, or only some subset thereof? And are stories that we generally DON'T call fantasy also demonstrating this quality?
Now if the answer to those last two questions are No and Yes, respectively, to portions sufficiently large, then we would have to conclude that the quality we've identified, however interesting it may be, does not in fact correspond to "Fantasy" and probably shouldn't be conceptually tied to that term. Otherwise people get confused and yell at us and start quoting Heidegger. And nobody wants that.
Okay, so what, core?
Well, I happen to like Celebrim's efforts. I find his efforts far more interesting than any "setting-based" definition, because it's more intellectually challenging. I need to spend more time thinking about the books themselves in order to determine which category they fall into. It seems to revolve around more "inherent" qualities of the stories the texts tell (as opposed to the texts themselves).
Let me try to refine Celebrim's a bit. To me, his definition suffers from broadness -- it can too easily be interpreted to apply to virtually any story.
I believe that fantasy stories involve an element that serves no other purpose than as a metaphor for power. Fantasy stories are stories that deal primarily with power -- the acquisition of, the loss of, the wielding of, whatever -- through metaphor. Whether that metaphor be dragons, or sorcery or the Force, they represent power, and their interactions with the characters in the story displays some sort of thinking/assumption/understanding of the nature of the relationship between power and the individual.
That's an important point, but I'm not sure it's central. Fantasy stories tend to be about the individual, as opposed to society. I think that distinction is actually starting to break down with writers like Mieville and Erickson, but if properly motivated I might make a run at defending it.
SF stories, on the other hand, ARE about society. Specifically, SF stories are speculations on what society will look like if some aspect of our life/technology/worldview changes. Often that's a technological breakthrough or contact with some other society, but the focus of SF stories is on how society responds to such a transformation. Greg Bear, Arthur C. Clarke, David Brin, all fall very clearly into this camp. Likewise Jerry Pournelle, Larry Niven's SF stories (phew!) and Asimov.
Okay, so how do well-known works stack up? Pretty well, I think.
LotR is obviously fantasy by this definition, as is Moorcock's Eternal Champion, Leiber, Howard (how many Conan stories are about how the barbarian's strength and natural cunning allows him to overcome the fearsome magic of the bad guys? Right, all of them. Except "The Phoenix in the Sword", I guess. But that STILL fits the definition beautifully), Brust, Cook and Erickson. And that's everyone I like, so THAT'S alright.
Some border cases that are maybe more controversial:
ERB's Barsoom books -- these are definitely fantasy stories by my definition, so I agree with Celebrim here. I frankly don't think the "setting" definitions do a very good job of classifying these as SF, either, so I don't think that weakens my definition much. But Barsoom is about John Carter's ability to weild power, which is "metaphorized" in the story by his superior strength and agility, and by the many goofy races and technologies, all of which do a good job of acting like assorted power tropes -- power through cranial development, power through religious fervour, power through philosophical goofiness, etc. John Carter interacts with these various metaphors for power and thus displays a certain relationship to power.
Star Wars is definitively fantasy, and again, I think the other definitions fall down on this one, too. The stories are about individuals coming to terms with power, as represented by the Force. Star Wars is a very long, very shiny, very noisy, rather infantile discussion on what it means to possess and make use of power, and how that possession and use affects the individual.
Well, that wasn't as thoroughly-thought-out as it might have been, I guess, but there you go. I've been on a cruise ship for seven days, what do you want?