Part 1 of this article is here.
In classic science fiction, the story is about an idea and its results. Given X, how is human society affected? If people lived forever, how would society change? If energy were unlimited and free, what would be different? If time travel were possible, what would that mean regarding alternate realities?
Some authors would do their darnedest to keep X as close to known science as possible. Hal Clement, for example would discuss at length the physics of heavy gravity planets and stars so that X would not be “fantastic” and he could explore the notion of a race of sentient beings evolving in those conditions. Other authors cheerfully threw physics out the window and just made up a few new rules (“yep, turns out we can read people's minds after all”) so that they could get on with exploring the results of X. As readers in the genre, we agree to accept the premise of X in order to explore the ramifications within the world of the story.
But no matter how fantastical X is, no matter how far from known science, everything else in the story plays according to the rules. The characters in the stories don't suddenly lose interest in basic emotions, in how to earn a living, in how to communicate with others (unless that's the premise of the particular X in the story, of course). They behave like characters we can understand in our own world, so that we can relate to them. However their behavior may be modified by X, we must still recognize them.
On the theory that we can best see a genre by looking at its weaker more conventional elements, I will define a mediocre science fiction book as having a clear idea X and regrettably puppet-like characters demonstrating the ramifications.
In heroic fantasy, not so much. There the story with its characters is the full story, and it's the magical trappings that tend to be decorative. A mediocre specimen would have a conventional hero tale in a place where magic just happens. This is, I think, a relict of the time when the stories of the encounter between humans and “the fair folk” were brief and one-sided. The fair folk and their world were uncanny, and the stories were about meeting the uncanny and returning again, not about the uncanny world itself. Elves could be “timeless” and obscurely motivated. The Queen of Elfland is the same whether you meet her in 800 or 1800 (but surely not the fashion of her dress!) and we are not concerned with why she wants a human in her entourage.
Those stories are evocative, certainly, but these days, we tell conventional tales about Elfland, a place like any other (from the point of view of story telling) inhabited by beings whom we can know, for all that they are powerful or even godlings. This Elfland is a very different place.
There seem to me to be two classes of fantasy in this modern sense: the stories where the different rules of magic are just as stringent as any X ideas in science fiction, and the rest. Tolkien is a model of the first sort. What magic there was in his world had limits. Galadriel could defend against the Dark Lord, but not defeat him arbitrarily. Even the elves carried burdens and made clothing. This of course supported the underlying pseudo-Christian philosophy of moral growth, sacrifice, and earned reward.
In the second sort of modern fantasy, otherworldly beings have special powers, but the details are not much explored. Sure, maybe a human visiting Elfland can't eat the food, but the author doesn't spell out whether the elves like the food, who raises it, do they get paid, and so forth. The elves wear beautiful clothing, but where do they get it? Do they make it themselves? Where does the material come from? How do they pay for it? If the clothing isn't real (a glamour, say), well are they all naked or wearing leaves underneath? Why would they want to do that? If the elves live a long time, what does that mean for their society? Do they have serial marriages? Many children or few? Inheritance difficulties? Do they take on different careers at different times? What about ambition? Are servants to be servants forever? Why would any world of intelligent beings be static?
In a science fiction story, in an alien world instead of Elfland, one might have all the same questions and not answer them, because the premise X is something else, and so these details are ignored in passing (this is how Eric Frank Russell can misplace an entire gender (*)). But in an otherworld fantasy, the premise is often the very existence of Elfland or of magic, and I think it behooves one to fill out some of the details accordingly to create believable motivations.
Where this is especially well done is in the well-fleshed out area of vampire fiction. These stories fully integrate the world of the vampire with the reality of living in the world. Taking Chelsea Quinn Yarbro's Saint-Germain books as an excellent example, we see that vampires are concerned with families, inheritance, economics, and a complete set of human motivations and behaviors that we can recognize. Like science fiction, given X (the existence of vampires), what would that imply?
In some ways, fictional elves and vampires have much in common: long life, founder relationships, special powers, interactions with ordinary humans. Why should elves be exempt from having a believable world with believable motivations, behaviors, economics, and history?
At the very least, maybe we can stop calling supernatural creatures from one culture by random names from other cultures and time periods. If they have a place in a fictional world, they must have a history there, too.
It's just too bad that my Hounds of Annwn series involves Welsh mythology, so all my nice consistent otherworld names will be unpronounceable. Oh, well, can't have everything.
* One of my favorite classic science fiction novels is Eric Frank Russell‘s Wasp (1957), where a human in disguise wreaks humorous psychological havoc on an enemy alien world during wartime by traveling through its cities suggesting the presence of terrorist organizations. There's only one main character, and a great many puppet villains. But that's alright, because in this entire book, praised for its “gritty realism,” set mostly in urban areas with crowd scenes, shops, and public transport, in a humanoid culture very like our own, there is not one single female character (or reference to one) of any kind, puppet or not. Anywhere. Doing anything.
This is not part of the premise, it just happens. The only time the word “she” appears, it refers to a car. And the hell of it is, you don't even notice, and I'm not sure Russell did, either. I must have read it half a dozen times as a teenager before it struck me.