When a story has enough success, it will have followers. When a story has enough followers, they will write fanfiction. Simplest explanation I can think of.
Of course, it’s not entirely accurate. Apart from the obvious problem with defining “enough”, and the flukes where one loyal fan writes most of the fanfiction or something, it’s not enough to say that a “fanfic” is simply a story that uses the characters and setting of an existing story or series. If that were true, every published Star Wars book would be fanfiction, as would an awful lot of other science fiction and fantasy stories.
What, then, sets fanfiction apart from “real” stories? In my mind, it’s when the story can stand on its own that it’s no longer a fanfiction. They can use someone else’s characters and settings, perhaps they can even use existing plot elements, even (who doesn’t?). But the story itself should be able to stand even for someone who had never experienced (read/watched/heard/etc.) the rest of the series.
One of the first published Star Wars novels (as opposed to comics, games, etc.) was Timothy Zahn’s Heir to the Empire. Zahn is a reasonably well-known sci-fi writer (partially due to the success of this book and its sequels) and has written plenty of non-Star Wars books as well. (If you like sci-fi, he’s worth reading.) One of the main reasons I find Zahn’s books so good is because although he uses Star Wars characters like Luke, Leia, Han, and Chewie, he isn’t afraid to introduce new characters that are just as important, such as Talon Karrde, Mara Jade, and Grand Admiral Thrawn. The antagonists of the story are not carbon copies of Darth Vader, Grand Moff Tarkin, and Emperor Palpatine, and the plot, although still the struggle of good against evil set in a Star Wars universe, is almost totally different from the original Star Wars trilogy. (Partially because the Rebels are no longer a ragtag band hiding from the Big Bad Empire; instead you get the newly established New Republic set against a much smaller Empire.
Whoo. Enough plot summary. The point I was trying to make is that while including Star Wars characters got people to read Heir to the Empire in the first place, and made some introductions less important, the story basically stands on its own. In addition, Zahn doesn’t just use the Star Wars universe; he builds on it. An awful lot of Star Wars books published after Heir to the Empire use what it establishes as canon fact, at the very least mentioning events that had occurred or species Zahn had introduced.
By contrast, Han Solo at Stars’ End (one of the first Star Wars novels ever, before The Empire Strikes Back was even released) and several of the books that use the prequel characters don’t add any significant new characters (or try and fail miserably, as their entire personality is defined in terms of Anakin or Obi-Wan). Nor do they really expand the Star Wars universe, although sometimes you can give them a little bit of credit for filling in the gaps.
Enough with the Star Wars, already. These are my main criteria for fanfiction vs. original fiction. If your story would work in a different context (not too different, but one without the prestige of whatever you’re writing on), if you’ve expanded the world you’re working in instead of just visiting all the same locations with the same characters, and perhaps if someone could write fanfiction based on your story, then it’s real. If you’re just cloning (sorry, I said I would stop) the plot/settings/characters, it’s probably fanfiction. More than half of the Redwall series and probably most Star Trek books in existence fall into this category, among dozens or hundreds of other instances.
It should be noted that writing good stories in an existing universe is both easier and harder than writing a completely original story. On the one hand, you’ve got a background all set up, along with some great characters you can use. On the other, if your characters act in a way that isn’t typical for them (as established by existing stories), your illusion of continuity with the rest of the universe disappears, and your story either becomes non-canon or simply bad fanfiction. I said I’d stop talking about Star Wars, so I won’t mention the Galaxy of Fear series, which was Goosebumps in space, and not exactly bad (though I don’t like horror, even kid’s horror), but not really Star Wars either. Ahem. Anyway, this is also why “shipping” and “slash fiction” are fanfiction, and in my opinion bad fanfiction; the entire appeal comes from the characters from an established story behaving in ways they never would.
So, is there a place for fanfiction? Well, one thing is it’s fun to write; right now I’d classify my “Feel the Night” as, well, Noteworthy fanfiction. Similarly, if you stretch the definition a little, Across the Universe was Beatles fanfiction. And of course some of my other writing friends like to throw out a quick one-, two-scene fanfiction based on a game, a book, or even each other’s stories. (And sometimes these have potential to be full stories; such as the ones where I haven’t played the game and liked what they wrote anyway. Good litmus test.)
Moreover, though, sometimes fanfiction is fun to read, even when it does add nothing new. Most books work off an established formula, and a fanfiction can still be more entertaining and a better pastime than a failed original story. And sometimes it’s just fun to see what would happen when you put characters in a totally random situation and let their personalities dictate what happens. (Writers have less control over their characters than you might think.)
Which brings us to books like Eragon. The plot of Eragon (and the rest of the series) is a very obvious composition of a multitude of fantasy clichés, ideas you can find in Lord of the Rings, Ursula K. Le Guin’s A Wizard of Earthsea (and later books), Anne McCaffrey’s Dragonriders of Pern series, and yes, Star Wars. There is very little in the plot that is original in any way, and the books are of the sprawling length usually only found in books by successful authors whose editors have decided to stay out of the way. (For an extreme example of this, see Kevin J. Anderson’s Saga of Seven Suns series, which has about three dozen plotlines and over three thousand pages so far. The series itself is interesting but not that interesting.) And the main character’s name is “dragon” with one letter shifted over; even if that wasn’t intentional, you’d think Paolini would have noticed this and been willing to change it. (Yes, some character names fit really well, but when even the names are cliché…) In any case, the length and lack of originality of Eragon, perhaps even utter lack of originality, has led some of my more purist writer friends to outright hate the book.
But me? Well, although it is pretty much fanfiction based on the entire fantasy genre, it is well-executed, and despite myself I like it. The formula has survived because it is well-received, and Paolini I guess has embraced that. I do have to say that my favorite story arc is the more original one centered on Eragon’s brother Roran in the second book, Eldest. But all-in-all, I think Eragon is proof that fanfiction isn’t all bad, not because it has everything that real fiction has, but because it’s also fun to read, and presenting tried-and-true stories well is a skill in and of itself.
It’s hard to think of fanfiction for non-sci-fi/fantasy stories, since the setting you borrow will be based on reality, the only thing you really get specifically is the characters. But it’s certainly possible; according to Wikipedia, Don Quixote had several unauthorized sequels published after its success. It’s the same story, using popular characters to drive an otherwise lackluster plot. (Not that I’ve read these so-called sequels.) On the other hand, though, some science fiction and fantasy can definitely stand with great “literary fiction”, even those which use an existing universe’s characters and/or setting. They shouldn’t ever be dismissed out of hand as “just” sci-fi/fantasy.
To conclude, it is true that I/we could easily live without fanfiction, but not without “novel” stories (pun intended). But fanfiction isn’t a bad thing, and we should certainly allow it to stay and grow. In its own weird way.