Also, why do we pick the pairings we pick? Obviously, some of it has to do with the Source Material, and some of it with genetics/hormones/chance, and some of it has to do with other fic and other fans within the fandom. Multiple reasons, etc. But a lot of the time, we go for pairings that meet our essential needs, the reasons we slash at all. Here's a non-scientific breakdown of Types of Pairings, and Why Why For the Love of God Why. (For my purposes here, I'm talking about same-sex, non-canonical pairings: Pureish Slash.)
THE NEXT LEVEL
This is sort of the foundation of slash as a genre, I think. These are two people (who may or may not be balding, co-dependent cops) who are so *partnered* to each other already, canonically, that it simply seems, if you have the slightest ounce of queer sensibility, a tremendous waste for them *not* to be sleeping together. You'd feel just awful for some poor SO who had to compete with the pre-existing soulmate/partner/spousal equivalent that at some point you throw up your hands and say, these people are going to be alone *forever* if they don't just get with each other -- if they don't, as any given member of NSync would say, Take it to the Next Level. Kirk and Spock. Jim and Blair. Fraser and whichever Ray you believe he can't live without, depending on whether you watched "Call of the Wild" with or without your fingers in your ears going "lalalalala, I'm not LISTENING!" (Not that there's anything wrong with that.) O'Brien and Bashir. Xena and Gabrielle (assuming that didn't go canon after I stopped watching. It didn't, did it?) Danny and Casey. Vince and Stuart. These are the pairings that, canonically speaking, you know will be standing when the dust clears, and no matter what happens, at the end of everything, they'll still have each other, whether or not they, you know, *have* each other. The slash, here, is in the queering of this kind of friendship; we are *slashers* because we look at those relationships as having an inherent sexual/romantic quality, whether or not canon backs us up on that (usually, that'd be "not"). On some level, possibly wired somehow into our DNA, most self-identified slashers can't help but look at relationships like that and think, "Dude, you're so married."
THE NEXT LEVEL, WE SWEAR!
A subset of the above, where *fandom,* and not canon, establishes the primacy of that relationship. In these pairings, there's some evidence that these people have that partnership/marriage/you and me against the world dynamic...but not as much evidence as we like to claim there is. As a fandom, we reimagine the relationship to mimic TNL pairings; it's a fandom-wide *choice* to interpret the relationship in that way. (Obviously, not everyone agrees. Not everyone agrees on *anything.* But within the fandom, most people will choose to believe.) Obi-Wan and Qui-Gon are maybe the best media example. Harry Potter and Ron, perhaps (I'm not well-versed enough in HP fandom to know how the fans view that relationshp, but my sense is that, maybe based on Ron's kidnapping for the test in GoF, there's a trend toward lionizing their friendship). Joe Dick and Billy Tallent, I think I'm inclined to categorize here; although most HCL fans mercifully realize that they've screwed up their relationship, most fic deals with them not as intimates who've gone their separate ways, but people who were *supposed* to be together forever, and managed to fuck it up through stupidity. Practically every damn RPS fandom has *some* fans who want to put their boys here, but the only instances I know of where the fandom as a whole tends to support the idea are Timbertrick and JoLa. I'm not an Andromeda fan, but I sort of vaguely think Harper and Tyr belong here; if I'm wrong, don't hit me in the face, please.
As in, you know, where there's smoke there's fire. These pairings tend to rely on the holy grail of Actor Chemistry. They just *look* at each other like -- well -- like not friends! Not like I look at my friends, that's for damn sure. In canon, they may be friends, or they may frankly seem to loathe each other, but either way, they just seem a little too attached. We think there might be something they're not telling us. Janeway/7. Buffy/Faith. Clark/Lex. Picard/Q. Garak/Bashir. Mulder/Krycek. Mulder/Skinner. Angel/Lindsey. Duncan/Methos. If you're not happy with what I said earlier, feel free to add Joe Dick/Billy Tallent in here instead. Father Mukada/Alvarez. Wes/Gunn, back before Gunn's personality switch. Frequently, TPTB are or seem to be conscious of the chemistry factor, and they'll make us their loyal slaves by tossing in Free Stuff, like double entendres or smooching or what looks a hell of a lot like flirting to the layperson. Nonetheless, they don't ever come right out and confirm the attraction; it's Subtext, meaning that if you are inclined to ignore it, there's still a perfectly servicable text in place. Any SDB combination can fit here, and so can a great many other RPS pairings -- Elijah/Dom and CKR/Hugh Dillon spring to mind. Alongside TNL, maybe even more so than TNL pairings, this is what people are talking about when they say whatever is *slashy.* They mean that it gives off a vibe of potential homoeroticism, while at the same time never establishing a canonical non-platonic relationship. By definition, words like "subtext" and "chemistry" mean that you'll never get total agreement on who should be here, either. I'm sure some people would put Angel/Spike in this category, although I don't see chemistry there and probably never will.
These require a bit more effort and commitment on the part of the writer. People fall in with these pairings because they think it would be cool if they were, and they'll find a way to make it work. Sometimes we have to ignore big chunks of canon, but that can happen to the best of fandoms; I don't mean it as a put-down. The Jossverse is especially prone to this sort of thing -- in fact, most BtVS/Angel slash is FX. Giles/Oz? Xander/Spike? Willow/Faith? Sure, why the hell not? Within the context of certain stories, it makes perfect sense. These rarely turn into megafandoms, however, because there is no *defining slashy essence* to these pairings. My Giles/Oz story is going to be pretty different from your Giles/Oz story, because there are a ton of blanks to be filled in, and we're going to fill them in very differently. Minor characters from some shows get play in this category. Sometimes, FX fic spawns fandoms-of-one (or almost one), where certain writers become fascinated in an oddball pairing and invest so much of their own work into it that people know the characters *as so-and-so writes them,* and can't imagine them written any other way -- Viridian's Pike & Benny stories come to mind. Ray/Ray fic is the ultimate FX pairing; we know just enough to make it *possible,* if you want to either write weird and not very convincing fic or pour a lot of energy into proving it to your audience. A lot of popslash falls into this category too, when it's based on particularly tenuous threads, but enough to convince multiple people: Justin/Wade, Justin/Nick, Britney/Christina, Chris/Rick the Temp. These pairings are generally not slashy, except that they are being slashed. In this case, it's not the characters but the *writers* who are "slashy." It's our own queer sensibilities that are being revealed here. Which is way cool.
Crossovers. Yeah, mainly crossovers. Also, people who are on the same show but have basically *no* contact with each other. These are pairings that are usually done once, for the purposes of one plotline or one "wouldn't this be so cool?" There's not much difference between FX and Hattrick pairings, except that the level of canonical contact between the characters sinks from "some, but nothing all that slashy" to "pretty much none." However, they fill the same niche, in that the writer's slashiness has prompted her to spin out this whole non-canonical, same-sex relationship, because she felt like it.
Now, what's interesting to me is that you can do any of these things with m/f couples as well. So these classifications are not *really* slash by definition, but in fact a breakdown of Unconventional Pairings. They're only slash because I'm limiting them to unconventional *same-sex* pairings, in a purely arbitrary way.
The whole point of this is that...yes. I think there's a level at which the same thing is happening when people write non-canon m/f stories as in "slash" per se. We're (a) positing that it would be cool if your best friend/partner and your love interest were the same conveniently packaged person, (b) getting off on a certain flirtatious vibe between attractive people that infuse the Source Material with juicy sexual tension, and/or (c) thinking up cool ways to get people we think would be compatible and/or hot together into bed. The same thing is happening...except that some of us like to see it happen to boys, or girls, or boys and girls.
Of course, I could slice vertically instead of horizontally, and I can do that very briefly. Some pairings are same-sex, and fans like that because the sexual and emotional dynamics of same-sex relationships appeal mightily to them, and they really could care less if the creators of Source Material are as interested as they are in exploring those dynamics. And then suddenly you can include all the people listed in the last taxonomy, plus Willow/Tara and Justin/Brian and whoever else. Instead of gender being the only thing that doesn't matter, it's the only thing that *does.*
So basically, I've just gone to a tremendous amount of work to prove about what I started out with, which is that you can fuck around with the definition of slash. And I like to think I'm closer to deciding how you *ought* to fuck around with the definition of slash, but...I don't know that I am. Obviously, it's time to make some dinner and contemplate my life.