Once in awhile someone will ask me "What, if anything, is verboten in today's permissive, literate erotica?" The answer is that pretty much anything is fair game, but there are what are called the four deadly sins: four subjects that a lot of publishers and editors won't (or can't) touch. These by no means are set in stone, but they definitely limit where you can send a story that uses any of them. So here, in a special series, are theses sins, and what – if anything – a writer can do with them.
As with any of the "sins", a story that deals with incest in a thought-provoking or side-ways humorous manner might not scream at an editor or publisher I'M AN INCEST STORY but rather as humorous or though-provoking, first, and as a tale dealing with incest, second. Still, once it comes to light there's always a chance the story might still scream a bit, but if you're a skilled writer telling an interesting story there's still a chance quality could win over the theme.
Unlike bestiality, has very, very few stretches (like aliens and myths with bestiality). It's very hard to stumble into incest. In short, you're related or you're not. As far as degree of relationship, that depends on the story and the intent: direct relations are damned tough to deal with, first cousins fooling around behind the barn are quite another.
Even though incest is pretty damned apparent in a story, that doesn't mean the theme or the subtext can't be touched on. Sometimes the forbidden or the unexpected laying under the surface can add depth to a story: a brother being protective of his attractive sister, a mother shopping for a date for a daughter, a father trying to steer his son's sexuality, a daughter's sexual explorations alarming (and enticing) a mother or father's fantasies, and so forth. Technically, some of these dip into incest, if not the act then at least the territory, but if handled well they can add an interesting facet to an otherwise pedantic story. It's a theme that's also been played with, successfully, for centuries. Even the myth of Pygmalion – a sculptor falling in love with his creation – can almost be considered a story of incest, as the artist was a parent, then a over.
Conversely, incest can dull a situation when the emotions of the lovers involved become turned: as an example, where a person begins to feel more of a caregiver or mentor than a partner: the thought or even fantasies around sexuality with the person being cared-for or taught start to feel inappropriate. Conversely, someone might enjoy the forbidden spice of feeling sexual towards someone they've only thought of as a son or daughter, mother or father figure. This is also an old plaything for storytellers, the most common being a person looking for a partner to replace the strength and nurturing left behind when they grew up and moved out – or, from the new partner's point of view, the shock in realizing they have been selected to fulfill that role.
As with any of these "sins", fantasy can be a factor in being able to play with these themes. Having a character imagine making love to their mom (shudder) is in many editors or publishers eyes the same thing as actually doing it – but accepting and using the theme in, say, play-acting, where the reality is separated because the participants aren't related in any way, is more acceptable. As with under-age play, S/M and dominance and submission games can also use incest as a spice or forbidden theme – especially in infantilism games, where one person pretends to be an abusive or nurturing parental figure. Once again, play versus reality (even imagined reality) can work where normally no one would dare tread.
The bottom-line, of course, is whether or not the story uses this theme is an interesting or though-provoking way or just as a cheap shot. If you have any questions, either try and look at the story with a neutral eye, ask a friend you respect for their opinion. But I wouldn't ask your parents –