There has been a lot of discussion about the genre of science fiction lately--though I suppose there always is. SF as marketing category, SF as set of reading protocols, SF as exemplifying didactic rationalism, even, heaven help us, SF as literature.
Genre (whether film noir, or jazz, or chili) is a good topic to argue about, because there is no bright-line rule dividing it from other examples of the form. There is always ambiguity. It is always, in some sense, statistical, and there are any number of edge conditions that those who favor liminal situations and ambiguity are naturally drawn to.
I've been thinking about genre lately. I write SF, but don't read a lot of it. I tend to read mysteries, when I read fiction--and Brain Thief is a mystery novel, perhaps before it is a science fiction novel. But, at least at this point in my attempt to get some clarity, bootlegging yet another genre into the discussion probably is not helpful.
One thing about genre is that you can't understand it without understanding who consumes it. And the audience is only implicit. You can watch any number of Busby Berkeley production numbers or Disease of the Week movies without really being able to figure out who they were made for. And every artist is conscious of his or her audience.
And, no matter what its literary pretensions, there is a core audience for science fiction, a rationalist, slightly Aspergers, system-loving, covertly romantic, optimistic group. The core group consumes vast quantities of its favored product. It's not the same audience in 2010 as it was in 1950, but certainly has some long-term similarities with it. For example, this audience has always enjoyed communicating within itself. It has new methods of doing it, but the drive has always been there.
I think understanding this core audience and its responses is the first step to understanding this genre. When someone claims Margaret Atwood, say, has never written science fiction (she's said this herself), what he really means is, what Atwood has written does fulfil this core audience's needs. It doesn't matter if the book is set in the future or whatever. The core audience has a need for mental integration, for underlying system, for extrapolation, for daring and romance, for sacrifice and visual drama, that that particular book does not provide.
This is not the key or the solution. But without taking the audience into account, and discussing only what is on the page, it's easy to go wrong. It's the first step to understanding genre.