This is a discovery I've come to recently, which I think is interesting enough to merit sharing. All fiction, however it's marketed, falls into one of two genres; fantasy or sci-fi. I'm aware there's a cachet about not being 'fantasy' or 'SFF', and that a good many authors will protest at being lumped in with fantasy or sci-fi, but that's just tough for them. Here's my argument:
Let's start with a quick piece of philosophy. What is 'a world' (or universe)? In fantasy and sci-fi, of course, we talk quite a lot about worlds - 'The World of Robert Jordan's The Wheel of Time', or 'The World of George R.R. Martin's A Song of Ice and Fire', for example. But what is a world?
The simplest answer to this question - the one, I think, which would be most common in the academic philosophy discourse on worlds - is that a world is a set of states of affairs. A state of affairs could be an object's existing, or an event's happening, or any combination thereof. Technically, a world is a set of states of affairs which is maximal in some way - that is to say, it's a complete set, capturing a whole environment of some kind. Parts of our universe, for example, are not literally universes in themselves. We can pass over this point, though - it's philosophically interesting, but not presently significant.
So a world is a set of states of affairs. The actual world - the one we're living in right now - is (as it probably should be) the easiest one to identify: it's the set of all states of affairs which actually or really occur.
A fictional world, then, is a set of states of affairs some of whose members do not actually occur (otherwise it's not fiction, of course). To put it another way, no work of fiction can ever, by definition, be set in the real world. This is the key point, really, and one that bears far more investigation than we can give it today; I'll certainly be coming back to it over the coming weeks.
It's an entirely reasonable definition of the fantasy genre to say it is concerned with fiction that occurs in worlds which are not ours. Science fiction is primarily concerned with worlds which ours might become. Since all fiction is set in a world which isn't ours (in some cases, though, a world which ours might turn into), all fiction must fall into one or other category, with the vast bulk falling under 'fantasy'.
Obviously, there are degrees of honesty in this. 'Classic' fantasy, running the gamut from Tolkein to Brandon Sanderson, is obviously and openly fantasy. Space opera is (at least very often) fantasy masquerading as 'classic' sci-fi. Technothrillers, romance novels and so on - stories which are set in close replicas of the real world which are twisted for fundamentally wish-fulfilment purposes - are fantasy by the back door, attempts to escape the scorn so frequently appended to the 'fantasy' label. Some works that start out as sci-fi become fantasy when their predictions fail to come to pass - 1984 and 2001: A Space Oddysey come to mind.
It might be claimed that there's a third category, one occupied by 'serious' writers tackling 'serious' matters, which is set either in 'the present' or at some point in the past, and whose worlds are effectively indistinguishable from our own because we do not have enough evidence to be able to prove that the events in them did not occur.
So, for example, it might be argued that Wolf Hall fits neither the fantasy nor sci-fi labels as I've just defined them, because it's a well-researched account of how things may very well have happened. Or, since Wolf Hall is about a noted historical figure, we could envisage a novel set further from the centres of power, about people unremembered by history, and one could argue that this is a form of temporally-reversed sci-fi, a 'possible past', legitimised by the extent of the author's research into the lives of people at the selected time.
There's a case to be made there, though as far as I'm concerned you're still talking about fantasy, since the states of affairs described in the novel, whatever their resemblance to anything that might have happened, came from the head and imagination of a modern author, not from matters of actual fact.
What of works set in the present day, which are nevertheless very serious about their non-other-worldliness? If we allow the premise that some works of fiction are indistinguishable from biography or history due to us being unable to prove that the events portrayed did not actually occur, then this will depend on setting - in some parts of the world, it would now be very hard to imagine events that truly did fall through this kind of epistemological hole, so thoroughly digitised, closed-circuited and surveilled are our lives.
Should we allow this premise, though? Not if we want to count the works as fiction, and one of the few clear-cut distinctions I think has any value is that between fiction and non-fiction. Allowing people to publish semi-fictional accounts of events as anything other than wholly fictional is a dangerous business, full of openings for soft and subtle propaganda. For a work to be posted as fact, whether historical or sociological, a rather higher standard of proof must be demanded.
Aaaand that's probably far enough with the argument, since we're getting into rather more difficult philosophical territory, and I intend this post mainly as an act of satire. Genres are a marketing tool, and this analysis is obviously useless from a marketing perspective - I have no more desire to see Pride and Prejudice shelved in the same section as The Lord of the Rings than anyone else. All I want to do at this point is point out one way in which the rejection of fantasy by that wonderful bastion of hubris, 'the literary establishment', is ridiculous.
As I'll be arguing over the coming weeks, fantasy has all the best tools for literary craftspeople, and 'realism' generally blunts the purpose of fiction altogether. History, sociology and biography are far better tools for studying the actual world than fiction, and fiction is much better at studying human beings in a peculiar but vital kind of abstraction.
By the by, if you're offended by the way I've talked about 'mainstream' or 'literary' fiction at any point in this article, tough. Fantasy authors and readers get exactly this kind of condescending crap all the time, and we put up with it well enough.