"If they're Yesterday and Today," Arhu said, "then where's Tomorrow?"
"Invisible," Urruah said. "Hard to make an image of something that hasn't happened yet. But he's there, Reh't is, whether you see him or not. Like all the best predators, you never see him till it's much too late. Walk right through him, feel the chill; he's there."
Arhu stared at the empty space between the two statues, and shivered.
-- from The Book of Night with Moon, by Diane Duane
Reh't's domain is the realm of science fiction -- worlds that might someday be. From a world defended by dragons to one where humans are enslaved by subhuman monstrosities, the only limit to science fiction is that it must be capable of existing in this Universe, under this Universe's rules of science (more or less). Within that single condition, anything goes.
My bookshelves include a wide variety of science fiction, from many different authors, using a multitude of different settings for their stories. Classifying science fiction is largely an exercise in futility -- there are so many genres, and so many sub-genres, and so many authors who don't fit neatly into any genre, that the best I can do is create a few obvious categories and toss the rest into a giant grab-bag.
To start with, there are several authors that I like so much I've collected large numbers of their novels. Each of these deserves a page of their own:
Next are a few specific sub-genres of SF:
- Hard-science SF is science fiction in which the emphasis is on the science. These authors follow the rules of known science (known at the time they were writing, at least) quite closely. Most of them also use the science as it should be used: as a support for the story and characters, and never as a replacement or substitution for story and characters.
- Military stories have been a staple of fiction as long as fiction's been around. Military SF consists of military fiction set against an SF background. The fact that it's science fiction means it stick pretty close to the rules of science, but military-SF authors often take some significant liberties with science in order to get their combat starships and cool weapons.
- There are a few authors who don't really qualify for a whole page of their own, but certainly do deserve a section of their own.
- A couple of authors in my library have accomplished the rare and special feat of writing good comedic SF.
- By far the largest part of my SF collection consists of a scattering of books from many different authors. Some of these are works from Golden Age SF authors that have stood the test of time. Others are somewhat newer. Many of them fit into recognizable sub-groups. Others ... don't. I just call them all "general science fiction."
- SF exists in visual media too, and sometimes those spawn written tie-ins. Novelizations of TV and movie scripts have been around as long as TV and movies have been, but in recent years a new type of tie-in has begun to proliferate: original stories based on TV series or movies. Star Trek really started this phenomenon back in the late 70s, but others have joined in, resulting in a flood of such tie-in novels. Most of them are pure junk, but a few are worth reading. My bookshelves include three major groups of tie-ins: