The definitions which have been proposed over the years range from the one given by Damon Knight, founder of the Science Fiction and Fantasy Writers of America (SFWA), which is the simplest, most tautological of the bunch:
"...[Science Fiction] means what we point to when we say it"
To others so elaborate and complex that they take up complete academic essays to fully explain it. However in recent years the term speculative fiction has gained a widespread acceptance, as an umbrella to cover what we laymen call science fiction, as well as some other genres dealing with issues and settings not normally found in mainstream, or realist, fiction.
But since the goal of this post is to give us a working definition of SF, I will try to compose a list of the tropes usually encountered in stories commonly accepted as SF. This will provide us with some tools to decide whether a given book can be considered SF or not.
- The story takes place in the future (from the authors time).
- The story revolves around a given "scientific" discovery or theory.
- It involves technologies not found in our world.
- Extraterrestrial beings are involved.
- The story takes place on other planets (one or more).
- Technological innovation plays a central role in the story.
- Society changes up to a point where we can no longer recognize it as our own.
- The setting for the story (backdrop)is not something found in our everyday life.
Aside from these main tropes, there are some rules which must be met in the telling of the story for it to be considered SF and not Fantasy, or any other genre.
- The setting must be coherent within itself.
- There must be a clear set of rules within the setting. (I.e, if pigs fly there has to be a rational explanation)
- Technological or social changes must be plausible (credible within the rules of the setting)
Now one thing that needs to be clarified here is that this list is by no means exhaustive, nut just the most prominent tropes and rules are contained in it; also for a given work (book, movie, TV show, comic) to be considered SF it must contain more than one of these tropes (and the more the better) and abide by all three of these rules, otherwise it would be possible to include non SF books into the genre.
Later on I will try to tackle the problem of defining Science Fiction from a more academic standpoint, for those who want to go deeper into the subject, but for now let it suffice with this brief summary of tropes and rules.
If you have any more tropes and rules that you feel should be included on the list be sure to let me know and I'll look into the matter.