I posed this question this question as the title of a blogpost the irst time on February 15, 2013. It's a topic that TV Tropes--unsurprisingly--has some thoughts on. This
scale is a bit granular and more detailed (and perhaps a bit more judgey). Here's my sort of summary of the basics of both of these:
Hard: So, on one end we've got fairly plausible stuff that mostly extrapolates on current technology. This includes stuff like William Gibson's
Sprawl series and the novels of Greg Egan (from the near future mystery
Quarantine to the far future
Diaspora). A game example is this category would be somethig like GURPS
Transhuman Space.
Medium: Getting a little more fantastic, we arrive in the real of a lot of TV shows and computer games. One end of this pretty much only needs you to believe in FTL and artificial gravity but is otherwise pretty hard. The fewer impossible things you're asked to believe (and the better rationalized the ones you are asked to believe in are), the harder it is. Hannu Rajaniemi's
Jean Le Flambeur trilogy falls here, on the harder end. The middle of this group adds in something like psionics (
Traveller gets in here, and a lot of science fiction novels, like
Dune and
Hyperion). The softer end throws in a lot of too-human aliens and "pure energy" beings (
Babylon 5, most
Star Trek).
Soft: Here lies fantasy but with a science fiction veneer and context. Some
Star Trek (the animated series, particularly) comes in here, and
Farscape. This is also the domain of
Star Wars. Simon R. Green's
Deathstalker cycle turns up here, too.
Ultra-Soft: Some
Star Wars tie-ins in other media come in here, as do things that include magic (or similar fantastic elements} mixed in with an otherwise soft sci-fi universe: This would include superhero sci-fi properties (the Legion of Super-Heroes and Guardians of the Galaxy) and comic book epic sci-fi (what might also be thought of as
Heavy Metal sci-fi) like
Dreadstar, T
he Incal, and
The Metabarons. It's possible it stops beings science fiction on the mushiest end of this catgory and just becomes "fantasy."
So what consistency of sci-fi is your favorite--particularly in regard to rpgs?