The more I read, the more I am convinced that the only real difference between fantasy and science fiction as genres is whether the processes behind the weird things are explained or not.
Science fiction: these creatures are the product of genetic manipulation of an alien species discovered on a planet where people were building a colony.
Fantasy: they're dragons. because magic.
Science fiction: humanity arrived at this world generations ago when their colony ship landed, and in the pursuit of their utopian ideals, made discussing their origins or the function of technology taboo, resulting in a class of "wizards" who are trained in the use of these ancient technologies. Now, they have been rediscovered when a ship crash-lands on the planet.
Fantasy: some guy fell through a magic portal and there's wizards.
Okay but y'all the thing you have to realize about all these examples is that I am not actually making them up, just fudging them a tiny bit.
Science fiction dragons: Pern.
Fantasy dragons: everything.
Science fiction wizards: fusion of Darkover and the Warlock series by Stascheff.
Fantasy wizards: The Wizard series, also by Stascheff.
@InspectorCaracal I think more useful division between genres would be hard/soft
Hard fantasy/sci-fi explains everything, soft fantasy/sci-fi doesn't explain shit
