I have a simple rule of thumb: is there more polished metal or more rough-sawed wood? The former betokens Science Fiction and the latter betokens Fantasy.
Consider Babylon 5, a TV show set on a space station in interstellar space. The various alien species could just as easily be replaced by Elves, Dwarfs, Orcs, etc. Or take Conan the Barbarian, he could just as easily be a post-apocalyptic tough-guy dealing with occasional bits of technology so advanced they're indistinguishable from magic.
When you try to enforce hard boundaries between SF and Fantasy, you have to answer questions: Can you go faster than light-speed and still be SF?
What about mind-reading through ESP? There's no science to justify these story elements, but during the golden age of SF, these things were scientifically plausible. Moreover at that time science-fact notions like programmable matter and nanotechnology were implausibly magical.
Years back I wrote a story wherein characters used "mental telephony": They had chips in their heads that allowed them to wirelessly communicate without speaking. I think that was clearly SF.Or consider time travel. I've heard some science fiction writer claim that all time travel stories are pure fantasy. If you go back in time, there is absolutely no way it won't change the present in some unpredictable way.
Chaos Theory tells us that a change as big as the mass of an electron at the opposite edge of the universe makes an observable, unpredictable difference.
Scale that up to the effects you'd get if you were to send Sid & Nell back to WW2 Greenland and you've got big trouble doing so without disrupting the time-line.
So, is Finding Time a collection of Fantasy or Science Fiction stories? Tell me what you think.
