Something occured to me today (in a very random, narrowly focussed, nerdy sort of way after reading a particularly entertaining bit of a fantasy novel revolving around alchemy): why are stories revolving around alchemy considered to be fantasy, rather than science fiction?

Bear with me. Stories about other branches of psuedo-science--stuff like telepathy, backwards travel through time and the possibility of anthropomorphic aliens travelling via faster-than-light space travel--are all considered to be science fiction as a matter of course. In fact, a good argument could be made that a story where the "science" part entirely stuck to real, legitimate science wouldn't be sci-fi at all. It would be regular realistic fiction.

(You can make, as apologists for so-called "hard" sf sometimes attempt, a case that certain recognizably classic sf props don't technically speaking *contradict* accepted empirical fact, however wildly they surpass it, but as a distinction that doesn't wash. After all, the same could be said of, say, invisible, undetectable fairies--prove they don't exist!--but no one would try to argue that stories revolving around such fairies would be "science fiction.")

Now, there's a separate argument about what if anything the utility is of spending time textually on elaborate attempts to massage the reader's sense of scientific plausibility, but--given this very basic realization that yes, Virginia, it's all fantasy--that's a purely aesthetic issue and can be left aside for the moment. (As a yet separate issue, it is of course good to be clear about exactly what the boundaries are of the speculative element of whatever you're doing and be scrupulously realistic about everything not specifically altered, but that's good advice that applies equally well to, say, a science fiction story about intergalactic spaceships or a historical fantasy story set in the court of Napoleon--the stuff you don't stipulate as being different should be portrayed as realistically as at all possible. Obviously. No genre difference lies therein.)

Now then, since alchemy was considered by practioners to be cutting edge rationalistic science ("natural philosophy" in the language then-current to enthusiasts like Newton and Lieniz) and was certainly no more explicitly rooted in explicitly non-rationalistic folk-lore than, say, the writings of twentieth century paranormal researchers trying to prove the existence of ESP. Given that, why classify it into the branch of fantasy ("fantasy and supernatural horror") that draws its basic sources from folklore, religious mythology, etc. and not the branch of fantasy ("scientifiction" in Gernsbackese or for the last eighty years or so "science fiction") drawing its basic sources from psuedo-science? I love both branches equally, this is just an idle curiosity about the classification scheme.