meBigGuy said:
Well, I'll stick with my definition of Science Fiction as fiction containing concepts at least presented as having been developed by science, however "impossible", and Fantasy as not invoking science. Trying to draw a line regarding your feelings about the supposed plausibility of the science seems to be the dividing line for Hard Science Fiction.
I have an issue with definitions like this in that whilst they are deceptively simple and clean they only really work for a narrow scope of SF or F. It's fine if the only SF you consider is that which contains spaceships and the only F you consider is a medieval setting with elves and dwarves. But both genres are far more than just that and the really interesting fiction makes things complicated.
Take Steampunk for example, sometimes considered a sub-genre of SF but many book stores stock it under fantasy. Look online and you'll find plenty of discussions about where it fits. Afterall the underpinning of Steampunk is presented as a science, it's just a science that we know to be wrong. Sometimes Steampunk also includes some magic but if Star Wars is allowed to have the force and hyperdrive yet be considered SF then why is magic and overly-capable-steam-engines not?
Going from another angle the "presented as science" gets a bit weak if you look at SF in which there is absolutely no in-universe explanation, or indeed consistency, to the technobabble, yet there are fantasy worlds with meticulously crafted magic systems with well defined rules that are studied and developed scientifically. As an example of the former consider Star Trek, a show that's massively inconsistent. From one episode to the next the characters will use their ship to do wildly different and novel things, many of which are never touched on again despite the world shattering implications. Like the episode where Reg reworks the deflector shield to instantly transport the Enterprise tens of thousands of lightyears, or the one in which a tractor beam is modified to push a sun, or any situation in which the holodeck is used to create intelligent avatars. Really this style is so much more similar to fantasy worlds like Harry Potter in which there's no clear rules to magic and any challenge can be fixed by using your wand in a different way.
Conversely Fantasy like the KingKiller Chronicles features a magic system that has meticulous rules (based on fundamental units of energy), is studied and practiced in a university setting and has "artificers" producing magical items in workshops to sell. The entire set up exactly mimics science and engineering development, just with a novel alteration to how the universe works. Star Trek on the other hand is soft fantasy with a technological skin. The problem with describing it by the skin is that you could class two works together that have absolutely nothing to do with each other and separate works that are closely linked. At that point the category is pointless, time wasting even.
I'm not saying that we should rebrand Star Trek fantasy and move a bunch of Fantasy books to the Science Fiction section. But I do think that strongly defining genres (or trying to) is a fools errand. There will always be something new or some examples that don't fit and the definition breaks. I think it's easier to describe a list of features and, if you want to, argue that the more things on the list a work ticks off the more SF-like it is.