Again I think precise definitions based on content don't work for this. Hard science fiction is a style. If not why is time travel usually hard sf but ghost normally fantasy horror? Style. (And before jumping in with counterexamples, please note the use of the word "usually".) Same thing about my earlier example of inherent abilities vs. learned. Plenty of counterexamples, but former is more common in fantasy, the latter in hard SciFi.

Unrelated: The westeros.org founders discuss the Winds of Winter chapter that GRRM released.

This is why there used to be a category called "Science Fantasy" which was all about the trappings of Science Fiction with non-scientific elements galore. So Star Wars would've landed in that category.

Also, there used to be a big strain of Fantasy written as sort of Alternative Science of which the Sprague De Camp/Fletcher Pratt Harold Shea stories were most famous. In these stories they use "symbolic logic" to enter mythic realms and have to figure out the rules of magic there which usually conform to some variation of Frazer's Sympathetic Magic.

This kind of sums it up:

Much of the series' attraction stems from the interaction of the psychologists' logical, rationalistic viewpoints with the wildly counterintuitive physics of the worlds they visit. Their attitudes provide something of a decontructionist look at the basic rationales of these worlds, hitherto unexamined either by their inhabitants or even their original creators. Essentially, they allow the reader to view these worlds from a fresh viewpoint.

"Reviewing the 1950 edition of The Castle of Iron, Boucher and McComas described the series as "a high point in the application of sternest intellectual logic to screwball fantasy."

Maybe the difference is exactly what you point out - the gap between what we understand and what the characters understand. To be "hard" anything, I think at least some understanding needs to be imparted to the reader.

The difference between science fiction and fantasy without the "hard' part is a more difficult question, honestly, which is why I actually prefer SF as in "speculative fiction" to stand for both. Obviously there are particular sub-genres that we put in one category or another; high fantasy, space opera, etc. I don't think those two are so different, stylistically - they're usually adventure stories, with different settings. But the settings mean we categorize them as fantasy and sci-fi respectively, which, fine. But Star Wars, for example, isn't hard anything, because it explains nothing and doesn't care. It became a bit harder with the midichlorians, but still left plenty of non-hardness to spare. But if you have magic or dragons or sword-and-sorcery, you have to be harder in order to qualify as sci-fi, in my mind.

For Harry Potter to be harder, and therefore more science-fiction-like, it would have to explain, to the reader, how magic works. Not what words you say to make kill somebody, but what happens in the brain of the wizard, the wand, the air between them. The explanation could be pretty half-assed (an organ near the liver serves to absorb energy from the warm air and focuses those energies toward the subject by way of electromagnetic waves, causing changes in their molecular structure) - I'd still probably call that fantasy, but it's a start.

To make it really cross over into science fiction, the explanation would have to be plausible and obey the fundamental laws of physics - conservation of energy and matter, etc, or at least offer a halfway believable attempt to explain why those laws are broken. If no such plausible explanation exists in modern science, a little hand-waving (positronic brains!) is absolutely allowed, and most science fiction includes some. The less handwavium, and the more the book cares that the reader believe the explanation, the harder it is. It would be tough to get HP to this point, since so much of the magic clearly break the laws of conservation of energy, momentum, and matter, not to mention thermodynamics.

To be really hard science fiction, the explanations need to be clearly based in scientific theory at the time of writing, and needs to be well-researched as well (quantum physics gives hard science fiction writers leeway to do lots of seemingly impossible things like communication that breaks the speed of light, but if that ever gets proven impossible they'll have to stop using it). Some theoretical extrapolation is allowed, but nothing that contradicts the world as science knows it.

But honestly, if you change Harry Potter to care about explaining how the magic works, you have a different book. You've changed the style. And that style is the key thing. I'd be willing to bet there are fanfics out there, probably starring Hermione or Snape (who is essentially a chemist, after all), that absolutely cross that line, and turn the HP universe into one closer to a SF universe.

But it's not enough that the universe is explained somewhere - if Tolkien wrote a treatise on magic and all of it's scientific backing, that doesn't make LOTR science fiction, because that explanation is not included in LOTR or used as part of the story. It's not even alluded to.

More on Science Fantasy from Wikipedia:

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A definition, offered by Rod Serling, is that "science fiction the improbable made possible; fantasy, the impossible made probable"[1]. The meaning is that science fiction describes unlikely things that could possibly take place in the real world under certain conditions, while science fantasy gives a scientific veneer of realism to things that simply could not happen in the real world under any circumstances. Another interpretation is that science fiction does not permit the existence of fantasy or supernatural elements; science fantasy does. Even the usage of this definition is difficult, however, as some science fiction makes use of apparently supernatural elements such as telepathy although science fiction can use telepathy or telekinesis because they deal with the mind and such abilities can be accessed or created through scientific means.

For many users of the term, however, "science fantasy" is either a science fiction story that has drifted far enough from reality to "feel" like a fantasy, or a fantasy story that is attempting to be science fiction. While these are in theory classifiable as different approaches, and thus different genres (fantastic science fiction vs. scientific fantasy), the end products are sometimes indistinguishable.

Arthur C. Clarke's dictum the "any sufficiently advanced technology is indistinguishable from magic" and Larry Niven's "any sufficiently rigorously defined magic is indistinguishable from technology" indicates why this is so: a writer can write a fantasy using magic of various sorts, and yet turn the story into science fiction by positing some highly advanced technology, or as-yet-unknown but ultimately thoroughly provable science, as an explanation for how the magic can occur. Another writer can describe a future world where technologies are so advanced to be invisible, and the effects produced would be classified as magical if they were only described as such. A world might include magic which only some people (or only the reader) know to be in fact technological effects.

re: preview chapter of WoW:

I really can't wait to see Stannis fort of Ice and Snow. I think it rocks and totally shows that he has accepted that winter is here.

And I'm trying to figure out why Brandon would want to save Theon.

Completely different - this looks interesting Quiet: The Power of Introverts in a World that Can't Stop Talking.

that doesn't make LOTR science fiction, because that explanation is not included in LOTR or used as part of the story. It's not even alluded to.

They don't reveal he's of a magical race in LOTR? Not even in the appendices? Is that reveal in the Silmarillion, then?

I don't see how being a wizard that studies and learns magic is any softer than someone who's born of a race that has that power inherent in them. I wouldn't inherently apply hard to either of them, but I would flip your order.

science fiction describes unlikely things that could possibly take place in the real world under certain conditions

Uh, politely, that's bullshit. Lots of sci fi describes things that couldn't possibly take place in *our* real world, because either the conditions are not stipulated, or they could never exist.

I'm pretty sure the backstory on Gandalf/wizards is in both the Appendices and the Silmarillion. Either way, it's canon and hardly obscure.

I follow an online book club called Sword & Laser (mostly on Goodreads but also a podcast), and in theory the book selections are supposed to alternate SF and Fantasy, but it's a rarity that a book falls 100% solidly into one category or the other.

(Probably the clearest example recently was Gene Wolf's Shadow and Claw - the combo of Shadow of the Torturer and Claw of the Conciliator that's currently in release - it's a post-technological world where a lot of the tech still functions, but the people in that universe have forgotten how and why it works, and so to them it's magic. To the reader, it's science fiction and to the characters, it's fantasy.)

I haven't read Hunger Games, but I decided to go through Mark Reads' review of them. Wow, what gets marketed as YA these days is a lot darker than what I read as a kid.

But I'm kind of sad at how shocked Mark is by some of the twists, how honestly surprised he is at how Katniss is treated and how the plot twists. Maybe I've seen too many war tribunals or read too many retrospectives to be surprised by what the Powers that Be do to their tools.

Well, sad isn't the right word, unless it's sad for my own cynicism.