[iansales]

Where's the "scientific advance" in 'Nightfall'? That's not a proper definition. Just because Asimov wrote science fiction, that doesn't mean he's qualified to define it. In fact, since when have authors either engaged in taxonomy, or been any good at it? (Except for those who also wrote criticism, of course - such as Damon Knight, Samuel Delany, James Blish, etc.)

And there's no such genre as science fantasy. That's two entirely different modes of fiction, not just two genres.