What is Science-Fiction and Fantasy?

As promised, here's a few throw-away definitions of science-fiction/fantasy and speculative fiction:

Kingsley Amis in his New Maps of Hell (1961) said that:

"Science fiction is that class of prose narrative treating of a situation that could not arise in the world we know, but which is hypothesized on the basis of some innovation in science or technology, or pseudo-science or pseudo-technology, whether human or extraterrestrial in origin."

Isaac Asimov said in Modern Science Fiction (1953) that:

"Science fiction is that branch of literature which is concerned with the impact of scientific advance upon human beings."

Meanwhile, Robert Heinlein said in The SF Book of Lists (1982) that:

"A handy short definition of almost all science fiction might read: realistic speculation about possible future events, based solidly on adequate knowledge of the real world, past and present, and on a thorough understanding of the scientific method. To make the definition cover all science fiction (instead of 'almost all') it is necessary only to strike out the word 'future'."

To contrast, Miriam Allen deFord said in Elsewhere, Elsewhen, Elsehow (1971) that:

"Science fiction deals with improbable possibilities, fantasy with plausible impossibilities."

And since we're dealing with fantasy, CN Manlove said in Modern Fantasy: Five Studies (1975) that fantasy is:

"A fiction evoking wonder and containing a substantial and irreducible element of supernatural or impossible worlds, beings, or objects with which the reader or the characters within the story become on at least familiar terms."

Meanwhile, Judith Merrill said in the same The SF Book of Lists (1982) that:

"Speculative fiction: stories whose objective is to explore, to discover, to learn, by means of projection, extrapolation, analogue, hypothesis-and-paper-experimentation, something about the nature of the universe, of man, of 'reality'."

There are a lot of definitions of what SFF and speculative fiction is but personally, I like this one from this guy:

"Another way to define speculative fiction is based on its intent:Science fiction (or realistic imaginative fiction) is the study of plausible future change upon the world as we know it.Fantasy (or unrealistic imaginative fiction) is the study of impossible change upon the world as we imagine it."

And that's just for starters...

(Forgot to add this here definition of horror, the third leg of speculative fiction, with Paula Guran noting that:

Like sex, horror is seductive-- enticing the reader to accept the forbidden; allowing a fascination with the carnal, the forbidden; titillating the mind as sex does both the mind and sense. Reading horror is an act of consensual masochism: you willingly submit to the pleasures of fear - scare me! Please?

Mea culpa.)