SF/Fantasy Classification

As a critic, I operate under certain basic assumptions, all eccentric, to wit:

1. That the term "science fiction" is a misnomer, that trying to get two enthusiasts to agree on a definition of it lead only to bloody knuckles; that better labels have been devised (Heinlein's suggestion, "speculative fiction", is the best, I think), but that we're stuck with this one; and [that] it will do us no particular harm to remember that, like "The Saturday Evening Post", it means what we point to when we say it.

-Damon Knight, _In Search of Wonder_, 2nd Ed. (Advent), pg.1

   This is a work in progress, but these classifications work pretty well for me, and might help others avoid some of those bloody knuckles. If you have comments, please let me know, I'd like to make this more universal.

Science Fiction (SF):

Stories set in a world based on some conjectured change in science, mathematics, technology, or culture. Normally, the change cannot be known to be utterly impossible at the time of writing, or it becomes fantasy. However, there is a borderline case of "one impossible assumption", such as _A Fire Upon the Deep_ by Vernor Vinge, or _Flatland_ by Edwin A. Abbot. These can usually be accepted as science fiction if science (mathematics, in the case of _Flatland_) is a central focus of the stories.

Science Fiction also includes, by default, anything with rockets or space travel, including _Dragonriders of Pern_ by Anne McCaffrey, and even _Santa Claus Conquers the Martians_; it might be bad Science Fiction, or even an SF/Fantasy crossover, but it remains SF.

Hard Science Fiction:

Science Fiction which conforms to all known laws of physics, and which specifically focuses on math, science, and technology.
Example: _Cryptonomicon_, by Neal Stephenson

Technothriller:

Science Fiction or Hard Science Fiction stories marketed as "mainstream" novels, usually set in the present or very near future.
Example: _Jurassic Park_, by Michael Crichton

Alternate History:

Stories where a change in historical events led to a different history than our own. This does not generally include future histories, but often does include magic or time travel.
Example: _Guns of the South_, by Harry Turtledove

Fantasy:

Stories which contain features which are blatantly impossible, usually magic.
Example: _Metropolitan_, by Walter Jon Williams

Supernatural Horror:

A subset of fantasy, usually set in the modern world, which is meant to horrify, scare, or gross you out. The impossible feature in horror is usually some life-form which is inimical to humans, but can also be revelations about the true nature of reality.
Example: "The Call of Cthulhu", by H.P. Lovecraft

Speculative Fiction (also "SF", which is very confusing):

Any or all of the above.