In 6th grade, the
reading instructor started a
unit on
speculative fiction. He gave what I consider to be the one of best and most useful definitions of it:
Speculative fiction is fiction that asks the question "What if..."
This definition envelops
alternate history, plain
science fiction,
hard sf,
soft sf,
horror, and
fantasy (both
alternate world and
sword and sorcery) quite readily. It could arguably be pushed to envelop
historical fiction and most other
fiction, but the "What if..." involved might get quite unwieldy. Speculative fiction tends to push on concepts of
reality — or focus on what is essential about our own
humanity. The term appears to have been coined by
Robert Heinlein, based on a brief search of that fountain of knowledge, Google.
Some examples of What if: