What is Science Fiction?
Genre authors weigh in.
Science fiction is really sociological studies of the future, things that the writer believes are going to happen by putting two and two together
... science fiction "is the myth-making principle of human nature today."
--Lester Del Ray
A science fiction story is a story built around human beings, with a human problem and a human solution, which would not have happened at all without its scientific content.
If anyone were to force me to make a thumbnail description of the differences between SF and fantasy, I think I would say that SF looks towards an imaginary future, while fantasy, by and large, looks towards an imaginary past. Both can be entertaining. Both can possibly be, perhaps sometimes actually are, even inspiring. But as we can't change the past, and can't avoid changing the future, only one of them can be real.
Pohlemic, SFC, May 1992