"Science fiction can be defined as that branch of literature which deals with the reaction of human beings to changes in science and technology."
-Asimov
"Science fiction is something that could happen—but you usually wouldn't want it to. Fantasy is something that couldn't happen—though you often only wish that it could."
-Clarke
"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 nature and significance of the scientific method.'
-Heinlein
"I will define science fiction, first, by saying what SF is not. It cannot be defined as “a story (or novel or play) set in the future,” since there exists such a thing as space adventure, which is set in the future but is not SF: it is just that: adventures, fights and wars in the future in space involving super-advanced technology. Why, then, is it not science fiction? It would seem to be, and Doris Lessing (e.g.) supposes that it is. However, space adventure lacks the distinct new idea that is the essential ingredient."
-Dick
I knew from the beginning that I was not doing science fiction. I was doing a space opera, a fantasy film, a mythological piece, a fairy tale. I really thought I needed to establish from the start that this was a completely made up world so that I could do anything I wanted."
-Lucas