"A science fiction 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.'

- Theodore Sturgeon, cited in James Blish, "Some Propositions" (1952)

Or

"Science fiction is a branch of fantasy identifiable by the fact that it eases the "willing suspension of disbelief: on the part of its readers by utilizing an atmosphere of scientific credibility for its imaginative speculations in physical science, space, time, social science, and philosophy." -Sam Moskowitz, introduction to Explorers of the infinity (1963)

Not quite? How about:

Jules Verne was my father.
H. G. Wells was my wise Uncle.
Edgar Allen Poe was the batwinged cousin we kept high in the back attic room.
Flash Gordon and Buck Rogers were my brothers and friends.
There you have my ancestry.
Adding, of course, the fact that in all probability Mary Wollstonecraft Shelley, Author of Frankenstein, was my mother.

- Ray Bradbury, introduction to S Is For Space (1996)

These and many more quotes by science fiction notables on all sorts of subjects are in Science Fiction Quotations From the Inner Mind to the Outer Limits, edited by Gary Westfahl with a foreword by Arthur C. Clarke.

Collected from a variety of sources, such as science fiction and fantasy stories, novels, films, and television programs, the quotations range from Actions ("There are times in life when the most comfortable thing is to do nothing at all. Things happen to you and you just let them happen." _ James Hilton, Lost Horizon (1933)) to Work ("Whenever you see a bunch of buggers puttering around talking about truth and beauty and the best way of attacking Ethics, you can bet your sandals it's because dozes of other poor buggers are doing all the real work around the place." - Terry Pratchett, Small Gods (1992)) This Yale University Press book has an invaluable Index of Authors, complete with birth and death dates, and Index of Titles of the source material.

If you enjoy browsing quotations on a variety of subjects by a variety of science fiction and fantasy authors, you will enjoy Science Fiction Quotations.