“If contemporary literary fiction doesn't read a bit like science fiction then it's probably not all that contemporary, is it”

T. S. Eliot in the Sunday Times, 1952; cited from David Chinitz T. S. Eliot and the Cultural Divide (Chicago: University of Chicago Press, 2003) p. 56
Criticism

The Twilight Zone, "The Fugitive" (1962).
The Twilight Zone

As quoted in an interview with David Duncan http://www.physics.emory.edu/~weeks/misc/duncan.html
Context: Science fiction, outside of poetry, is the only literary field which has no limits, no parameters whatsoever. You can go not only into the future, but into that wonderful place called "other", which is simply another universe, another planet, another species.

Source: Vehicles: Experiments in Synthetic Psychology (1984), p. 1

"The Right of Things to Come", presentation for the Science Fiction Research Association (1978), as published in Castle of Days (1992)
Nonfiction

The Paris Review interview (2010)
Context: Science Fiction is the fiction of ideas. Ideas excite me, and as soon as I get excited, the adrenaline gets going and the next thing I know I’m borrowing energy from the ideas themselves. Science fiction is any idea that occurs in the head and doesn’t exist yet, but soon will, and will change everything for everybody, and nothing will ever be the same again. As soon as you have an idea that changes some small part of the world you are writing science fiction. It is always the art of the possible, never the impossible.

A Conversation With Neal Stephenson http://www.sfsite.com/10b/ns67.htm