All fiction is metaphor. Science fiction is metaphor. What sets it apart
from older forms of fiction seems to be its use of new metaphors, drawn from
certain great dominants of our contemporary life — science, all the sciences,
and technology, and the relativistic and the historical outlook, among them.
Space travel is one of these metaphors; so is an alternative society, an
alternative biology; the future is another. The future, in fiction, is a
metaphor.

A metaphor for what?

If I could have said it non-metaphorically, I would not have written all these
words, this novel; and Genly Ai would never have sat down at my desk and used
up my ink and typewriter ribbon in informing me, and you, rather solemnly,
that the truth is a matter of the imagination.

Science fiction … means what we point to when we say it.

Science fiction is the search for a definition of mankind and his status in the universe which will stand in our advanced but confused state of knowledge (science), and is characteristically cast in the Gothic or post-Gothic mode.

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.

Science fiction literature's focus is on ideas, the concept of change, and the impact on humanity. Those concepts are hard to capture on film. They work better in the mind.

The way to teach in this world is to pretend you're not teaching. Science fiction offers the chance to pretend to look the other way while teaching. Science fiction is also a great way to pretend you are writing about the future when in reality you are attacking the recent past and the present. You can criticize communists, racists, fascists or any other clear and present danger, and they can't imagine you are writing about them.

Yet, if there is the possibility of this satisfaction from accurate prophecy in science fiction, there is also the reverse. Science fiction offers its writers chances of embarrassment that no other form of fiction does. After all, if we may prove accurate in our predictions, we may prove inaccurate as well, sometimes ludicrously so.

This is an exercise in fictional science, or science fiction, if you like that better. Not for amusement: science fiction in the service of science. Or just science, if you agree that fiction is a part of it, always was, and always will be as long as our brains are only miniscule fragments of the universe, much too small to hold all the facts of the world but not too idle to speculate about them.

Science fiction encourages us to explore... all the futures, good and bad, that the human mind can envision.

Science fiction, as I like to define it, is fiction based on the imagined exploration of scientific possibility. The distinction from fantasy—or from other sorts of fantasy—lies in the word possibility.

Science fiction is a dialogue, a tennis match, in which the Idea is volleyed from one side of the net to the other. Ridiculous to say that someone 'stole' an idea: no, no, a thousand times no. The point is the volley, and how it's carried, and what statement is made by the answering 'statement.' In other words — if Burroughs initiates a time-gate and says it works randomly, and then Norton has time gates confounded with the Perilous Seat, the Siege Perilous of the Round Table, and locates it in a bar on a rainy night — do you see both the humor and the volley in the tennis match?

But science fiction’s entanglement with theology goes far deeper... Writers in this genre explore the consequences of technological innovation for human communities and individual human lives, whether those consequences are intentional or accidental, emotional or economic. They consider the impact that scientific theories and concepts have had on our understandings of what it means to be human, and on the limits of individual human identity. They examine how the characteristics that make us human (big brains, tool-making hands) might also lead to the end of humanity, either with a bang (“Terminator 3: Rise of the Machines”) or a whimper (“Day of the Triffids”) or both (“Threads,” “The Day After”). As such, science fiction asks its audiences not just who they think they are, but who they want to be. It creates visions both of the world as it could be and as it must not be allowed to be, with science and technology together building the future of faith.

Science fiction is a natural, in a way, for any kind of radical thought. Because it is about things that have not happened and do not happen. It's usually placed in the future, but not always. It's very fruitful if you want to present the concerns of any marginal group, because you are doing it in a world where things are different.

I have come to prefer something looser, a rough sort of definition which says simply that science fiction attempts to portray that which does not exist, a speculative reality, but endeavors to explore the consequences of such a speculation in a rigorous, systematic, and scientifically plausible way.