Definitions of Science Fiction

Damon Knight
science fiction is what we point to when we say it.
In Search of Wonder: Essays on Modern Science Fiction. Advent Publishing, Inc.
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Brian W. Aldiss
Science fiction is the search for definition of man 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 mould.
Trillion Year Spree: the History of Science Fiction (London, 1986)
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Kingsley Amis
Science Fiction is that class of prose narrative treating of a situation that could not arise in the world we know, but which is hypothesized on the basis of some innovation in science or technology, or pseudo-technology, whether human or extra-terresial in origin.
New Maps Of Hell (London, 1960)
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Benjamin Appel
Science fiction reflects scientific thought; a fiction of things-to-come based on things-on-hand.
The Fantastic Mirror-SF Across The Ages (Panthenon 1969)
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James O. Bailey
The touchstone for scientific fiction, then, is that it describes an imaginary invention or discovery in the natural sciences. The most serious pieces of this fiction arise from speculation about what may happen if science makes an extraordinary discovery. The romance is an attempt to anticipate this discovery and its impact upon society, and to foresee how mankind may adjust to the new condition.
Pilgrims Through Space and Time (New York, 1947)
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John W. Campbell, Jr.
The major distinction between fantasy and science fiction is, simply, that science fiction uses one, or a very, very few new postulates, and develops the rigidly consistent logical consequences of these limited postulates. Fantasy makes its rules as it goes along...The basic nature of fantasy is "The only rule is, make up a new rule any time you need one!" The basic rule of science fiction is "Set up a basic proposition--then develop its consistent, logical consequences."
Introduction, Analog 6, Garden City, New York, 1966
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Edmund Crispin
A science fiction story is one which presupposes a technology, or an effect of technology, or a disturbance in the natural order, such as humanity, upto the time of writing, has not in actual fact experienced.
Best Science Fiction Stories (London, 1955)
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Amit Goswami
Science Fiction is that class of fiction which contains the currents of change in science and society. It concerns itself with the critique, extension, revision, and conspiracy of revolution, all directed against static scientific paradigms. Its goal is to prompt a paradigm shift to a new view that will be more responsive and true to nature.
The Cosmic Dancers (New York, 1983)
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James E. Gunn
Science Fiction is the branch of literature that deals with the effects of change on people in the real world as it can be projected into the past, the future, or to distant places. It often concerns itself with scientific or technological change, and it usually involves matters whose importance is greater than the individual or the community; often civilization or the race itself is in danger.
Introduction, The Road To Science Fiction, Vol 1, NEL, New York 1977
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Eric S. Rabkin
A work belongs in the genre of science fiction if its narrative world is at least somewhat different from our own, and if that difference is apparent against the background of an organized body of knowledge.
The Fantastic In Literature (Princeton University Press, 1976)