Peter Nicholls (writer) in the context of "Soft science fiction"

There have been many attempts at defining science fiction. This is a list of definitions that have been offered by authors, editors, critics and fans over the years since science fiction became a genre. Definitions of related terms such as "science fantasy", "speculative fiction", and "fabulation" are included where they are intended as definitions of aspects of science fiction or because they illuminate related definitions—see e.g. Robert Scholes's definitions of "fabulation" and "structural fabulation" below. Some definitions of sub-types of science fiction are included, too; for example see David Ketterer's definition of "philosophically-oriented science fiction". In addition, some definitions are included that define, for example, a science fiction story, rather than science fiction itself, since these also illuminate an underlying definition of science fiction.

The Encyclopedia of Science Fiction, edited by John Clute and Peter Nicholls, contains an extensive discussion of the problem of definition, under the heading "Definitions of SF". The authors regard Darko Suvin's definition as having been most useful in catalysing academic debate, though they consider disagreements to be inevitable as science fiction is not homogeneous. Suvin's cited definition, dating from 1972, is: "a literary genre whose necessary and sufficient conditions are the presence and interaction of estrangement and cognition, and whose main formal device is an imaginative framework alternative to the author's empirical environment". The authors of the Encyclopedia article—Brian Stableford, Clute, and Nicholls—explain that, by "cognition", Suvin refers to the seeking of rational understanding, while his concept of estrangement is similar to the idea of alienation developed by Bertolt Brecht, that is, a means of making the subject matter recognizable while also seeming unfamiliar.

John Frederick Clute (born 12 September 1940) is a Canadian-born author and critic specializing in science fiction and fantasy literature who has lived in both England and the United States since 1969. He has been described as "an integral part of science fiction's history" and "perhaps the foremost reader-critic of science fiction in our time, and one of the best the genre has ever known." He was one of eight people who founded the English magazine Interzone in 1982 (the others included Malcolm Edwards, Colin Greenland, Roz Kaveney, and David Pringle).

Clute's articles on speculative fiction have appeared in various publications since the 1960s. He is a co-editor of The Encyclopedia of Science Fiction (with Peter Nicholls) and of The Encyclopedia of Fantasy (with John Grant), as well as the author of The Illustrated Encyclopedia of Science Fiction, all of which won Hugo Awards for Best Related Work (a category for nonfiction). He earned the Pilgrim Award, bestowed by the Science Fiction Research Association for Lifetime Achievement in the field of science fiction scholarship, in 1994. Clute is also author of the collections of reviews and essays Strokes; Look at the Evidence: Essays and Reviews; Scores; Canary Fever; and Pardon This Intrusion. His 2001 novel Appleseed, a space opera, was noted for its "combination of ideational fecundity and combustible language" and was selected as a New York Times Notable Book for 2002.