The Encyclopedia of Science Fiction in the context of "John Clute"

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.

Space travel, or space flight (less often, starfaring or star voyaging) is a science fiction theme that has captivated the public and is almost archetypal for science fiction. Space travel, interplanetary or interstellar, is usually performed in space ships, and spacecraft propulsion in various works ranges from the scientifically plausible to the totally fictitious.

While some writers focus on realistic, scientific, and educational aspects of space travel, other writers see this concept as a metaphor for freedom, including "free[ing] mankind from the prison of the solar system". Though the science fiction rocket has been described as a 20th-century icon, according to The Encyclopedia of Science Fiction "The means by which space flight has been achieved in sf – its many and various spaceships – have always been of secondary importance to the mythical impact of the theme". Works related to space travel have popularized such concepts as time dilation, space stations, and space colonization.

Peter Douglas Nicholls (8 March 1939 – 6 March 2018) was an Australian literary scholar and critic. He was the creator and a co-editor of The Encyclopedia of Science Fiction with John Clute.