In this perspective, SF [sic] should not be seen (as I will argue at length in the theoretical part of this book) in terms of science, the future, or any other element of its potentially unlimited thematic field. Rather, it should be defined as a fictional tale determined by the hegemonic literary device of a locus and/or dramatis personae that (1) are radically or at least significantly different from the empirical times, places, and characters of “mimetic” or “naturalist” fiction, but (2) are nonetheless —to the extent that SF differs from other “fantastic” genres, that is, ensembles of fictional tales without empirical validation— simultaneously perceived as not impossible within the cognitive (cosmological and anthropological) norms of the author's epoch.

— Darko Suvin, Metamorphoses of Science Fiction: On the Poetics and History of a Literary Genre (1979, rev. 2016).