High Quality Content by WIKIPEDIA articles! Science fiction includes such a wide range of themes and subgenres that it is notoriously difficult to define. This is a list of definitions that have been offered by authors, editors, critics and fans over the years since science fiction became clearly separate from other genres. 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.