Most fantasy uses magic or other supernatural elements as a main plot element, theme, or setting. Magic and magical creatures are common in many of these worlds.
An identifying trait of fantasy is the author's use of narrative elements that do not have to rely on history or nature to be coherent. This differs from realistic fiction in that realistic fiction has to attend to the history and natural laws of reality, where fantasy does not. In writing fantasy the author creates characters, situations, and settings that are not possible in reality.
Many fantasy authors use real-world folklore and mythology as inspiration; and although another defining characteristic of the fantasy genre is the inclusion of supernatural elements, such as magic, this does not have to be the case. For instance, a narrative that takes place in an imagined town in the northeastern United States could be considered realistic fiction as long as the plot and characters are consistent with the history of a region and the natural characteristics that someone who has been to the northeastern United States expects; however, if the narrative takes place in an imagined town, on an imagined continent, with an imagined history and an imagined ecosystem, the work becomes fantasy with or without supernatural elements.
Fantasy has often been compared to science fiction and horror because they are the major categories of speculative fiction. Fantasy is distinguished from science fiction by the plausibility of the narrative elements. A science fiction narrative is unlikely, though seemingly possible through logical scientific or technological extrapolation, where fantasy narratives do not need to be scientifically possible. Authors have to rely on the readers' suspension of disbelief, an acceptance of the unbelievable or impossible for the sake of enjoyment, in order to write effective fantasies. Despite both genres' heavy reliance on the supernatural, fantasy and horror are distinguishable. Horror primarily evokes fear through the protagonists' weaknesses or inability to deal with the antagonists.