Science fiction and fantasy, like all other fiction, is storytelling. All fiction can be defined as characters with a problem in search of a solution. Science Fiction and Fantasy are related genres, with many authors writing in both fields.
Science fiction is not fiction about science; it’s fiction about characters who are affected by science. The characters could be humans, aliens, machines, sentient rocks—whatever. But since we are human writers and readers, the problems that challenge the characters will necessarily be “human” problems (even if your protagonist is an extraterrestrial).
The key to the definition of science fiction is that the story’s problem could not happen except for the science. That is, some aspect of technology, or a future or alien society or environment, challenges the characters. If you remove these science-based elements from the plot, you don’t have a science fiction story.
This is close to the definition of a fantasy story, where characters face some aspect of the paranormal, or a magical society or environment. The characters must cope (learn and grow) in relation to the supernatural challenges they face.
The difference between science and fantasy fiction is that the latter stories contain elements that are known to be impossible (f.g., a magic watch that stops time, enabling the hero to walk through a “time-frozen” world). Science fiction contains plot elements that might be possible someday—the technologies don’t violate the known laws of physics.
If your hero gains the power to read minds through a magical incantation, or by allowing a female wizard to inhabit the left half of his body, your story is sheer fantasy. But if the power to read minds comes from an abrupt evolutionary mutation, or from genetic engineering, or computer-brain interfaces, then it’s not magic—it’s perhaps possible—and your tale is science fiction.
Both science fiction and fantasy require the reader’s willing suspension of disbelief, for while science fiction is based on explanations and extrapolations of known science, common story elements like faster-than-light travel or “sub-space” communication fall into a gray area within the genre.
Ursula LeGuin, who excels at both genres, says of fantasy:
It’s affinity is not with daydream, but with dream. It is a different approach to reality, an alternative technique for apprehending and coping with existence. It is not anti-rational, but para-rational; not realistic, but surrealistic, super-realistic, a heightening of reality. In Freud’s terminology, it employs primary, not secondary process thinking. It employs archetypes. Fantasy is nearer to poetry, to mysticism, and to insanity than naturalistic fiction.
In both fictions, metaphors often lie at the heart of the tale. Take the metaphor, “edge of the world.” Science fiction could tell of an immense artificial habitat that rings a star, constructed of material from its demolished solar system. In Larry Niven’s Ringworld, the “edge of the world” is a thousand-mile high curving wall that holds in the atmosphere.
A fantasy, on the other hand, might be about a world with a sharply defined edge, beyond which there is only the abyss. Magical folk have settled Border Town, built along this brink. Their houses have windows and doors only on the side overlooking the Known. All, that is, except Quest House—which has windows and doors facing the Unknown.
Beware Techno-babble: The jumpship carrying medicine to combat the Vlorg Plague at New Tokyo Colony develops a phase uncoupling in the wave intolerator. The clock ticks down as the hero rigs a Lipschitz wave-bridge out of a laser spectroscope, a rectal thermometer and an ancient Bic lighter. The colony is saved!
Big deal. The problem was imaginary and so was the solution.
On the other hand, one could imagine a story about a ship rushing medicine to a colony infected with a deadly virus, in which the time-pressed crew must deal with the real problem of the effects of high acceleration/rapid deceleration on human bodies, and in which the solution is not techno-nonsense, but a tragic personal sacrifice.