The simplest definition is to say that, where normal stories are about rescuing princesses from pirates, science fiction stories are about rescuing space-princesses from space-pirates.
Behind this facetious definition there is a thought worth examining:
All stories are falsehoods used to reveal some truth. The falsehood is one the storyteller and the audience tacitly agree shall be treated as true for the purposes of telling the tale. In this respect, the storyteller is a magician who enchants his audience; they are willing to believe the unbelievable, to suspend their disbelief. But if he makes too great a demand on their willing suspension of disbelief, the spell is broken, and his illusion stands open to their contempt as a cheap trick.
Different audiences will place this ‘point of disbelief’ at different heights.
For example, in a comedy, the audience is willing to accept the most unlikely and unrealistic coincidences in plot or stunts in action, merely because it is funny. The tolerance is high. In a gritty action thriller, however, any unrealistic detail, such as shooting seven bullets from a six-shooter, will break the spell for a serious audience.
Every reader will recognize when it has happened once or twice that his point of disbelief has been notched upward. Let me use a war picture as an example. When the hero runs through a hail of machinegun bullets fired by Nazis unscathed (or, in Science Fiction, when he runs through a lightningstorm of blaster fire from Imperial Stormtroopers) something clicks in our brains, and we smile, and settle back in the theater seat, and we don’t take the movie was seriously as we did the moment before. We might still like it: but now it is a ‘popcorn’ movie, light entertainment. Our tolerance for unreality for light movies is more generous than for gravid ones. Compare that, on the other hand, with the opening sequence in SAVING PRIVATE RYAN, where the whistling storm of machinegun-fire was realistic and horrifying. No one was running around protected by an invisible aura of ‘main character glow’. The point of disbelief was low.
When we have put our tolerance at the high point, either because it is a genre we like or an author we like, we react grumpily to any evidence that the scenes are unrealistic. Complaints seen like nit-picking, small-mindedness. The complainer cannot get in the spirit of things. He is trying to break the spell.
What makes the calculation of where to put the point of disbelief complex is two factors:
First, unbelievable things actually do happen in real life: there are moments of high heroism and deep horror, eerie coincidences and true love. There really are men like Napoleon and George Washington, who change history. Stories are supposed to be about the unusual: anyone who works on a newspaper can tell you that.
Second, the craft of the artist consist of certain tricks and devices he uses to make the unbelievable seem real. This is called verisimilitude. Verisimilitude is the illusion of reality: a thing that is not real, but which seems realistic.
Stephen King writes with masterful craft by using settings and people as one might find in any small town in America; only after the reader is habituated into trusting these descriptions, do odd, and then unearthly elements begin to intrude on the picture. He is correctly regarded as a fine horror writer, perhaps the finest, because of his mastery of this device of verisimilitude.
There is a famous scene in Homer, when Andromache brings her baby out to say farewell to Hector before that warrior prince issues forth to battle. Astyonax is startled by the plumes on his helm of his father and begins to cry. This is the type of realistic detail suddenly makes the unearthly elements in the epic seem more realistic. When Hector batters down the gate of the Achaian palisade, he hoists a rock so large that “two men, such as men are now, could not have lifted it.” The fact that the baby was startled by his gleaming armor makes Hector seem like a real person; even when he does feats no one now-a-days can do, the feeling of reality is maintained. Instead of shaking their heads, and saying no one could lift up so large a rock, the listeners nod and listen.
Now, along the spectrum of realistic to unrealistic fiction, Speculative Fiction (by which I mean Science Fiction and Fantasy together) occupies the more unrealistic side. Indeed, Speculative readers not only tolerate but demand that a high demand be placed on their imaginations: they want to see life or Mars, or Barsoom, or Middle Earth, or in the Year 2000 or in the Hyperborean Age. We place the point of disbelief very high.
The separation of fantasy from science fiction is merely the difference in the craft of verisimilitude used. Fantasy impersonates the tone and style, the tropes and details of medieval and ancient songs, epics and folktales. Unearthly and unbelievable things can happen in Middle-Earth, provided they seem to happen in the same mood and atmosphere as ORLANDO FURIOSO or LE MORTE D’ARTHUR. If the mood is not broken, the audience will accept the illusion as real.
Science Fiction impersonates science. The science does not need to be real, but it needs to produce a realistic illusion. Time Travel, or Faster-Than-Light drive, are both as fantastical as Santa’s Elves: but, in the communal imagination of SF, they are assumed to be the product of scientific investigation, built in a workshop or lab, produced by the same ingenuity as Robert Fulton or the Wright Brothers.
This point is worth dwelling on. In order to create verisimilitude in THE TIME TRAVELER, the author H.G. Wells has a frame in the first chapter. The scene opens with an unnamed first-person narrator describing a conversation at a dinner party: the idea that time is a dimension that can be crossed like length, breadth, and height are introduced, and a machine for crossing time, similar to a flying machine, comes on stage as a prop. Now the reader is ready to accept the idea of a man who crosses time in a time machine the way a sea-traveler crosses the sea in a steamship. The Ghost of Christmas Yet to Be might bring Scrooge into the future to view a prophecy, but this is a supernatural visitation. The Time Traveler’s vehicle is natural, a product of his workshop, no more supernatural than a steam engine. But without the frame of the dinner party, where we meet the Time Traveler, without the initial theoretical discussion, the stress on the readers willing suspension of disbelief would be greater.
This is the unique property of Science Fiction. The readers of Science Fiction are expected to know something about modern science, and they expect that whatever fantastic adventure about to be told them will be framed in terms of some explanation that is plausibly scientific. Whether the science fiction is hard or soft depends on how implausible the scientific explanation is, and how central the story it is.
Science fiction readers expect to be convinced by having a discussion or lecture take place in the text, which has enough real science to make the fake science seem real. These lectures are unknown in other genres.
Tales where the props and settings from science fiction are merely thrown in for flavor, or to produce a background of wonder, are rightly called Space Opera: adventure stories that take place in space, no different, really, than similar tales taking place in remote jungles, pirate-infested seas, golden palaces, or the mountains of Tibet. STAR WARS, for example, is space opera, since the science is there merely for flavor. The same tale could have taken place, almost unchanged, in the fairytale Japan of legend.
There is, by the way, a similar division in fantasy between hard and soft, or high and low. Fantasy that accurately follows the ancient models of the world, now lost, which our ancestors knew, is realistic fantasy (if we can use that term). The language is elevated, the action is mannered. Sword and Sorcery stories follow the themes of ancient epics and folktales. Oriental fantasy follows the model of Arabian Night’s Tales, with their strange vistas, Jinn-haunted palaces, and cruel bejeweled splendors. The ‘Dying Earth’ tales of Jack Vance are a superb example of this opulent oriental flavor, even though they take place in the Far Future rather than the Far East.
Fantasy where the characters talk and act like middle-class gamers from Southern California, except that they swing swordsand shoot lightning from their fingertips, is a tale where the fantasy settings and props are merely thrown in for flavor. We should call such unrealistic fantasy Elf Opera.
But the point, the main point, of speculative fiction, both fantasy and science fiction, is that they are both ultramundane. Fantasy is unearthly, and science fiction is extraterrestrial. They deal with things that do not happen in the here-and-now. Either the setting is in another world Beyond the Fields We Know, or something from the Other World or Outer Space has intruded into our comfortable little reality. When something from Beyond intrudes into our little world, the reaction is either terror or awe. All the old SF magazines had titles reflecting this: Thrilling, Wonder, Amazing, and so on. Any definition of Science Fiction or Fantasy that does not point to this central characteristic of unearthliness is defective.