The Definition of Science Fiction

This definition cuts through some of the muddle that tends to bog down defining Science Fiction in terms of calling it a literature of the scientific: as if H.G. Wells’ Time Traveler is somehow more realistic or more scientific than the time-travel of the Mark Twain’s Connecticut Yankee or Dickons’ astonished Scrooge.
My point is that the same magical and mythical elements as appear in all fiction appear in Science Fiction, except that they are re-cast in terms that the modern Darwinian point of view will admit. A few examples will suffice:

• SF has supermen but not demigods. Paul Mu’ad Dib is not meant by his inventor, Frank Herbert, to be a real messiah sent by a real God on a real divine mission: Paul is a super-human, a product of eugenic breeding to the stage of development beyond human. He is no more a prophet than The Gray Lensman, who was likewise a super-man, a product of eugenic breeding. If Herbert had meant Paul to be a real Messiah, the Jihad he foretells would have been cast in the tale as a victory: instead it is depicted as an unmitigated disaster that Paul is powerless to stop.
• SF has no giants, but plenty of giant robots: just ask Daisaku Kusama (or Johnny Sokko, take your pick).
• SF has The Invisible Man but not Rings of Invisibility. When Angelica or Gyges or Frodo Baggins uses a ring to turn invisible, neither has to worry about leaving footprints in the snow. When John Griffon turns invisible, however, he has to run around in the nude, and the retinas of his eyes still reflect a bit of light. Now, a nude scientist is no more real than an invisible damsel, an invisible tyrant, or an invisible hobbit, but an invisible man who has to shed shirt and face-bandages to turn invisible is more realistic: HG Wells has thought through the day-to-day practical details of what invisibility would actually entail if it were possible.
• SF has no magic, but plenty of psionics. The Gray Lensman can read minds. The Slans can read minds. The Psychohistorians can read minds. The Jedi can read minds, sort of. Vulcans can read minds. The  Martians from MARTIAN CHRONICLES can read minds. The Martian from LAST AND FIRST MEN can read minds, at least of other Martian cloud-masses. The Martian from THE JUSTICE LEAGUE can read minds. The Martians from A PRINCESS OF MARS can read minds, or, somehow, make it so that clean-limbed fighting men of Virginia can read their minds when he is on their world. The Martian from MY FAVORITE MARTIAN can read minds. What is the difference between magic and psionics? Nothing except for the world view: magic lives in worlds where there are spirits. Psionics is an application of a yet-undiscovered branch of psychiatry: the technology of parapsychology.
• SF has no gods or genii but plenty of Arisians, Eddorians, Talosians, Organians, Metrones, and other godlike superbeings.
• SF has no monsters, strictly speaking, no children of Echidna, but it has plenty, nay, a superabundance, of monstrous mutants, usually caused by radiation, or dinosaurs melted from ancient glaciers, and it has plenty of alien critters. There is hardly a planet in space that does not have a dinosaur or a ten-limbed lion on it.

My point here is that the scientific revolution did indeed revolutionize our view of the world and our place in the order of creation: but it did not revolutionize, or even change, the way to tell a tale. You cannot tell a really good tale without gods and monsters (well, maybe Tolstoy could, but he might need Napoleon, who almost counts as a monster) but in Science Fiction these things have to come from Mars or Antares, or some place farther yonder: because we have sailed the seas that Odysseus sailed, and seen no sign of Scylla.
Mars was once beyond the edge of our maps, and so Barsoomians could be imagined there. If you want to have your hero teleported to a distant land for a sword fight or to win the heart of a space princess, Alpha Scorpii is a better bet than Mars, these days.