It has been said that heresy is the revenge of a forgotten truth. - R. A. Lafferty

Science Fiction is a group of symptoms and not a disease,” so a medical student (failed) told me once. “It's like the old disease hydropsy that doctors treated for so long before discovering that it was only a collection of symptoms, sometimes for a heart disease, sometimes for a liver or kidney disease, or sometimes even for a septic throat.”
Well, the symptoms for Science Fiction are a prowling avidity to search out and read certain occult texts; an uneasiness or excitement that permates the whole routine of life; it's the ‘itchy ears’, as mentioned in Scripture, seeking for ‘new things’. The symptoms are usually a falcon-like hunting or questing; a series of sudden tuneful encounters; a group of euphorias and buoyancies that cry in opposite directions to be hoarded like misers' treasures and simultaneously to be shared with fellow sufferers of the symptoms; feeling that the ‘World We Live In’ is somehow masked and needs to be unmasked. These and other symptoms indicate either a strange disease or diseases, or they indicate a perpetually new kind of health.
Tracing the symptoms back to the ‘disease’ does indicate that the disease is multiple, that it has such names as Hard Science Fiction, Soft Science Fiction, High Fantasy, Low Fantasy, Non-Conforming Adventure Fiction. And sometimes it bears such non-consensus names as Biological Fiction, Ontological Fiction, Eschatological Fiction (did Teilhard, for instance, know that he was writing Eschatological Fiction?), Theological Fiction, or Psychological or Philosophical or Technological or Geological or Historical Fiction. These things and many others share the same complex of symptoms.

Atrox Fabulinus, the Roman Rabelais, once broke off the account of his hero Raphaelus in the act of opening a giant goose egg to fry it in an iron skillet of six yards' span. Fabulinus interrupted the action with these words: “Here it becomes necessary to pause for a moment and to recount to you the history of the world up to this point.”
After Fabulinus had given the history of the world up to that point, he took up the action of Raphaelus once more. It happened that the giant goose egg contained a nubile young girl. This revelation would have been startling to a reader who had not just read the history of the world up to that point; which history — being Fabulinian in its treatment — prepared him for the event.

There are no rules. We do whatever seems the most fun.