Classification of Science Fiction

Hard Science Fiction is the rarest variety, where the science is integral to the story. Recent examples include Cramer's Einstein's Bridge and Charles Stross's Accelerando (Singularity).

Soft Science Fiction itself falls into several categories, military, romantic, and humorous science fiction are all common, where the science is reasonably accurate, but other aspects of the story dominate. Most of David Weber's and John Ringo's military SF fall in here. Also, Lois McMaster Bujold's Barrayar series, most of the works of Robert Heinlein, Greg Bear, and many others who primarily tell stories but with accurate science in the background.

Pseudo-science Fiction is by far the most common. Pseudo-science is nonsense that pretends to be scientific; non-entertainment versions include perpetual motion machines, the Dean drive, homeopathy, chiropractic, quantum mysticism, and much more. Virtually all SF movies are pseudo-science based; they cannot usually get even the most basic facts right. Star Wars, Star Trek, Armageddon, The Core, none of these or many others I could list have anything resembling real science in their stories. Many write "science fiction" with little or no real science; L Neil Smith's libertarian fiction; Steve Perry's martial arts fiction; Frank Herbert's Dune series (Brian Herbert and Kevin Anderson's prequels and sequels are even worse); Lee and Miller's Liaden Universe novels; superhero movies and novels.

Fantasy - Not even related to science. I have never quite figured out how "Fantasy and Science Fiction" came to be considered a single category. I mean "Mystery and Science Fiction" or "Romance and Fantasy" make as much sense as categories.