How hard is that SF? – Pharyngula mentions a survey that someone once did, asking people to rate various science-fiction movies on two dimensions. Hard: a work "takes great care in accurately presenting then-known scientific facts". Soft: a work "often and casually violates our understanding of science as it was know at the time of its creation". Optimistic/Utopian: a work's main message is "positive and optimistic towards science and technology or that it portrays a utopian future as a direct result of that". Warning/Dystopian: a work's main message is "a warning against the dangers of science and technology or that it portrays a dystopian future as a direct result of that". There is another sort of hard vs. soft distinction. Hard: nuts-and-bolts science fiction. Soft: psychological and sociological science fiction. Grading Science Fiction for Realism goes into gory detail about the "scientific" hard-vs.-soft dimension. "Present Day Tech" -- Cutting edge Present Day Tech, some developments and speculation, but nothing major that has not been attained today (so no AI). Basic space exploration, very near future -- Technothrillers, Allen Steele's Orbital Decay Ultra Hard (Diamond Hard) -- Plausible developments of contemporary technologies - AI, Constrained Nanotech, DNI, Interplanetary colonisation, Genetically engineered lifeforms. Nothing that conflicts with the laws of physics, chemistry, biology etc as currently understood -- William Gibson, Neil Stephenson, Kim Stanley Robinson's "Mars" Trilogy, Robert Forward Very Hard -- Plausible developments of provocative contemporary ideas, bot nothing that conflicts with the known laws of physics, information theory, etc - Assembler Nanotech, Nano-Goo, Uploads, Interstellar colonisation, Relativistic ships, vacuum-adapted life -- Greg Egan, Linda Nagata, Greg Benford's Galactic Center series, Stephen Baxter's Manifold Series, GURPS Transhuman Space Plausibly Hard -- The above but with the addition of some very speculative themes, some of which may well turn out to be impossible, others may be possible. Requires some modification of current understanding, but nothing that is logically impossible, or has been conclusively proved to be impossible (so no FTL without time travel) - Wormholes, Reactionless Drive, Sub-nanotech (Femto-, Plank, etc), Domain Walls, exotic matter, FTL drive with time travel, etc. -- Stephen Baxter's Xeelee universe, Greg Bear's Forge of God series, Orion's Arm Firm -- As realistic as the above categories were it not for unrealistic/impossible plot devices (e.g. FTL without time travel paradoxes), although these are kept to a minimum as much as possible -- Asimov's "Foundation" Series, "Giants" series by Hogan, Vinge's A Fire Upon the Deep and A Deepness in the Sky Medium -- Similar to the above but with a larger number of unrealistic plot devices; e.g. FTL without real explanation (or with pseudo-explanation), alien biota in some instances very similar to terragen life, psionics, a great many alien civilizations. However still preserves plot and worldbuilding consistency, and the science is good and consistent -- Niven's "Known Space" series, Robert Heinlein's Starship Troopers, Banks' "Culture" novels, David Brin's "Uplift" series, Frank Herbert's Dune, Traveller RPG Soft -- A number of unscientific themes - e.g. aliens as anthropomorphic "furries", handwavium disintegrator guns, Alien Cultures and psychology all extremely uniform, and so on. However, still retains story consistency -- Various TV series: Babylon 5, Farscape, Andromeda, Matrix, StarGate for the most part Very Soft -- As above but either even more unscientific elements (humanoid of the week, lifeless planets with breathable atmosphere, etc), and story with less consistency -- Various TV and movie series; for the most part the Star Trek Canon and Star Wars Canon Mushy Soft -- As above but even more unscientific (alien races never before encountered speak perfect English without a translator, animals too large to stand in Earth gravity (Godzilla), weapons that make energy beams without putting energy in, interstellar travel without FTL or centuries long voyage, mutants with super energy powers, etc) -- Godzilla, Comic Book Superheros, badly written TV sci fi, elements of some franchises Most visual-media SF is well on the soft side, it must be said. Arthur C. Clarke's stories are well on the hard side: Present-Day Tech: The Ghost from the Grand Banks (raising the Titanic) Ultra Hard: Fountains of Paradise (space elevator - some nano for diamondoid materials, but completely plausible, rate of current development makes this possible in the very near future) Plausibly Hard: Rama (megastructure spacecraft, logically explained), 2001 (both book and film) ultrahard science except for the monolith, etc. The film is some of the hardest space-travel science fiction that's ever appeared in visual media. Isaac Asimov's stories are at least Firm, and I'd rate his robot stories Ultra Hard, unless one counts the robots' positronic brains. However, their positronic nature is not necessary for the stories. Turning to optimism vs. pessimism, Star Trek is notable for its optimism, for featuring a future where all of humanity and many other species can coexist and work together. I remember someone claiming that much of its competition features people on the run and being chased by various enemies. I'd also say that IA's Foundation and robot stories are also on the optimistic side. So how does your favorite science fiction rate along these dimensions?