My complaints:

* AlastairReynolds' ''[[http://en.wikipedia.org/wiki/Technology_in_Revelation_Space Revelation Space]]'' series: Has no FTL travel but does contain several superscience technologies, e.g. the Conjoiner near-lightspeed drive, space/time manipulating weaponry, messages from the future to the past (also the basis for FTL messaging). There ''is'' a form of FTL travel present, but it tends to [[spoiler:get one's civilization ''eaten'' by the [[CosmicHorror Inhibitors]]; ''realistic'' Cosmic Horrors.]]
This is way off.

* JerryPournelle's CoDominium SharedUniverse: MilitaryScienceFiction hard enough to chip teeth. It has a PortalNetwork and a ForceField designed by Dan Alderson, a RealLife celebrated scientist at JPL.
Is mentioning his credentials necessary? It makes it sound like he actually worked out the engineering for them, when really they require just as much phlebotinum as any other PortalNetwork or ForceField, without even basing the former on the actual[[hottip:*:Well, actual to the best of my knowledge as someone completely uneducated in science.]] theory of wormholes. The verse's hardness is in obeying MagicAIsMagicA, and in having sufficient limits on the phlebotinum's abilities that they don't make the setting unrecognizably fantastic.

* ''No FTL'': Perhaps slightly softer than the above, but the physicists will forgive a lot for appeasing their Einstein-worship. Ken Burnside has a [[http://www.projectrho.com/rocket/rocket3al.html particularly scathing rant]] to that end.
**Which section of the page is the rant in? None of the titles seem to fit.
*** The rant is near the very end, and well, I'll just quote the relevant part:
----> '''Ken Burnside''': ''How would you react to a game that purported to be about, say, Marines and their tactics and utilizations that insisted that the best formation for them to attack in was walking on their hands, with their rifles clenched between their knees, shoulder to shoulder, in tight formations, through beaten zones for artillery strikes and into machine gun kill zones? Would you accept it if I told you that this was the result of a heretofore unknown doctrinal innovation made at some point 600 years in the future? Or, would you demand to know WHAT doctrinal innovation made this the best way to conduct an assault with Marines on the ground?''

* ''[[{{ptitleh3elkyxdypyw}} 2001: A Space Odyssey]]'': Unusually among films and TV series with space travel, the vacuum of space [[SpaceIsNoisy is actually silent]]. Oddly enough, this is one of the few cases where the book is softer than the movie, due to going further into the details. The iconic monolith is ill-defined, but never really breaks any physical laws.
I think the fact that the protagonist becomes a giant space baby made of energy should be taken into consideration here; not to mention the shameless use and/or abuse of AncientAstronauts.
--DocumentN
* I think this example is only meant to refer to the movie version, not the book; and the movie version really is harder. Perhaps it should be split up into two examples, with the book going under "FTL," and the current example staying where it is? Anywho, I don't think it's fair to say the AncientAstronauts trope is "abused" here; it's done about as "hard" as possible. In fact, by the TvTropes definition, AncientAstronauts is when "gods and creatures from ancient myth turn out to have been "only" visiting aliens." And that's definitely NOT what takes place here. As for the ending sequence, again, nothing is made explicit. It's a very confusing sequence. The book has a lot of soft stuff happening at this point, but in the movie, at this point, everything that's happening might as well be entirely in the protagonist's head. (In fact, when this troper watched it - before reading the book - he assumed that it *WAS* all happening in the astronaut's head.) I think the movie kept all the soft stuff subtle and ambiguous enough that it should be considered hard sci-fi, especially considering how much effort was put into making the vast majority of what happens in the film very, very realistic.

* I feel compelled also to note (here, so as not to spoil the pun) an old axiom: There is science fiction that bends the laws of science, engages in wild flights of fancy with no solid foundation and generally does things simply because they look cool. Then there is science fiction that ''admits'' it does all that stuff. Hard vs. Soft sci-fi is a false dichotomy.

* I'd really prefer to see LarryNiven's KnownSpace bumped up a category or two based on the laughable evolutionary biology of the setting...

* What about GunBuster?

* I'm a little confused about the Accelerando entry: "Charles Stross's Accelerando series: An Einsteinian universe without FTL but with traversable wormholes..." Aren't traversable wormholes ''a kind of FTL''? Or does the series explicitly make a distinction? I don't think this affects where the entry is on the scale at all, I'm just wondering because of the way it's worded.

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RobinZimm: Did a significant rewrite. Old text below for the record.

->The fun, and the material for this article, lies in treating the whole thing as a game. I've been playing the game since I was a child, so the rules must be quite simple. They are: for the reader of a science-fiction story, they consist of finding as many as possible of the author's statements or implications which conflict with the fact as science currently understands them. For the author, the rule is to make as few such slips as he possibly can.
--> -- Hal Clement, "Whirligig World" (1953)

->Mind you, anything written by Doc Smith tends to be rather light on plausibility. You know what "hard science fiction" is, right? Well, Smith's work is so soft it squishes.
--> -- "Ward", rec.games.frp.{{gurps}}, 5/1/2002

"Hard" SpeculativeFiction is firmly grounded in reality, with few fantastic flights of fancy not justified by Science™.

"Soft" SciFi is more flexible on the rules.

The existence of FasterThanLightTravel generally makes a series "softer"; the more restricted or inconvenient FTL becomes, the "harder" the series feels. SpaceIsAnOcean automatically pushes a show into "soft" territory, while SpaceIsNoisy makes it feel that way, even if there's a reason. {{Real Robot}}s are by definition "harder" than {{Super Robot}}s, although neither of them qualify as truly Hard Sci-Fi. TV tends to be softer than movies, which tend to be softer than books. Stories set TwentyMinutesIntoTheFuture tend to be harder than stories set in TheFuture, simply because there's less change from the present-day. HumanAliens and RubberForeheadAliens are typically "soft"; AbsentAliens and StarfishAliens are more "hard" options. All of these examples, of course, have loads of exceptions.

A useful rule of thumb might be derived from Jim Kakalios's rule of "miracle exceptions" in his "Physics of Superheroes" articles -- while many stories require a willing suspension of disbelief, the best ones may require only one leap of faith from an established scientific principle, or just "[[MinovskyParticle one big lie]]"; the more "exceptions" required, the harder it is to accept the story in real terms. A link to the idea can be found [[http://www.it.umn.edu/news/inventing/2002_Spring/superhero.html here]].

Another useful rule of thumb: A character is shown a time machine and asks, "How does it work?" In hard SF the answer will be: "A good question with an interesting answer. [[{{Infodump}} Please have a seat while I bring you up to speed on the latest ideas in quantum theory, after which I will spend a chapter detailing an elaborate, yet plausible-sounding connection between quantum states, the unified field theory, and the means by which the brain stores memory, all tied into theories from both Einstein and Hawking."]]

In soft SF, the answer will be: "You sit in this seat, set the date you want, and pull that lever."

(Note this is not ''universally'' true; you can skip over the details as long as the basic explanation you give doesn't seem to [[MagicAIsMagicA conflict with anything that's been established so far]].)

Some writers of hard Science Fiction write about areas where they already know a great deal of science fact and/or research the science behind the stories.

The [[MundaneDogmatic Mundane Manifesto]] is one attempt to define a set of rules for writing a hard SF story or series, by deliberately forbidding many of the traditional tropes of media Sci-Fi.

"Hardness" is not, however, a simple two-category sorting function, or even a one-dimensional continuum. Many series depart from reality in different ways, and for different reasons. Nevertheless, here's a grossly simplified attempt at a list, from softest to hardest. Don't take it as gospel; just look at the size of the arguments on the discussion page.

Note that this list only tracks SciFi series, which are meant to take reality and diverge from it. Fantasy series need not apply, even though many of the softest {{Space Opera}}s have been accused of being just fantasy stories with spaceships and ray guns. Similarly, a series that revolves around a BlackBox is hard to classify until you know what the BlackBox is.

Finally, remember that harder is not always a good thing. Some authors try so hard to make a story realistic they forget plot and characterization, and others may try to justify their occasional break from reality with {{technobabble}}, although the most famous example's [[StarTrek on the soft end]]. Thus, neither side is truly better than the other, and which side you prefer depends on personal taste and where a person's WillingSuspensionOfDisbelief lies.

The name comes from the [[http://en.wikipedia.org/wiki/Mohs_scale Mohs scale of mineral hardness]].

[[http://www.kheper.net/topics/scifi/grading.html This]] site contains more of this type of classification, if you are interested (note, that, comparing that site to this page's grouping, series that appears in Minovsky Particle section and below can be considered to be at least hard, though not always).

Not to be confused with SlidingScaleOfRealisticVersusFantastic and SlidingScaleOfLikeRealityUnlessNoted.

'''''Please note:''' This list is ranked. That means Soft stuff goes on top, and Hard stuff goes on the bottom. Softer items are closer to the top, while Harder items are further away towards the bottom. So, if you know about a really, really hard work of sci-fi, don't place it under "Hardest"; instead, place it at the very bottom of the list, right above "Hardest".''

::''Old level definitions:''
'''Softest''' : The MST3KMantra is your SurvivalMantra. YourMileageMayVary as to how soft these marshmallows are.

''ImportedAlienPhlebotinum'': There are technologies that break the laws of physics, but we don't have any real idea how they work, or they are dependent on a resource that apparently appeases some higher power.

''MinovskyParticle'': The laws of physics are broken in a specifically declared way. Expect hundred-page dissertations on fictional physics and [[MagicAIsMagicA consistent internal rules]].

''FTLTravel'': The ''only'' departure from reality is that we've finally outsmarted Einstein -- at the very least to [[SubspaceAnsible send messages]].

''No FTL'': Perhaps slightly softer than the above, but the physicists will forgive a lot for appeasing their Einstein-worship. Ken Burnside has a [[http://www.projectrho.com/rocket/rocket3al.html particularly scathing rant]] to that end.

''{{Unobtainium}}'': Comprised solely of theoretical yet plausible elements. NO FTL in any way, shape or form.

''NextSundayAD'': The only thing unrealistic is that it hasn't happened -- ''yet''. The only way to grade these is by their age. Newer means harder; one can always tell when ScienceMarchesOn.
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TwinBird: Is it just me, or does ''StarWars'' seem way to low on the scale? I mean, it at least ''feels'' softer than all StarTrek and SuzumiyaHaruhi.
* RobinZimm: The list isn't well sorted within each category, I believe.