The Mohs Scale of SF Hardness

In the ongoing discussion this corner of fandom has been having about genre, a sub-argument broke out about what counts as “hard” SF. Some people think “hardness” is a yes or no property and are indignant if some work is excluded. So it’s time to go over the Mohs Scale of SF Hardness.

(For non-geologists, the Mohs scale is a way of rating the hardness of rocks. It ranges from talc (anything can scratch it) to diamond (no lesser rock can scratch it). For genre discussions this is, of course, a metaphor.)

Disclaimers up front: “Hardness” is a separate property from whether a story is entertaining, actually science fiction, part of a particular sub-genre, or possessing the Campbellian “sense of wonder.” Yes, there are stories that are diamond-hard without stirring any sense of wonder. Us Hard SF fans call them “boring.”

Eight: Starting at the hardest level of hardness, there’s Real Life. Everything in the story exists today. SF fans consider this the least interesting level. Pulp stories with hard-boiled detectives are here.

Seven: The next level is A Simple Matter of Engineering. The gadgets in the story are compliant with known science and could be built if we put in the effort. The settings are as realistic as current knowledge allows. The Martian is at this level with the exception of its initial dust storm. The ion drive of the Hermes and automated Martian fuel manufacturing landers are just awaiting funding. The recent discovery of permafrost in the Martian soil means the hero could have dug for his water instead of messing with hydrazine (shudder) but this doesn’t make the story less hard, it just dates it. James Cambias’ Corsair is here, and hasn’t been ruined by a new discovery yet.

One problem with this level of hardness is that it only makes sense a short distance into the future. If your story is set a thousand years from now it’s ludicrous to think there will be no new rules of physics discovered in that time. If the setting isn’t as different from today’s as our lives are different from the world of 1000 AD that’s a failure of imagination.

Six: The third level is One New Thing. Invent a gadget, scientific law, or strange place, and examine the implications as it interacts with known reality. Heinlein’s The Moon Is a Harsh Mistress is level two with a spontaneously-created artificial intelligence. Niven’s “Inconstant Moon” is Real Life with an exploding sun.

Five: New Physics is where writers can invent lots of stuff. The trick to keeping it on this level is picking a few new inventions and dealing with their consequences rigorously. The Mote In God’s Eye and the related stories of Pournelle’s CoDominion series were here–Alderson drive, Langston Field shield, and weird yet plausible aliens.

Four: Artificial Gravity and Other Toys. Spaceships no longer need seat belts. This can still involve running numbers: Weber’s Honor Harrington series includes careful calculations of how much acceleration ships of each size can get from their gravitic impellers. This can still be “sense of wonder” hard SF. Ringworld had all sorts of impossible tech (teleporters, hyperdrive, invulnerable hulls, hereditary luck, and the scrith the Ringworld was made out of) but expanded our imaginations with what could be done with it.

Three: Who Cares How it Works? Spaceships fly, blasters zap, Death Stars blow things up. The gadgets enable the heroes to do their stuff. Numbers are a distraction. Firefly and Star Trek fall here. Most space opera is here as well, such as Lee and Miller’s Liaden series.

Two: Add A Dash of Magic. It looks like a cyberpunk or space opera setting, but some of what’s going on is just beyond physics. Star Wars Jedi can control minds, hurl objects, and create lightning with their minds.

One: Never Mind Science. Sometimes the author wants to do something and doesn’t care if it’s proven impossible. Mammals interbreed with egg-layers, rocks hang in the air, and Rule of Cool is all.

Too complicated? Oh, it gets worse. Many stories are rigorous in some areas of science and hand-wave others. An argument broke out over Dune in the CH comments. Where does it rank on this scale? The treatment of ecology is at One New Thing–a desert dominated by sandworms, with the implications for human society and future terraforming worked out in detail. Meanwhile the Bene Gesserit and Navigators Guild were effectively working by magic.

Another example of that mixed level is Bujold’s Vorkosigan series. Most tech in the stories is generic space opera, but the biological tech for reproduction, genetic engineering, and terraforming approach A Simple Matter of Engineering in the detail and accuracy provided. Whether this counts as “hard” SF depends on which aspect the viewer cares most about. If forced to assign a label I’d go with “partially hard” or “biologically hard,” which I’m sure amuses the twelve year olds in our midst.

So where is the line for defining something as “hard” SF? With most of the other things we argue about in the genre war it’s a matter of taste. I’ve noticed the most common line is artificial gravity. If the author make the crew strap in for acceleration and float the rest of the time the book will be called hard SF even if he’s resorting to blatant handwaves such as passing through a “loop of cosmic string” to travel between star systems.

This also points out the weaknesses in the definitions people are tossing around for “Campbellian SF.” Plenty of non-hard SF books such as Ringworld and Hogfather (a pure fantasy) provide the sense of wonder or “conceptual breakthrough” Campbellian fans desire.

The “hardness” of a story is just one way to describe it, separate from whether it includes any entertainment or other qualities. A hard SF story doesn’t guarantee it will provide sense of wonder. What the term “hard SF” does is give readers an idea of what to expect from the story, so they have a hint of whether it’s what they’re looking for. Which is all any genre label is really useful for.

FOOTNOTE: TVTropes has a version of this scale but I disagree with part of their analysis so I wrote this.

John W. Campbell versus Appendix N

There’s been some discussion here about the battles over science fiction sub-genres. The folks at Castalia House complain a lot about John W Campbell Jr’s destruction of the heroic tradition in fantasy literature. I have to wonder how he pulled that off. His power was holding the editorship of one magazine: Astounding, later Analog, from 1937 to 1971. He turned that into the flagship of Hard SF, aka Blue SF, and boosted the careers of many writers. He’s been praised as the most influential editor ever . . . by writers whose careers he started and sustained.

I don’t disagree that he was willing to sacrifice heroism and Christian values in stories to get the technical content he wanted. But how much impact did he have outside of the pages of his own magazine?

Fortunately we have a reference for heroic stories: Appendix N. Let’s take a look at those writers and stories and see how much of a dent JWC made in them.

Appendix N Author Careers

This graph looks at how many of the 28 Appendix N authors were active in each decade (excluding posthumous publications). We can see many of them were producing past Campbell’s death in 1971. Michael Moorcock, God bless him, had an original story out in 2014. The graph peaks in the 1960s because the list doesn’t include anyone whose first publication was after 1966 (Bellairs).

Looks like JWC didn’t ruin that many careers. He even published some writers who appeared in Appendix N, such as Poul Anderson’s math puzzle story “The Three-Cornered Wheel.”

But did he force those writers to do different kinds of stories? Let’s graph the works by their publications. Many were series, so those appear in all decades from start to end, again excluding posthumous publications or series continued by new authors (We’ve seen that later authors were not always doing Appendix-N worthy work).

Appendix N Works by Decade

Not as smooth a curve as the authors’ careers, but clearly the bulk of the Appendix N stories were published after JWC began his reign of terror, not before. As a destructive tyrant he doesn’t seem to be much of a success.

Another claim is that JWC tried to wipe out fantasy writing to reserve the shelves for the science side of science fiction. I don’t know how well that matches with when JWC founded the fantasy magazine Unknown Worlds, but let’s see if we can detect his impact.

Wikipedia provides a convienent, if fuzzy, source of data for this. It has categories by decade and genre for its novel pages. Wikipedia’s biases are well known, but consistent. So we can use this to get a feel for how many fantasy novels were released each decade.

I’m just not seeing a 1937-1971 reign of terror there. Yes, there’s a dip in the 1940s. Given that World War II created a paper shortage and put many writers in uniform, I don’t think we can give JWC credit for that. Afterwards the number just keeps soaring. There’s people writing fantasy, and presumably reading it.

Applying the same technique lets us compare fantasy and science fiction. Wikipedia says:

Now that’s interesting. Science Fiction started outselling Fantasy in the 1930s and kept going. The WWII dip was there, JWC couldn’t save his beloved genre from global catastrophe, but after that SF took off and kept going with up to five SF novels for every fantasy one. The genres are closer together now as fantasy production takes off.

Some of that is undoubtedly categorization. There’s a big fuzzy area between Hard SF stories with screwdrivers and Tolkienesque quest fantasy. Star Wars could be classed as “Swords and Sorcery with spaceships” instead of an SF story with fantastic elements if that’s how the marketers wanted to pitch it.

But one thing is certain: fantasy never went away. The number of fantasy books published kept increasing through John W. Campbell Jr.’s career. If he tried to stop that, he failed.

So now what? Is there anything written past 1980 worth reading?

The key test of Appendix N isn’t just that they were good stories. They were the stories that inspired Dungeons and Dragons. In fact they inspired more than D&D. Lovecraft’s stories led to the Call of Cthulhu RPG and its descendents. There’s an Elric RPG. Conan has some RPGs of his own, as well as a GURPS book.

GURPS is a good starting point for looking at other books impacting role-playing games. Steve Jackson has built one of the longest careers in the gaming industry by surfing the trends. Let’s look at his take on Appendix N.

GURPS Conan is the obvious starting point. Other Appendix N authors receiving the GURPS treatment were L. Sprague de Camp (Planet Krishna), Jack Vance (Planet of Adventure), Phillip Jose Farmer (Riverworld), Andre Norton (Witch World), and Lovecraft (multiple variants on Cthulhu).

What post Appendix N authors have a GURPS book? Horseclans (Robert Adams), Uplift (David Brin), Vorkosigan (Lois Bujold), Humanx (Alan Dean Foster), War Against the Chtorr (David Gerrold), Wild Cards (GRR Martin), Discworld (Terry Pratchett), Callahan’s Crosstime Saloon (Spider Robinson), Illuminati (Shea & Wilson), and New Sun (Gene Wolfe). If you include comic authors there’s Hellboy (Mike Mignola) and Case & Andy (Andy Weir).

Some RPG inspiration is going on there. But GURPS is a narrow segment of the RPG market. What’s going on elsewhere?


Anne Rice’s Interview With a Vampire led to Vampire: the Masquerade and the many other World of Darkness games (arguably the anti-D&D, but it brought lots of people to the table which makes it a significant influence).

William Gibson’s Neuromancer sparked the cyberpunk genre. Shadowrun was the most famous of these, but there’s several others including a GURPS book.

Gibson teamed with Bruce Sterling to write The Difference Engine, creating steampunk. Again, there’s multiple RPGs in this subgenre.

And that’s just the famous ones. Glen Cook’s Black Company series spawned an RPG. I’m sure there’s lots of others out there I’ve never heard of.

More than game books, we need inspiration from stories. There are two science fiction novels that stand above the three decades for that: A Fire Upon the Deep (Vernor Vinge) and The Diamond Age (Neal Stephenson). Either could keep a gaming group in ideas for years.

I grant those are both on the science fiction side of the genre divide, because that’s where I spend the most of my time. Please nominate your fantasy contenders in the comments.