This was 'ported over from the Paksworld blog, on the grounds that it might interest others who don't read fantasy. If you read it there, it's pretty much the same.
Ritual disclaimer: nobody gets through a long writing career without some mistakes. You will sometimes trust the wrong research source (even if it’s someone who should have the knowledge you’re looking for–say a fire department veteran you’ve asked about a procedural point in managing a multi-alarm fire…and no, this isn’t a problem I’ve had.) No writer knows everything, and every writer must, at some point, trust a map, or a reference book, or a person who seems to have first-hand knowledge.
But there’s a huge difference between occasionally trusting the wrong source and not looking something up at all. Writers should look things up in the best source they can find or beg/borrow/get via Interlibrary Loan before they plan a book or a chapter–and should let the facts dictate how the story goes, rather than ignoring the facts because they already have a fantasy-version in mind.
Early on, I saw this most in regard to horses. Fictional horses could do things no live horse could do…behaved as no live horse behaves…and certain types of fictional horse existed in historical periods where that horse did not exist. Later, I saw it in regard to aircraft (including the contest entry of a private pilot who should have known better), biology (how plants actually work, how an ecosystem functions, even what human anatomy is like on the inside) and weaponry, from knives to artillery.
This is not to say that the far-future sword or firearm has to be just like the ones we know in every detail. In the Liaden books by Sharon Lee & Steve Miller, for instance, an alien species called the Clutch Turtles has a subgroup that makes–or rather grows–incredible knives that are apparently stone but whose characteristics are unstonelike. Because they had the good sense not to tell too much (they don’t give you a long infodump on the chemical composition) I can accept that Clutch knives are better than steel and unlike anything we know. Fine–it’s far-future SF, the Clutch are alien, the planet on which the knives are grown are not Earth. Their humans also have “pellet guns” for sidearms: they appear to function like any other pistol, and since no caliber or other details are given, and the function depends on the shooter’s accuracy, I’m not bothered by concern that the “pellets” aren’t just like the .22 longs I use when plinking at a stack of cans.
Swords are the same kind of thing. I have a fair knowledge of real swords–their weight, their length, their balance as fighting weapons. I know that many different styles of sword (or blade longer than a knife) have existed and been used in different cultures and each one has its benefits. I’ve learned some of them to a very amateur level; I’ve read translations of famous fencing manuals, and quite a bit of history about how swords were used in individual and mass combat. If a character pulls a sword and the writer doesn’t tell me the wrong details about it (it’s too heavy, it’s the wrong length/weight/whatever for the style the character uses) I will accept any reasonable move with that sword.
And again, for bows: I have a crossbow built on a historical model. I’ve shot both simple and recurved bows (not recently, though.) I’ve done the reading on the use of archery of various styles in warfare of various places. I know from historical records what shooting a heavy longbow does to the archer’s body over time. I know a little about bow woods, about bow strings, about how arrows were made and fletched, and so on. So if a writer doesn’t violate the realities of archery, I’ll sit there and read the story and not be thrown out.
Beyond weaponry, there’s the craft of warfare–the stuff I learned first reading Caesar and then reading military history and some modern manuals while I was on active duty. I’ve continued with that, paying attention to the professional-level stuff when I could get it and ignoring (for writing purposes) the stuff you see in movies and on TV. What makes a good movie (at least for light viewing) does not necessarily make a good book, as we’ve discussed.
Any time a writer specifies a detail…often in a number…someone with real expertise is going to perk up his/her ears and check it out. Connie Willis commented once that writing historical novels set during the Civil War meant having all the Civil War buffs sort of hovering over you, ready to pounce on the slightest error. I’m alert to certain kinds of errors, but not to all (I could read bad sailing-era stories in which the sails were given the wrong names and never be bothered…but call a horse a “bay” and then specify its mane is “gold” and I’m poised for the kill.* Fail to grasp the difference between speed of light and speed of sound…I’ll detect that. ** Fail to grasp the implications of speed of light at stellar distances, and ditto.*** Don’t know whether the firearm’s ammunition is traveling faster than the speed of sound? That’s something to look up. Designing the moon of a gas giant and want something small to have a breathable atmosphere? Best look up tables of density and understand the effects of a very steep gravitational gradient.****
One reason is that if you get in the habit of skimping on research in one area (did people in X century wear underclothes?) you will soon begin skimping in others. A writer improves only by being tough on himself/herself, by striving for accuracy even in completely fictional situations. The other reason is that some readers will already know more than the writer, and of those some are especially sensitive to errors. (Like Connie Willis, I know this because I’ve made mistakes a reader has caught. )
Readers come to fiction hoping for a good experience, however that reader defines a good experience. In general, unless in the mood I used to have during Finals, when I’d read Doc Savage books for the sheer joy of poking fun, mistakes interfere with the reader’s good experience. They make readers mistrustful, unable to sink into the story, anxious about how bad it’s going to be…how many mistakes they’ll be expected to swallow. And whatever affects readers’ satisfaction affects readers’ behavior in buying books.
* Horse colors describe patterns: a bay horse always has a black mane and tail. The color of the body does not define the term for common US/English color names. A chestnut and a bay may both have the same shade of brown on the body, but will only the bay will have a black mane and tail. (Other cultures may divide up the equine color patterns differently, and that can be a useful thing to do if readers realize it's different from "here.")
** On this and other Earthlike planets with the same density of atmosphere, the speed of sound lags the speed of light... a lot. Thus if you and the other guy are shooting at each other across a valley, you will see the muzzle flash well before you hear the shot. Stories in which the sound and the flash come together over such distances are…wrong.
***If you have a method of instantaneous communication across interstellar distances, and something goes *poof* over there, your communications will be cut off years before you see that star go nova or disappear or whatever. In one bad SF story I read, someone is looking up through a transparent dome at the very distant star…as he chats on this instant-phone-thing. As the conversation is cut off, he sees the star disappear. (Hairpulling and book throwing by this reader ensued.) If you have no instantaneous communicator, you would experience an “outage” at the same time the start disappeared, but your conversations would be very….very….slow…"HI, Jim, how are you and the kids?" and forty years later (for a star 20 LY away) "Ron--we're going great. Wish you were here." "Who's Ron--I got this number eight years ago?" and forty years later, "This number is no longer in service."
****In one story, a gas giant’s moon was supposed to be small enough to walk around in a couple of hours, be completely barren with no water resources, and yet hold a breathable atmosphere…people walked around without helmets or any other air supply and seemed to have roughly Earth-normal gravity at the surface. Er….not. Without plants and water, the atmosphere isn't going to be breathable. If you postulate some non-biological way of getting an atmosphere with a high enough partial pressure of oxygen to allow humans to stroll around outside without supplementary O2 then you have to make it plausible.