Over the weekend, while working on Unmortal (we're at what amounts to a "draft 1.3" now, more on that later), I took a bunch of notes in re things that needed to be at least mentioned in the book, even if they didn't have to be expanded on tremendously. Bits of world background, references to things that deserved to be expanded, stuff like that. It struck me that there's roughly two ways to work such things into a story -- the Shoehorn Method and the Scissor Method.
The Shoehorn Method is just what it sounds like. You take everything that came to mind, and you cram it into the book somewhere. If the total size of the book bumps upwards because of it, so be it. It wouldn't be seemly to leave crucial details on the floor. With the Scissor Method, though, you take the elements of what you want to put in and pare them down until only what intersects with the story you are telling is left. Then you lay that pared-down piece into a place that receives it well.
The Shoehorn Method is "easier", in theory anyway, because you don't have to do very much selecting and fitting. You can just write. And since books these days tend to be outsized by default -- because the publishing industry loves to sell people one huffed-and-puffed story for the price of five slim-and-trim ones -- readers tend to go gamely along, and never wonder why they're getting bored halfway through a story where not much actually seems to be happening.
The Scissor Method is harder, because you have to actually think about the intersection between your story's narrative and the material you want to relate. But it's more rewarding, because it's more organic -- it reads more naturally, and gives you more chances to actually talk about what's going on, not just forward facts to the reader. And it allows you to respect the existing scope of your work, so it doesn't inflate itself spontaneously.
Scissoring forces you to think about the material from the point of view of the people telling and receiving the information, and how they might go about doing it from their own frame of reference. Otherwise you end up with something like that joke short story floating around out there, the one that describes two people taking a bus or train or something somewhere, with the mechanisms of the train described with the same kind of breathless overkill used to talk about faster-than-light travel or what have you. "The device in his pocket, barely bigger than his spread palm, was connected to a worldwide information network. All he needed to do was tap its touch-sensitive screen and he could bring up everything from the news of the day to a million video programsdfglkjhblmgndf5;5y$Rfv
... Sorry, I fell asleep just typing that drivel. Can't imagine what it's like for you to read it.
You always want to be conscious of how people in any setting don't explain too much to each other, and too many of the wrong things. Most of us are able to succinctly summarize some kind of major historical event like 9/11 or the Bay of Pigs in a sentence or two. And when we do, we tend to do so as part of our personal perspective, not as some potted historical rundown. We don't need to know everything, just what matters to then and there and the folks in question.
Another thing that comes up here a lot is when people have an exotic setting (well, exotic to us), and bring in some audience-identification character who knows nothing about how things work, and so gets it all explained to them in painful detail for the benefit of us simps. I've always hated this technique, because it's lazy in its own way -- it means the author didn't think how it might be possible to elegantly relate this information.
What's more realistic is to have two or more people, each of whom knows something but not everything, and you give each of them a chance to explain what they're best suited to explain. And those explanations don't have to be explanations, either. They can be framed as commentary on the fact that something works, or doesn't work, as it does ("Last time I tried this I ended up with a spare head for a week"), or as notes about how it fits (or doesn't) into the world at large ("We keep this up, they're going to ban breathing altogether"), and so on.
I suspect many people shoehorn for a couple of reasons. One is an attachment to the underlying material -- they're so in love with every detail of it, they have to put it in there. Another is fear of being seen as threadbare: All those other books plump with detail, so if I don't do that with my book, I'm not going to measure up. The first of these must be combated by keeping the focus and framing of the story always within view. Again, the way publishing works these days operates against that because it disincentivizes people from telling one good, solid story instead of a slew of slack ones. The second is a factor of the first, and once you realize publishing surrounds us with bad examples that don't have to be emulated, it's liberating.
I am entirely guilty of infodumping myself, but I've always at least tried to make it interesting. The opening bits of Fall Of The Hammer relate the backstory of the world by way of a father telling his son. And not just as "here's how things are" but as "here's what we lost because of what things are". In other words, as personal perspective, not just as facts. I felt like I veered a little close to that superficial "lyricism" many fantasy stories get lacquered with (more because they don't want to look boring next to the competition than because they have anything actually pretty or absorbing to share), but again, I did my best to make it feel like active knowledge between the people in the story, not something passively conveyed to us alone.
Another way I was guilty of this was in Always Outnumbered, Never Outgunned. For around the first third or so of the story, I worked in a number of interstitial flashback chapters that provided backstory about the main character, and some crucial bits about how things worked in the book's universe. It brought the book up to about 210,000 words, or around 500 pages. I'd been aiming for about 50-60K less than that. But I left it in, because a) without it you don't get the same sense of context, b) it explains a number of things by way of example, and c) I tried to keep it fleet of foot as a reading experience. I didn't want people dreading those parts of the book if I could help it.
So, no, I'm not perfect either. I only give advice like this because I have some idea of why it matters.
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Other Lives Of The Mind