For purposes of shorthand, I call idea generation, "glimmers."
I call them "glimmers' because it is best to keep them vague and shimmering at first, before they calcify into something I can't change.
They come in two types.
First, the plot generation glimmers, which is the overall direction, theme, character development I'm shooting for. "Premise" feels like too solid a word for this, but I need to have strong glimmers of these things before I start a book. If the underlying ideas aren't strong enough, they won't carry the day and the story will peter out. That happens occasionally, though I'm pretty careful these days not to just go off half-cocked.
"The Toad King" was a little bit under-cooked before I started it, because I figured the character was interesting enough to carry the story and because I meant it as a novella. As it happens, the character was strong enough for about 2/3rds the story, but came up a little short in overall story generation, so I've struggled a bit.
I've got it now, so that's good. I have a glimmer of how I want the plot to go.
Secondly, the specific glimmers that bring the scenes alive. So for instance, in this current chapter I've come up with the idea of the Toad King robbing the main temple, with the help of Quarry and Marna.
However, that's all I had.
What I needed was "how" and "when" and "why" and "what" happens. I need telling detail, character actions, scene-setting, all of that.
Again, just as it is dangerous to start a book without strong enough premises, it is dangerous to start a chapter without sufficient visual and auditory glimmers. I mean, I can do it with just single glimmer sometimes, but the story always seems thin to me when I do that. I've learned to gather a dozen or more glimmers before I'd actually start the chapter. (My walks were especially useful for that--but I haven't walked for two months...)
Yesterday, I sat down to write the robbery chapter, and nothing came. Nothing at all.
Rather than force the issue, I didn't start.
Just before bed, I had two glimmers. One--that the good guys harness a Monster of the Abyss to be the diversion, and Two--they rob in the daytime.
Today, I've come up with about a dozen more glimmers, enough to start the chapter.
Usually I come up with a dozen more glimmers in the course of writing, along with the business at hand, hopefully for a fully fleshed-out story. This process hasn't been as smooth as usual lately, but I've had lots of distractions. But little by little, it's coming together.
As long as the glimmers keep coming, I can keep writing. It scares me to death sometimes that the glimmers feel so fragile and vulnerable.
I just have to keep the faith they're there waiting when I'm ready.
5 days ago