I hold the idea of leitmotifs at arms length. I understand the dramatic appeal, but I often find its execution, as a composer and a listener, overwhelmingly literal. Plus, it's often the case that when I try to assign a given piece of musical material a very literal dramatic meaning, I'm confronted by two issues: one, that in an entirely appropriate moment, I'm instead pulled towards another musical solution, or two, that in an entirely inappropriate moment, I find myself wanting to deploy an 'out of place' motif.
That said, even though I write intuitively, I can't tell you the number of times a motif takes on a very clear meaning post-facto. I think of it this way: if it's true that musical material carries with it emotional and semantic connotations, even if you use it whenever you want, you only want to use it when it serves the dramatic moment. By looking at when you used it retroactively, you figure out the long way 'round what meaning its presence carries for your story, and the total effect is often much more naturalistic and sophisticated than if you ham-fistedly try and force a meaning onto your material in advance.
A great example of this is the vamp that forms the accompaniment for much of "Without You". That accompaniment actually started in a song called "Duty", which was ultimately cut when I replaced the Demagogue with the Apprentice. I liked it quite a bit, though, so I used that figure to introduce "You Go", and then again to close "Eternity", both of which I wrote before "Without You". (I further used the RH figure all over the place, from "Ten Suns" to "Jade Rabbit"- have fun spotting it throughout the War Story.)
When I finally got to "Without You", then, I knew it'd be based off of that musical cell. One, because it's only ever been associated with the Wife's presence, and two, because it's so strong and singular within the palate of the War Story, it would stand out like a sore thumb if it didn't get a 'source song'. So I combined it with the sus2 figure from the bridge of "You Go" and got that AABA figure the Wife, and later the Apprentice, sing. The song in context turned out to run at a clip, as to keep the momentum up at a moment when the story is hurtling towards its conclusion.
It took until after the first production at Yale that I realized what was going on with the motif. It's slowest when the Wife is sickest and the heat is most oppressive, it's a little bit faster after the suns have been shot out of the sky, and it's finally liquid-smooth when she begins her recovery. That music is her life force, and over the course of the evening, we get these windows into her vitality and hear it return to her bit by bit as the motif loses its sluggishness. I'm certainly not clever enough to plan something that sophisticated, but I'm just clever enough to lean into it, and build that discovery into my process.
TL;DR: Instead of setting out to write leitmotifs, try developing material more freely throughout your score, then stepping back and capitalizing on the patterns that developed intuitively. You may discover your hindbrain has been smarter than your forebrain ever could be. (Jason knows what I'm talking about.)
"I'm getting stronger here without you/But getting stronger isn't getting better/When you're who all my strength is for..."
