Words and Music

Dedicated readers of this blog--yes, good sunny morning to you, Aunt Huck and Uncle Jim--will know I've been writing a musical called Charlotte and Wilbur, which I may have typed as Wilbur and Charlotte once or twice.
First draft finished, it's on hiatus for the month while I write something else.
When I say 'finished,' I mean the first draft of the book is finished, with notes for some songs and fragments of lyrics, but no complete songs.
Last night I caught an interview between Andre Previn and Stephen Sondheim from 1977. In their "what comes first, the music or the lyrics" chat, Sondheim says usually he hears the rhythm of the melody, then he finds the words. He cites Cole Porter writing "it was just [pause] one of those things" as that rhythm first, then later as the famous melody, here done by Rosemary Clooney.
So, says Sondheim, I look for two things: a title line that sums up what the song is saying, and a rhythm. "From there, melodic ideas form."
This all makes perfect sense to me, given my limited experience with such matters. 
But, as I say, I'll be getting to all that later. The interview with Previn and the wonderfully articulate Sondheim, by the way, is one of the best I've seen.