I tend to fall in the "The Melody was good enough for Woody, It's good enough for me" pile of song writers. There are a few song I've written that use trad melodies "The Mother's Kiss" for instance.

And others that I think are my own tho' with inspiration from another source. Dig into "Photographs far enough and you may find a snatch or two of "Easy and Slow."

I will very often be driving and singing to a melody on the radio that I have found I like. Only I'll be singing made up as you go lyrics and wishing I had a tape recorder.

I'm leaning toward the "Find the Melody" first school and add the words as you go.

Don