Exactly right, Tootler. This is one of the reasons that most composers prefer to start with the words rather than with the music. The words (presumably a poem) give you a sense of the rhythm right off. And what the words are about give you the mood. And reading it aloud a bunch of times can give you clues as to what would be appropriate with both rhythm and melody.

The really heavy-duty, instrutrial-strength songwriters like Bellini, Verdi, Puccini, and so forth, usually picked an existing (play, novel, something like that), then commissioned someone to turn the play into a "libretto" or "little book," versifying as much as possible of the original work. Then, with that to go on, they started to work writing the music. Verdi's Il Trovatore came from a play, as did his Rigoletto. Puccini's La Boheme started out as a novel. So did Bizet's Carmen. Schubert, when he wrote lieder (art songs), usually started with poems others had written and set them to music.

This doesn't mean you couldn't do it the other way around, of course. Some folks prefer to do it that way.

Don Firth

There are nine and sixty ways
Of constructing tribal lays,
And every single one of them is right!
                         —Rudyard Kipling