Dermod, interesting, I take you to mean that rhyme is the same as form to the extent that it's an example of an element of form? But there are some other, maybe lesser, but convincing ways to organise words, and rhyme itself doesn't constitute form to the extent that the pattern of rhymes does. Again, John Lennon's Across the Universe doesn't sound so odd or outre. Rhyme is hard to work around, but it's interesting how and especially why one might make it work. It's just a sort of repetition.

   Mark, now, to me a melody without rhythm is nearly inconceivable, while a song without rhymes is a special case, but not so far out there.