I never understood that "upper limit music lower limit speech" slogan until now. I'm still not sure I understand it like LZ understood it, but it means something to me. For me speech is the original music. Music had to have developed out of speech. Poetry and music are the only two things that have rhythm in the original sense (and dance, but dance almost always has music with it. You don't dance a rhythm, you dance to a rhythm.) But music tends to obliterate speech. Its rhythms are more powerfully immediate. So poetry is situated within a wide range between relatively unmusical speech (I say relatively because speech is always musical) and a kind of relatively nonverbal music ("relatively" because music always seems a form of speech; it always seems to be saying something even when it is instrumental.)

Like the word "phrase" that can be a linguistic phrase or a musical phrase, but nothing else. It applies only to these two domains and nowhere else, and has an equivalent meaning in both domains.

And don't forget "lower limit refrigerator magnet."

UPDATE: What makes one poem (or poet) cantabile and another not? That's a mystery.