My friend Angie (the philosopher with the "special conversational backwardness" I mentioned earlier) wrote the following:
"I think I've told you my brother has been working on poetry in his creative writing class, although he doesn't like the idea of conforming to rules to make a poem, which I learned about a very long time ago but can't for the life of me remember. So he tells me very brief half-descriptions about the kinds of poetry his professor 'ran through,' on the day of class, but because he is uninterested and because they don't spend a lot of time learning about the specific rules and meter for kinds of poems, he can't tell me much about it."
This provoked the "special conversational backwardness" of the poet, or perhaps especially of the formal poet:
"You had not told me about your brother's class. I would encourage him to consider the 'rules' of poems not as rules but as patterns that people have found effective in the past. That is, the sonnet is the way it is not because of some arbitrarily established 'rules' but because poets and readers have found that shape to be particularly powerful. The sonnet is not a set of rules but a powerful tool for the production of the aesthetic effects that one wants to achive with lyric poetry."
And here I would add that the same, of course, can be said for other forms, and for rhyme and meter: these "rules" existed for so long not because they were rules but because they were effective tools for generating the kinds of effects people wanted to generate in or experience with poetry.