Physique, temperament, religion, politics, and immediate circumstances all play their parts in formulating one's theories on verse. And then they play them again and differently when one is writing it. No matter what theories one may have, I doubt very much that they are in one's mind at the moment of writing a poem or that there is even a physical possibility that they could be. Theories can only be based on interpretations of other poets' poems, or one's own in retrospect, or wishful thinking.
(Quoted in Brett Millier's biography Elizabeth Bishop: Life and the Memory of It)