I think most poets of a high calibre work in this way to some degree or other—typically hearing first lines of poems simply come into their head, sometimes even as heard voices, successively followed by a flow of words, lines, and passages that come as naturally as leaves to a tree, and are imbued with what Eliot called the auditory imagination, a deeper level of meaning that is not contained in the literal meaning of the words, but—on another level—in the sounds of the words, their origins and accumulated meanings and resonances, and their emotional suggestivity, until the poem peters out, completes itself, and the poet knows it.
Axé.