"Some poets speak of hearing a voice speaking to them, and say that they write almost to dictation. I do not know whether my early scientific training is responsible for my using a less picturesque vocabulary, or whether their process really differs from mine. I do not hear a voice, but I do hear words pronounced, only the pronouncing is toneless. The words seem to be pronounced in my head, but with nobody speaking them. This is an effect with which I am familiar, for I always hear words even when I am reading to myself, and still more when I am writing. In writing, I frequently stop to read aloud what I have written, although this is really hardly necessary, so clearly do the words sound in my head.
The subconscious is, however, a most temperamental ally. Often he will strike work at some critical point and not another word is to be got out of him. Here is where the conscious training of the poet comes in, for he must fill in what the subconscious has left, and fill it in as much in the key of the rest as possible. Every long poem is sprinkled with these lacunae; hence the innumerable rewritings which most poems undergo. Sometimes the sly subconscious partner will take pity on the struggling poet and return to his assistance; sometimes he will have nothing to do with that particular passage again. This is the reason that a poet must be both born and made. He must be born with a subconscious factory always working for him or he never can be a poet at all, and he must have knowledge and talent enough to ‘putty’ up his holes …”
—Amy Lowell, from “The Process of Making Poetry” in The Creative Process: Reflections on Invention in the Arts and Sciences (University of California Press, 1985).