Added note on register

The language of poetry has to be different from the language of prose, but this does not imply a higher register. You can't mark the difference simply by elevating the lexicon. By the same token, you can't simply lower your register to a flat colloquial level and expect it to automatically work, just as you can't stuff indifferent prose into rhyme and meter and expect it to become poetic.

What is the difference, then? It's a difference in attentiveness to language. Suppose you do want to use the word "iridescence." James Tate might use it ironically, essentially saying: "look at how corny this word is in this context, it's as though Aunt Mildred just found it in a thesaurus." Henry Gould might use a hifalutin word because it's appropriate to his speaker, the particular poetic voice and persona he's developed: it is the right word for him and he knows exactly what he's doing with it. Logopeia is using words with this particular sort of attentiveness. You establish a relation between the way you are using the word and every other conceivable use of the same word. Look at this insight from Rae Armantrout:

I miss circumstance
already--

the way a single word
could mean

necessary, relative,
provisional

and a bird flicks past
leaving

the sense that one
has waved one's hand.