More than 100 years earlier, John Stuart Mill said: "Poetry and eloquence are both alike expression or utterance of feeling. But if we may be excused the antithesis, we should say that eloquence is heard, poetry is overheard. Eloquence supposes an audience; the peculiarity of poetry appears to us to lie in the poet’s utter unconsciousness of a listener. Poetry is feeling confessing itself to itself, in moments of solitude, and embodying itself in symbols which are the nearest representations of the feeling in the exact shape in which it exists in the poet’s mind. Eloquence is feeling pouring itself to other minds, courting their sympathy, or endeavoring to influence their belief or to move them to passion or to action."
But one of my favorite quotes is from Gertrude Stein, who said in 1935: "Poetry is I say essentially a vocabulary just as prose is essentially not. And what is the vocabulary of which poetry absolutely is. It is a vocabulary based on the noun as prose is essentially and determinately and vigorously not based on the noun. Poetry is concerned with using with abusing, with losing with wanting with denying with avoiding with adoring with replacing the noun. It is doing that always doing that, doing that doing nothing but that. Poetry is doing nothing but using losing refusing and pleasing and betraying and caressing nouns.... So that is poetry really loving the name of anything and that is not prose."
Is that last quote poetry, or prose? Perhaps it depends on whose definition you believe in.