From Aristotle's "The Art of Poetry," Aristotle, tr. Philip Wheelwright. Indianapolis: The Odyssey P., 1951.

The difference between the historian and the poet is not that one writes in prose and the other in verse. No, the real difference consists in this, that the one speaks of what has occurred, the other of what might occur. Hence poetry is something more philosophical and more highly serious than history, for poetry tends to express universals, history particulars (301-302).

From Sir Philip Sidney's The Defence of Poesy

Poesy ...is an art of imitation, for so Aristotle termeth it in the word mimesis--that is to say, a representing, counterfeiting, or figuring forth--to speak metaphorically, a speaking picture--with this end, to teach and delight.

From William Wordsworth's Preface to the Lyrical Ballads.

poetry is the spontaneous overflow of powerful feelings: it takes its origin from emotion recollected in tranquillity: the emotion is contemplated till by a species of reaction the tranquillity gradually disappears, and an emotion, kindred to that which was before the subject of contemplation is gradually produced, and does itself exist in the mind.

From Matthew Arnold's The Study of Poetry

We should conceive of it [poetry] as capable of higher uses, and called to higher destines, than those in which general men have assigned to it hitherto. More and more mankind will discover that we have to turn to poetry to interpret life for us, to console us, to sustain us. Without poetry, our science will appear incomplete; and most of what now passes with us for religion and philosophy will be replaced by poetry.

From Marianne Moore," Poetry" (PIE 879-80)

I, too, dislike it: there are things that important beyond all this fiddle. Reading it, however, with a perfect contempt for it, one discovers in it after all, a place for the genuine.

From Roman Jakobson's Language in Literature, ed. Krystyna Pomorska & Stephen Rudy. Cambridge, MA: Belknap Press, 1987.

the content of the concept of poetry is unstable and temporally conditioned....But how does poeticity manifest itself? Poeticity is present when the word is felt as a word and not a mere representation of the object being named or an outburst of emotion, when words and their composition, their meaning, their external and inner form, acquire a weight and value of their own instead of referring indifferently to reality (378).

From Lewis Turco's The New Book of Forms. Hanover: U.P. of New England, 1986.

what differentiates the poet from other writers is the focus on mode, on language itself...Poetry can this be defined as the art of language.

From Mary Kinzie's The Cure of Poetry in the Age of Prose. Chicago: U. of Chicago P., 1993.

Poetry is language carried to the highest expressive power commensurate with clarity of representation (ix).