Poetry can quite easily be seen as the poor relation of the arts. Collections of poetry sell in remarkably small numbers and almost nobody earns a living from writing the stuff. And yet, if the internet is to be believed, hundreds of thousands of people seem to be writing poetry, and a lot of them are also discussing this most noble of arts in blogs and other online forums. One of the things most often discussed is the fundamental question, "what is poetry anyway?"
In his Poetics, Aristotle defines poetry as the form of mimesis that utilises rhythm, language and harmony, and says that it is the use of harmony that distinguishes poetry from the other language-based forms. This notion of poetry as verbal music was expanded by Thomas Campion in his Observations in the Art of English Poesie, where he talks of poetry as the "ioyning of words to harmony". In the early 20th century, Ezra Pound recast Aristotle's definition as, "Poetry is a composition of words set to music".
This definition is attractive, but not without its problems. We cannot be certain what Aristotle meant by harmony, and his "mimesis", implying as it does notions of what we would call realism, would omit, among other things, most Surrealist poetry. Pound's restatement may seem less problematic, but it is both too inclusive and, potentially at least, too exclusive.
It is too inclusive because not all compositions of words set to music are poetry, nor are they intended to be (I'm sure you can all insert your own examples here). It becomes too exclusive when it is interpreted as meaning that poetry and song are equivalent terms (try singing Paradise Lost or Pound's own Canto LXXXI). And where do sound and concrete poetries sit in this definition?
Campion also talks of poetry "raysing the minde to a more high and lofty conceite". This view, in which the teaching of morality is, to quote Philip Sidney's Defense of Poesy, "the very end of poesy", leads inexorably to Shelley's own Defence and the suggestion that "poets are the unacknowledged legislators of the world".
This is, it seems to me, the most dangerous definition for a poet to accept, and not just because we have come to see morality as relative rather than absolute. The Irish poet Brian Coffey wrote that "the political use of words kills the capacity to use words to make poems", and I am inclined to agree. The poet who would enter into the sphere of the legislator, either political or moral, is likely to find that the debasing of language in these spheres becomes something of a problem for the making of poems. For me, at least, poetry has more to do with uncertainty than certainty, questions than answers.
Other definitions of poetry have tended to avoid questions of harmony and morality entirely. For instance, William Carlos Williams wrote that a "poem is a small (or large) machine made out of words". Williams points to a distinction between prose and poetry that, by analogy, lies somewhere in the self-sustaining economy of effort and complete lack of sentimentality that characterises machines. Williams's words also, I believe, sit very comfortably with Samuel Taylor Coleridge's famous dictum, "I wish our clever young poets would remember my homely definitions of prose and poetry; that is, prose - words in their best order; poetry - the best words in their best order."
This last is the definition that most pleases me. Now all we have to do is agree on what we mean by the "best words" and the "best order" and we're laughing.