Poetry does not consist of "artistically" placed line breaks, ignoring capitalization, or other gimmicks of typesetting. Nor is a powerful use of the language with memorable phrases necessarily poetry. Consider the following familiar passage:
We hold these truths to be self-evident, that all men are created equal, that they are endowed by their Creator with certain unalienable Rights, that among these are Life, Liberty and the pursuit of Happiness.--That to secure these rights, Governments are instituted among Men, deriving their just powers from the consent of the governed, --That whenever any Form of Government becomes destructive of these ends, it is the Right of the People to alter or to abolish it, and to institute new Government, laying its foundation on such principles and organizing its powers in such form, as to them shall seem most likely to effect their Safety and Happiness.These are stirring words, and the passage is a beautiful use of the English language, but it is not poetry; nor would it become poetry merely by writing it in this form:
we hold these
to be self-evident, that
are created EQUAL,
that they are endowed by their Creator with certain unalienable
that among these are
and the pursuit of Happiness....
Others may disagree, but I maintain that this Tony Bennett song is not merely bad poetry, it is not poetry at all:
If I ruled the world
Every man would be as free as a bird
Every voice would be a voice to be heard
Take my word we would treasure each day that occurred....
Ugh! Look at what is happening there: the need to force each line to rhyme with "bird" is ruling over the composition like a Sith Lord, cruel and despotic. There is no feeling that the rhyme occurred naturally and the poet had real freedom.
I am not, therefore, insisting that rhyming is the essence of poetry, so that anything that rhymes is a poem, and anything that does not rhyme is not a poem. For example, although my background means that I surely cannot fully appreciate it, I acknowledge that Oriental poetry, such as genuine Japanese haikus, really are poetry.
So what is poetry? My answer is that poetry is text that has been voluntarily submitted to a significant arbitrary constraint but is written with such skill that the constraint does not seem to limit or force the text. The constraint is arbitrary, but there must be a constraint. The constraint needs to be "significant" and "voluntary", or else a term paper or business letter (both of which have the constraint of standard forms) would qualify. Let me know if you have a counter-proposal!
Let me close with a particularly nice passage from "The Garden Party" by Hillaire Belloc:
For the hoary social curse
Gets hoarier and hoarier,
And it stinks a trifle worse
The days of Queen Victoria,
They married and gave in marriage,
They danced at the County Hall,
And some of them kept a carriage.
AND THE FLOOD DESTROYED THEM ALL.