In his short new book The Hatred of Poetry, Ben Lerner glosses the problem like this: the poet wants to say more than can be said, wants language to do more than it does, wants to transcend. (The poet who merely wants to communicate would do better, in Richard Hugo’s advice, to use the phone.) The consolidation of this ambitious but diffuse impulse into a verbal act — the arrival at actual terms fixed on the page — is an unacceptable circumscription of the impulse, a failure. But the failure is unavoidable. It inheres in the activity of putting words on paper. Lerner writes: “Poetry isn’t hard, it’s impossible.”
“Poetry” here names that utterance which would somehow surpass the limits of speech: a conceptual category that, though by definition empty of examples, tempts the history of literary production like the ghost of some God or father we could have known or might know yet but can’t humanly grasp. The poet feels the dull memory of other knowledge of the tongue and can’t reproduce it. She has to use the words there are for such things as have names — language is the fallen medium, built of worn material — but what she wants from an act of reference exceeds what any amalgam of communicable content can actually do. She wants to make moonlight felt, not speak again the name of the moon.
more here.