Historically, there are hierarchies of purity. Certain aspects of poetry are very, very pure. The lyric poem can’t be anything but the lyric poem. If you want to do what Sylvia Plath is doing, you cannot get discursive, you can’t get philosophical. You’re caught and wriggling on the psychological pin in the way that she was, basically. And that’s the experience of the poem. Ashbery’s “Self Portrait in a Convex Mirror” is essayistic and discursive. A lot of Ashbery’s gestures are a part of the world of lyric poetry. But a lot of them are part of the world of the essay. He used to write art criticism, and so was steeped in prose. The barriers between genres were low for him. The barrier, on the other hand, between the short story and everything else is high, very high. The short story is protected, enclosed in its garden: what Lorrie Moore writes, what Alice Munro writes. But Ashbery wrote a book called Three Poems comprising three long pieces of prose that are extremely essayistic in the way they think and move. They don’t resolve, they don’t get anywhere, but they’re like essays.
Phenomena are always determined by history. You abstract certain qualities and say that they define a genre. A long, discursive Ashbery poem is nothing like an essay by George Orwell, which has an intention. The intention of an essay by George Orwell, like “Such, Such Were the Joys,” is to change society by making us aware of class differences and their harmful consequences. And a long, discursive Ashbery poem has little in common with that. But it has a lot in common with an essay by Montaigne, because Montaigne is inviting you into his mind, and the movements of his mind…rather than the content of his judgment. So you can’t say, “Well, the essay is this and the poem is that.” You can’t make credible hard-and-fast characterizations, especially now, when there’s so much intermingling.
-- Vijay Seshadri, at The Believer Logger