There is no stable definition of what counts as a poem. Is it prosody? Rhyme? An emotional quality? A decision on the part of the writer? The reader? Is it just a superlative? What’s a prose poem? And so on. I think what makes poetry “special” in this regard is precisely the assumptions and expectations that gather around the amorphous term. And part of this has to do with how “poetry” can name, independent of actual poems, a kind of limit case of language—the desire to do something with words that we can’t actually do. 

Ben Lerner