What does it mean to have an "ear"?

 It is odd, because what an ear is more literally is a capacity to hear, not to produce sound. So, listening and hearing come before producing. (An ear for verse, a musical ear.). If you can't hear Milton's blank verse as blank verse (not just prose, as some people thought when he started writing like that) then you probably couldn't write blank verse. 

I remember a famous poet telling me "Ashbery has no ear." William Logan writes that Brodsky had "a wooden ear" (in English, not in Russian).  I think I have an ear (passively, in my reading; actively in writing, I'm not so confident.).  What's interesting is that you have to be able to hear what you yourself are doing, like hearing a melodic phrase before you play it on your instrument.  

I dislike Hopkins, but he heard things in a particularly unique way and was able to write that way, to put that on the page. With other poets I can't hear anything. 

***

It was funny looking back at that Andrew Gelman post, that someone in the comments said that I didn't know much about poetry, because I was obviously unaware of the genre of the prose poem.  But prose poems still have prosody in them (by the way, no etymological connection between the pros of prose and the pros of prosody.). They still have to do something to charge language with meaning.  Think of the first page of Beckett's Ill Seen Ill Said.  It is though the division of lines into verse could prod the reader's attention to rhythm, with the same readers being deaf to the sound of a paragraph of prose.