Robert, in truth I think you're right. Keats' thrush, in 1818, seems to have every reason to sing, energetically consoling the listener, and the poet has no trouble ventriloquizing him in a very convincing way.

But in 1899 Hardy's assertion is such a qualified one; it's the drear surrounding --nothing to sing about -- that leads the speaker to say "That I could think there trembled through/ His happy good night air/ Some blessed Hope..."

So yes, Hardy's clear that he's projecting an interpretation. But I'm not sure he thinks the bird's unknowable -- he does, after all, call it a "happy good night air" and one could speculate that in a subtle way, ending the penultimate line with "knew" at least points in the direction of that elderly songster being certain.

I think that Bunting poem is amazing, too -- thanks, Jim -- and what a great talking-back to Keats and to Hardy. It's ingenius that the thrush's dire song is framed by a few words from the human speaker, so that here the two kinds of consciousness sit side by side. Does Bunting parody Hardy by lettting us hear what the thrush is really saying, then echoing Hardy's judgement of the song as a "happy good night air"?

A long ways, from 1818 to 1964.