The thing about the Larkin "sentence" is, perhaps foremost, that it does not seem--is not, really--grammatically incorrect. The ending on the verb and other nearly, but not quite, quaint arrangements of the parts of speech are true to the subject of the horses "at grass". Is it archaic or "poemy"? No. It's great poetry. I don't want to know anything about how this kind of thing is done. There is no formula. I'd scoff at any that is presented. It is largely a matter of taste and something that comes without thinking about it.
|