From The Paris Review: W. H. Auden, The Art of Poetry (interviewed by Michael Newman):
You have always been a formalist. Today’s poets seem to prefer free verse. Do you think that’s an aversion to discipline?
Unfortunately that’s too often the case. But I can’t understand—strictly from a hedonistic point of view—how one can enjoy writing with no form at all. If one plays a game, one needs rules, otherwise there is no fun. The wildest poem has to have a firm basis in common sense, and this, I think, is the advantage of formal verse. Aside from the obvious corrective advantages, formal verse frees one from the fetters of one’s ego. Here I like to quote Valéry, who said a person is a poet if his imagination is stimulated by the difficulties inherent in his art and not if his imagination is dulled by them. I think very few people can manage free verse—you need an infallible ear, like D. H. Lawrence, to determine where the lines should end.