Some poets have considered free verse restrictive in its own way. In 1922, Robert Bridges voiced his reservations in the essay "Humdrum and Harum-Scarum". Robert Frost, in a comment regarding Carl Sandburg, later remarked that writing free verse was like "playing tennis without a net." Sandburg responded saying, in part, “There have been poets who could and did play more than one game of tennis with unseen rackets, volleying airy and fantastic balls over an insubstantial net, on a frail moonlight fabric of a court.” William Carlos Williams said, "Being an art form, a verse cannot be free in the sense of having no limitations or guiding principles." Yvor Winters, the poet and critic, said, "…the greatest fluidity of statement is possible where the greatest clarity of form prevails. … The free verse that is really verse—the best that is, of W.C. Williams, H. D., Marianne Moore, Wallace Stevens, and Ezra Pound—is, in its peculiar fashion, the antithesis of free."