Poets define their own historical moment by exhibiting their allegiance to some historical myth. John Ashbery … has chosen the myth of the Golden Age. Such an age can be named only when it is past. Ours, says Mr. Ashbery, is a Silver Age, an age of decline; and the title of his new book ["As We Know"] is a compressed statement of the regret that colors all his moods: We know too much; not enough remains for us to make or do. In a Golden Age, as Mr. Ashbery knows, we get "The Iliad," or "Song of Myself"—in a Silver Age, the curious felicities of Horace and the Alexandrians, or of Mr. Ashbery's recent work. He will, of course, puzzle some of his readers by regarding himself in this light: he has often seemed a poet steeled against misgivings, and too restless to hazard a backward glance...