A true poem traces the outlines of the unspeakable, without releasing the tension in a banal attempt to express the truth outright. Eliot’s Prufrock never reveals the overwhelming question the reader is to be led to ask. The voice delineating Keats’ Grecian urn assures us that heard melodies are sweet, but those unheard are sweeter. Rilke’s marble torso of Apollo stares all the more urgently for the fact that the passage of time has stolen its head — leaving only imagined…