In 1799 William Blake reminded the Reverend Dr. Trusler, "The wisest of the Ancients considerd what is not too Explicit as the fittest for Instruction, because it rouzes the faculties to act." This comment may be applied to the rhetorical activity of much Romantic poetry as well, especially in poems in which logical structures—the plots of an argument, a tale, or an informing legend—are the expected means of instruction. The Rime of the Ancient Mariner, The Thorn, "La Belle Dame sans Merci," and "Ode on a Grecian Urn" all unfold mysteries against potential sources of interpretation: moral lessons, arguments, glosses, village testimony, portentous encounters, spectral legends. Yet however much such sources may "rouze" the mind to render intelligible "what is not too Explicit," in these poems, the materials invoked for that purpose themselves become invaded by what Keats calls "uncertainties, Mysteries, doubts." If these poems arouse...