Italo Calvino cast his lofty thoughts toward the pending millennium long before the rest of us. Now that the zeitgeist has caught up with him, it seems a good time to revisit his Six Memos for the Next Millennium, an investigation into the literary values that he wished to bequeath to future generations. Calvino, the author of Invisible Cities, If on a Winter's Night a Traveler, and other postmodern fictional works, was to deliver these five "memos" (there was to be a sixth) as Harvard's Charles...