A Canticle for Leibowitz is based on three separate shorter works published during the 1950s. Since the different parts are so widely separated in time, each has a separate cast of characters (except for Benjamin who is more a peripheral commentator on the action than a protagonist) and a different set of political, social, and technological problems. The danger a writer faces in such a situation is that the work may lack unity — it may seem to be three distinct stories on related themes that have been conveniently packaged together as a book, but not a novel. Miller overcomes this difficulty brilliantly, in part by the essential thematic unity of his work, but also by his use of a variety of images and motifs that serve both to link the three parts and to emphasize their significant differences.

The novel's progression from Dark Age through Renaissance to...