Take a story's temperature by studying its tone. Is it hopeful? Cynical? Snarky? Playful?
Realismus Ipso Facto Ironica
Which, of course, translates to "realism by the fact that it is ironic to be realistic and all, and a bag of chips." We think. Our Latin is pretty rusty. And wasn't particularly good to begin with.
But the tone of A Canticle does strike an excellent balance between the realistic and the ironic even if we can't write it in Latin. Just consider this little tidbit:
Having completed the facsimile, Brother Francis found himself disappointed. The drawing was too stark. There was nothing about it to suggest at first glance that it might be a holy relic. The style was terse and unpretentious—fittingly enough, perhaps for the Beatus himself, and yet— (7.86)
We can see realism in the way Brother Francis approaches the Memorabilia. As he plans to illuminate the copy, he considers how to best display the work of his soon-to-be patron saint. The tone of the story realistically portrays the reverence one would expect a monk to have for such a holy relic.
But then the whole scenario rests on a comfy cushion of irony. We know the blueprint shows the guts of a "'STATOR WNDG MOD 73-A 3-PH 6-P 1800RPM 5-HP CL-A SQUIRREL CAGE'" and realize this is just a perfectly ordinary part of a perfectly ordinary motor (7.54). Leibowitz created the thing as an electrician, not a saint. It's no holier than any number of other such doodads we have lying around patent offices.
This tone of realism-resting-on-irony continues throughout the story, although not always with such comical results. Images of war are always presented in detail, but the characters engaged in those wars never actually want to be fighting them.
Like the Poet at the end of Fait Lux. Characters like Hannegan and the Defense Minister—the ones who seek out the bloody battles—don't fight them themselves.
Ah. Realism and irony: what a wickedly awesome pair.