Zola, born in 1840, two years before Stendhal died, and one year after the appearance of the daguerreotype—the first commercially practical photographic process—referred to this impossible reproduction of a consensus reality as “idealism,” and opposed it with “naturalism,” which characterized novels that sought to expose the forces that produced that consensus. The naturalist novel, from its birth in the late nineteenth century through its disguised heyday in the twentieth, has been precisely about how reality is “made,” as distinct from what reality “is.”

Zola defined this naturalistic approach in an essay that responded to a medical text by a contemporary, the physiologist Claude Bernard, which attempted to transfer the scientific method governing experimentation in chemistry to the precincts of biology—the treatment of disease. It was Zola’s goal to diagnose French society as a doctor would a patient’s body: by analyzing its comorbid maladies one at a time, with a nib as sharp as a scalpel. Only after this diagnosis would treatment—extraliterary, political treatment—be possible.