In the final chapter of Gustave Flaubert’s “ Sentimental Education ” (1869), Frederic Moreau and his old school chum Deslauriers reminisce by the fireside. They trade news about mutual acquaintances, many of whom have featured vividly throughout the previous 400 pages. “And as they exhumed their youth,” Flaubert writes, “at every sentence they kept saying: ‘Do you remember?’ ” We take leave of the two as they recall an event predating the novel: a doomed trip to a brothel. “ ‘Ah, that was our best time!’ said Frederic. ‘Could be? Yes, that was our best time!’ said Deslauriers.”

As literary historian Peter Brooks describes it in his persuasive new book, “ Flaubert in the Ruins of Paris ,” that scene captures much of what contemporary critics found so baffling and distasteful in Flaubert’s novel. The protagonist, somewhat of a rake and a social climber to begin with, has just withstood a series of personal and political upheavals. He has seen his romantic hopes dashed, pursued affairs anyhow, taken part in a duel, run for public office and witnessed mass insurgency and bloodshed — the Revolution of 1848, which forms the backdrop of Frederic’s vacillations.

And yet, by ending on the brothel episode, Flaubert implies that “everything we have read in this long novel has been somehow off target, mere sequel to the important but unrecorded event,” Brooks writes. He argues that the deflationary tendency so marked in “Sentimental Education” proceeded from Flaubert’s scorn for most political movements and the chronic delusions that enable them. Especially now, when our political rhetoric is so overheated — not to say overblown — readers can find sanctuary in Flaubert’s oblique humor, his deadpan narration.

Brooks is a dependable tour guide to the novel and its reverberating lessons. To perform this function, he relies on Flaubert’s correspondence with fellow-novelist George Sand, on archival photos of 1870s Paris and on his estimable gifts of rapportage.

When Flaubert came to write “Sentimental Education,” he was looking back on a failed revolution. Although the French king, Louis-Philippe, abdicated in early 1848 and a provisional government took charge, it was rocked by class warfare and proved alarmingly fragile. Only three years later, Louis-Napoleon (a nephew of Napoleon Bonaparte) mounted a successful coup and became emperor. That episode occasioned Karl Marx’s celebrated statement about the way history repeats itself: “the first time as tragedy, the second time as farce.” Frederic and his hapless entourage register this anticlimactic mood in word and deed. They “prove inadequate to this moment,” Brooks writes, “a moment at which history itself, paradoxically, seems to stumble and fall.”

Unlike a character out of, say, Balzac, Frederic drifts with the tide. Neither swimming to safety nor smashing on the rocks, he’s trapped in an eddy. “There is a kind of serial unfolding of the plot, one thing leading to another without a return to any master plot for one’s life,” Brooks notes, conceding that “Sentimental Education “remains a book that challenges more than it pleases” (although talents as varied as Émile Zola, Ford Madox Ford and Franz Kafka swore by it). Henry James, an avowed fan of Flaubert, nevertheless called Frederic “an abject human specimen” and wrote that the reader is bound to ask: “Why, why him?”

One answer to this question, Brooks suggests, is that Frederic’s paralysis amid the overwhelming pace of regime change is a legitimate response for a character in a new kind of historical novel, one that can treat the conditions of shock and incredulity that so many political spectators feel in our own time. Given the daily tumult of 1848 Paris, to presume that Frederic could “offer an adequate consciousness of the event would be a falsification, or else madness,” Brooks reasons. Rather than intervene, the sane thing is to “do no harm” — a stance that Brooks calls Flaubert’s “moral imperative,” noting that the novelist had a physician-father and thus may have been influenced by the Hippocratic oath. For the new historical novelist, then, “the past is beyond redemption. The telling has to offer its own reward.” From this angle, Brooks offers, it’s entirely appropriate that Frederic and Deslauriers squander the ending of “Sentimental Education” on a ribald tale. But the telling — or Flaubert’s telling — must studiously avoid falsehood, which can be betrayed in high-mindedness or sloppy diction. To Flaubert, “bad style, especially the remnants of Romantic illusionism, is lying, and therefore to be censured,” Brooks explains.

By bringing “style” into it, Brooks nods to Flaubert’s reputation as a compulsive tweaker, someone who could spend all day reworking a paragraph. While it’s true that he viewed his calling as monastic in its solitude and scholarly devotion, “Flaubert was too much the historian to stand aside from the world,” Brooks claims. In 1870-1871, soon after “Sentimental Education” saw print, Paris was gripped by another revolution, leading to another radical experiment in self-government (the ill-fated Paris Commune), which yet again provoked a brutal crackdown from reactionary forces. As if that weren’t enough, the city had starved all winter, under siege by the Prussians. Afterward, Flaubert toured the city ruins with his friend Maxime du Camp, to whom he lamented that if only his countrymen had read “Sentimental Education,” the Terrible Year might have been averted.

What can “Sentimental Education” teach us today? According to Brooks, it reveals “the tragicomic inability of human beings to produce the results they seek in management of public affairs.” The antidote, Flaubert believed, is to understand human motives through what he called “science” — essentially the social sciences — and through “novels of the analytic exactitude sought by Flaubert.”

And not a minute too soon. Next year, France must reckon with the 50th anniversary of another Parisian revolt: the student strikes of May 1968. Meanwhile, the nation is conducting an election that carries existential overtones. What do the French say? La plus ca change?

Sunil Iyengar’s poems and book reviews appear in various periodicals, and he directs research at the National Endowment for the Arts.