It’s hard to say which of those hats Barzun wears more gracefully. He’s the last of the great polymath scholars: he taught at Columbia from 1929 to 1975, while turning out authoritative, wonderfully readable books on (deep breath) literature, science, race, history, teaching, Romanticism, crime fiction, Lincoln, William James, Berlioz and the trio of Marx, Darwin and Wagner. “From Dawn to Decadence” is his masterwork: it pulls together these people and themes and hundreds more, from John Calvin to Johnny Rotten, the Inquisition to the Internet, dada to double-entry bookkeeping. Ever hear of Comenius, the 17th-century school reformer, feminist and pacifist who championed prenatal clinics and marriage counseling? Barzun has. He knows the very phrase “Western culture” may set your teeth on edge. But he argues that the West, far from a monolithic bulwark against “diversity,” is “the mongrel civilization par excellence”; the systole and diastole of contractive monoculturalism and expansive multiculturalism are its heartbeat.

Or were. By the late 20th century, Barzun writes, “Pluralism had disintegrated and Separatism took its place.” In the United States, the notion of an ethnic “melting pot” had become offensive; everywhere, the modern nation-state, “the greatest political creation of the West,” began disintegrating into its old ethnic constituents. In science, no truth seemed permanent or useful. In the arts, every mode was exhausted, from neoclassicism to primitivism to terminal irony. “Ridicule, denial, anti-art and sensory simplicity mean that culture and society are in the decadent phase,” he writes, “when it is everybody’s duty to do his share of ground clearing.”

This sympathy with the principled destroyers of a culture as well as its creators sets Barzun miles above rear-guard actions in the tired “culture wars.” “From Dawn to Decadence” will go down in history as one of the great one-man shows of Western letters, a triumph of maverick erudition like Johnson’s Dictionary or Burton’s “Anatomy of Melancholy”–assuming, as Barzun does not, that there’ll be a history for it to go down in. Forget the few trifling errors and some pop-culture cluelessness. Like his great models–such as Diderot, Voltaire and Hazlitt–he loves clarity and wit, and hates pedantry. He always makes room for a beguiling curiosity, like the 1771 Encyclopaedia Britannica entry on “laughter” (“the eyebrows are raised about the middle and drawn down toward the nose”), or an irrelevant, revelatory moment: James walking Freud to a train station in Massachusetts, “carrying Freud’s suitcase and suffering an angina attack, but tactfully concealing it from Freud, who noticed it all the same.”

If writers half Barzun’s age were half as frisky, maybe the culture wouldn’t be so doggone decadent. It’s not just his trendy cyber-arrows referring you ahead (>) or back (<) to page numbers for related topics, or the zippy abbreviations 17C or 20C that save pages of enturies, or the magazine-style sidebar snippets from Pico della Mirandola, Wordsworth, Ice-T–you know, people like that. It’s his sharp images (“Kant posited a mind that acts like a waffle iron on bat-ter”), dry one-liners (“On [Victoria’s] possessions the sun never set–a thought that her English subjects curiously found ad-vantageous”), vigilance about words (“the computer, which despite its name is not in essence a calculating machine”), even a hint of self-mockery (“These three facts together seem significant–of what, it is not easy to say”). Then again, if the culture were still at the top of its game, Barzun might be writing patriotic epics in rhymed couplets or Pindaric odes to Newtonian physics instead of telling, with lucid skepticism, the damnedest story you’ll ever read.

From Dawn to Decadance: 500 Years of Western Cultural LifeJacques Barzun HarperCollins 877 pages. $36