The poet Philip Larkin, who grew up in England loving the American jazz of the 1930s and 1940s, wrote a newspaper column about jazz for many years. Eventually, however, around the time Charlie Parker replaced Louis Armstrong as the presiding god of jazz, Larkin began to loathe the new records he was being sent. Even the way the music was written about had changed, he complained: “there was something about the books I was now reading that seemed oddly familiar. This development, this progress, this new language that was more difficult, more complex, that required you to work hard at appreciating it…Of course! This was the language of criticism of modern painting, modern poetry, modern music.” Parker was to jazz what Picasso was to painting and Pound was to poetry: in Larkin’s eyes, they all shared “a quality of irresponsibility peculiar to this century, known sometimes as modernism.”

In the 20th century, all of the arts suffered a version of the modernist crisis, sundering their connection with their traditional audience while becoming exponentially more complex. But none of the genres Larkin mentions, not even poetry, was more traumatized by this rupture than classical music. For 200 years — say, from Bach to Shostakovich — European art music was one of the glories of civilization. Music enjoyed new masters and new masterpieces in every generation, a devoted and serious audience, and a vital connection with the wider intellectual world. Living in Vienna in the 19th century must have been rather like living in Athens in the 5th century B.C.E., or in Renaissance Florence: The ordinary concertgoer was fed on a steady diet of masterpieces. Then, after World War II, it all stopped. People still go to concerts of classical music, and thanks to recording technologies, it has never been easier to experience even the most minor works in the repertory. But the repertory itself is essentially closed. The problem is not that most people cannot name a single living composer, since, in a mass-media age, celebrity and genius will only find each other by accident. The problem is that even people who can name living composers — who have heard about Glass and Gorecki, or even Golijov and Gubaidulina — don’t particularly want to listen to their work. What composers need to say does not seem to be what audiences want to hear. Educated people, who will happily read a new novel or look at a new painting, leave the concert hall when a piece of new music is on the schedule. As the Sun’s Fred Kirshnit noted in a review of a Mostly Mozart concert this summer, you could tell there was a contemporary work on the bill because all the best seats were empty.

In such a climate, the role of the critic becomes especially important, and exceptionally difficult. The critic of the serious arts — poetry, painting, music — is addressing readers who are not just indifferent to new work, but feel justified in their indifference. The critic’s first job, then, even before he evaluates individual works, is to make the reader feel uneasy about his ignorance—to convince him that the art in question is vital and serious, deserving of complex attention. A reader who has always heard that classical music is dead must first be convinced that it is alive.

No critic at work today does this better than Alex Ross, who writes about music for the New Yorker. The tone of belligerent defensiveness that afflicts so many classical-music writers — see Norman Lebrecht, author of “Who Killed Classical Music?” — is never to be heard from Mr. Ross. He knows that this sort of raise-the-drawbridge, circle-the-wagons mentality, while it may afford a mournful, self-righteous pleasure to those inside the classical music world, is designed to drive everyone else away. Instead, Mr. Ross takes the opposite approach: he writes about even recondite works and obscure composers with intelligent absorption. He offers a skeptical world living proof that a smart, curious listener can find pleasures and challenges in new music — whether that music is opera or free jazz or avant-garde pop. As a result, he is one of the few critics in any genre whose recommendations always carry weight. If Mr. Ross likes Björk and Milton Babbitt, you at least want to try to like them too.

In his long-awaited first book, “The Rest Is Noise” (Farrar Straus Giroux, 640 pages, $30), Mr. Ross brings his gift for authoritative enthusiasm to a whole century’s worth of music. The book opens with Richard Strauss’s “Salome” and concludes with John Adams’s “Nixon in China,” emblematic operas from the beginning and the end of a challenging musical epoch. Along the way, Mr. Ross shows us Mahler earning a fortune in New York and Schoenberg scraping by in Los Angeles; takes us to the premieres of “The Rite of Spring,” which caused a riot in Paris, and of Shostakovich’s “Leningrad” Symphony, broadcast defiantly over no-man’s-land to the city’s Nazi besiegers; introduces us to the avant-garde cabals of Darmstadt’s Summer Courses for New Music and the trippy California experiments of Harry Partch. Wherever music has flourished or struggled valiantly for survival, over the last hundred years, Mr. Ross is there.

The result is a massively erudite book that takes care to wear its learning lightly. There are no musical examples in “The Rest Is Noise,” and while Mr. Ross discusses some technical points — the polyrhythms of Stravinsky, the atonality of Schoenberg — it is not necessary to read music to understand his larger themes. Rather than delving deep into a particular composition, like a musicologist, Mr. Ross aims for synthesis, placing each work against the background of its composer’s life and times. This is music history for readers who know more history than music.

And as Mr. Ross shows, in the 20th century, the two could never be separated; each pressed against the other with terrible force. In an age of historicism, composers became extremely self-conscious about their place in the evolution of music. The pressure to make it new, to invent a technique or principle that had never been thought of before, could be constructive: Claude Debussy went to Javanese music for new harmonies, Igor Stravinsky mined Russian folk music for new rhythms. But it also prompted a kind of musical arms race, in which composers competed to make their works as harshly up-to-date as possible. The key figure here was Arnold Schoenberg, whom Mr. Ross presents as a vain, unpleasant, dictatorial genius. When Schoenberg wrote that tonality had decayed through “inbreeding and incest,” that “the end of the system is brought about with … inescapable cruelty by its own functions,” he was using the kind of apocalyptic rhetoric favored by racist cranks in turn-of-the-century Vienna. The obsession of German music with ideas of degradation and redemption was perfectly captured by Thomas Mann in his novel “Doctor Faustus” (1947); no wonder Mr. Ross titles his chapter on Schoenberg “Doctor Faust.”

At the same time as music grew obsessed with history, history took a sinister interest in music. Mr. Ross shows that both Hitler and Stalin were dangerously interested in music, though in ideologically divergent ways. To Hitler, who saw Gustav Mahler conduct “Tristan und Isolde” in 1906 and never forgot it, music was a mystical emanation of the German spirit. He made regular pilgrimages to Bayreuth, and held forth at dinner on the merits of various conductors (he did not like Herbert von Karajan, even though he was a Nazi). When Hitler came to power, Richard Strauss, for one, was delighted: “Thank God,” he said, “finally a Reich Chancellor who is interested in art!” Yet the Nazis’ purge of Jewish musicians, and their bullying use of Beethoven and Wagner to whip up patriotic emotions, left a permanent taint on the German musical tradition. Since 1945, Mr. Ross writes, German composers have been trying to purge themselves of that guilt: “Sixty years after the Wagner-loving Hitler killed himself in Berlin, pundits could still be heard declaring that clear-cut repetition of material or a non-ironic use of triads betrayed a fascist mentality.”

By the last third of the 20th century, it seems clear that the pressure of history had driven composers a little bit insane. Much of the music Mr. Ross discusses in the later chapters of “The Rest Is Noise” is strictly conceptual, noteworthy only for the ways it violates tradition or expectation. Elliott Carter’s Piano Concerto is scored for 50 strings, each playing a different part simultaneously; Karlheinz Stockhausen’s “Gruppen” splits the orchestra into three groups, situated at different spots in the concert hall; Alvin Lucier’s “Music for Solo Performer” is a translation of his brain’s alpha waves into patterns of percussion; most famously, John Cage’s “4’33″” is “performed” as an interval of pure silence. Experiments like this can also be found in visual art and literature, and in every case they are purely parasitic; without the prior existence of positive artistic achievements, their purposeful vandalism would be meaningless.

Mr. Ross, in keeping with his usual practice, almost never says a skeptical word about even the most extreme musical absurdities. But it is clear that he is much happier writing about recent composers who use tradition creatively, not destructively, and whose accomplishments are more than theoretical. Mr. Ross devotes more space to Benjamin Britten’s opera “Peter Grimes” than to any other single work, relishing both its sound and its psychosexual subtlety. And he is reverently curious about Olivier Messïaen, who fused Catholic masses and birdsong to create a new sound of holiness. These artists are the rare, inspiriting exceptions in a period whose “overall trajectory,” as Mr. Ross admits, looks like “one of steep decline.” “The Rest Is Noise” does not exactly overturn that conventional verdict, but it proves that even in the 20th century, there is more than enough music for a lifetime of thinking and listening.

akirsch@nysun.com