What a difference a century makes. In 1903, comparatively few Americans took anything like a passionate interest in the arts. Only two living American novelists, Mark Twain and Henry James, had done major work, and Twain's was long behind him. Our best painters, the American impressionists, hewed to a style frankly derivative of their European models; our art museums were narrowly provincial in scope and ambition. We had no great composers, no great poets or playwrights, no ballet companies, and only a handful of symphony orchestras and opera companies.

Merely to draw up such a list, though, is to see how radically the arts in America were transformed in the 20th century. Under the aspect of modernity, the United States came to play a central role in all the arts. (We even invented three new art forms -- jazz, modern dance, and the motion picture.) In addition to producing world-class artists of our own, this country attracted emigrés from all over the world whose work was promptly absorbed into the mainstream of American culture. Moreover, the mass media made the fruits of this great transformation available not merely to a highly educated elite class but to any American who cared to partake of what the British poet Matthew Arnold so famously called "the best that has been thought and said in the world."

To be sure, ours is essentially a popular culture, and one cannot fully appreciate any kind of American art without acknowledging the extent to which so much of the best of it springs from that culture. The art critic Clement Greenberg, among the first commentators to single out "middlebrow" popular culture as a threat to the integrity of high art in America, once referred to "the American mind" as typified by "its positivism, its unwillingness to speculate, its eagerness for quick results, and its optimism." But he failed to realize that those traits might themselves serve as the basis for a characteristically American style in art, one that would amalgamate high, middle, and low, thereby ennobling popular culture even as it popularized serious culture. It was a tricky balancing act, and many artists found it hard to keep from slipping into the slough of pandering.

But it was possible, and today no one needs to be persuaded of the significance of those modernists who spoke in the crisply empirical, immediately accessible tone of voice now acknowledged by the whole world as all-American. Louis Armstrong, Fred Astaire, Willa Cather, Aaron Copland, Stuart Davis, Duke Ellington, F. Scott Fitzgerald, Robert Frost, John Ford, George Gershwin, Howard Hawks, Edward Hopper, Flannery O'Connor, Jerome Robbins, Frank Lloyd Wright: Surely these and others like them rank high among our exemplary figures, the ones whose work is indelibly stamped "Made in U.S.A."

And what of the state of American art now that the modern era has come at last to an end? For the most part, it is quite astonishingly vital and promising, though some art forms, not surprisingly, are in better shape than others. But it is also true that art in America is coming out of a bad patch. Starting in the 1960s, American culture, for the first time in its brief history, fell victim to a bad idea, one that for close to a quarter-century held considerable sway over our artists and critics. All at once, it seemed, we had lost our collective willingness to make value judgments -- to take Duke Ellington seriously while simultaneously acknowledging that Aaron Copland was the greater composer. In its place, we got postmodernism, which not only denied that either man was great, but rejected the very idea of greatness itself.

Taken literally, "postmodernism" means nothing more than that which came after modernism, and by the 1960s, the modern movement in art, for all its epochal significance, was nearing the end of its run. Not that all modernists had ceased to do important work. (A few, such as the modern-dance choreographer Paul Taylor and the abstract-expressionist painter Helen Frankenthaler, are doing it to this day.) Still, the modern movement as a whole had degenerated over time, as movements will do, into a rigid ideology whose spokesmen habitually drew false conclusions from false premises. Those were the days when abstract painting, atonal music, and plotless dance were being presented as historically inevitable, a quasi-Marxist argument whose makers not infrequently sought to quash dissent, also ?la Marx. It was time for a change, but the one that came would prove reminiscent of political commentator H.L. Mencken's definition of democracy as "the theory that the common people know what they want, and deserve to get it good and hard."

For all the reams of fuzzy prose that have been penned on the subject of postmodernism, its underlying premise is straightforward. To coin a paradox, postmodernists are absolute relativists. They disbelieve in truth and beauty, claiming instead that nothing is good, true, or beautiful in and of itself. Rather, "goodness," "truth," "beauty," and "quality" are constructs imposed by the powerful on the powerless for political purposes. Hence there can be no great art and no great artists (except for Marcel Duchamp, the patron saint of postmodernism and its own exemplary figure). Shakespeare? Beethoven? Cézanne? Mere capitalist tools, used to anesthetize the masses and prop up the decadent ruling classes of the West. To the postmodernist, randomness was as good as order, noise as good as music, and all artistic statements were created equal, though those made by the nominally powerless were more equal than others.

As a theory, postmodernism is so patently absurd as to need no refuting -- save by the immediate experience of great art -- but its purely practical consequences have not been altogether negative. For one thing, it put a long-overdue end to the stifling late-modernist monopoly. Precisely because of its indifference to "quality," postmodernism also encouraged the blending of dissimilar styles, an approach well suited to American artists, who have always had a knack for melting down unlikely combinations of cultural ingredients into such shiny new alloys as jazz and modern dance. It gave tradition-loving artists room to maneuver, especially those classical composers who still believed in the natural law of tonality, which had long since been declared anathema by the avant-garde.

Most of the time, though, postmodern audiences were expected to make do with the resoundingly empty gestures of conceptual art and minimalist music, in which theory replaced content. (The critic Hugh Kenner once defined conceptual art as that which, once described, need not be experienced.) In the whole history of art, no major theoretical movement has produced more theory and less art than postmodernism. Ultimately, it amounted to little more than a set of attitudes, foremost among them the marginalization of the idea of beauty and its replacement with the sniggering, fearful Irony Lite that was the hallmark of American culture in the 1990s. It was an aesthetically sterile position, and for that reason it was doomed -- though no one could possibly have envisioned the terrible occasion that proved that it, too, had run its course.

The destruction of the World Trade Center, among countless other things, may well have brought an end to the unthinking acceptance of postmodern relativism. On that never-to-be-forgotten morning, Americans awakened to the crudest possible reminder that some things are not a matter of opinion. Even the most fashion-obsessed neighborhoods of Manhattan found themselves awash in fear and bedecked with flags, and the word "evil" quickly reentered the vocabulary of a generation of educated innocents who thought there was no such thing.

Something similar happened when, a few days later, musicians in New York and elsewhere began giving memorial concerts to which the public flocked. What did they come to hear? Yo-Yo Ma played Bach at Carnegie Hall; Placido Domingo sang Otello at the Metropolitan Opera House; Kurt Masur and the New York Philharmonic broadcast Brahms' German Requiem to the entire country over the Public Broadcasting System. And did anybody complain because the Met performed Verdi instead of Arnold Schoenberg? To ask the question is to know the answer. "One greatly needs beauty when death is so close," old King Arkel sings in Debussy's Pelléas et Mélisande. What Americans wanted in their time of need was beauty, and they never doubted for a moment that such a thing existed.

But this collective renewal of belief in the power of truth and beauty did not suddenly take place on the morning of September 11, 2001. It was already in the wind, just as postmodernism itself was not so much an era as an episode, a gradual transition from one cultural epoch to the next. What we are now seeing, by contrast, is the emergence of a genuinely new style for which no one as yet has coined a better name than "post-postmodernism." It was evident, for instance, in the growing willingness of independent-minded American filmmakers to engage directly -- and beautifully -- with the problem of postmodern relativism. One encountered it, for instance, in Terry Zwigoff's Ghost World, the poignant story of two disaffected teenagers trapped in a grubby pop-culture hell of strip malls, convenience stores, and round-the-clock Muzak, set adrift on the sea of relativity by their barely visible baby-boomer parents. Or You Can Count on Me, written and directed by the playwright Kenneth Lonergan, in which we meet Terry, an immature small-town drifter, and Sammy, his stay-at-home older sister, orphaned in childhood and desperately lonely as young adults, deeply flawed but not without virtue, seeking to make their way in a world that no longer has much to offer in the way of certainty. Revealingly, Lonergan himself played the role of a Methodist minister so afraid of being judgmental that he is reluctant to assure Sammy that the adulterous affair in which she is engaged is endangering her soul. ("Well, it's a sin," he says, "but we don't tend to focus on that aspect of it, right off the bat.")

Another key figure in the new post-postmodern style is the modern-dance choreographer Mark Morris, whose work appeared at first glance to be quintessentially postmodern in its ironic distancing from emotion, though the best of Morris's dances, in particular the masterly V and L'Allegro, il Penseroso ed il Moderato, now seem to me to have that unabashed emotional and expressive directness without which no art can be truly great. I would not be at all surprised if cultural historians of the next century, looking back on the art of the present day, point to Morris as a key figure -- perhaps even the key figure -- in the transition to post-postmodernism.

Like so many artists who have been touched by postmodernism, Morris continues to defy ready categorization, and I expect that the fluidity of idiom typical of his work will turn out to be the one enduring legacy of the postmodern moment. "Boundaryless" polystylism, for example, is now very much the thing in contemporary popular music. To name only a few of its more notable practitioners, the classical-soprano-turned-Broadway-diva Audra McDonald, the theatrical songwriter Adam Guettel, the jazz musicians Pat Metheny, Luciana Souza, and Ethan Iverson, the bluegrass band Nickel Creek, and the big-band composer Maria Schneider are all making music that is, in Duke Ellington's useful phrase, beyond category.

Nor is such rampant hybridizing limited to the field of pop music. What mixed-media pigeonhole, for instance, can accommodate the adult "comix" of Daniel Clowes (the creator of Ghost World) and "picture stories" of Ben Katchor? From Morris's dance-driven operatic productions to Susan Stroman's part-danced, part-acted Contact, a Broadway "musical" in which nobody sings, American theatergoers also find themselves delighted by works of art whose genre cannot be easily defined. Were Basil Twist's fanciful, visually rich "stagings" of Berlioz's Symphonie fantastique and Stravinsky's Petrushka puppet shows or ballets? And what about Robert Weiss's adaptation of The Kreutzer Sonata, in which the dancers of Carolina Ballet were joined by two actors for an intensely compelling version of the Tolstoy novella, accompanied by the music of Beethoven and Janácek? Was it a ballet or a play? Or do such distinctions simply not matter any more?

To mention Carolina Ballet is to be reminded of another important trend in post-postmodern art, the "deprovincialization" of America's regional performing-arts groups. Not only are our medium-sized cities capable of supporting first-rate opera and ballet companies, but many of these groups are doing better work than their New York-based counterparts. Most of the fresh, engaging new productions currently being presented by New York City Opera, for instance, originate at Glimmerglass Opera, a "regional" company based in upstate New York. Similarly, a fast-growing percentage of the leading dance companies in the United States, among them Carolina Ballet, Dance Theatre of Harlem, Miami City Ballet, Pacific Northwest Ballet, San Francisco Ballet, and the Kennedy Center's Suzanne Farrell Ballet, are "Balanchine companies" led by New York City Ballet alumni who danced for George Balanchine and whose superbly danced repertories consist in large part of their mentor's work. The city long known as "the dance capital of the world" may well be on the verge of becoming no more than primus inter pares in the increasingly decentralized world of post-Balanchine ballet.

All this suggests that when it comes to post-postmodern art in America, it doesn't much matter where you do it or what you call it, so long as the results are beautiful. And it is no coincidence that post-postmodern artists are increasingly willing to use that word without encasing it in the protective quotation marks of irony. "Trying to compose beautiful things, I say what I mean and mean what I say," explains Paul Moravec, a member of the group of American classical composers that I have dubbed the New Tonalists. "The irony in my work is not glibly postmodern, but rather the essence of making audible the experience of fundamental paradox and ambiguity." Lowell Liebermann, another American composer who has repudiated the hard-edged nihilism of the avant-garde to embrace traditional tonality, agrees. "Of course there's a backlash from the old guard," he says, "but the tide is finally turning."

Osama bin Laden and his cronies, the ones who banned secular music from Afghanistan, would scarcely have approved of such talk. For them, as for every other zealot who murders in the name of a false god, earthly beauty is a mere illusion, a distraction from the One True Cause. But if September 11 taught us anything, it was that beauty is real, as real as evil, and worth fighting for. That is what Liebermann, Moravec, Mark Morris, Kenneth Lonergan, and the rest of America's post-postmodernists are doing. They are fighting for the right to make beautiful art -- and winning.

Terry Teachout, the music critic of Commentary and the drama critic of the Wall Street Journal, writes "Second City," a column for the Washington Post about the arts in New York City. His writings about books, dance, film, music, and the visual arts also appear regularly in National Review, the New York Times, and many other American magazines and newspapers. His most recent book is The Skeptic: A Life of H.L. Mencken.