"If it was never new, and it never gets old, then it’s a folk song," Llewyn Davis says, brandishing his guitar during a set at the Gaslight. That’s a pretty good definition, one that certainly applies to "Hang Me, Oh Hang Me," the chestnut that opens "Inside Llewyn Davis," Joel and Ethan Coen’s intoxicating ramble through Greenwich Village in 1961, before the neighborhood was annexed by New York University and Starbucks.

‘INSIDE LLEWYN DAVIS’ Rated: R Opens today at Kahala 8

Llewyn’s repertoire and some aspects of his background are borrowed from Dave Van Ronk, who loomed large on the New York folk scene in its pre-Bob Dylan hootenanny-and-Autoharp phase. Oscar Isaac, who plays both Llewyn and the guitar with offhand virtuosity, is slighter of build and scowlier of mien than Van Ronk, with a fine, clear tenor singing voice. But in any case, this is not a biopic, it’s a Coen brothers movie, which is to say a brilliant magpie’s nest of surrealism, period detail and pop-culture scholarship. To put it another way, it’s a folk tale.

The story — a wobbly, circular journey to nowhere in particular and back, with stops in Chicago, Queens and the Upper West Side — is nearly as old as narrative itself. An important character is named Ulysses, whose ancient wanderings inspired "O Brother, Where Art Thou?," the Coens’ earlier venture (also in the company of the music supervisor T Bone Burnett) into American vernacular musical traditions. The loneliness and romance of the traveling life are echoed in the ballads, sea chanteys and blues reveries that Llewyn and his fellow chirpers like to sing. The lyrics palpitate with the pain of loss and leave-taking: "I’m 500 miles from my home"; "I’ve been all around this world"; "Fare thee well, my honey, fare thee well." Llewyn, still grieving over the death of his musical partner (heard singing in the voice of Marcus Mumford), is a bit more prosaically adrift, stumbling from one friend’s couch to another, wearing out his welcome faster than his shoes.

But if Llewyn is an archetype, he is also a familiar kind of Coen antihero, the latest face in the gallery of losers, deadbeats and hapless strivers the brothers have been assembling, over 16 features, for nearly 30 years. These dudes are usually at the mercy of other people, a hostile universe and their own stupidity. Above all, they are the playthings of a pair of cruel and capricious fraternal deities whose affection for their creatures is often indistinguishable from contempt.

Unlike Barton Fink, Llewyn is a genuinely talented artist. Unlike Larry Gopnik in "A Serious Man," he is not merely the innocent, passive victim of cosmic, domestic and professional malpractice. He is, to some extent, the author of his own fate. "You’re like King Midas’ idiot brother," says Jean (Carey Mulligan), a fellow folk singer whose nest Llewyn has fouled, offering a precise and scatological explanation of just what she means.

The catalog of Llewyn’s lapses is extensive and fills the spectrum from casual bad manners to epic jerkiness. He makes the hostess (Robin Bartlett) cry at a dinner party in Morningside Heights, swears in front of his young nephew in Queens, heckles other acts at the Gaslight, and has a habit of getting women pregnant, including Jean, who is romantically and harmonically attached to a singer named Jim (Justin Timberlake). The only misdeed that seems to trouble Llewyn’s conscience at all is letting an orange cat escape from an apartment where he’s crashing. It’s almost as if he thinks that rescuing the animal will make up for everything else he has done.

Llewyn is a fairly unpleasant guy, though the other inhabitants of his world are not much better. The nice ones — a couple of tall, affable singers (Stark Sands and Adam Driver, suggesting Tom Paxton and Ramblin’ Jack Elliott), a kindly Columbia University sociologist (Ethan Phillips) and the unsuspecting Jim — serve as targets for his sarcasm. The rest are mostly a parade of grotesques, including music promoters, union officials and an imperious, drug-addicted jazzman (John Goodman) whose company Llewyn must endure on a long car trip.

They are the equivalent of goblins and monsters, placed in the path of the hero to strengthen his character and test his resolve. But since this is a Coen brothers film, it is predestined that Llewyn will fail and that we will laugh both at and with him as he deals with a world full of cretins, including the one he sees reflected in the windows of the subway train.

His world, though, is also an enchanted place, animated by the dark, nimble magic of the Coens and their collaborators. Production designer Jess Gonchor, art director Deborah Jensen and cinematographer Bruno Delbonnel conjure a Manhattan of faded denim and espresso-bar steam, a wintry island that we might recognize from old album covers. And amid the smart pastiche and the sly, carefully constructed jokes there is a thread of real emotion, a strain of melancholy deeper and more mysterious than mere sympathy.

Sympathy may not be what Llewyn deserves. He doesn’t ask for it, and Isaac, a versatile character actor here ascending to the highest levels of his craft, refuses the easy road of charm. Like his character, he trusts his own professionalism and the integrity of the material. Llewyn is not a showman. He relies, sometimes foolishly, on the strength of his voice, his playing and the resonance of those old songs.

The musical performances do more than enrich the movie; they complete it. Two in particular deliver on the promise of the title, illuminating the strange way that borrowed words and chords can tap into reservoirs of otherwise inaccessible feeling. When Llewyn sings "The Death of Queen Jane" at an audition and "Shoals of Herring" in his father’s room at a rest home for retired seamen, you feel the full weight of his humanity, even though he is really just doing his job.

One of the insights of "Inside Llewyn Davis" is that hard work and talent do not always triumph in the end. Like most of the Coens’ movies, this one sidesteps the political turmoil of its period, partly because it is a fable, not a work of history. (The public affairs of the time get a shout-out in the form of a goofy novelty song called "Please Mr. Kennedy," a barely topical sendup of the space race and the New Frontier.) But there is nonetheless a strong, hidden current of social criticism in the brothers’ work, which casts a consistently skeptical eye on the American mythology of success.

Winners do not interest them. There’s no success like failure, and failure’s no success at all. That observation was made by Bob Dylan, like Joel and Ethan Coen, a Jewish kid from Minnesota and, like them, possessed of a knack for conscripting the American popular art of the past for his own idiosyncratic genius. His art, like theirs, upends easy distinctions between sincerity and cynicism, between the authentic and the artificial, and both invites and resists interpretation.

So I won’t speculate further on what "Inside Llewyn Davis" might mean. But at least one of its lessons seems to me, after several viewings, as clear and bright as a G major chord. We are, as a species, ridiculous: vain, ugly, selfish and self-deluding. But somehow, some of our attempts to take stock of this condition — our songs and stories and moving pictures, old and new — manage to be beautiful, even sublime.

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Review by A.O. Scott, New York Times