WROTE THE poet: "Full many a flower is born to blush unseen, and waste its sweetness on the desert air."

We meet one of these latent bloomers in "Inside Llewyn Davis," though his particular fragrance derives from too many clubs, too few showers.

Llewyn (Oscar Isaac) is an itinerant folksinger who crashes on couches, bums cigarettes and money and meals, and repays all of this with indifference, anger, sarcasm.

You wonder why people put up with him. Until he picks up a guitar and sings. Then you get it. And you get why the Coen brothers made Llewyn the subject of their sad, funny movie - a beautiful wreath laid at the tomb of the unknown artist.

Llewyn is very loosely based on Dave Van Ronk, a semi-obscure figure in the 1960 New York folk scene that would soon give way to bigger names (Bob Dylan) and more commercial acts. (See below.)

Art and commerce is a treacherous intersection, and one that's long fascinated the Coens. In their universe, a grifter can blunder into a hit record ("O Brother Where Art Thou?"), or a talented artist like Davis can blunder out of one.

Remember, in "O Brother," the dumbfounded George Clooney, as Everett McGill, hopping onstage to sing "Man of Constant Sorrow" to thunderous applause?

The beat is repeated in "Inside Llewyn Davis."

A jaded, superior Davis sits in a Greenwich Village club and listens to colleagues (Justin Timberlake, Carey Mulligan) sing the dog-eared folk standard "500 Miles," then turns to look, incredulously, as a rapt audience joins the chorus.

McGill is a con man, Davis a true artist, but they share bewilderment at the mysterious, elusive mechanism that connects art to its audience.

There's a bit of the Coens in Davis, a fellow who follows his muse without regard to commercial prospects. In Davis' case, to his chronic detriment; the movie is his slow, agonizingly funny slide toward oblivion.

There is some debate among critics as to whether Llewyn is sizable talent lost to history or a slightly second-rate also ran. I'd say Isaac's solo in the first three minutes of the movie erases all doubt. Beautiful within the story, within the boundaries of the performance itself. (Isaac sings three complete songs, all recorded live on set, all on the soundtrack.)

So why isn't this singer a star? Well, there's his personality. He heckles other acts, insults benefactors, rebukes his agent. A few scenes with his ex-flame (Mulligan) are a quick sketch of his shortcomings as a romantic partner.

In due time, he's estranged from her, his family, his agent, from friends, from money, from musical gigs, from New York.

Here "Inside Llewyn Davis" indulges the Coens' taste for the road movie. Chicago-bound Davis hitches a ride with a snobby jazzman (John Goodman) who gives the purist a hilariously bitter taste of his own judgmental medicine. Their driver (Garrett Hedlund) appears to be some kind of proto-Beat poet.

It all leads to Llewyn's hasty audition before a folkie kingmaker (F. Murray Abraham, based on impresario Albert Grossman).

Llewyn's choice of material and his performance on the cold, empty stage perfectly illuminate his character and contradictions. What a scene. Horrifying yet somehow funny, watching Grossman assess Llewyn's prospects is like watching Steve Buscemi being fed to a wood chipper in "Fargo."

Davis, though, keeps singing, keeps traveling, and we get one more wonderful song from him, back in New York.

He's in a room with his estranged father, now in the throes of dementia, and sings a ballad from his youth. Perhaps the words and music fall on deaf ears. Perhaps they go out to all fathers no longer present.

Again, the song, like the others, brings meaning to earlier scenes, to favorite Coen brothers' themes. Its lyrics, of a seafarer finally at rest, are sung by a man who helps a cat named Ulysses return to his home - the closest thing the movie has to a plot.

You are pulled through by the performances, by the stunning period detail of folk scene New York, circa 1960 - the clubs, the acts, the album covers. The more you know of folk minutia, the more of a kick you'll get out of it.

And the more you might come to see the Coens as folkies, roots artists themselves. What is "Raising Arizona" if not a funny, cinematic folk song about the southwest? They've been singing ever since, of people (The Dude) and places and periods (the depression South of "O Brother," the border country of "No Country for Old Men," now 1960 New York) that add up to a country and culture.

What we're likely to end up with, when all is said and done, is a song of ourselves, unsurpassed in American movies.

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