NEW YORK (AP) — "If you're trying to assign the trait of maturity to us, frankly, it won't wash."

A conversation with the filmmaking brothers Ethan and Joel Coen has only just gotten started when Ethan, quite gleefully, puts a stop to any discussion of growth, evolution or development.

Now in their late 50s, the Coens have a host of awards, including best picture for their tense, bone-dry Cormac McCarthy adaptation "No Country for Old Men." Their last film, the much Oscar-nominated Charles Portis adaptation "True Grit," was an unexpected box-office hit, earning $250 million worldwide. Somewhat shockingly, they are — to use the much sought-after label in their "O Brother, Where Art Thou?" — bona fide.

Their latest, the folk music tale "Inside Llewyn Davis," continues the trend of awards-season releases with more realism than, say, the screwball of "The Hudsucker Proxy" or the surrealism of "The Big Lebowski."

The Coens don't dismiss the trend. They just predict its imminent expiration date.

"If you're trying to make a developmental statement about us," Ethan explains, "it might not ..."

"It might not stand the test of the next movie," says Joel, finishing the sentence. They chuckle with tickled delight, like boys who are getting away with something, at the thought of their next opus. (More on that later.)

For now, there's "Inside Llewyn Davis," the latest zag in a career full of wholly unpredictable hopscotching through noir ("Blood Simple," ''Miller's Crossing"), farce ("Burn After Reading," ''The Ladykillers") and less categorical quandaries ("A Serious Man").

Tracking the Coens is, famously, a fool's game. What leads them down Los Angeles bowling alleys? Or into a '50s-era barber shop? Aided by the Dave Van Ronk memoir "The Mayor of MacDougal Street," they arrived at specifically 1960-61 Greenwich Village for "Inside Llewyn Davis" because it exists on the cusp of history, ahead of Bob Dylan's arrival.

Oscar Isaac stars as the title character, a folk guitar player and singer whose beautiful playing is contrasted by his foul-mouthed, cynical downtown life, which he spends hopping from couch to couch, gig to gig. The Coens, with T Bone Burnett, fill the film with full performances of less famous songs from the era, all but one of which was filmed live (rather than to playback).

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On a recent fall afternoon, the Coens granted an interview with The Associated Press at their Tribeca office, a narrow three-story apartment with editors working on the bottom floor on a concert documentary of the movie's music, to air on Showtime on Dec. 13. To accommodate a reporter, Ethan lugged a chair up to the small top-floor perch where the brothers brainstorm and script.

From here their movies are born, generated from the pingponging between their similarly imaginative, comic minds.

"We were just sitting around the office talking about nothing, as we do, and (Joel) said, 'OK, supposing it begins in an alley behind Gerde's Folk City and somebody beats the (expletive) out of Dave Van Ronk?'" says Ethan, while Joel laughs. "That's the beginning of what movie?"

They start most films in this unusually specific way. "Miller's Crossing" began with a hat floating away into the woods. "Burn After Reading" started when they pronounced that they would never, ever open a film "CIA Headquarters: Langley, Virginia." But the sheer antithesis of the idea became its greatest attraction: They peopled their version of a hyper-techno spy thriller with the most emphatically human characters.

Some openings don't immediately lead anywhere. They had the start of "O Brother" — "three dopes chained together" — but didn't know where it went for three or four years. "Fargo" got stuck midway: "For a year and a half, I would open up the drawer and it would say: 'Interior: Shep's apartment. Carl is screwing the escort,'" Joel recalls.

Often, their genre hopping is predicated more on books than movies. "Miller's Crossing" was an attempt to do Dashiell Hammett, says Ethan. "The Man Who Wasn't There" was self-consciously James M. Cain. "Big Lebowski" was their version of Raymond Chandler.

They were extremely faithful to the texts the two times they've adapted books ("True Grit" and "No Country"). Both novels appealed partly because, Joel says they're "not anything like what we've done."

"There was a moment on "No Country For Old Men" when I saw Javier (Bardem) walking down the street with the compressed air and the kettle thing about to kill Chip Love, and I said to Ethan, 'I'm actually glad I didn't think of that,'" says Joel.

The look of "Inside Llewyn Davis" (cinematographer Bruno Delbonnel stepped in for their usual director of photography, Roger Deakins, while he worked on "Skyfall") was inspired by things like the album cover of "The Freewheelin' Bob Dylan" and a YouTube video of Jack Kerouac wandering around the Village.

It's the fifth film for the Coens with Burnett, who describes his role as "the piano player in the theater."

Their scripts are usually set before shooting, the dialogue made precise. (Ethan, who has written plays on his own, once penned a poem "to the English language" in which he thanked it for all it had given him, especially its help in picking up girls.)

Says Isaac, "There's no vanity. They don't even tell you if it's good." Justin Timberlake, who plays a more chipper folk singer, says "They're laser focused, but they keep the blood pressure right at the same level." Carey Mulligan, who plays a singer bitter from a regretful night with Llewyn, says, "They kind of want you to just do your job."

"Inside Llewyn Davis" is in many ways a film about the vagaries of show business success: Llewyn's fate hinges on catching a break. But the Coens' destiny was never much in question. Not long after Joel graduated from film school, he and Ethan were able to find funding for their debut, "Blood Simple," which was received well.

"It could have gone the other way," says Ethan. "We're on the other side of the coin than this character."

"But look around at all the people you know, who do all kinds of things, a lot of those people are just as good as you are at what they do," says Joel. "And some of them really struggle. What is the reason for that?"

Right now, the brothers are plainly excited about what they're writing, which they proudly explain, is set in ancient Rome. It's the allure of the unexpected, all over again.

"It's like: Would you ever do a sandal movie?" laughs Joel. "It's big," says Ethan, grinning. "We're interested in the big questions. And we don't (expletive) around with subtext. This one especially."

Though their movies usually revel in the absurdity of life's predicaments, Ethan promises this film has answers: "It's not like our piddly 'A Serious Man.'" Chimes Joel: "That was a cop-out. We just totally chickened out on that one."

"We hadn't grown up," says Ethan. "In that respect, OK, we have matured. We're ready to answer the big questions now."

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Follow AP Film Writer Jake Coyle on Twitter at http://twitter.com/jake_coyle