w/The Diviners/The Mercy SeatTues., June 14, New World Brewery, Ybor City. 9 p.m. $7."I've got a pretty good work ethic," says Will Sheff, singer-songwriter for Okkervil River, toward the end of the short phone interview. "I think the hard work is a valuable thing."Sheff is nominally talking about his Austin, Texas-based rock/roots/folk/pop/Americana band's always-rigorous touring schedule. But the conversation he's ending has served to illustrate that his motivation applies to every facet of the Okkervil methodology.

Sheff is speaking from the studio in fellow Austinite Brian Beattie's backyard shed, placating a rock writer while simultaneously greeting members of an arriving string section, setting up an impending recording session, and answering other insistent calls on the cell phone he's obviously carrying around in his other hand.

One easily assumes that as soon as he signs off the interview, he'll step into the booth and begin conducting the folks heard opening instrument cases and asking questions in the background. Maybe he'll invent a new instrument, and write a new opera on it while doing so.

Originally convened in '98, Okkervil River's last four years have shown both the productivity and learning curve of a group ill-suited to lethargy or laurel-resting. Since 2002, the band has toured pretty much ceaselessly, and released three critically lauded, increasingly complex and compelling full-lengths.

The first of these (and second album overall), Don't Fall in Love with Everyone You See, introduced a then largely acoustic guitar-driven sound to a cult following beyond its adopted hometown, and found Okkervil River saddled with the alt-country assignation that still occasionally haunts them. Down The River of Dreams (2003) brought more underground acclaim, more organ tracks, further refinement of Sheff's thoughtful yet unpretentious lyrical bent, and even more touring.

And with the April release of the deep, thematic Black Sheep Boy came the unmistakable signs of having moved up another level. Offers to open for buzzy major-label acts. Financial equilibrium (though not profit, yet). The sort of hip-crit accolades reserved for below-the-radar combos talented and self-aware enough to successfully traverse the career-maiming minefield that is The Concept Album.

"I hesitate to call it a concept album," says Sheff. "I tried to not tie up all the loose ends. I hate it when, and this probably sounds arrogant, but there's a boringness when [a subject] gets so worked over."

Rather than beating a constrictive topic or storyline into submission, Sheff and company instead chose to musically and lyrically wander a wider area of related ideas and emotions.

"I wanted to leave it very open, and have an album with certain threads, the same threads weaving through it," Sheff says, "where the tones and instruments and themes are limited, where we're focusing on the same themes and sounds and, in some cases, the same words. We're not covering everything in the world."

Black Sheep Boy's, um, concepts – free will; finding unabashed relish in experiencing both the pleasures and pains of living, loving and making mistakes in the name of fulfilling the self – all grew out of a small patch of soil that Sheff found particularly fertile: the song of the same name, by late '60s/'70s singer-songwriter Tim Hardin.

Now far more well-known by other artists' versions of his tunes (most notably Bobby Darin's smash cover of "If I Were a Carpenter" and Rod Stewart's take on "Reason to Believe"), Hardin was once a jazzy, introspective contender, but his more out-there lyrical ideas and a heroin habit derailed his career, and he died of an overdose in 1980.

Sheff doesn't claim to be a Hardin superfan, but has enjoyed the troubadour's work since being introduced to it by his father. He found something singularly inspiring in "Black Sheep Boy," which appears on the Okkervil River album, and is thematically expanded upon by a few more of the CD's tracks. More than anything, he was drawn to the titular character of Black Sheep Boy, and that character's drive to live on his own terms, good or bad.

"I thought that's a really interesting attitude, very different than the sort of sanctimonious, moralizing, hand-wringing time we live in, and I sort of liked that opposite," he says, adding with a laugh, "and it sounded like a cool concept for a piece of William Schaff art."

(Schaff's evocative, vaguely disturbing artwork has graced most of Okkervil River's releases.)

"[Hardin's song] was more like a jumping-off point than a key to or center of the album," he continues. "I basically just really liked the idea and image of the song, and wanted to write a sequel. And I got carried away – the shortest sequel is five minutes long, and one of them is nine. I started having so much fun, I started to realize that there was a lot of pleasure down that path."

The chancy exercise in world-making has certainly paid off: Black Sheep Boy is sure to grace innumerable year-end Top 10 lists. And while Sheff says he's through with the Black Sheep Boy's reality from a creative standpoint, the band isn't quite done with the character yet; the string-section studio session Sheff's currently obsessing over is for a forthcoming companion EP comprising several of the songs written for Black Sheep Boy, but left off the disc due to space constraints.

"I knew I wanted to put them all together and do a disc called Appendix," he says. "It's sort of like the rest of the stuff. I started working on it a little bit more to distinguish it from the record and to feel a little bit like the last word on the record."

The whole thing seems a bit more involved and high-flown than the doings of the average rock 'n' roll band, and Sheff speaks often and emphatically about music in general, and rock in specific, as art. He believes it so fully that the adjective so often used to describe Okkervil River – "literary" – seems to him to be less than complimentary.

"That's cool; any kind of tag that people can put on something that makes them feel they can understand it more, that's fine," says the songwriter. "I'm eventually gonna not want to be associated with any one thing. I like books, and I like to read, but it's almost insulting to music to say it's good, it's literary. What about being musical?

"I guess I would just say that rock music is not literature, nor should it be. It definitely shouldn't be. And I'd hate for people to go, 'I'm gonna set this passage from Lord Alfred Tennyson to a Bo Diddley beat, and I'll be the next Decemberists, the next Okkervil River.' I'd find those people and punch them in the face."

scott.harrell@weeklyplanet.com