Gabriel Kahane with Present Music Saturday

Gabriel Kahane sat at a grand piano as he rehearsed his “For the Union Dead” with Present Music Thursday, but a banjo rested in an open case at his feet.

That image sums up the you composer-performer’s career to date and his way of thinking about music. He recognizes the old categories — high and low musical cultures, classical and pop — and sees some use in thinking of music in those terms. But he feels entirely at home in all musical regions and sees no reason to refrain from mixing idioms.

The banjo is his, and he will abandon the piano to pluck it in five movements of his “For the Union” with Present Music Saturday night (Sept. 12) at Turner Hall.

The text is serious: Robert Lowell’s cycle of nine poems, from 1955-’56, oblique contemplations on the Union cause in the Civil War and what it accomplished and what it did not.

The piece also involves flute, trumpet, violin, viola and voice, and much of the writing for these instruments and for the piano is complex and virtuosic.

Kahane, 28, does his own singing. In the stretch I heard, “The Neo-Classical Urn,” his light, refined tenor reminded me a little of Peter Pears (a mid-century musician of note who, as it happens, figures in “February House,” a musical theater piece Kahane is writing).

Later, he told me that he doesn’t sound like that all the time, even within the confines of “For the Union Dead.”

“I sing very differently in this piece,” he said later, over an early dinner between rehearsals. “You heard that quasi-operatic, art-song style, but there’s also this very simple style, where the vibrato goes away.”

That crops up when he picks up the banjo, which he considers essential to the mood of the piece. Naturally, the singing turns more vernacular and folkish when he plays it.

Kahane, the son of the Jeffrey Kahane, a highly regarded classical pianist, thinks of his career as falling into three distinct but occasionally overlapping roles: singer/songwriter, musical theater composer, and concert/new music composer-performer.

He writes pop songs, and he has an indie-rock band. He’s writing a musical. He worked playing and singing standards in piano bars in New York. He’s maintained at least a little of all of that as his concert/new music commissions have taken off. He’s writing for the Kronos Quartet just now, on top of everything else. The one thing he’s pretty much left behind is playing jazz piano.

“Craigslistlieder,” a song cycle setting actual ads from Craigs List, is Kahane’s signature piece. It caught the attention of people with the resources to commission his work and allowed him to quit tending bar, quit teaching piano, and make music full time.

The fourth Craig’s List song gives an idea of the way Kahane mashes up styles and combines virtuosity with the vernacular:

“For the Union Dead” arose from Kahane’s desire to work with six like-minded New York musicians, who assemble now and then into a group they call yMusic.

“We’re all classically trained,” he said, “but can shift effortlessly to vernacular style. We’ve all played in indie rock bands. We want to bring the classical refinement of classical music to pop, and we want to bring the sexiness of pop to classical.

“The way we think about rhythm is fundamentally different in pop and classical. In classical music, we’re taught tune chords, but we’re often not taught to use our ears in a rhythmic way. In pop, there’s a different intuition about rhythm and about groove.”

Present Music is the first band other than yMusic to take on “For the Union Dead.” So far, so good; violinist Eric Segnitz, violist Brek Renzelman, cellist Karl Lavine and the composer seemed very comfortable with the music Thursday.

Kahane has a charming, poetic way of getting his ideas across:

“It’s Brahms there, for a hot moment,” he told his colleagues, about one fleeting passage; the reaction was “A-ha!” When Segnitz inquired about general mood, Kahane said: “It should be a little bit knowing, but not ironic. It doesn’t want to feel like a joke.”

While Kahane toiled at his composition, he didn’t really understand its meaning; he just made it. The meaning emerged for him later, and is still sinking in.

The last of Robert Lowell’s poems is with the poet’s consideration of the Boston monument to Robert Gould Shaw, the white commander of the first African-American regiment in the Civil War. Shaw died in battle and was buried in a mass grave with his slain troops.

Lowell pondered the state of black America in 1955 as he wrote about an 1897 monument commemorating events of the 1860s. The currency of all this hit Kahane with unexpected force when he happened on the first casting of that monument during a visit to Washington, D.C. The chain from music to poem to monument to war to racism became clear to him in a way that it wasn’t as he wrote the music.

“I felt a resonance between the poem and what has happened since the election (of Barack Obama) and what we’ve seen from the ‘birthers’ and now with health care,” Kahane said. “These last few months have given the work new meaning for me.”

Hear more of Gabriel Kahane’s music at gabrielkahane.com.

Who: Present Music, with Gabriel Kahane

What: Music by Kahane, John Adams

Where: Turner Hall Ballroom, 1032 N. 4th St.

When: 7:30 p.m. Saturday, Sept. 12

How Much: $20, $30; call Present Music, (414) 271-0711, or the Turner/Pabst box office, (414) 286-3663