Forty years ago, when the founding members of the Kronos Quartet first convened in Seattle, they weren’t thinking about changing the world. Instead, they were puzzling over a purely musical problem, as David Harrington explains.

“I was just hoping we’d get to the point of being able to play Black Angels later that year,” the violinist reveals in a telephone interview from San Francisco, the band’s home since 1978. Whether he and his colleagues were successful, he doesn’t say—but Kronos did go on to record the definitive version of American composer George Crumb’s taxing masterpiece in 1990.

In many ways, though, that’s among the least of its accomplishments. More significant, according to another American modernist, Philip Glass, is that Kronos has revolutionized the way contemporary music for string quartet is presented, both at home in the United States and around the world.

“There are all kinds of quartets that are making a living playing new music, which never used to happen,” says the pioneering minimalist, reached at home in New York City. “I can remember growing up in the ’50s and going to hear the Budapest Quartet: they would play a piece of Haydn, and then they would play a new piece, and after the intermission they’d play a piece of Beethoven, and that was what they did. It was a formula; it was depressingly regular. They’d play one new kind of piece—or very often they didn’t.”

Today, Glass estimates, there are at least 50 professional string quartets specializing in contemporary music, and nearly all of them owe a significant debt to Harrington, his fellow violinist John Sherba, violist Hank Dutt, and cellist Sunny Yang. Not only did Kronos—and its record label of 27 years, Nonesuch—prove that challenging modern music could be marketable, the group has also helped develop that repertoire, commissioning more than 800 new scores from composers both emerging and established.

Glass has contributed several of those works, and when Kronos celebrates its 40th anniversary at the Chan Centre for the Performing Arts this weekend, the occasion will be made even more festive by the world premiere of his String Quartet No. 6. Although memorable might be a better word than festive: the 76-year-old Glass is known for bright, up-tempo, and generally consonant scores, but both he and Harrington suggest that his new work is darker and more dissonant than many of his earlier undertakings.

“It’s hard to describe harmony, but there are moments when you recognize the world of Philip Glass as created over many years,” says the violinist. “You recognize that you are a part of that world, but it feels like an extremity. It’s like John Sherba, our other violinist, was saying the other day: ‘It feels like a late quartet.’ It’s like there’s nothing wasted, nothing superfluous. It’s like everything is focused—and I think all of his quartets are that way, but somehow this one is even more that way, really.”

“I’ve gotten really interested in the notes that don’t fit into the harmonies,” Glass offers. “What are those notes? Are they just ornamental notes, or do they suggest a function that we don’t even know yet? If I’m writing a piece and I play a harmony and it’s not the expected harmony but I know it’s the right one, those are legitimate questions.”

The composer—who’ll join CBC Radio’s Eleanor Wachtel for an on-stage conversation prior to the show—adds that his new and more expansive harmonic palette has raised the eyebrows of a few of his close musical colleagues, but not of Harrington and crew.

“With David,” Glass says, “there’s no precipice he will not jump off of.”

This artistic daring is reflected in the program Kronos will present at the Chan. In addition to the new Glass, the quartet will deliver the Canadian premiere of Montreal-based Nicole Lizée’s Hymnals, and a reprise of Toronto agent provocateur John Oswald’s electronically augmented Spectre. Perhaps even more radically, the group will also perform two pieces from the Muslim world—the Iranian folksong “Lullaby” and Ottoman Turkish composer Tanburi Cemil Bey’s “Evic Taksim”—next to “Sim Sholom”, Judith Berkson’s setting of a traditional Jewish melody.

On the purely musical level, this interest in the music of Eastern Europe and the Middle East stems from Harrington’s long-standing fascination with the way that Jewish liturgical singing influenced the violinists of the late 19th and early 20th centuries, most notably Fritz Kreisler and Jascha Heifetz. But there’s a subtle political agenda to his programming, too, although when asked about that he gives a circuitous answer.

“Recently, we played in Munich—and, believe me, I will answer the question,” he says thoughtfully. “But I had dinner with a wonderful composer the night before, and he pointed out that the statue of [notorious anti-Semite Richard] Wagner, about 50 yards from the concert hall, was where Wagner originally wanted to establish Bayreuth. And apparently the king wouldn’t allow it. Well, as it turned out, the next night we were playing Aleksandra Vrebalov’s arrangement of Wagner’s prelude from Tristan and Isolda, and right next to that we were playing ‘Sim Shalom’.

“And that was not such a hidden agenda at all,” he continues. “I feel that the prelude from Tristan and Isolda is one of the greatest pieces of music that I’ve ever encountered in my life, and I thought it was about time that it shared the same stage and the same air with cantorial music. So the answer [to whether Kronos has a political agenda] is yes. I like it when we play Palestinian music next to Jewish music next to Iranian music.…I mean, to me, concerts can be places where things can actually work out, and they can maybe give us the energy to see to it that the rest of the world can find ways of getting along.”

Given that keeping a string quartet together for 40 years is in itself a feat of diplomacy, Harrington surely knows of what he speaks.