Fifty years ago, when Stephen Stills and Judy Collins first met, the world was a different place. Change was in the air, and music carried the burden of the hopes and dreams of a generation that imagined that anything was possible. No one could have known in 1967 what heights, or what challenges, lay ahead for the two young musicians who became friends, and then lovers, while standing together atop the world of popular music. Musing on his memories of their tumultuous encounter, Stills wrote a song about Collins, “Suite: Judy Blue Eyes,” that would become the indelible opening number on the eponymous first album by Crosby, Stills, and Nash. The group’s close high harmonies, along with the song’s intricate emotional density and epic length, set a high-water mark that was never surpassed in their distinguished career.

Collins, for her part, went on to become an iconic performer and one of the most popular recording artists of the 1970s, earning a Grammy in 1968 for her version of Joni Mitchell’s “Both Sides Now” and charting consistently with an ambitiously diverse range of material for the remainder of the decade. Who else but Judy Collins could have put both Stephen Sondheim’s “Send in the Clowns” and the traditional hymn “Amazing Grace” into America’s Top 40?

This Saturday, October 28, Stills and Collins will hit the stage at the Arlington together with a great band and armed with material from their 2017 album of duets, Everybody Knows. The record glows with the warmth of a familiar fire, and the concert is certain to melt the hearts and refresh the memories of those who appreciate what these two artists have come to represent. I spoke with Collins recently about the experience of touring with Stills, and about the motivation that has kept her so productive as she approaches her seventh decade of performing. Asked about the experience of singing together, Collins said that “the resonance of the unison parts we have been doing is beyond belief,” adding, “it’s like finding a golden key.” She acknowledged that, while his voice may have less of the silken luster of her instrument, there’s something about his grainy tone that can conjure the idealism of the 1960s in a single phrase. When the audience hears Stills sing, Collins said, “they just go nuts. It’s like they can’t believe what they’re hearing, and it gives them courage, the courage to resist.”

In addition to her long career in music, Collins has found time to write a dozen books in multiple genres, including the 2011 memoir Sweet Judy Blue Eyes, which opens with her account of the love affair with Stills. She’s typically both proud and humble about her prodigious output, claiming that she wrote in order “to learn the English language.” After so many years and so much life, both good and bad, Collins sings as she writes, from a rare depth of experience. Although it was the title track of her first masterpiece album, a 1968 recording that happens to feature the guitar playing of Stills, the classic song “Who Knows Where the Time Goes” sounds even more resonant and fitting in the version included on the album the pair released this year. Few performers in any genre can lay claim to such an enduring legacy.

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Stephen Stills and Judy Collins play Saturday, October 28, 8 p.m., at The Arlington Theatre (1317 State St.). For tickets, call (805) 963-4408 or visit axs.com.