The term folk singer brings to mind an overly earnest performer with an acoustic guitar in hand and songs with a social consciousness, a political agenda or at least good stories. One word that probably doesn’t pop into a lot of heads when thinking of folk songs is soulful. Then again, a lot of heads probably have never been exposed to versions of “Blowin’ in the Wind” by O.V. Wright or “A Hard Rain’s a Gonna Fall” by the Staple Singers or, more recently, a funked-up “This Land Is Your Land” from Sharon Jones and the Dap-Kings. When the seemingly disparate worlds of folk and soul collide, the results tend to thrill.

So what does this have to do with the upcoming show that brings Patty Griffin and John Prine to Cary? Granted, these days Griffin fits snugly in the Americana/Triple A category, while Prine’s reached the point where his primary classification is simply “Legend.” But both have roots in the folk tradition, with Prine’s earliest songs being witty but penetrating, often presented as solo acoustic, and with Griffin getting her start in the coffeehouses of greater Boston. And both have had their songs recorded by soul singers.

In 1973, unsung hero (then and now) Jerry “Swamp Dogg” Williams covered “Sam Stone,” one of those songs from Prine’s early days, and his naturally wounded near-keen of a voice took the tale to a new level of yearning and despair. A year earlier, Bettye LaVette recorded Prine’s “Souvenirs” in Muscle Shoals, turning it into a six-minute-plus thrill ride of emotion. When LaVette played The ArtsCenter this spring, she made “Souvenirs” the centerpiece of her show. Sitting at the front of the stage, she soul-whispered the song as the band gradually filled in behind her, with the stripped-down delivery and her seasoned vocals adding gravity to the line “Broken hearts and dirty windows make life difficult to see.”

On last year’s Buddy Miller-produced Nashville, Solomon Burke gave legendary voice to Griffin’s “Up to the Mountain” (a one-way conversation of sorts with Martin Luther King Jr.), with Griffin providing harmonies. Just as LaVette had claimed ownership of the “broken hearts” line, Burke took control of “Sometimes I feel like I’ve never been nothing but tired/ and I’ll be working, working ’til the day I expire.” You can feel bone-deep how the years have piled up. Could that be the very definition of soulful?

John Prine and Patty Griffin are at the Koka Booth Ampitheatre Friday, Aug. 17. The concert starts at 8 p.m., and tickets range from $25 to $47.50.