'I tell the fans the story of the music . . . and then I say, 'This is what Mr. [Bill] Monroe and Earl Scruggs and Lester Flatt would have sounded like if they had a really hot piano player."

Ricky Skaggs is talking over the phone from his Nashville home about his collaboration with Bruce Hornsby. The bluegrass master and the piano-playing pop star put out a self-titled album last year, and they'll perform together Saturday night at the Kimmel Center, mixing string-band chestnuts with Hornsby hits like "The Way It Is" and "Valley Road."

Skaggs, 53, has been a tireless champion of bluegrass since returning to the fold a decade ago after a stint as a mainstream-country hitmaker. The Kentucky native and 11-time Grammy winner also loves to spread the word about the history of the music. The latest album by the virtuoso instrumentalist and his band, Kentucky Thunder, is called

Honoring the Fathers of Bluegrass, Tribute to 1946 and 1947,

drawing particular attention to Monroe, Flatt and Scruggs.

When he plays with Hornsby, however, Skaggs' purist tendencies get shaken up, in a good way.

"Me and the boys all have learned to listen to each other play a whole lot more," the alumnus of Emmylou Harris' Hot Band says. "The main theme in this collaboration has been: Watch Bruce and see where he takes off and goes, because he doesn't always go by the rules."

"It has given us the freedom that if we want to take two solos back to back, who's going to sue us? Normally you'd have a tendency to want to do everything just like the record. We didn't necessarily jazz it up. And I think Bruce has brought a jazz element, which is very akin to bluegrass in one way: That is just the free-formness of the music, playing by ear, going by inspiration. . . ."

This "new-found craziness" also appeals to Hornsby, Skaggs says.

"He loves to do [the old bluegrass standards], because not only does it help to move the show along, tempo-wise, but a lot of his music is not that fast. He loves the challenge of being able to play as fast as we do. . . . And the fans love it."

Ricky Skaggs and Kentucky Thunder with Bruce Hornsby play at 8:30 p.m. Saturday in Verizon Hall at the Kimmel Center, 360 S. Broad St. Tickets: $55 and $65. Phone: 215-893-1999.

Contact staff writer Nick Cristiano at 215-854-4641 or ncristiano@phillynews.com.