Way back in 1975, Waylon Jennings posed the question that still frames the debate of what it means to be a country music rebel.

Sneering at "rhinestone suits and new shiny cars" and "the same old tune, fiddle and guitar" that he saw and heard as signs of commercial indulgence and artistic stasis, the outlaw icon asked: "Are you sure Hank done it this way?"

Hank, of course, would be Hank Williams, the Hillbilly Shakespeare who is the subject of Marc Abraham's widely panned, Tom Hiddleston-starring new movie, I Saw The Light. Hank Sr.'s pithy, honky-tonk oeuvre is the bedrock that modern country music was built on.

For the twangphobic who might profess to, in the words of a Robbie Fulks song, like "Any Kind of Music But Country," he's sort of like Kurt Cobain in a cowboy hat: a hard-living tragic genius dead before he got out of his 20s who's remained a touchstone of incorruptible authenticity ever since.

Why is Cobain germane to a discussion of country music rebellion, occasioned by the death of the great Merle Haggard? In part because of Sturgill Simpson, a softhearted tough-guy contrarian likely to do the opposite of what's expected of him, much like the Hag. The artist frequently heralded as an uncompromising savior of a genre beset with too many truck-drivin', bonfire-burnin' bros expresses his rebel bona fides on A Sailor's Guide to Earth (Atlantic ***1/2). Simpson's excellent and unpredictable third album, structured as a musical missive to his 2-year-old son, includes a thoroughly reimagined cover of Nirvana's "In Bloom."

But before we detail the ways in which Sturgill tends to zig where he would be expected to zag, let's set awhile in appreciation of that headstrong spirit in Merle, who was one of the last of the remaining classic country titans - along with the deceased Johnny Cash, Buck Owens, George Jones, and Tammy Wynette and the thank-God-they're-still-with-us Willie Nelson, Loretta Lynn, and Dolly Parton.

My point about country rebellion essentially being conservative is this: As America became a less agrarian and more suburban nation, and the music attempted to leave its rural roots behind, there's been a cyclical push and pull from traditionalists to save the heart and soul of the music by returning to the old ways.

So when acts from Garth Brooks to Shania Twain to Kenny Chesney have leaned more and more toward pop (and in the case of current chart toppers such as Luke Bryan and Jason Aldean, hip-hop and hair metal) in pursuit of stadium-size mainstream audiences, the rebel cry is often a conservative call to turn back the clock: Let's get back to the way Hank done it, dad-gummit!

Which is not to trash the traditionalists among us. For my money, there's much more fertile artistic ground being worked by artists such as Jason Isbell and Ashley Monroe, who are more likely to be found under the alt-country or Americana headers than on tightly formatted country radio playlists.

Current standouts include Margo Price, the Nashville bandleader who played Saturday Night Live this month and whose Midwest Farmer's Daughter, recorded for Jack White's Third Man label, emphasizes her rural beginnings, and Hayes Carll, the Texas storyteller after the manner of Guy Clark and Townes Van Zandt whose fifth and best album, the deeply personal Lovers and Leavers, is wizened and wounded. (Carll plays World Cafe Live in West Philadelphia as part of the NON-COMMvention in May.)

Haggard, of course, was an emblem of the old ways and proud of it. He once wrote a song called "In the Good Old Days (When Times Were Bad)." When news came of his death on the day he turned 79, I went back and looked up one of my favorites among the stories I've written for the Inquirer, talking with Hag at QVC studios in West Chester in 1999.

He told me, "I've been a nostalgist all my life," and he talked about how his favorite artists, like Woody Guthrie and Bob Wills and Jimmie Rodgers, all recorded in the years just before he was born.

But Haggard was not a rebel only in that he questioned the validity and soulfulness of what passes for contemporary country. He also refused to be put in a box musically, or to hew to anybody's idea of what traditionalism means. As a singer, Haggard could phrase with a sophistication akin to Sinatra, and his fabulously freewheeling band, the Strangers, specialized in what he called "po'boy jazz."

"We try to be different," Haggard said that day. "We try to have a little sound of our own. We try to intertwine twangy country music with twangy rock-and-roll music with rhythm and blues and a little jazz. It's sort of a four-way deal here."

It's that instinctual adventurousness that most closely connects Simpson with Haggard. The vocalist that the singer from Versailles, Ky. - pronounced "Ver-sails," in the Southern way - most resembles is Jennings, in his tendency to growl with a burly rumble that sends the immediate message he's not someone to be messed with.

On Sailor's Guide, Simpson sometimes employs his voice in surprising ways, as on the whispery "Breakers Roar," a gentle self-reflection whose musings are set off by gorgeous steel guitar lines. Simpson blew plenty of minds with druggy, deep thinking on 2014's Metamodern Sounds in Country Music, but the departures are different this time.

For one thing, there are horns. On the self-produced Sailor's Guide, Simpson - who served three years in the U.S. Navy, and who comes by his nautical references honestly - effectively employs the brass section of Sharon Jones' band the Dap-Kings. It's a joy to hear arrangements that build walls of sound that don't succumb to old-school soul clichés. Elsewhere, Simpson puts strings and bagpipes to use, like a rugged hillbilly not afraid of embellishing with countrypolitan production touches.

Sailor's Guide gets plenty aggressive and rocked out at points, like on "Brace for Impact (Live a Little)," the opening-credits music on HBO's nutty and wildly inconsistent '70s soap opera Vinyl, and the closing antiwar salvo "Call to Arms." But a sweet, subtler moment comes with "In Bloom," the very sing-alongable Nevermind song in which the ever-conflicted Cobain bellows about a fan "who likes all our pretty songs / And he likes to sing along. ... But he don't know what it means."

Simpson sings the song as a love letter to his son, to Cobain, and to the 37-year-old singer's younger self: "For me, that song has always summed up what it means to be a teenager," he wrote in a note announcing the album. "And I think it tells a young boy that he can be sensitive and compassionate - he doesn't have to be tough or cold to be a man."

Rather than rage, Simpson sings with quiet tenderness, and has the temerity to change a key line, adding "to love someone" to the "don't know what it means." I'm not convinced the additional lyric improves the song. In fact, I'd say it undermines it slightly. But as a real rebel would, it shows Simpson being unafraid to mess with what he considers a sacred text, if that's what he needs to do to make it his own.