"What do you think?" I asked a friend this past weekend when one of Bob Dylan's new Frank Sinatra covers came on The Current.

"I think," she said, "it sounds like Bob Dylan is just singing whatever the hell he wants."

She probably wasn't the only one to be struck by the impression that Dylan's choice of artist to pay tribute with his new album Shadows in the Night—released today—was more than a little random. An entire album of Frank Sinatra songs? In 2015? Why, Bob?

Of course, Dylan needs no explanation or justification, and he never has. Forty-plus years later, fans are still scratching their heads about the songs recorded in the binge of covers that appeared on Self Portrait and the unauthorized release Dylan in the early 1970s. "Big Yellow Taxi"? "Mr. Bojangles"? Those, at least, came from Dylan's contemporaries—and the traditional songs he covered on the one-man acoustic garage records Good As I Been To You and World Gone Wrong came from the same body of work he'd waded into as a young folkie. But...Sinatra?

Jon Bream observes thematic connections between Sinatra's lovesick ballads and Dylan's recent work, suggesting that maybe the time had simply come for Dylan to sing these songs. Certainly, the "Stay With Me" that appears on the album and that Dylan started using last year as a show-closer fit like a glove with the world-weary musings that Dylan composed for Tempest—Dylan's most recent album of original material, from which his current set list draws heavily.

Dylan also told AARP that he's been contemplating an album of standards since Willie Nelson released Stardust in 1978. In that long AARP interview, Dylan speaks in detail about how he and his band arranged the Sinatra songs for a small group—not an obvious decision given that the songs were made famous in full orchestral arrangements—and how he hopes to bring them alive for a new audience.

One of the most telling comments in the interview comes when Dylan speaks of Sinatra's vocal style. "Frank sang to you, not at you," observes Dylan. "I never wanted to be a singer that sings at somebody. I’ve always wanted to sing to somebody. I would have gotten that subliminally from Frank many years ago. Hank Williams did that too. He sang to you."

There, Dylan identifies one of Sinatra's most crucial influences on today's pop music—an influence filtered through Dylan himself. Sinatra was one of the leading artists who reinvented popular music as a genre with the superstar solo singer at its center. Williams did the same for country music, and all of them went to school on Louis Armstrong's seminal career as a jazz trumpeter and vocalist. In that way, Sinatra's artistry was key to the kind of intensely personal rock music that made Dylan a legend.

In the 1940s, Sinatra emerged as a vocal star with a rabid following that set the template for later rockers like Elvis Presley. Reemerging in the early 1950s after a slump that had looked to many like the end of his superstar career, Sinatra traded his starry-eyed youth for a newfound mature savvy and showcased his interpretive skills with thematic collections like 1955's In the Wee Small Hours, records that helped to pioneer the idea of a concept album. The 1960s saw the emergence of the Rat-Pack-era swinger Sinatra, the Vegas icon whose singing made up in sheer forcefulness and continued interpretive skill what it lost in youthful smoothness. Sinatra kept singing into his final years, drink in hand and legend in place.

The achievement of Dylan's greatest work is to marry the narrative folk tradition with the newborn force and freedom of rock and roll, using the resulting music as a vehicle for inventive, literary personal expression. Dylan is of course a great writer, and a great songwriter, but he's also a great singer: his detailed phrasing and innovative technique lend as much meaning to his words as the melodies or arrangements do, which is why he emphasizes—when speaking, now, of Sinatra—that "you have to believe what the words are saying and the words are as important as the melody." Dylan's music works because you believe him, and he learned that from Sinatra.

Dylan's regarded by many as a "bad" singer—which, of course, to Dylan's many devotees is completely missing the point. Dylan's intentionally rasping style isn't just a tribute to his hero Woody Guthrie, it's an extreme exercise in the philosophy that what matters isn't the notes you sing, it's how you sing them. By discarding conventional standards of vocal performance, Dylan became an exemplar of total authenticity. Though Sinatra wasn't as radical in his expression, he didn't turn his songs into standards by delivering machine-stamped perfection: it's Sinatra's alternating swagger and vulnerability that invites listeners in, that turns the songs into complete worlds in which to live.

It's because Dylan intuitively understands the importance of delivery and phrasing that his work has remained so compelling over the past couple of decades, even as his voice has become wracked. Most aging singers just try desperately to keep up with their younger selves, maybe dropping an octave or two; when Dylan's peer Gordon Lightfoot performs live these days, entire phrases are so far beyond the range of Lightfoot's elderly voice that they'll simply disappear.

Instead of taking that futile approach, Dylan invented a whole new vocal style for himself; you can hear him experimenting with it on Oh Mercy, and on Time Out of Mind it comes into full flower. Instead of trying to sing the same parts he used to sing, Dylan sings them differently—yet with just as much, perhaps even more, expression. That's yet another trick Dylan learned from Sinatra, whose musical style and identity evolved as he aged, giving his career a remarkable longetivity as he remained not just active but relevant from the Big Band era all the way to the Band's era.

Another telling moment in the AARP interview comes when Robert Love asks Dylan whether he grew up thinking of Sinatra as "square." Dylan says absolutely not: "I don’t think anybody would have been bold enough to call Frank Sinatra square." That makes sense: while Sinatra may or may not strike you as cool, without Ol' Blue Eyes, "cool" would have a whole different meaning.