When rock and roll emerged from Mississippi or Georgia or Tennessee or Illinois sometime in the early nineteen-fifties, it was a lawless mishmash of musical institutions, some ancient, some new. Its unruly roots—the incongruous coupling of the sacred and the profane—came to determine much of the genre’s mythos. By the sixties, its edicts, as set out by early practitioners like Chuck Berry, Jerry Lee Lewis, Fats Domino, and Little Richard, were decreed in full: rock and roll should be scrappy and instinctive, a wild and unstable expression that appears free of mediation or meddling, even (especially) when it’s not. Thus its most iconic poses: Pete Townshend clobbering the stage with an electric guitar, Jimi Hendrix humping his amplifiers, Janis Joplin, onstage at Woodstock, shaking from heroin and whiskey.

The War on Drugs, a Philadelphia-born outfit fronted by the thirty-eight-year-old guitarist and vocalist Adam Granduciel, does not subscribe to this ethos. Instead, it makes the old clichés seem tired. The band’s songs are performed and recorded in such a way that it’s impossible not to be cognizant of their polish—of labor invested. Though other contemporary bands have made ambitious and exacting music, few are quite so painstaking. Yet the War on Drugs is, to my ears, the best American “rock” band of this decade; it is certainly the one that makes the genre feel most alive.

The group’s fourth album, “A Deeper Understanding,” which comes out on August 25th, is a big and purposeful record that shares some genetic material with late-career releases by Rod Stewart, Dire Straits, Tom Petty, and Don Henley—the songwriting lacks the wholeness and negligence of youth, but hasn’t yet been softened by the capitulations of adulthood. Spiritually, Granduciel is still looking; nothing is secured or presumed.

Philadelphia in the mid-aughts was a very good place and time to be a guitar player. The War on Drugs began, in 2005, as a collaboration between Granduciel and Kurt Vile; later, as the leader of the Violators, Vile perfected a guitar style and tone that married the disaffection of Sonic Youth with the stoned, flickering warmth of the Grateful Dead. Another Philadelphia native (and former Violator), the guitarist Steve Gunn, relocated to Brooklyn and made several albums of warm but terrifically complex music. The War on Drugs made its début with “Wagonwheel Blues,” in 2008, and, following Vile’s departure and several more lineup changes, released its second record, “Slave Ambient,” in 2011. Both were favorably received, but it took “Lost in the Dream,” from 2014, to realistically suggest Granduciel as rock’s next torchbearer. He even looked the part: long and wavy brown hair, Wayfarers, a seemingly infinite collection of vintage denim jackets.

“Lost in the Dream” was conceived mostly at Granduciel’s three-story row house in Philadelphia’s South Kensington neighborhood. He has since recounted the way panic attacks and bouts of listlessness led him to a near-obsessive immersion in his work. Compulsive tinkering in the studio has sunk lesser writers; too much fussing can make a record claustrophobic and overwrought. Somehow, for Granduciel, sealing himself inside allowed for an opening. Music became a viable proxy for actual living—a scout dispatched over the hillside, a manner of exploring the world without directly engaging it. Despite the intensity behind the album’s production, there are plenty of joyful moments—like “Red Eyes,” a song so plainly exultant that, even after a hundred listens, its chorus still feels like cresting a mountain.

Granduciel relocated to Los Angeles after the release of “Lost in the Dream” (he is in a relationship with the actress Krysten Ritter, who stars in the Marvel television series “Jessica Jones”), and his new songs are indebted, in ways both subtle and overt, to his present landscape. It’s hard to say precisely what would comprise a Los Angeles canon—I imagine Warren Zevon, Randy Newman, Fleetwood Mac, Neil Young’s “Tonight’s the Night,” and Guns N’ Roses’ “Appetite for Destruction,” though others might choose N.W.A.’s “Straight Outta Compton,” Joni Mitchell’s “Blue,” or Frank Ocean’s “Channel Orange.” It is even more difficult to specify how the city impresses itself on the records made there. I tend to think of L.A.’s influence not so much as a relentless sunniness but as a wide-eyed searching of the horizon. Granduciel has always written dynamic, propulsive melodies that beg for long stretches of good road. But “A Deeper Understanding” has more scope than anything he has done before. When each constituent bit locks into place, the massive scale and deep texture of the work is thrilling. It contains all the expansiveness of the West, and some of its optimism, too.

Lyrically, “A Deeper Understanding” is a record about self-interrogation. Most of Granduciel’s earlier songs address a near-constant process of revision and reinvention. Here, though, Granduciel is more assured than ever. One of the new album’s best tracks, “Holding On,” acts as a spiritual continuation of “An Ocean Between the Waves,” another cut from “Lost in the Dream,” and though the new song never quite resolves the older song’s visceral fears (“Can I be more than just a fool?” Granduciel worried), it does render them smaller. Granduciel seems more cognizant of what’s at stake (“Once I was alive and I could feel, I was holding on to you,” he sings), yet he approaches heartache with ambivalence, a cool acceptance of life’s unpredictable flow. “I keep moving on the path, holding on to mine.” He sounds nearly serene—or at least like someone who has recently seen an ocean.

Throughout “A Deeper Understanding,” Granduciel’s vocals are soft, steady, and almost without origin. Though he occasionally moves into a more discordant, nasally voice—borrowing, for a moment, the sourness of Bob Dylan—it’s often hard to distinguish his singing from any number of gauzy, fading synthesizers. The War on Drugs remains chiefly a guitar band—this is especially true when it performs live—but there are an awful lot of keyboards on the new record, including Wurlitzer, Mellotron, Hammond organ, and several vintage analog synthesizers (or reissues of vintage analog synthesizers), like the Arp Odyssey and the Oberheim Xpander. The synthesizers, especially, give “A Deeper Understanding” a dreamy, almost illusory quality.

That sensibility is augmented by the running length of most of the album’s songs—six or seven minutes (“Thinking of a Place,” which was released as a twelve-inch single for Record Store Day, clocks in at more than eleven minutes)—and how they snake to curious places. Halfway through “Up All Night,” a song about managing the nocturnal willies, the melody—a gentle electric-piano riff that recalls Bruce Hornsby—is displaced by Granduciel’s crackling guitar. The shift should be disorienting, but because of the song’s dream logic it takes a moment to realize you’ve been jolted awake.

“A Deeper Understanding” is the band’s first album for a major label; it left the Indiana-based indie Secretly Canadian and signed a two-record deal with Atlantic Records shortly after “Lost in the Dream” was released. “They should be gigantic,” Jimmy Iovine, a co-founder of Interscope Records who has produced albums by Bruce Springsteen, U2, and Meat Loaf, told Billboard in a 2015 interview. So far, however, the War on Drugs is not making any concessions to the mainstream market, where shorter, sparser songs now dominate.

Perhaps no concessions are necessary. The intricacy of Granduciel’s songwriting and production—the way his urgent, interior searching yields strange tapestries—isn’t immediate in the way, say, a punk-rock song can be. Rather than knock you over, it slowly fills a room, and lingers. Yet his work seems to communicate something vital about the internalization of modern life, the ways in which we now manage, negotiate, and curate expression before uploading it to one platform or another. That these machinations are laid plain—that this music does not aspire to spontaneity—makes it feel more true. ♦