This article is part of a series on creative pairs. To read the introduction, click here. To read the first part of the Beatles essay, click here.

"The tension between the two of them made for the bond." —George Martin

To the public, Lennon and McCartney famously declared themselves a fused pair. As soon as they began to write together, they decided to share credit regardless of individual contribution.   At the top of their music sheets, they would write, "Another Lennon/McCartney original." They collapsed the space between them—not even an "and" would divide their names, just a slash.

But the joint credit also served as balm on the cuts of a constant, intense—though often joyful—competition. "Imagine two people pulling on a rope," said George Martin, "smiling at each other and pulling all the time with all their might. The tension between the two of them made for the bond."

Martin's image is perfect. John and Paul constantly pulled away from each other—and moved closer at the same time. Their competition actually enhanced their individual differences, even as it brought them into a relationship that was itself a third entity, the space where two circles overlap.

Even in their early years, when, as John said, they wrote "nose to nose" and "eyeball to eyeball" Lennon/McCartney songs clearly bore the stamp of their primary creators—John usually dwelling on betrayal and loneliness ("Tell me why you cried/ And why you lied to me") and Paul on devotion and connection ("There's really nothing else I'd rather do/ 'Cause I'm happy just to dance with you").

At the same time, the songs clearly evolved through a shared vision—at first, for engaging, infectious, emotionally direct pop, later for more ambitious, far-reaching ideas and sounds. Their harmonies make the chemistry and connection palpable, along with an implicit communication that extended to the whole band— "just being able to sort of blink," Lennon said, "or make a certain noise and I know they'll all know where we are going."

Creative Pairs: Lennon and McCartney

The nature of John and Paul's intimacy evolved over the years. In the early days, the partners were hardly ever apart. In Hamburg, the Beatles famously played for hours at a time (adding up, as Malcolm Gladwell has pointed out, to the famous 10,000 hours of "deliberate practice" that Anders Ericsson has determined leads to true mastery.) Paul and John essentially lived together on the road; even on days off, they got together to write.

After August 1966, when they stopped touring, their lives were more separate. John lived in a mansion in the suburbs of London with his wife and son. Paul lived in London, first with his girlfriend Jane Asher's family, and then in a townhouse not far from the EMI studios on Abbey Road.

In part because each man grew as an artist, in part because they marinated in wild, innovative scenes, in part because they turned so much of their ferocious energy into a meticulous, relentless and inventive use of studio technology, the songs, beginning with the album Revolver, began to take on new color and oddity and elegance. Lennon wrote the lyrics for "Tomorrow Never Knows"after reading The Psychedelic Experienceand following its instructions on an LSD trip: "Turn off your mind relax and float downstream." When it came time to record the song, he told George Martin that he wanted the sound of a hundred chanting Tibetan monks. He also suggested that he be suspended from a rope, get a good push and sing while spinning around the mike.

McCartney, meanwhile, edged into an almost operatic narrative style with "Eleanor Rigby," and his infectious pop developed new layers as with "Got To Get You Into My Life."

According to the conventional wisdom, their drift apart had begun. But the increased distance sometimes functioned like the space between boxers in a ring—giving more room for a powerful shot. "He'd write 'Strawberry fields,' I'd go away and write 'Penny Lane,' " McCartney said. "If I'd write 'I'm Down,' he'd go away and write something similar to that. To compete with each other. But it was very friendly competition because we were both going to share in the rewards anyway."

Friendly, but with a sharp edge. "I would bring in a song and you could sort of see John stiffen a bit," Paul said. "Next day he'd bring in a song and I'd sort of stiffen. And it was like, 'Oh, you're going to do that, are you? Right. You wait till I come up with something tomorrow.' "

The favorite back-and-forth—who was the real genius in the pair?—looks to set one on a pedestal. But when we look closely at the back and forth, that debate's most cherished assumptions come into question—for example, that John charged ahead with the musical avant-garde while Paul nurtured traditional elements of melody and symmetry. It's true that John tended to stick his finger in the audience's eye while Paul usually preferred to coo to them. John's "Revolution 9" may be the oddest, most dissonant thing ever laid down on a big pop album and Paul's "Let It Be" and "Hey Jude" set a standard for sweetness and formal perfection.

But in some ways, it was Paul who forged the frontier and John who raced to catch and exceed him. From 1966 to '68, John lived a weird, sleepy, deeply interior life. He spent days on end dropping acid and watching television. Paul, meanwhile, threw himself into the London art world and its "happenings"—performances that blurred the boundary between artist and audience. In 1965, their music publisher Dick James gave them each a Brenell Mark 5 tape recorder. While John used his to record rough demos, Paul, immersed in the experimental work of composers like John Cage and Karlheinz Stockhausen, jiggered the machine to disable the erase head and make tape loops of layered sounds. He brought these to the Beatles sessions to create the sound for "Tomorrow Never Knows," the famous "John" song.

" I lived a very urbane life in London," McCartney remembered. "John used to come in from Weybridge … and I'd tell him what I'd been doing: 'Last night I saw a Bertolucci film and I went down the Open Space, they're doing a new play there.' "*

Paul said John would reply: "God man, I really envy you."

In 1966, a far-out artist named Yoko Ono moved to London from New York City. Paul not only met her first; he had helped create the Indica Gallery where she and Lennon met. * Though it took several years to ripen, Lennon eventually threw himself into the relationship—he literally asked people to consider them JohnandYoko. (Yoko made for the third person, following Pete Shotton and Paul McCartney, with whom he collapsed his name.)

Joined with her, John left no doubt who would be master of the avant garde. Where Paul had merely attended happenings, John and Yoko staged them. Where Paul used his tape loops to extend the pop form and kept his wildest, most experimental recordings in the can, John insisted that "Revolution 9" go on a Beatles record.

The point here isn't to identify whether John or Paul was the "real" edge, but to underscore how keenly they watched each other. Indeed, Paul's dive into the London art scene may itself have been a reaction to his image as the "cute" Beatle, compared with John, the "smart" one.

This constant give and take took a decisive shift in August 1967, when the band's manager Brian Epstein died. For some time, Epstein had been more figurehead than real leader—and it is telling that, by the mid-1960s at least, he deferred to Paul far more than to the others. But in a tenuous democracy led in strange fashion by two principals, he gave cover, the way even a weak parent will for squabbling boys.

Paul had asserted control before Epstein's death, when he conceived of Sgt. Pepper's Lonely Hearts Club Bandand dominated the sessions. With Brian gone, Paul's role as a de facto manager became far more obvious—and far more threatening to John's own sense of control. "Paul had a tendency to come along and say well he's written these ten songs, let's record now," John said, claiming that he and George became "side men for Paul." But this bitter language came later. And for a long while, he acquiesced. He was too checked out to do much of anything else.

The traditional story is that John withdrew from the band even further when he took up with Yoko. She is cast as usurper—provoking rifts that led to the band's demise. But on closer look, we have to ask whether John actually used her to assert his dominance—to claim his rightful, incontestable leadership. To the others, John's insistence that Yoko be treated as an equal seemed preposterous. But for John—however aware of his audaciousness—it all still fit: It was his band. He could bring in new members the same way he'd brought in Pete Shotton, the way he replaced Bill Smith with Len Garry—the way he brought in Paul. As strange as it might sound, even John's dramatic break with the band can be seen as a power move—a backhanded form of engagement. In September 1969, as Paul urged that the Beatles get back to their roots and play live shows, John shot back, in the account given by biographer Bob Spitz, "I think you're daft. I wasn't going to tell you, but I'm breaking the group up."

The language is key. John's leaving the band would mean its dissolution. He later made the claim explicit: "I started the band. I disbanded it. It's as simple as that."

But the break was hardly simple. It's not even clear that Lennon wanted a final break. For all his bluster in the band meeting, he never made his decision public—which is to say, he never made it real. To the contrary, just months after he told Paul he wanted a "divorce," he talked publicly about the band recording again and even touring. "It'll probably be a rebirth, you know, for all of us," he said. Perhaps John needed to believe he could end the band in order to stick with it.  

At first, Paul showed signs that he would step back and let John get what he needed. He saw the choice, he said later, to accept Yoko or to lose John, and he chose the former: "When you find yourself in times of trouble … let it be."

But now, at a moment of great turmoil, two new factors came into play. For years, George Harrison had been the "quiet Beatle" at the side. Literally, as John and Paul faced the crowd side-to-side in performance, he stood far off facing them. But as he grew into his own—writing songs like "Something" and "Here Comes the Sun"—he bristled at Paul's bossiness and grew positively indignant at taking instructions from John's wife. At one point, according to George Martin, he and Lennon even came to blows. His energy made the tenuous balance between John and Paul much less stable.

Meanwhile, the Beatles, as a business, were in such a freefall that John predicted they could go completely broke. Someone needed to take control at Apple Corps, a wildly ambitious holding company that had turned to chaos. Paul wanted his new bride Linda's father and brother, Lee and John Eastman, to run Apple. But in another impetuous power move, John summarily signed with Allen Klein, a brash manager with a reputation for bullying record companies for higher royalties. (Klein was also a questionable character; he basically stole ownership of the Rolling Stones' catalog and later went to jail for tax fraud.)

George and Ringo followed John and signed with Klein. Paul held out. But for all his defiance, his vulnerability came strongly into play, as well. He had never yielded his essential devotion to John—and the rejections devastated him. "John's in love with Yoko," he said. "He's no longer in love with us."

As Paul wrote in "Let It Be," the light always shined on him, even on cloudy nights. But now, as a storm raged, he fell into a profound depression. He stayed in bed and drank through the day. "Boy, you're going to carry that weight a long time"—this grew out of his despair, he said. But he also wrote, in what seems a plea to his partner, "You and I have memories, longer than the road that stretches up ahead."

In the spring of 1970, with tensions among the four Beatles still at a fever pitch, Paul released a solo album and included a short Q&A that he authored with his publicist. It included this exchange.

Q: Are you planning a new album or single with the Beatles?

PAUL: No.

Q: Is this album a rest away from the Beatles or the start of a solo career?

PAUL: Time will tell. Being a solo means it's "the start of a solo career …" and not being done with the Beatles means it's just a rest. So it's both really.

Like John, Paul hardly said the band had broken up for good. "It's just a rest," he said.

But newspapers seized on the first public acknowledgment of the band's rumored troubles. "McCartney Breaks Off With Beatles," ran the New York Times headline on April 11, 1970. This loss of face—the public acknowledgment of a coup—was more than John could stand. "I was cursing," he said, "because I hadn't done it. I wanted to do it, I should have done it. Ah, damn, shit, what a fool I was."

The time had long passed where he could just take a washboard and break it over a mate's head. The fight between these two partners now had the whole world in thrall. They would never work together again. But the history of their partnership was just beginning to be written. Hardly a straightforward account, it would be another winding road on their path together.

Read the third and final piece in the Beatles series.

Correction, Sept. 20, 2010: This sentence originally misspelled the name of the town of Weybridge. (Return  to the corrected sentence.)

Correction, Sept. 30, 2010: This sentence origianlly misspelled the name of the Indica gallery. (Return to the corrected sentence.)

Like Slate on Facebook. Follow us on Twitter.