'Stairway to Heaven' is the latest casualty in a wave of litigation over composer royalties. Why do so many hit songs lead to copyright suits?

I'd just celebrated my 14th birthday when Led Zeppelin released the song "Stairway to Heaven." One of my buddies purchased a copy of the album Led Zeppelin IV before the rest of us knew about it—we were still listening to smarmy middle school songs—and scrawled out the lyrics to "Stairway to Heaven" on a piece of looseleaf paper. He proudly displayed it to me, announcing that it was a poem he had written.

For a few days, I believed my friend's bold claim, and admired him as the rising literary lion of our ninth grade class. Then I heard "Stairway to Heaven" on the radio, and his scam was exposed. He gave up poetry after that.

It's not always so easy to prove musical plagiarism. And now that same song, "Stairway to Heaven" is at the center of another battle over ownership. The estate of guitarist Randy California claims that Led Zeppelin took a key section of their hit from his rock instrumental "Taurus," featured on a 1968 album by the rock band Spirit.

California drowned in 1997, while trying to save his son from a rip current, and can't offer his own testimony under oath. But in an interview in Listener magazine conducted shortly before his death, he griped, "I'd say it was a ripoff. And the guys made millions of bucks on it and never said 'Thank you,' never said, 'Can we pay you some money for it?' It's kind of a sore point with me."

The disputed passage is just ten seconds of music. Ten seconds may not seem like much—especially in the context of an 8-minute song featuring several distinct melodies, each with different harmonies and rhythmic support, as well as marked changes in tempo and dynamics. But the proliferation of hit songs built on samples from older recordings has increased our sensitivity to the commercial value of even the tiniest musical memes. Fortunes can be made or lost on a few seconds of original content.

What a change from an earlier day! For decades, jazz musicians built song after song on borrowed harmonies, often taking the entire chord progression from a pre-existing work. And no one got sued. Blues musicians were even more brazen. They frequently claimed credit for songs, even when they had borrowed chords, melody and lyrics. But the recent trend is clear. Nowadays, even tiny appropriations and casual resemblances can spur legal action.

Led Zeppelin suffers from a long, troubling history of appropriating the music of other artists.

In the case of "Stairway to Heaven," the disputed passage involves a fairly simple descending pattern that might easily have been composed independently by musicians unaware of each others' work. In fact, Davy Graham relied on a similar passage in his intro to "Cry Me a River" back in the '50s. You can hear another variant of this figure in the intro to Johnny Rivers's "Summer Rain." I suspect that a thorough investigation of old folk and pop music recordings would turn up many other examples.

Despite what some have claimed, the cited passages from "Stairway to Heaven" and "Spirit" are not identical. Led Zeppelin's version, played by guitarist Jimmy Page, is less predictable than California's motif, and (dare I say?) more aesthetically pleasing. Page disrupts the pattern in the second bar, moving up to the ninth, and fleshes out the figure with more harmonic support. But the similarity is striking nonetheless. The "Stairway to Heaven" passage is also in the same key and tempo as "Taurus"—adding to the plausibility of the infringement claim.

If I were judging this matter solely on the musical evidence, I would hesitate before awarding a share of the royalties to Randy California's estate. But other factors clinch the deal for me. Led Zeppelin made its first U.S. tour as opening act for Spirit, and even performed a cover version of a Spirit song. Jimmy Page almost certainly heard "Taurus" in person, if not on record, long before he composed "Stairway to Heaven." This chronology destroys Led Zeppelin's most plausible line of defense, namely that Page came up with a similar piece of music on his own without knowing about the pre-existing work.

In addition, Led Zeppelin suffers from a long, troubling history of appropriating the music of other artists. Many rock artists "borrowed" material from black blues artists, but few did so with more audacity than Jimmy Page. Led Zeppelin has made out-of-court settlements over material lifted from Howlin' Wolf and Willie Dixon. Page has also been forced to acknowledge his use of Jake Holmes' "Dazed and Confused" and Anne Bredon's "Babe I'm Gonna Leave You." By even the loosest interpretation of copyright law, this band is a serial offender.

Yet Page can justifiably point an accusing finger at his peers and predecessors. The blues and rock tradition were largely built on borrowings of this sort. As noted above, the same blues musicians who had their songs appropriated by rockers, had previously lifted works from their own ranks. For more than a half-century before "Stairway to Heaven," recording artists had been doing this, usually with impunity. Indeed, some of the most revered figures in traditional music, icons such as Bob Dylan, Robert Johnson, and Alan Lomax, validated the practice with their personal example. I applaud the integrity of Eric Clapton, who ensured that aging bluesman Skip James received royalties when Clapton's band Cream recorded "I'm So Glad." But other rockers were hardly so scrupulous. You could write a very long book about the blues songs they stole.

In all fairness, let's acknowledge that some of these borrowings are inadvertent. Rod Stewart eventually admitted that portions of "Do You Think I'm Sexy" came from a song by Brazilian artist Jorge Ben Jor, but denied that the appropriation had been deliberate. He probably heard the song during a Brazilian tour, and the melody simply stayed in his head.  A similar process may have led George Harrison to borrow elements of "My Sweet Lord" from Ronnie Mack's "He's So Fine." When Paul McCartney came up with the melody to "Yesterday," he initially feared that it was an old song that he was recalling.  Eventually he decided that "Yesterday" was his own invention, but some have suggested (although not convincingly, in my opinion) that Nat King Cole's 1953 recording of "Answer Me, My Love" was an unconscious inspiration for the work.

This problem will only get worse in the future. We live in a cut-and-paste society in which borrowings of this sort are pervasive, and few are outraged. But the problem is aggravated immeasurably by the simplicity of current-day pop music. Chord changes have gotten downsized, and sometimes disappear completely. Melodies are often semi-sung chants, or rely heavily on repeated notes and small step and half-step intervals. You would need to go back to the 19th century to find rhythms in popular music with so little syncopation. With ingredients so meager, claims of originality are harder to prove, and cases of infringement (intentional or otherwise) more likely.

Take the case of Robin Thicke's hit song "Blurred Lines," which Marvin Gaye's family believes infringed on the soul singer's "Got to Give It Up." Certainly the two tracks resemble each other, but the similarity is little more than a groove—or what Gaye's family called the "sound" and "feel." These are difficult attributes to define in precise terms, and when you start pursuing musicological analysis, the resemblance begins to break down. The two songs aren't in the same key and don't have the same harmonies. On the other hand, chords and key signature played little role in the success of Thicke's twerking anthem. If these songs were more complex, the case would be easier to decide, but Thicke relied so heavily on the danceable beat as the 'hook' to propel his hit, that he opened himself up to precisely this type of litigation.

Can we limit these bickerings over royalties in the future? I doubt it. Perhaps if we went back to composing four-part fugues and three-part inventions—or even 32-bar songs with a modulation in the bridge—plagiarism would be easier to determine, and thus perhaps less frequently perpetrated. But when whole careers are now staked on micro-sized melodies and formulaic rhythms, the lawsuits are bound to proliferate.

So give Jimmy Page some credit. He may have sampled too much even before sampling existed. He may have illegally borrowed black music to build his own bankroll. He may even have usurped his most famous guitar melody. And he's certainly kept lawyers busy figuring out the ramifications. But in each these practices, he was clearly ahead of his time.