Rock and roll legends Led Zeppelin have been accused of a lot of wrongdoing over the years, from sexual misconduct with marine animals to hiding Satanic messages in their songs. This week, the band is back in the public eye, defending itself in court against a new and even more potentially damaging (if equally unsurprising) allegation: namely, that “Stairway to Heaven,” the band’s signature tune and 31st on Rolling Stone’s list of the “500 Greatest Songs of All Time,” was stolen from a now-forgotten psychedelic rock band called Spirit.

The trial, which began on Tuesday, may seem to many onlookers like a classic David-and-Goliath scenario, in which the scrappy underdogs finally have a chance to settle the score with the big, bad superstars who took all the credit for their unsung work of musical genius. While this would make a great straight-to-VH1 movie (and I’m certain it will, if Spirit ultimately prevails), the reality is of course more complex, and the stakes are actually far higher than mere writing credit and a couple million dollars. The outcome of this case could reverberate in ways that alter our understanding of copyright, change the sound of popular music, and shift the balance of power within the global music industry, rigging the game even further in favor of the major labels and to the detriment of independent musicians and their fans.

It’s an odd case, starting with the plaintiff. It isn’t a member of Spirit. It’s Michael “Mick” Skidmore, a journalist who’s written liner notes for bands like Jefferson Airplane and New Riders of the Purple Sage, and the current administrator of the Randy Craig Wolfe Trust. Randy Craig Wolfe was the legal name of Randy California, Spirit’s original lead singer, guitarist, and songwriter, who died in 1997, according to the complaint, “saving his son from being swept out to sea.” The defendants in this copyright infringement case are the three surviving members of Led Zeppelin, their publishing company, and their record label.

In a nutshell, Skidmore claims that the distinctive acoustic guitar riff at the beginning of “Stairway” (recorded in 1970-71) was taken directly from a Spirit song called “Taurus,” which Led Zeppelin heard while on tour with the other band in the winter of 1968-69. Though Wolfe never made an infringement claim during his lifetime, the complaint cites an interview conducted shortly before he died, in which the songwriter lamented that “it was a rip-off. And the guys made millions of bucks on it and never said, ‘Thank you.’”

At first glance, there’s good reason to believe the case has merit. While the members of Led Zeppelin have repeatedly claimed never to have heard “Taurus” before they were sued (“Something like that would stick in my mind,” guitarist Jimmy Page told the courtroom this week), that seems unlikely given their touring history with Spirit. And, as the complaint points out, they’ve been accused of infringing on musical copyrights by other artists in the past, and have settled several of those suits, in some cases giving credit and royalties to the aggrieved parties. Most damning of all, the songs in this case actually do sound pretty similar; a non-musician, hearing each guitar riff once or twice, could be forgiven for thinking they’re the same song.

Yet these facts alone aren’t—or shouldn’t (we’ll get to that later)—be grounds for a successful finding of infringement. To begin with, while the riffs are similar, they’re not actually the same. Any guitarist worth her salt could tell you as much, and even a layperson looking at the notes printed on a page would have to agree they’re two distinct melodies. Though this might sound like quibbling, it makes a huge difference when it comes to copyright law. That’s because the law doesn’t protect ideas, only the specific expression of an idea. This is why the Hunger Games, Maze Runner, and Divergent franchises can happily coexist on the screens at your local IMAX theater. And the fact that Suzanne Collins doesn’t own the exclusive rights to “dystopian post-apocalyptic young adult science fiction with a romantic element” is good for everyone involved—more entertainment for us, more employment for writers, actors, and filmmakers, and more profit for big media companies.

Second of all, according to copyright law, you can only claim infringement against someone to protect an original work of authorship. For instance, if I had written a story about a man named Noah who builds an ark to save humanity and a bunch of animals from a flood, I couldn’t sue Darren Aronofsky for making a film with the same plot and characters. That’s because it wasn’t my idea to begin with; we both based our work on the Bible, which was itself probably based on older myths. In the language of copyright law, the Biblical tale of Noah is what’s referred to as “prior art”—something that predates the allegedly infringed work, undermining the validity of the infringement claim altogether.

The same applies in the case of “Stairway to Heaven”; even if Led Zeppelin did write the song immediately after hearing “Taurus,” it’s not clear that what they took was original to the older song. Both tunes are based on a descending chromatic A-minor harmonic structure, which basically means playing one of the most common chords in Western music (a minor triad), then moving the lowest note one piano key at a time for a few bars, from the root down to the fifth. This trick, which is sometimes referred to as a “line cliché” or a “lament bass,” has been around for hundreds of years in the classical music world, and appears in the work of Henry Purcell, J. S. Bach, and countless others.

When Spirit used the lament bass technique in 1968, it wasn’t even new to the world of acoustic folk-rock guitar. A great example of prior art in this case is Davey Graham’s 1959 version of “Cry Me A River.” Although his work isn’t widely known these days, Graham was highly influential in his time (his Wikipedia entry lists him as an influence on Zeppelin’s guitarist Jimmy Page), and even a layperson listening to his guitar work on “Cry Me A River” could easily discern the same basic riff that’s at issue in this case.

So if “Taurus” and “Stairway” are technically different on the written page, and if their substantial similarities are both derived from prior art, why is there a lawsuit at all? Furthermore, why did Skidmore wait 20 years after Wolfe’s death to claim infringement? The answer to both questions is the same: the blurring of copyright’s bright line separating “idea” from “expression,” and an increasing willingness on the part of judges and juries to hear infringement where once they may just have heard influence or homage.

This is the same general legal and cultural trend that contributed to a victory for Marvin Gaye’s children last year in their suit against against Robin Thicke and Pharrell Williams, when the 2013 summer party hit “Blurred Lines” was found to infringe upon the 1977 groove classic “Got to Give It Up,” despite having a different melody and diametrically different lyrics (the decision is currently under appeal, and the outcome of that appeal will obviously have significant consequences for Skidmore v. Led Zeppelin). That case, too, was widely understood as a victory for the underdog, as well as a win for authenticity and soul over crass commercialism.

Yet, ironically, if the Gaye family and Skidmore prevail in their suits, it will only make popular music less innovative and further consolidate ownership of the industry in the long run. The reason for this is simple: if the bar for copyright infringement gets lower, then the risk of getting sued gets higher—especially in the world of pop, where music tends to be both highly formulaic and highly profitable. Greater risk means higher cost, which means that only the companies with the deepest pockets and the best lawyers can afford to bring new music to market.

If Led Zeppelin loses, and the once bright line between idea and expression continues to blur, this new legal standard would be one more weapon in the arsenal protecting the three major record labels and three major music publishers from outside competition—a power they desperately covet in this age of YouTube stars and mixtape hits. Don’t be fooled: David might win the battle, but Goliath ends up winning the war.

Aram Sinnreich is an Associate Professor at American University’s School of Communication and author of the recent book The Piracy Crusade.