“The trial and the legal process have been a long climb up the Stairway to Heaven.”

— Judge Margaret McKeown

“And if you listen very hard, the tune will come to you at last.”

— Stairway to Heaven

You’ll forgive me, I hope, for not being a huge fan of the band Led Zeppelin, since they formed seven years before I was born, had their biggest period in the four years before I was alive, and broke up as a band when I was five. Probably not surprising that my parents didn’t let their preschooler listen to a lot of “Living, Loving Maid” or “Dazed and Confused.”

But there’s no denying that Led Zeppelin was the biggest musical act of the post-Beatles, 1970s rock scene. Between 1969 and 1979, they released seven consecutive No. 1 or No. 2 albums. Their biggest hit, “Stairway to Heaven,” was the most requested radio song of the entire decade. Through multiple tours, in multiple countries, several other acts opened for them, and among those acts was a group called “Spirit.” Spirit’s affiliation with Zeppelin, and the fact that they had the opportunity to hear each other’s music, would end up playing a huge factor in a court case decades later.

Among Spirit’s songs was an instrumental piece called “Taurus.” It was written by guitarist Randy Wolfe (who performed under the name Randy California), who passed away in 1997. Spirit’s biggest hit was 1968’s “I Got a Line On You,” which went to No. 25 on the Billboard charts, and led to them appearing as the opening act for Zeppelin’s December 1968 concert in Denver, and two outdoor events the following July. With permission, Zeppelin used part of the Spirit song “Fresh Garbage” in a medley that they performed on tour.

And that was about it for the relationship between the two bands until Wolfe died in 1997. When he passed, his assets went into a trust, and in 2006, a new co-trustee took over the management of that trust. The new trustee zeroed in on a long-held belief by members of the band that the famous opening notes of “Stairway to Heaven” had been copied almost directly from “Taurus.”

In 2014, the trust and Spirit bass player Mark Andes filed a copyright infringement lawsuit against Led Zeppelin asking for millions of dollars in damages for stealing the song. Their choice of where to file the suit was no accident — for reasons that I’ll spell out in a moment. But the lawsuit was originally unsuccessful, was overturned on appeal, and this week, the 9th Circuit Court of Appeals reversed itself in a landmark copyright case.

The lawsuit was filed in California, not just because the parties had done business there, but because the 9th federal circuit has long had a different way of evaluating copyright cases than the rest of the country. The 9th Circuit has instituted a policy of its own making called the Inverse Ratio Rule. Under the Inverse Ratio Rule, a jury is to judge the likelihood of a copyright infringement not just on the similarity of the works, but also on an examination of whether the party alleged to have copied the work had extensive access to the work that was copied. If so, then a lower standard of proof was necessary to establish the infringement. Because Spirit knew that Zeppelin had access to their work, it made sense for them to file their case in the 9th Circuit.

Other federal courts had refused to adopt the rule, and the matter had not yet reached the U.S. Supreme Court to sort the policy out. But now it won’t need to, because Zeppelin’s attorneys convinced the 9th Circuit to scrap the Inverse Ratio Rule after 43 years of using it. The basis for that decision was modern technology.

The 9th Circuit reasoned that access to a work used to be a big deal. If you weren’t around someone to hear their song, and didn’t have access to a copy of their recordings, then you couldn’t possibly have copied it. But now, everyone has access to everything, because almost everything is available online, via a streaming service, etc. Thus, no one really has more or less access, and the Inverse Ratio Rule becomes meaningless.

To illustrate the point, you can judge for yourself whether the two songs are similar enough to constitute copyright infringement, as both songs are available on YouTube. Who would have guessed that Led Zeppelin and Spirit would lead to a groundbreaking change in copyright law over a song that was recorded nearly half a century ago.