Musician Lana Del Rey arrives at the MTV European Music Awards in London on Nov. 12. (Vianney Le Caer/Invision/AP)

In the quarter-century since its release, the song “Creep” by Radiohead has become something of a case study in pop music plagiarism, perennially showing up on those lists of sound-alike songs that tend to circulate whenever musicians sue each other for copyright infringement.

After Radiohead released the breakthrough hit in 1992, a pair of songwriters, Albert Hammond and Mike Hazlewood, noticed that it bore more than a few similarities to a song called “The Air That I Breathe” that they had composed for The Hollies two decades earlier. Hammond and Hazlewood sued, and Radiohead agreed to give them co-writing credits.

Fast forward to 2018 and, in a development dripping with irony, Radiohead is reportedly preparing a legal fight to protect its artistic and pecuniary interests in “Creep.”

On Sunday, Lana Del Rey confirmed rumors published over the weekend in a British tabloid that Radiohead frontman Thom Yorke and the band’s other members were considering suing her for copyright infringement over the song “Get Free” from her most recent album.

“It’s true about the lawsuit,” the 32-year-old singer-songwriter tweeted. “Although I know my song wasn’t inspired by Creep, Radiohead feel it was and want 100% of the publishing — I offered up to 40 over the last few months but they will only accept 100. Their lawyers have been relentless, so we will deal with it in court.”

It’s not clear whether Radiohead’s attorneys had actually filed court papers or were still in talks with Del Rey’s legal team. Representatives for Radiohead and Del Rey didn’t immediately respond to requests for comment Monday morning.

Whatever the case, it doesn’t take a trained musical ear to hear the overlap between “Get Free” and “Creep,” and “Creep” and “The Air That I Breathe.” All three songs are in different keys, but they follow an almost identical chord progression, played at about the same tempo.

The thing that makes the similarities between the songs so distinct and particularly easy to point out is the last chord in the progression. It’s called a minor fourth, and it gives the tunes a somewhat darker, more anxious feel because it doesn’t technically fit the key of the piece. In music theory terms, this technique is called modal interchange. In plain terms, it means making a song sound different by playing notes that you’re not technically supposed to play.

On “Creep,” you can hear the minor fourth as Yorke sings the line “your skin makes me cry” during the verse, or “I don’t belong here” during the chorus. On “Get Free,” it comes when Del Rey sings “to the reveal of my heart” or “and the darkness from the arts.” And on “The Air That I Breathe” it comes on the second half of the line “can’t think of anything I need.”

Countless pop songs have used this technique over the years, although not in exactly the same way that those three do. A similar type of progression was prevalent in doo-wop of the 1950s, on songs such as “Sixteen Candles” by the Crests. Later, the Beatles made wide use of the minor fourth — “Blackbird” and “When I Saw Her Standing There” are two examples — as did David Bowie on songs like “Space Oddity.”

You also can hear it on more recent fare, such as Green Day’s “Wake Me Up When September Ends.” And Radiohead has used it on songs other than “Creep,” including “My Iron Lung” and “No Surprises.”

So there’s nothing copyrightable about the minor fourth in and of itself. But if the apparent legal battle between Radiohead and Del Rey does wind up in front of a judge, “Get Free” could become a case study of its own.

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