Led Zeppelin's lead singer Robert Plant and guitarist Jimmy Page must face a US jury trial over whether they stole opening chords for their 1971 classic "Stairway to Heaven."
In a decision on Friday, US District Judge Gary Klausner in Los Angeles said "Stairway" and the 1967 instrumental "Taurus" by the band Spirit were similar enough to let a jury decide whether Plant and Page were liable for copyright infringement.
A trial is scheduled for May 10.
The lawsuit was brought by Michael Skidmore, a trustee for the late Randy Wolfe, also known as Randy California, who was Spirit's guitarist and the composer of "Taurus."
Skidmore said Page may have been inspired to write "Stairway" for Led Zeppelin after hearing Spirit perform "Taurus" while the bands toured together in 1968 and 1969, but that Wolfe never got credit.
The defendants said Wolfe was a songwriter-for-hire who had no copyright claim, and that the chord progressions were so clichéd that they did not deserve copyright protection.
But the judge said a jury could find "substantial" similarity between the first two minutes of "Stairway" and "Taurus," which he called "arguably the most recognizable and important segments" of the songs.
"While it is true that a descending chromatic four-chord progression is a common convention that abounds in the music industry, the similarities here transcend this core structure," Klausner wrote. "What remains is a subjective assessment of the 'concept and feel' of two works ... a task no more suitable for a judge than for a jury."
Klausner dismissed claims against Led Zeppelin bassist John Paul Jones and Warner Music Group Corp.
He also said the trustee can get only 50 per cent of any damages awarded, citing a 1967 contract that Wolfe signed.
"This case, from our perspective, has always been about giving credit where credit was due, and now we get to right that wrong," Francis Malofiy, a lawyer for Skidmore, said by phone.
A lawyer for the defendants did not immediately respond on Monday to requests for comment.
According to the complaint, Wolfe complained about the similarities of the songs in an interview shortly before he drowned in 1997 in the Pacific Ocean while attempting to rescue his son.
"Stairway to Heaven" is a track on Led Zeppelin's untitled fourth studio album, often referred to as "Led Zeppelin IV."
The case is Skidmore v Led Zeppelin et al, US District Court, Central District of California, No. 15-03462.