Led Zeppelin will have to re-do a trial on whether the song is an infringement of Spirit's "Taurus" after the Ninth Circuit flags improper jury instructions and says the jury should have gotten to hear the recording.

A copyright battle over Led Zeppelin's iconic song "Stairway to Heaven" is back on after the Ninth Circuit Court of Appeals on Friday partially vacated the trial court's judgment in favor of the band and remanded the case for a new trial.

The lawsuit was brought by Michael Skidmore, the Trustee for deceased songwriter Randy Wolfe (best known as Randy California), who composed Spirit's "Taurus" in the late 1960s. The complaint — 43 years in the making after much discussion in the musical community over whether "Stairway to Heaven" plagiarized "Taurus" — explicitly demanded a rewriting of rock history.

In June 2016, Led Zeppelin prevailed at trial after the jury heard Led Zeppelin members Jimmy Page and Robert Plant testify, as well as a Spirit bandmember, musicologists and other witnesses about the similarity between the songs. The jury didn't hear the recording of "Taurus" because the song was copyrighted before sound recordings were covered under federal law.

In today's opinion, a panel of appellate justices holds that the jury was improperly instructed about unprotectable music elements and improperly instructed on originality. Although the panel confirms that the scope of protection for an unpublished musical work under the old copyright law is defined by what was deposited with the Copyright Office and that the playing of "Taurus" couldn't be used to prove substantial similarity, the 9th Circuit determines that the recording should nevertheless have been played for the purpose of demonstrating Led Zeppelin's access to the song.

Here's the full decision.

Many legal observers expected a legal battle over "Blurred Lines" between the heirs of Marvin Gaye on one side and Robin Thicke and Pharrell Williams on the other to provide guidance in song theft cases. Earlier this year, the 9th Circuit upheld the "Blurred Lines" verdict but stopped short of delivering such expected guidance thanks to a failure by Williams' attorney to properly preserve certain issues for appeal.

The dispute over "Stairway to Heaven" has now stepped in to provide useful instruction in copyright trials examining songcraft.

Circuit Judge Richard Paez begins his majority opinion by going through the history of the case, the allegations made, and reviewing standards in copyright cases — namely, that plaintiffs must show a valid copyright and that defendants copied protected aspects of expression. The judge also notes that independent creation is a complete defense against a claim of copyright infringement. Paez continues by saying that where there is no direct evidence of copying, a plaintiff can attempt to prove it circumstantially by showing that the defendant had access to a work and that both works share similarities probative of copying. Perhaps most controversially, Paez adopts what's known as the inverse ratio rule: When a high degree of access is shown, a lower amount of similarity is needed to prove copying.

On appeal, Skidmore first argued that the trial judge had failed to give an instruction that selection and arrangement of otherwise unprotectable musical elements are protectable.

Paez expresses concern that the extrinsic test — an examination of so-called objective factors of similarity — isn't properly being administered and ultimately agrees with Skidmore on this point. He writes, "The district court’s failure to so instruct the jury was especially problematic in this case, because Skidmore’s expert, Dr. Stewart, testified that there was extrinsic substantial similarity based on the combination of five elements — some of which were protectable and some of which were in the public domain."

Unprotected elements of a song may include the notes or scale of a song, but the arrangement is obviously key.

As for originality, the jury instruction stated that copyright does not protect chromatic scales, arpeggios or short sequences of three notes.

Skidmore argued, and Paez again agrees, this was in error.

"There is a low bar for originality in copyright," he writes. "Copyright extends to parts of a work created (1) independently, i.e., not copied from another’s work and (2) which contain minimal creativity. Most basic musical elements are not copyrightable. In Swirsky, however, we recognized that while 'a single musical note would be too small a unit to attract copyright protection ... an arrangement of a limited number of notes can garner copyright protection.'”

Paez sums it up by concluding that these jury instructions were erroneous as the jury was told that public domain elements are not copyrightable "even if they are modified in an original manner or included as part of a selection and arrangement. We further conclude that these instructions were prejudicial as they undermined the heart of Skidmore’s argument that 'Taurus' and 'Stairway to Heaven' were extrinsically substantially similar. Because the district court erred both in the formulation of the originality jury instructions and in withholding a selection and arrangement instruction, we vacate the judgment and remand for a new trial."

The appellate decision continues by noting that the jury ended its deliberations after deciding that "Taurus" and "Stairway to Heaven" were not substantially similar under the extrinsic test. Thus, the jury never got to the question of whether copying had occurred. As such, the judge finds the absence of a jury instruction about the inverse ratio rule was irrelevant and harmless.

"Because we are remanding for a new trial, however, we note that in a case like this one where copying is in question and there is substantial evidence of access, an inverse ratio rule jury instruction may be appropriate," he writes. "Here, there was substantial evidence of access, and indeed, the jury found that both James Page and Robert Plant had access to 'Taurus.' On remand, the district court should reconsider whether an inverse ratio rule instruction is warranted unless it determines, as a matter of law, that Skidmore’s 'evidence as to proof of access is insufficient to trigger the inverse ratio rule.'”

As part of what will now take place at the trial court upon remand, the appeals court seems to think a playing of the sound recording is in order. Again, while the sound recording can't be protected under federal copyright law, that doesn't mean it's necessarily off limits for all aspects of the adjudication.

"Skidmore argues that by not allowing the jury to observe Page listening to the recordings of 'Taurus,' the effect of the court’s ruling was to decrease the probative value of Skidmore’s questioning of Page," states the opinion. "Although the jury could still draw conclusions and inferences from Page’s demeanor during his testimony, allowing the jury to observe Page listening to the recordings would have enabled them to evaluate his demeanor while listening to the recordings, as well as when answering questions. Limiting the probative value of observation was not proper here, as the risk of unfair prejudice or jury confusion was relatively small and could have been reduced further with a proper admonition."