Hyunseok Kim | Three Approaches to the “Substantial Similarity” Standard in Copyright Infringement Cases

Background

Every composer in conservatory studies Igor Stravinsky. Pupils who admire his trailblazing compositional techniques might be surprised to discover his source of inspiration. Stravinsky famously declared that “a good composer does not imitate; he steals.”

“Stealing” musical ideas has a rich and long history. Far from being forbidden, it has been a cornerstone in the evolution of music. J.S. Bach based his music on Lutheran hymns and drew heavily on Dietrich Buxtehude’s style. Johannes Brahms frequently invoked folk tunes by expanding musical structure laid out by his predecessors, notably Beethoven.

While borrowing once signified homage and creative reinterpretation, the modern music industry has turned it into a legal and economic battleground. As music evolves beyond traditional tonality and today’s popular songs become shorter, averaging just over three minutes, the focus on melody, particularly the “hook,” has increased dramatically.

Moreover, the economic stakes of modern music have only grown. The Recording Industry Association reported that recorded music generated $17.1 billion in revenue in 2023, an 8% increase from 2022. A single hit song, like Ed Sheeran’s “Shape of You,” can amass over 4 billion streams on Spotify alone. These trends have elevated the complexity of copyright disputes, where courts must balance protecting original expression with preserving room for creativity.

This tension is especially clear in how U.S. courts evaluate “substantial similarity,” the legal standard for determining whether one work has unjustly copied another. Different circuits apply distinct tests, which often lead to varied outcomes. This article examines the three main approaches: the Second Circuit’s “ordinary observer” test, the Sixth Circuit’s “fragmented literal similarity” approach, and the Ninth Circuit’s two-part test that combines extrinsic and intrinsic analyses.

Issue

How should courts determine substantial similarity in music copyright cases?

The Split

Second Circuit

The Second Circuit uses the “ordinary observer” test, which asks whether an average lay observer would think the alleged copy, as a whole, sounds like the original. Structured Asset Sales, LLC v. Sheeran, No. 23-905, 2024 U.S. App. LEXIS 27752, at 22 (2d Cir. Nov. 1, 2024).

In 2014, Ed Sheeran and Amy Wadge released “Thinking Out Loud,” a Grammy-winning hit, which was later alleged to infringe Marvin Gaye and Ed Townsend’s 1973 classic “Let’s Get It On.” Plaintiff Structured Asset Sales, partial owner of “Let’s Get It On” royalties, claimed infringement based on similarities in harmonic rhythm and chord progressions. The district court granted Sheeran’s motion for summary judgment, reasoning that the chord progression and harmonic rhythm in “Let’s Get It On” are so commonplace, both individually and in combination, that protecting them would effectively create an impermissible monopoly over basic musical building blocks. This conclusion was grounded in “common sense” principles of musical composition. Id. at 29.

The appeals court affirmed the district court’s decision, holding that the legal question is whether the “total concept and overall feel” of the two songs is substantially similar and that this determination depends on the perception of lay listeners. Id. at 29. The court ultimately concluded that no jury could find that, taken as a whole, “Let’s Get It On” and “Thinking Out Loud” are substantially similar and affirmed the judgment. Id.

Under this approach, courts consider certain fundamental elements like chord progressions but ultimately rely on the jury’s assessment of whether the overall “feel” of the works conveys substantial similarity.

Sixth Circuit

The Sixth Circuit uses a modified “ordinary observer” test, the "fragmented literal similarity" approach. The test has two parts: (1) Identify which aspects of the artist's work are protectible by copyright, and (2) determine whether the allegedly infringing work is substantially similar to the protectible parts of the artist's work. Bridgeport Music, Inc. v. UMG Recordings, Inc., 585 F.3d 267, 274 (6th Cir. 2009). In determining whether the protectible parts are substantially similar, the court uses the “ordinary observer” test. Id. at 276.

The court in Bridgeport v. UMG formulated and applied this test, setting a new standard. In 1982, George Clinton created "Atomic Dog," which became a funk era anthem and one of the most sampled works in rap and hip-hop. The song featured distinctive elements including the phrase "Bow wow wow, yippie yo, yippie yea," use of the word "dog" as musical punctuation, and rhythmic panting. In 1998, Public Announcement released "D.O.G. in Me," which allegedly copied these elements. After a jury found infringement and awarded $88,980 in damages, UMG appealed, arguing these elements were too basic for copyright protection.

The Sixth Circuit upheld the jury verdict, emphasizing that even small amounts of copying may constitute infringement if the copied portion is qualitatively important to the original work. Id. at 275. The court paid attention to the fact that the Bow Wow refrain was "one of the most memorable parts of the song” and was often licensed on its own. Id. at 273.

Under this approach, two pieces may be substantially similar if they are similar to lay listeners in essential parts, even if they do not sound similar as a whole. This stands in contrast to the Second Circuit's emphasis on overall similarity.

Ninth Circuit

The Ninth Circuit employs a distinctive two-part substantial similarity test requiring both "extrinsic" and "intrinsic" analysis. Gray v. Hudson, 28 F.4th 87, 96 (9th Cir. 2022).

This framework faced a major test in Gray v. Hudson, where Christian hip-hop artists claimed Katy Perry's hit "Dark Horse" copied an eight-note ostinato (repeating musical figure in the bass) from their song "Joyful Noise." Initially, a jury found infringement and awarded $2.8 million in damages. However, the district court granted judgment as a matter of law to Perry, which the Ninth Circuit affirmed.

The court in Gray started its analysis by considering two elements: (1) whether defendants had "access" to their work and (2) whether the ostinatos in both songs "are substantially similar." Id. The court turned to the “substantial similarity” analysis, holding that since this case fails the test, there was no need to turn to the “access” test. Then, the court stated the extrinsic test requires distinguishing the protected and unprotected material in the plaintiff's work. Id.

Despite a musicologist’s testimony that two bass melodies are similar in multiple aspects, the court held that those similarities were not legally sufficient. Id. at 103. The court held that the sequence of notes in question was not a melody but an abstract sequence of pitches, suggesting it was not "rhythmically organized" so as to form an "esthetic whole." While an eight-note melody may be copyrightable, the abstract eight-note pitch sequence that is a component of the melody is not. Id. at 99, 100.

The Ninth Circuit’s approach differs from other courts’ in the sense that it can rule without relying on the sound or feel of music but only on objective measures such as pitches and rhythm.

Looking Forward

In sum, the Second Circuit relies on the “feel” of the entire piece, while the Sixth Circuit utilizes essential “fragment” of the piece. The Ninth takes a further step and sometimes decides using only extrinsic parts of music.

The divergent approaches are significant, because they lead to different outcomes. Taking “Atomic Dog” from Bridgeport Music as an example, it is quite possible that the case would have turned out differently across the circuits. Under the Second Circuit’s approach, despite identical key elements, a reasonable jury could have found the works not substantially similar as a whole because the similarities are dispersed among other musical elements. The Ninth Circuit’s test presents even more uncertainty; the court would need to either develop new analytical tools to evaluate non-traditional musical elements like spoken words and rhythmic panting, or fall back on its intrinsic test, essentially mirroring the Second Circuit's approach.

These splits matter because modern music increasingly builds on existing works in creative ways. Sampling, interpolation, and homage have become standard creative techniques. Different rules in different circuits create uncertainty for artists and potentially chill musical innovation. The United State Supreme Court may take some music copyright cases such as Cox Communications, Inc. v. Sony Music Entertainment No. 24-171, 2024 U.S. LEXIS 4863 (Nov. 25, 2024). However, the current Court’s focus seems to be enforcement, procedural rules, and secondary liability rather than the core question of how to compare musical works.

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