Arnstein v. Porter, 154 F.2d 464 (2d Cir. 1946)
Arnstein v. Porter is a cornerstone of American copyright infringement doctrine and a foundational case in the law of substantial similarity.
In a copyright infringement action alleging musical plagiarism, must the case be submitted to a jury where the plaintiff presents evidence from which a reasonable factfinder could infer (1) the defendant's copying of the plaintiff's work and (2) that any copying constituted unlawful appropriation judged by the response of the ordinary lay listener?
Copyright infringement requires proof of (1) copying of the plaintiff's work and (2) unlawful appropriation of protectable expression. Copying may be established by direct evidence or inferred from the defendant's access to the plaintiff's work plus similarities that are probative of copying. Unlawful appropriation (substantial similarity of protectable expression) is judged by the response of the ordinary lay listener, not by expert musical analysis. Expert testimony may assist on the copying inquiry but is generally improper on the unlawful appropriation inquiry. Issues of credibility and the lay listener's reaction are for the jury; where a reasonable jury could find access and unlawful appropriation from the evidence, judgment as a matter of law is inappropriate.
Yes. The Second Circuit reversed the judgment for the defendant and remanded for trial, holding that Arnstein's evidence—viewed favorably to him—was sufficient to require submission to a jury on both copying and unlawful appropriation under the ordinary lay listener standard.
Arnstein v. Porter is a bedrock case in copyright law for three reasons: (1) it establishes the two-step framework distinguishing copying from unlawful appropriation; (2) it cements the ordinary lay listener (ordinary observer) standard for unlawful appropriation, reserving that evaluation to the jury; and (3) it limits summary judgment or directed verdicts in infringement cases where credibility and lay reaction are central. Modern courts continue to cite Arnstein when parsing the difference between probative similarity (to prove copying) and substantial similarity (to prove unlawful appropriation of protectable expression), and when determining the appropriate role of expert testimony.