For copying to be actionable, it must amount to an improper appropriation of the plaintiff’s work. To prove improper appropriation, the plaintiff must show that the defendant’s work is substantially similar to the original, copyrightable expression in the plaintiff’s work. Unlike the inquiry into factual copying, any similarities found between the defendant’s work and the unoriginal or non-copyrightable elements of the plaintiff’s work are disregarded in the improper appropriation calculus.
The traditional test for substantial similarity requires a subjective, factual analysis called the “audience test.” Its goal is to determine whether an ordinary observer, “unless he set out to detect the disparities [between the works], would be disposed to overlook them, and regard their aesthetic appeal as the same.” The test exists in several incarnations and is also called the “ordinary observer test.” Another routinely cited statement of the audience test, originally articulated in the context of music, is “whether defendant took from plaintiff’s works so much of what is pleasing to the ears of lay listeners, who comprise the audience for whom such popular music is composed, that defendant wrongfully appropriated something which belongs to the plaintiff.” The audience test, therefore, essentially asks whether the defendant wrongly copied enough of the plaintiff’s protected expression to cause a reasonable lay observer to immediately detect the similarities between the plaintiff’s expression and the defendant’s work, without any aid or suggestion from others.
The audience test can be a confusing topic because it has been modified countless times by courts across the circuits in order to address the facts of individual cases. According to some scholars, the audience test does not traditionally require dissection and filtration of the plaintiff’s work to separate out non-copyrightable subject matter. Most modern courts, however, at least implicitly, do perform this task. Typically, only after such dissection and filtration occurs, do courts ask if the ordinary observer would find substantial similarities between the plaintiff’s remaining protected expression and the defendant’s work. Although there is case law to the contrary, scholars generally agree that this is the correct approach. Without applying such dissection and filtration, a court could still find improper appropriation where the “total concept and feel” of the works remains substantially the same, even if the defendant has only copied the unprotected elements of the plaintiff’s work. These scholars contend that the plaintiff should not enjoy the copyright monopoly over the unprotected elements of his or her work regardless of whether the overall look and feel of the defendant’s work is perceived as the same by an ordinary observer.
The inherent subjectivity of the audience test typically allows the fact finder to substitute his or her own observations of the work for those of the ordinary observer. However, when the work at issue is directed at a specific type of audience, such as children for example, this substitution is improper, and the fact finder must consider only the intended audience’s reaction when applying the test.
The lack of uniformity in precisely how the circuits apply the legal standards for copyright infringement, especially the audience test, suggests that copyright holders should exercise caution when deciding whether to allege or defend infringement actions. First, circuit precedent of the chosen court should be examined to see how these standards may have been modified in that jurisdiction. Second, factually similar cases should be analyzed because the application of infringement standards can vary depending on the type of work at issue. Both of these important variables can alter the standards for copyright infringement as articulated above and in Part I of this article.
 See Peter Pan Fabrics, Inc. v. Martin Weiner Corp., 274 F.2d 487, 489 (2d Cir. 1960).
 Arnstein v. Porter, 154 F.2d 464, 473 (2d Cir. 1946).
 See 4 Melville B. Nimmer & David Nimmer, Nimmer on Copyright § 13.03[E] (2011).
 Compare Nimmer, supra note 3, § 13.03[E] (criticizing the audience test as having always been improperly applied to works as a whole without first dissecting and filtering them) with 2 Paul Goldstein, Goldstein on Copyright § 9.3.1 (3d ed. 2011) (characterizing the audience test as traditionally only analyzing those protected elements of the plaintiff’s work left following dissection and filtration of all unoriginal and non-copyrightable subject matter from the work).
 See Goldstein, supra note 4, § 9.3.1; Joshua M. Dalton and Sara Cable, The Copyright Defendant’s Guide to Disproving Substantial Similarity on Summary Judgment, Landslide, July/August 2011, at 26-29.
 See Goldstein, supra note 4, § 9.3.1; Nimmer, supra note 3, § 13.03[E].