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Substantial Similarity

Illustrates the "substantial similarity" doctrine from U.S. copyright law, using a set of case summaries.


Copyrightable works are original works of authorship fixed in any tangible medium of expression.

Extrinsic-Intrinsic Test

The extrinsic-intrinsic test is a two-part test for substantial similarity used in the Ninth Circuit. It was laid out in Sid & Marty Krofft Television Productions, Inc. v. McDonald’s Corp. The first part of the test considers “extrinsic” similarity. For that part of the test, the Krofft court analyzed the similarities in the ideas of the works. However, the Ninth Circuit subsequently updated the test, and now the extrinsic test focuses on the objective similarities of the works’ ideas and protectable expressions. For this extrinsic part of the analysis, expert testimony may be taken into consideration. The second part of the test considers “intrinsic” similarity. The factfinder undertakes a purely subjective evaluation of the total concept and feel of the two works. Expert testimony is not allowed on this issue. Some other circuits have adopted the extrinsic-intrinsic test, albeit with their own variations. Some circuits adopted the Ninth Circuit’s nomenclature but gave the extrinsic-intrinsic test very different meanings.

Idea/Expression Dichotomy

The idea/expression dichotomy is the principle that copyright protects the original expression of ideas but does not protect the ideas themselves. For example, the idea of creating fashionable dolls with exaggerated features is not protected by copyright law. Only the original expressions of a designer’s idea are protected, such as the designer’s unique choice of hair color and style, clothing, or accessories for the dolls.

Inverse Ratio Rule

The inverse ratio rule says that when the showing that defendant had access to plaintiff’s work is very strong, the bar for showing similarity between the works is correspondingly lower. In addition, when the showing similarity between the works is very strong, the bar for showing that defendant had access to plaintiff’s work is correspondingly lower. Not all circuits follow this rule. For instance, the Second Circuit has rejected it. The Ninth Circuit does follow the inverse ratio rule. It is a part of the extrinsic analysis in the extrinsic-intrinsic test.

Judgment as a Matter of Law

Judgment as a matter of law (JMOL) is available to a party if no reasonable jury could find otherwise. A party can move for judgment as a matter of law after the opposing party has presented its case to the court. Even though the timing of the motion is different, the legal standard for judging substantial similarity in JMOL is similar to that applied in summary judgment.


Merger is the principle that when there are only a few possible ways to express an idea, those expressions are not protectable. They “merge” with the unprotectable idea. This means that individual words, single colors and short phrases are not protected by copyright. More complex expressions that are very conventional or factual may also be unprotectable. For example, consider the following sentence: Marie Curie was born on November 7, 1867. This sentence is one of the only ways of expressing this information in English. Thus, it is likely uncopyrightable due to the merger doctrine. More complex expressions are also unprotectable if the expressions are dictated by efficiency concerns.

More Discerning Observer Test

The “more discerning observer” test is used to assess substantial similarity when the plaintiff’s work has both protectable and unprotectable elements. The factfinder must first weed out the unprotectable elements before assessing the similarity of the defendant’s work to the protectable elements as a whole. The test is used in the Second Circuit.

Ordinary Observer Test

The “ordinary observer” test is used to assess substantial similarity when the plaintiff’s work is completely original. The test asks if an average lay observer would be predisposed to overlook the differences between the works and consider the overall aesthetics of the works the same. If the plaintiff’s work has both protectable and unprotectable elements, then the “more discerning observer test” is applied instead. The test is used in several circuits, including the First Circuit, the Second Circuit, the Third Circuit, and the Fifth Circuit.

Public Domain

Works that are not subject to copyright are in the public domain. They may be used without permission.

Scènes à Faire

The scènes à faire doctrine says that when an element of a work is customary in a particular genre, it is not protectable. For example, although some plot elements can be protected by copyright, parents’ disapproval of their children’s romantic choices is a very common plot element and thus is not protectable. Similarly, although the composition of a photograph can be protected by copyright, certain compositions are so conventional that they cannot be protected by copyright. For example, while you would obtain a copyright if you photographed someone’s face straight on and framed it in the middle of the shot, your copyright would not allow you to prevent someone else from composing a photograph the same way. In addition, the scènes à faire doctrine denies protection to expressions dictated by external factors such as industry norms and consumer demands.

Substantial Similarity

Substantial similarity is a level of similarity that shows improper appropriation of the plaintiff’s work, one of the requirements for a prima facie infringement claim. If the similarity of the defendant’s work to protectable elements in the plaintiff’s work is minimal, or if similarity only exists with regard to unprotectable elements of the work, then there is no substantial similarity.

Summary Judgment

Summary judgment is available to a party if there are no disputed issues of material fact and the party is entitled to judgment as a matter of law. Motions for summary judgment are made before trial. When ruling on summary judgment motions, the court does not adjudicate issues of fact. It focuses instead on whether or not there are disputes about material facts that would need to be resolved at trial. The moving party has the burden to show there is no dispute about material fact. The court interprets evidence in favor of the nonmoving party. 

The circuits differ in the standard they apply for granting summary judgment on substantial similarity. The Second Circuit rules on substantial similarity as a matter of law at summary judgment if (1) the similarities between the two works are limited to unprotectable elements, or (2) the evidence is so clear that a reasonable jury could only reach one conclusion. This is not the case in every circuit. The Ninth Circuit always reserves the issue of intrinsic similarity for the jury, if the plaintiff can prove the works are extrinsically similar.

“Total Concept and Overall Feel” Test

The “total concept and overall feel” test is a test of substantial similarity. Under this test, the court compares the defendant’s work and the plaintiff’s work for similarities in their non-literal elements, such as the original selection, coordination and arrangement of expressions. The test is intended to prevent courts from mechanically dissecting the works and comparing only the separately copyrightable elements.