by Dennis Crouch
The Supreme Court recently received a petition for certiorari from NexStep, Inc., challenging a Federal Circuit decision that epitomizes a four-decades-long trend of restricting the doctrine of equivalents (DOE). The petition in NexStep, Inc. v. Comcast Cable Communications, LLC (No. 24-1137), presents a fundamental question: Has the Federal Circuit improperly shackled the doctrine of equivalents with rigid, formulaic requirements contrary to Supreme Court precedent? More particularly, the petition asks: “Whether a patentee must in every case present ‘particularized testimony and linking argument’ to establish infringement under the doctrine of equivalents.”
- Dennis Crouch, Doctrine of Equivalents: Expert Testimony Must Include Particularized Links, Patently-O (Oct. 22, 2024) (discussion of the original CAFC decision).
The case also has a nice baseball analogy. The patent requires a “single action” performed by a user, and the accused device needs three button pushes. The patentee’s expert, when presenting the DOE case to the jury, used a baseball pitcher analogy – recognizing that throwing a ball includes numerous small steps to accomplish the single action of throwing. The argument here, which the jury agreed was meritorious, is that the three button pushes – while not literally the same as a single action – was the equivalent and thus infringing. The Federal Circuit wanted more – holding that the jury did not have enough evidence to reach that conclusion.
DOE Under Siege: The doctrine of equivalents has long served as a safeguard in patent law, protecting inventors from those who make insubstantial changes to avoid literal infringement. As the Supreme Court explained in Graver Tank & Mfg. Co. v. Linde Air Prods. Co., “to permit imitation of a patented invention which does not copy every literal detail would be to convert the protection of the patent grant into a hollow and useless thing.” 339 U.S. 605, 607 (1950). Despite the doctrine’s importance, its practical application has been steadily eroded by the Federal Circuit. NexStep’s petition represents perhaps the clearest opportunity in decades for the Supreme Court to restore the doctrine’s intended flexibility and to realign Federal Circuit jurisprudence with Supreme Court precedent.
The NexStep Case: A Study in Simplicity: At its core, NexStep involves a straightforward comparison. NexStep’s patent covers a “concierge device” that initiates technical support for household devices that are responsive to “a single action performed by a user.” The accused Comcast smartphone application allows requires a short sequence of button presses to achieve the result.
The jury was asked to decide whether Comcast’s sequence of two or three button presses was equivalent to the patented “single action.” After hearing testimony from NexStep’s expert, Dr. Selker, who explained that several button presses perform the same function in the same way to achieve the same result as a single action—much like throwing a baseball is considered a single action despite requiring multiple steps—the jury found infringement under the doctrine of equivalents.
However, both the district court and a divided Federal Circuit panel set aside the verdict. The majority held that Dr. Selker’s testimony failed to provide “particularized testimony and linking argument” explaining why the button presses were equivalent to a single action. This was despite Dr. Selker’s explanation that both achieved the same purpose of initiating the troubleshooting process without requiring the user to undertake significant additional steps. NexStep then sought rehearing en banc, but the full Federal Circuit declined that petition in January 2025.
The Federal Circuit’s Rigid Formula: The issue in NexStep extends beyond a single case. It represents the culmination of a decades-long trend in which the Federal Circuit has transformed the doctrine of equivalents from a flexible inquiry into a rigid one requiring stylized expert testimony in every case. This requirement for “particularized testimony and linking argument” has its roots in Federal Circuit decisions like Lear Siegler, Inc. v. Sealy Mattress Co. of Mich., Inc., 873 F.2d 1422 (Fed. Cir. 1989), and Texas Instruments Inc. v. Cypress Semiconductor Corp., 90 F.3d 1558 (Fed. Cir. 1996). Over time, the court expanded this requirement to effectively mandate that patentees provide expert testimony applying a specific formula in all cases.
As Judge Reyna noted in his NexStep dissent, the majority “concocts a rigid new rule that in all cases a patentee must present expert opinion testimony to prove infringement under the doctrine of equivalents.” The majority confirmed this rigidity, stating: “[O]ur precedent requires particularized testimony and linking argument, regardless of the complexity or the simplicity of the underlying technology.”
The Supreme Court’s Historical Commitment to Flexibility in Patent Law: The Supreme Court’s rejection of rigid formulations in patent law reflects a consistent doctrinal approach spanning more than 170 years. This commitment to flexibility—particularly in the doctrine of equivalents—has repeatedly emphasized substance over form and case-specific analysis over bright-line rules.
In Winans v. Denmead, 56 U.S. 330 (1853), the Court established that courts and juries must “look through the form for the substance of the invention.” Addressing a patent for a conical frustum-shaped railroad coal car, the Court held that an accused car with a different shape could still infringe if it embodied the same principle and achieved the same result. Justice Curtis warned that “the property of inventors would be valueless, if it were enough for the defendant to say, ‘your improvement consisted in a change of form; I have not taken that, and so have not infringed.'” Winans. This principle was reinforced in Union Paper-Bag Machine Co. v. Murphy, 97 U.S. 120 (1877), where the Court articulated the classic function-way-result test. The Court declared that two devices that “perform the same function in substantially the same way, and accomplish substantially the same result” are legally equivalent, “though they may differ in name or form.” Id. Significantly, the Court established that a “substantial equivalent of a thing is the same as the thing itself”—emphasizing the contextual, case-specific nature of equivalence and rejecting the notion that any rigid formula could be applied across all cases.
In Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605 (1950), the Court gave modern shape to the doctrine of equivalents, holding that “one may not practice a fraud on a patent” by making only insubstantial changes. The Court’s language was unequivocal about the doctrine’s flexible nature, declaring that equivalence is “not the prisoner of a formula” and that proof “can be made in any form: through testimony of experts or others versed in the technology; by documents, including texts and treatises; and, of course, by the disclosures of the prior art.” This explicit rejection of formulaic approaches underscores the Court’s commitment to preserving the doctrine’s adaptability across diverse technological contexts.
When the Court revisited the doctrine nearly five decades later in Warner-Jenkinson Co. v. Hilton Davis Chemical Co., 520 U.S. 17 (1997), it reaffirmed this flexible approach while establishing certain guardrails to prevent the doctrine from eliminating claim elements entirely. While requiring element-by-element analysis, the Court explicitly noted that “the particular linguistic framework used is less important than whether the test is probative of the essential inquiry”—i.e., substantive analysis is prioritized over rigid formulation. The Court characterized infringement under the doctrine as “a question of fact” for the jury, subject to certain legal limitations, but did not prescribe any specific evidentiary formula for proving equivalence. This right to a jury is protected under the Seventh Amendment of the U.S. Constitution.
Most recently in Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722 (2002), the Court unanimously overturned the Federal Circuit’s absolute bar on asserting the doctrine of equivalents after narrowing claim amendments. The Court emphasized that the “doctrine of equivalents is necessary to ensure that imitators cannot end-run patent protection by making insubstantial changes” to claimed inventions. Id. While again acknowledging the need for boundaries, the Court adopted a flexible, rebuttable presumption approach to prosecution history estoppel rather than an absolute rule that would have excessively “cabined” the doctrine’s application.
This historical trajectory demonstrates a longstanding commitment to flexibility in patent law—particularly regarding the doctrine of equivalents. The Court has consistently:
- Emphasized the importance of protecting the substance of inventions over rigid adherence to form
- Rejected bright-line rules that would undermine the equitable nature of patent protection
- Favored case-specific, factual determinations over formulaic approaches
- Preserved the role of juries in determining factual questions of equivalence
- Maintained that while there must be limits to the doctrine, those limits should not be so rigid as to defeat the doctrine’s essential purpose
The Supreme Court’s rejection of the Federal Circuit’s rigid tests in cases like KSR International Co. v. Teleflex Inc., 550 U.S. 398 (2007), Octane Fitness, LLC v. ICON Health & Fitness, Inc., 572 U.S. 545 (2014), and Halo Electronics, Inc. v. Pulse Electronics, Inc., 579 U.S. 93 (2016), is thus not merely a recent trend, but a continuation of a doctrinal approach dating back to the nineteenth century—one that consistently prioritizes flexible, case-specific analysis over rigid formulations.
The Problem of Vitiation: Although vitiation is not at issue in NexStep, it is still a bug in my bonnet. This judicially created concept prevents a patentee from using the doctrine of equivalents to completely eliminate a claim limitation by finding its opposite to be an equivalent. The vitiation concept emerged as a rhetorical tool but has evolved into a de facto legal limitation. While courts initially described it as an application of the all-elements rule—that equivalence must be shown for each limitation of a claim, not the invention as a whole—vitiation has taken on a life of its own.
Courts frequently use vitiation to preclude DOE application — taking it from the jury — when the accused product contains the “opposite” of a claimed feature. For example, in Moore U.S.A., Inc. v. Standard Register Co., the Federal Circuit held that a “majority” could not be equivalent to a “minority” without vitiating the claim limitation. 229 F.3d 1091 (Fed. Cir. 2000).
The difficulty here is that DOE already allows for infringement when aspects literally claimed in the patent are not found in the accused device. Vitiation then invites judges to make subjective determinations about whether finding equivalence would “entirely vitiate” a claim element—often without clear standards for what constitutes “vitiation” versus permissible equivalence. This has created a “vitiation escape hatch” that defendants can use to avoid DOE infringement as a matter of law, further eroding the doctrine’s effectiveness. What began as a shorthand explanation for the all-elements rule (articulated in Warner-Jenkinson) has evolved into an independent legal doctrine that short-circuits the factual inquiry at the heart of DOE analysis. This evolution merits closer examination.
A Sensible Approach to Equivalence: A more balanced approach would respect the Supreme Court’s guidance that the doctrine of equivalents should be a flexible, case-specific inquiry. This would include:
- Tailoring the evidence to the technology: For simple technologies and comparisons, courts should not require extensive expert testimony explaining the obvious. As Judge Reyna noted in his NexStep dissent, “the jury did not need expert testimony to answer the technologically-simple question presented here of whether several button presses are equivalent to a ‘single action.'”
- Allowing multiple forms of evidence: Courts should follow Graver Tank‘s instruction that proof of equivalence “can be made in any form,” including documents and non-expert testimony.
- Limiting vitiation to truly antithetical substitutions or eliminate the doctrine altogether as generally accounted for by the element-by-element requirement.
- Respecting the jury’s role: Courts should be reluctant to take this determination away from the jury.
All that brings me to strongly support NexStep petition in this case. It is a simple technological comparison that was given to a jury to decide.