Nautilus, Inc. v. Biosig Instruments, Inc.: Supreme Court Strikes Down the Insolubly Ambiguous Definiteness Standard in Favor of a Reasonable Certainty Standard

7 min

On June 2, 2014, a unanimous United States Supreme Court held that the Federal Circuit’s test for determining whether patent claims meet the definiteness requirement of 35 U.S.C. § 112, ¶ 2, did not satisfy the statute’s definiteness requirement. Prior to the Court’s ruling, the Federal Circuit held that in order to satisfy the definiteness requirement, a patent owner need only show that a challenged claim is “amenable to construction,” and not “insolubly ambiguous.” The new standard announced by the Court requires that the claims of a patent, when read in light of the patent’s specification and the prosecution history, inform with reasonable certainty those skilled in the art about the scope of the invention. Nautilus, Inc. v. Biosig Instruments, Inc., No. 13-369 (June 2, 2014).


Biosig owns U.S. Patent No. 5,337,753 (“the ’753 patent”), which is directed to improved grip-activated heart rate monitors typically associated with exercise equipment. Biosig initially brought a patent infringement suit against Nautilus in the U.S. District Court for the Southern District of New York in 2004, alleging that Nautilus manufactured and sold exercise equipment that included the patented heart monitor device covered by the product claims of the ’753 patent. While that litigation was pending, the U.S. Patent and Trademark Office (“USPTO”) granted Nautilus’ request for ex parte reexamination of the ’753 patent, and the parties thereafter agreed to voluntarily dismiss the suit without prejudice, allowing Biosig to refile if the reexamination proceedings were resolved in Biosig’s favor.

The patentability of the ’753 patent was confirmed during reexamination without any required claim amendments, primarily due to Biosig’s arguments that the asserted prior art references did not disclose the claimed spacing of the electrodes and resulting elimination of electromyogram (EMG) signals. Biosig thereafter reinstituted an infringement action against Nautilus in 2010.

During claim construction proceedings, Biosig successfully convinced the district court that the claim term “spaced relationship” – which describes the spacing of two sets of electrodes on the heart rate monitor bar that, when gripped by a user, are used to read a user’s heart rate – should not be limited to particular distances, and that arguments made during reexamination of the patent did not constitute a disclaimer of claim scope. The district court subsequently construed the term as “a defined relationship between the live electrode and the common electrode on one side of the cylindrical bar and the same or a different defined relationship between the live electrode and the common electrode on the other side of the cylindrical bar.” After the claim construction order issued, Nautilus moved for summary Page 1 of 3 6/2/2014 judgment that the ’753 patent was invalid on the grounds that “spaced relationship” rendered the claims indefinite under 35 U.S.C. § 112, ¶ 2. Following a hearing, the district court granted the motion, noting that “a spaced relationship did not tell me or anyone what precisely the space should be …. Not even any parameters as to what the space should be …. Nor whether the spaced relationship on the left side should be the same as the spaced relationship on the right side.” Biosig Instruments, Inc. v. Nautilus, Inc., No. 1:04-cv-06654, Dkt. No. 75 at 23 (S.D.N.Y. Mar. 1, 2012).

Biosig’s motion for reconsideration of the district court opinion was denied, and it subsequently filed an appeal to the Federal Circuit. Writing for the court, Judge Wallach held that the claims were not invalid for indefiniteness, reversed the district court decision, and remanded for further proceedings. In doing so, the court applied the standard set forth in Datamize, LLC v. Plumtree Software, Inc., 417 F.3d 1342, 1347 (Fed. Cir. 2005), which states that a claim is indefinite only when it is “not amenable to construction” or “insolubly ambiguous.” See Biosig Instruments, Inc. v. Nautilus, Inc., 715 F.3d 891, 898 (Fed. Cir. 2013). The court further noted that, so long as a meaning of the claim is discernible, the claim will be found sufficiently definite, even if the task of discerning the meaning is “formidable” and “the conclusion may be one over which reasonable persons will disagree.” Id. at 901-02. The court found this standard to comport with the statutory presumption of patent validity that all issued patents enjoy, as set forth in 35 U.S.C. § 282. Id. at 902. Turning to the claim term at issue, the court stated that because the district court was able to construe “spaced relationship,” a finding of indefiniteness would require a showing that a person of ordinary skill would find that term insolubly ambiguous. This was not the case with the ’753 patent because it was found to disclose “certain inherent parameters of the claimed apparatus, which to a skilled artisan may be sufficient to understand the metes and bounds of ‘spaced relationship.’” Id. at 899. In addition, the court held that functional language found later in the claim in which the term “spaced relationship” appears describes how the spaced relationship “contributes to the removal of noise signals,” and thus can be used to discern the meaning of the claim. Id. at 904. Judge Schall filed a concurring opinion in which he agreed that the claim term was sufficiently definite, but stated that he would have limited the court’s analysis to just the “spaced relationship” element, without referring to the functional language contained in the remainder of claim 1. Id. at 905-06.

On January 10, 2014, the Supreme Court granted Nautilus’ petition for a writ of certiorari, which presented the following questions: “Does the Federal Circuit’s acceptance of ambiguous patent claims with multiple reasonable interpretations—so long as the ambiguity is not ‘insoluble’ by a court—defeat the statutory requirement of particular and distinct patent claiming?” and “Does the presumption of validity dilute the requirement of particular and distinct patent claiming?” Oral argument was heard on April 28, 2014, and the Court issued its opinion on June 2, 2014.

The Court’s Opinion

The Supreme Court held that the Federal Circuit’s standard for claim definiteness, which required only that a claim be “amenable to construction” and not “insolubly ambiguous,” failed to satisfy the requirements for claim definiteness set forth in 35 U.S.C. § 112, ¶ 2.

The Court first noted that claim definiteness must be evaluated from the perspective of a person skilled in the relevant art at the time the patent was filed, and that the claims must be read in light of the patent’s specification and prosecution history. The Court also noted the “delicate balance” between the “modicum of uncertainty” that is inherent in written language, and the need to Page 2 of 3 6/2/2014 avoid providing incentive for patent applicants to “inject ambiguity” into claims. The Court held that a proper balance is found where a patent’s claims, viewed in light of the specification and prosecution history, inform those skilled in the art about the scope of the invention with reasonable certainty.

The Court next addressed the Federal Circuit’s “insolubly ambiguous” standard for determining claim definiteness. The Court found that the “amenable to construction” or “insolubly ambiguous” language lacks precision and has the potential to breed confusion in the lower courts. Further, the Court stated that tolerating imprecision in claim language that falls just short of “insolubly ambiguous” would diminish the public-notice function of the definiteness requirement, and foster a “zone of uncertainty” as to the scope of the claims.

In a footnote to the opinion, the Court noted that the presumption of validity does not alter the degree of clarity that § 112, ¶ 2 demands from patent applicants, which neither party disputed. However, the Court declined to address whether factual findings subsidiary to the ultimate issue of definiteness fall within the clearand-convincing standard, and whether findings of fact by the USPTO should be accorded any deference in the inquiry.

With respect to the claims of the ’753 patent, the Court did not express an opinion as to the definiteness of the challenged claims, and instead remanded the case so that the Federal Circuit may reconsider, under the proper standard, whether the relevant claims are sufficiently definite.