There is one case on the U.S. Supreme Court’s patent heavy docket this term that has the potential to impact every issued patent. That case is Nautilus v. Biosig Instruments.1 Nautilus has the potential for such broad impact because it addresses how precise patentees must be in defining their invention; in patent parlance, the issue is called indefiniteness. Two compelling and competing ideals underlie the debate.

On one side is the inventor trying to describe in words an invention that, by definition, has never existed before. This already difficult task is somewhat at odds with absolute precision because an overly precise patent might superficially restrict the scope of the inventor’s patent. For example, if the inventor built a machine where two components were 2 inches apart, a patent drafter would be loath to limit the patent to claiming that these components were exactly 2 inches apart. After all, a competitor might be able to use the inventor’s idea by simply making those components 2.25 inches apart. Thus, skilled patent drafters typically avoid drafting claims—the portion of the patent that lays out the metes and bounds of protection—with overly precise language. This practice is largely sanctioned by the patent law, which has long recognized that unduly narrow patents do not provide adequate rights to incentivize inventors to disclose their discoveries.

On the other side is the public. A patentee receives a limited monopoly from the government that allows her to exclude all others from practicing the invention. In return, the issued patent informs the public of the inventor’s technical achievements thereby promoting science and the useful arts. But there is a strong policy interest in not allowing patentees to extend their monopoly beyond what is fairly due. The claims of a patent are intended to provide notice to the public of the boundaries of the exclusionary right, much like a deed to land. Vague claims, however, create a zone of uncertainty over the boundaries of the patentee’s monopoly to the detriment of the public. Thus, when “clever” patent drafters write vague and malleable patents, they frustrate the patent bargain. This problem is twofold. An ambiguous patent fails to adequately teach the inventor’s new discovery to the public and it also discourages investment in competing technology due to uncertainty in the scope of the patent.

Nautilus, the petitioner, contends that the Federal Circuit has set the balance between these ideals too far in favor of patentees and created an unacceptable zone of uncertainty around the scope of each patent. Nautilus asks the Supreme Court to require more precision from patentees and make it easier for defendants to prove indefiniteness.

History of the Case

The dispute between the parties involves heart rate monitors for treadmills and other exercise equipment. These heart rate monitors use sensors located in the equipment’s handles to read the user’s pulse while exercising. A problem with these types of sensors is that, in addition to detecting the desired heart signals, they also detect unwanted impulses generated by a person’s muscles that interfere with the heart rate measurement. Biosig’s invention is a device that employs sensors under both of the user’s hands. Because of the nature of the signals involved, combining the signal from the user’s two hands subtracts out the muscle signal and amplifies the heart signal.

After Biosig sued Nautilus for infringement, Nautilus asked the Patent Office to reexamine Biosig’s patent in view of a prior art heart rate monitor that was very similar to Biosig’s patent. In the reexamination proceeding, Biosig distinguished its invention over the earlier heart rate monitor because, according to Biosig, the sensors in its invention were spaced in a particular way that resulted in the muscle signals from the left and right hands being substantially equal. The prior art reference cited by Nautilus had left and right handed sensors and combined their signals to remove the muscle signal, but it did not specifically state that the signals generated by its left and right sensors were substantially equal.

The problem for Biosig was that its patent did not clearly describe the importance of sensor spacing to the generation of equal muscle signals. To fill this gap, Biosig submitted a declaration of the inventor explaining this fact to the Patent Office during reexamination. In view of the declaration, the Patent Office reconfirmed the patentability of Biosig’s invention.

When the case returned to litigation the district court set to the task of construing the “spaced relationship” limitation that Biosig relied on to distinguish its patent over the prior art. The court construed the limitation twice. Biosig objected to the court’s first tentative construction and convinced the court to adopt a broader construction. Nautilus moved for summary judgment that this broader construction was indefinite. When the court tried to evaluate the definiteness of the “spaced relationship” limitation, the court concluded that the arguments made by Biosig to the Patent Office were internally inconsistent and “gibberish.” Because the court could not discern any parameters for what the “spaced relationship” should be, it found the claim indefinite.

Biosig appealed to the Federal Circuit, which reversed the district court and held that the term “spaced relationship” was not indefinite.2 Applying its “insolubly ambiguous” standard for indefiniteness, the Federal Circuit found that the claim provided “inherent parameters” and functional requirements that defined the scope of the claim. The Federal Circuit also relied on the inventor’s declaration, which stated that a person of skill in the art could perform conventional testing to determine the spacing needed to satisfy the functional requirements. The concurrence, however, found that the term “space relationship” was definite on its own, without the functional limitation.

The Supreme Court granted certiorari on the following questions: (1) Whether the Federal Circuit’s acceptance of ambiguous patent claims with multiple reasonable interpretations—so long as the ambiguity is not “insoluble” by a court—defeats the statutory requirement of particular and distinct patent claiming; and (2) whether the presumption of validity dilutes the requirement of particular and distinct patent claiming.

Supreme Court Review

On appeal, Nautilus argues that the insolubly ambiguous standard is an unjustified departure from the statutory standard for claim precision, which requires that claims “particularly point[ ] out and distinctly claim[ ] the subject matter which the inventor … regards as the invention.”3

According to Nautilus, the Federal Circuit’s test permits too much uncertainty and encourages courts to rescue vague patents by picking a construction even when the decision is arbitrary and unpredictable. For example, under Federal Circuit case law, a patent is sufficiently definite “[i]f the meaning of the claim is discernable, even though the task may be formidable and the conclusion may be one over which reasonable persons will disagree.”4

Nautilus contends that its case epitomizes the problem with the Federal Circuit’s test. The jurists reviewing Biosig’s patent offered at least four different constructions of the claim at issue. The district judge construed the claim and then later reversed himself providing a second construction. The Federal Circuit majority offered a third construction, and the concurring Federal Circuit judge offered a fourth. To Nautilus, the fact that the Federal Circuit found this patent sufficiently clear despite the disparity of views by the judges whose job it was to construe the patent is proof positive that the Federal Circuit’s test is too lenient. Nautilus quotes Federal Circuit Judge S. Jay Plager’s comment from an earlier indefiniteness case to emphasize the extent of ambiguity currently permitted: “It is not until three court of appeals judges randomly selected for that purpose pick the ‘right’ interpretation that the public, not to mention the patentee and its competitors, know what the patent actually claims.”5

Nautilus continues that patentees, with little risk of a court finding patents indefinite, are encouraged to claim vaguely because it significantly increases the burden on a competitor of interpreting and defending against an infringement claim. Moreover, vagueness provides opportunities for a patentee to adapt the scope of its claim during litigation to read on a particular product or avoid prior art.

Thus, Nautilus asserts that the insolubly ambiguous standard violates the statutory requirement of particular and distinct claiming and frustrates the public notice function of patent claims. In the view of Nautilus and its amici, inventors are in the best position to avoid this socially undesirable outcome because they know best what they actually invented. The law should therefore incentivize inventors to be crystal clear in their claiming, and the Federal Circuit’s high bar for indefiniteness should be rejected.

Perhaps surprisingly, Biosig and its amici do not make much effort to defend the “insolubly ambiguous” standard. Instead, Biosig, the government, and some other amici argue that “insolubly ambiguous” is not really the test the Federal Circuit applies when determining indefiniteness. Rather, “insolubly ambiguous” is just shorthand for the actual test which finds a claim indefinite when “reasonable efforts at claim construction result in a definition that does not provide sufficient particularity and clarity to inform skilled artisans of the bounds of the claim.”6

The American Intellectual Property Law Association (AIPLA), writing as amici, concurs that the Federal Circuit’s “insolubly ambiguous” standard is merely a shorthand phrase for the actual analysis applied. But the AIPLA goes further than Biosig and acknowledges that the use of the shorthand language has a tendency to mislead and should be rejected for that reason.

While the “insolubly ambiguous” standard, be it in fact or in name, has few defending it, Nautilus’ proposed alternative test for indefiniteness also faces strong opposition. Nautilus asserts that a patent claim is indefinite if it is “susceptible to more than one reasonable interpretation.” This test follows directly from Nautilus’ arguments about the important notice function of patents. After all, if there are two reasonable constructions, how will the public know which interpretation is correct?

As Biosig and other amici point out, however, Nautilus’ test goes too far. If a patent claim could be invalidated by reasonable disagreement over the claim’s meaning, then very few valid patents would exist. Nearly every patent case has some issue of claim construction that involves a court choosing among possible claim interpretations. But Nautilus’ test essentially says if a claim needs to be construed, then it is invalid for indefiniteness. Contrary to Nautilus’ test, the Supreme Court has long held that “in a case of doubt, where the claim is fairly susceptible of two constructions, that one will be adopted which will preserve to the patentee his actual invention.”7 Thus, the mere fact that a patent requires some interpretation cannot lead to an invalid claim. Nautilus is essentially asking the court to tear down the patent system and start over, an unlikely outcome.

With regard to the Supreme Court’s second question presented, Nautilus argues that indefiniteness should not be determined in view of the statutory presumption of validity. The presumption of validity is an evidentiary burden premised on the assumption that the Patent Office has correctly applied its expertise in allowing valid patents. In Nautilus’ view, however, this evidentiary burden should not impact the legal question of whether a patent complies with the statutory requirements of particular and distinct claiming. Courts must construe claims to provide a definition as a matter of law. In making that determination, courts should not be encouraged to permit legally ambiguous claims merely to preserve their validity.

While all admit that the ultimate determination of indefiniteness is a question of law, Biosig responds that one has to evaluate substantial underlying factual questions to determine indefiniteness. Specifically, the determination is based on how a person skilled in the art at the time of the invention would interpret the claim in view of the knowledge in the art at that time. Thus, in Biosig’s view, these underlying factual issues warrant the presumption of validity.

Turning to what the Supreme Court is likely to do, neither the Federal Circuit’s insoluble ambiguity test nor the petitioner’s two reasonable construction test appears viable. But the Supreme Court has typically been reluctant to formulate interpretive tests in patent law. Instead, the court will likely issue a “guidepost” opinion that relies on the statutory language, past precedent, and broad principles to reorient the law as it has done in recent cases on patent eligible subject matter, i.e., Bilski v. Kappos and Mayo v. Prometheus.8 In ruling, the court may use the presumption of validity issue to more significantly change the balance between inventors and the public. A holding that courts should not use the presumption of validity to justify picking an ambiguous construction would significantly alter indefiniteness law and patent practice as a whole.

Practice Tips

Irrespective of what the Supreme Court decides, patent attorneys can start preparing for the decision now.

Litigants involved in pending patent litigation may want to begin reevaluating indefiniteness issues in light of the impending change in the law. The high standard to show indefiniteness under current Federal Circuit law has typically made this issue a lower priority for defendants. If the Supreme Court signals that the indefiniteness standards should be loosened, defendants will likely push these issues more strenuously without fear that the courts will simply rescue vague patents.

Patentees should hedge the issue by including some more precisely drafted claims in their patent applications. Importantly, however, patentees must ensure that their patent specification is detailed enough to support these more precisely drafted claims. Nevertheless, patentees should still draft other claims that provide more flexibility. With a mix of claims, patentees can be assured to have at least some definite claims no matter what the law is after Nautilus. Finally, should the Supreme Court significantly lower the burden to show indefiniteness, patentees should evaluate their existing patent portfolio to consider whether any patents should be submitted to the PTO for reexamination or reissue to draft more precise claims.

Richard F. Martinelli is a partner and Nicholas H. Lam is an associate at Orrick, Herrington & Sutcliffe in New York.


1. Case No. 13-369.

2. Biosig Instruments v. Nautilus, 715 F.3d 891 (Fed. Cir. 2013).

3. 35 U.S.C. §112(b).

4. Biosig, 715 F.3d at 901-02.

5. Enzo Biochem v. Applera, 605 F.3d 1347, 1348 (Fed. Cir. 2010) (Plager, J., dissenting from denial of petition for rehearing on indefiniteness).

6. Citing Biosig, 715 F.3d at 898.

7. McClain v. Ortmayer, 141 U.S. 419, 425 (1891).

8. Bilski v. Kappos, 130 S. Ct. 3218 (2010); Mayo v. Prometheus, 132 S. Ct. 1289 (2012).