While the question was answered by the Supreme Court in Nautilus, Inc. v. Biosig Instruments, 134 S. Ct. 2120 (2014), the Federal Circuit, in The Dow Chemical Company v. Nova Chemicals Corporation (Canada),(2014-1431, 2014-1462) clarified  how the indefiniteness analysis is carried out, particularly with regard to the use of extrinsic evidence, burden of proof, and standard of review.

In 2010, Dow had enforced U.S. Patents 5,847,053 and 6,111,023 against Nova on an improved plastic stronger than conventional plastics allowing use of thinner films. The plastics were characterized as having a “slope of strain hardening coefficient” greater than or equal to 1.3. Nova defended alleging indefiniteness because the specification failed to say how to measure the “slope of strain hardening coefficient,” a concept not in the prior art.

In 2012, (2010-1526, Fed. Cir. Jan 30, 2012), the Federal Circuit affirmed, finding the claims invalid and not indefinite under the prevailing “insolubly ambiguous” test. The Federal Circuit stated a claim is definite if “one skilled in the art would understand the bounds of the claim when read in light of the specification . . . .” (citing Exxon Research & Eng’g Co. v. United States, 265 F.3d 1371, 1375 (Fed. Cir. 2001)). The Federal Circuit concluded that although the patent specification lacked certain details of how the “slope of strain hardening coefficient” was determined, a person of skill in the art would understand how to determine the value based on the teachings of the specification and the knowledge in the art. The Federal Circuit, again quoting Exxon, stated that “the test for indefiniteness is not whether the scope of the patent claims is easy to determine, but whether ‘the meaning of the claim is discernible, even though the task may be formidable and the conclusion may be one over which reasonable persons will disagree’ . . . .” (Exxon, 265 F.3d at 1375).

During Nova’s appeal of another issue, the Supreme Court decided Nautilus, Inc. v. Biosig Instruments, 134 S. Ct. 2120 (2014) which held “insolubly ambiguous” was “more amorphous” than the law allowed and stated “a patent is invalid for indefiniteness if its claims, read in light of the specification delineating the patent, and the prosecution history, fail to inform, with reasonable certainty, those skilled in the art about the scope of the invention.”

In 2015 the Federal Circuit reanalyzed the claims under Nautilus and found the claims indefinite (Dow Chem. Co. v. Nova Chems. Corp., 803 F.3d 620, 635 (Fed. Cir. 2015)). In this decision, Judge Dyk stated, “there can be no serious question that Nautilus changed the law of indefiniteness.” Nautilus requires the claims “must provide objective boundaries for those of skill in the art” and that “the patent and prosecution history must disclose a single known approach or establish that, where multiple known approaches exist, a person having ordinary skill in the art would know which approach to select.”

The 2015 Dow ruling was the first signal that the Federal Circuit treated Nautilus as redefining the standard for indefiniteness. After remand of Nautilus, Judge Wallach rejected the idea that the Supreme Court had set a stricter standard for indefiniteness. Judge Wallach argued the Court “modified the standard by which lower courts examine allegedly ambiguous claims; we may now steer by the bright star of ‘reasonable certainty,’ rather than the unreliable compass of ‘insoluble ambiguity’.” Biosig v. Nautilus, 783 F.3d 1374, 1379 (Fed. Cir. 2015). Indeed post-Nautilus, the Federal Circuit only found claims invalid for indefiniteness in one or two isolated cases (likely indefinite pre-Nautilus) and continued to rely on pre-Nautilus jurisprudence when evaluating claims for definiteness.

In the present ruling, the Federal Circuit responded to Dow’s petition for rehearing and rehearing en banc of the 2015 ruling. While denying Dow’s petition, the court clarified certain aspects of how the indefiniteness inquiry is applied.

In arguing against rehearing, Nova said the prior Dow decision (2015) held that extrinsic evidence was inadmissible on indefiniteness. Judge Moore stated, “We do not view the Dowdecision as standing for such a sweeping change to our law or as limiting extrinsic evidence in this manner. Appreciating what a skilled artisan knew at the time of the invention is pertinent to whether the claims are reasonably clear in their meaning and scope. A question about the state of the knowledge of a skilled artisan is a question of fact, likely necessitating extrinsic evidence to establish.” Judge Moore also noted that in the remand of Nautilus, the court considered the knowledge of one skilled in the art in conjunction with the prosecution history in deciding the claim terms at issue were definite. Biosig Instruments, Inc. v. Nautilus, Inc., 783 F.3d 1374, 1382–84 (Fed. Cir. 2015). Judge Moore concluded, “Thus, Dow does not and cannot stand for the proposition that extrinsic evidence cannot be used to establish the state of knowledge of the skilled artisan, for example, whether one of skill in the art would know which measurement technique to employ to determine the maximum slope of a curve.”

Regarding the standard of review, Dow argued the Federal Circuit applied a de novo review to reverse the findings of fact which underlie the legal question of indefiniteness. Judge Moore said, “The Dow decision cannot change the Supreme Court’s recent holding, unequivocally clear, that fact findings which rely upon extrinsic evidence must be given deference on appeal.” Dow cited two prior Federal Circuit decisions (Teva Pharm. USA, Inc. v. Sandoz, Inc., 789 F.3d 1335, 1345 (Fed. Cir. 2015) and Interval Licensing LLC v. AOL, Inc., 766 F.3d 1364, 1371 (Fed. Cir. 2014)) as examples of instances where the court analyzed fact findings underlying the indefiniteness inquiry for clear error. Judge Moore noted that in Teva,the issue was a legal question on which the district court was reversed and that Interval Licensing did not involve extrinsic evidence. Judge Moore concluded, “When the jury renders a general verdict on validity or indefiniteness, we must presume all fact findings in support of that verdict. … And when we review jury fact findings, we do so for substantial evidence. … Whatever the results of Dow, it should not be viewed as having changed this well-established law.”

Dow also reaffirmed the proposition that the burden of proving indefiniteness remains on the party challenging validity by clear and convincing evidence.

While questions remain about Nautilus under 25 USC 112, the Federal Circuit does provide some helpful guidelines here for future cases.