On October 15, the Supreme Court heard oral argument on the standard of review for Markman orders construing the meaning of claim terms. Teva Pharmaceuticals USA, Inc. v. Sandoz, Inc., 723 F.3d 1363 (Fed. Cir. 2013), cert. granted 134 S.Ct. 1761 (2014). Teva is the only patent case accepted so far this term for Supreme Court review. The Supreme Court held almost 20 years ago that patent claims are construed by the court, not a jury. Markman v. Westview Instruments, Inc., 517 U.S. 370 (1996). The Federal Circuit has held that claim construction orders are reviewed de novo on appeal. Cybor Corp. v. FAS Technologies, Inc., 138 F.3d 1448 (Fed. Cir. 1998).
Issues of fact determined by the trial court, however, are generally subject to the "clearly erroneous" standard of review. Fed. R. Civ. P. 52(a)(6).  Factual determinations may be subsumed in the legal conclusion regarding the construction of a claim term. Are factual findings subject to de novo review or the clearly erroneous standard?
In Teva, the District Court found the patent claims valid and infringed. After de novo review, the Federal Circuit found certain claims invalid for indefiniteness. The claim term "average molecular weight" was subject to three different possible measurements. The District Court relied in part on the Teva expert’s testimony in determining a person of ordinary skill in the art would know which of the 3 possible measurements to use. The Federal Circuit deemed the specification ambiguous and rejected the District Court construction, thereby invalidating some of the claims as indefinite. In all other respects, the District Court was affirmed.
After noting that claim construction "is an issue of law that we review de novo.", the Federal Circuit held that the district court's calculation of the percentages represented by the ratios in the patent claim ("approximately 6:2:5:1") is part of the infringement analysis and is reviewed for clear error. Using this deferential standard, the Federal Circuit found that the court did not clearly err in concluding the accused products literally infringed the remaining valid claims.
The Supreme Court recently upheld a deferential standard of review for findings of fact in awarding attorneys' fees in patent cases. The Supreme Court held these fact intensive determinations can only be reversed for "abuse of discretion". Highmark, Inc. v. All Care Health Management Systems, Inc., 134 S.Ct. 1744 (2014).  A question of law based on underlying mixed questions of fact was not subject to de novo review; instead, the district court determination was entitled to deference.
"Because §285 commits the determination whether a case is 'exceptional' to the discretion of the district court, that decision is to be reviewed on appeal for abuse of discretion.
Traditionally, decisions on ‘questions of law’ are 'reviewable de novo,' decisions on 'questions of fact' are 'reviewable for clear error,' and decisions on 'matters of discretion' are reviewable for 'abuse of discretion.' …
Although questions of law may in some cases be relevant to the §285 inquiry, that inquiry generally is, at heart 'rooted in factual determinations'."
Highmark, 134 S.Ct. at 1748-49.
In Highmark, the attorneys' fee statute allocated the determination to the discretion of the district court. The case law on claim construction, however, is not based on statutory language in the Patent Act allocating the determination of the meaning of claim terms. And the claim construction process is not as “deeply rooted in factual determinations”.
The American Intellectual Property Law Association ("AIPLA") filed an amicus brief arguing claim construction is ultimately a question of law subject to review de novo; however, subsidiary issues based on extrinsic evidence (evidence outside the patent itself and the prosecution history) should be reviewed for clear error. The amicus brief argues the clearly erroneous standard applies to factual determinations for other mixed questions of law and fact in patent cases, for example -- in determining obviousness (In re Huang, 100 F.3d 135, 138 (Fed. Cir. 1996)) , enablement (PPG Industries, Inc. v. Guardian Industries Corp., 75 F.3d 1558, 1564 (Fed. Cir. 1996)) , the on sale bar (Ferag AG v. Quipp, Inc., 45 F.3d 1562, 1566 (Fed. Cir. 1995)), and inventorship (Sewell v. Walters, 21 F.3d 411, 415 (Fed. Cir. 1994)).
Throwing caution to the wind, I humbly predict the Supreme Court will hold that findings of fact subsumed in claim construction are subject to the deferential clear err standard of Rule 52(a)(6). This standard of review could add greater predictability to appeals in patent cases.