Historically, the Federal Circuit has reviewed claim construction determinations de novo. This standard of review resulted in the circuit court reversing approximately 30% of the cases appealing that issue.1 In Teva Pharmaceuticals USA, Inc. v. Sandoz, Inc.,2 the Supreme Court held that the Federal Circuit must now review factual determinations made by a trial judge during claim construction for “clear error,” a substantially more deferential standard of review.3 The Court also provided guidance on which aspects of the claim construction process will now be reviewed under the “clear error” standard.

Patent validity and infringement turn on the words in a patent’s claims because those claims define the scope of the patentee’s rights. The Supreme Court held in Markman v. Westview Instruments, Inc.4 that the responsibility for construing those words during claim construction is reserved “exclusively” for the judge. Since the Supreme Court’s 1996 Markman decision, the Federal Circuit has considered claim construction entirely a question of law and reviewed all aspects of it de novo on appeal.5 Teva Pharmaceuticals changes appellate review of claim construction by clarifying that claim construction involves both “factual” and “legal” determinations. It holds that Federal Rule of Civil Procedure 52(a)(6) governs all “factual” determinations, even those made in claim construction, and, under that Rule, the Federal Circuit may not reverse a trial judge’s “factual” findings unless they are “clearly erroneous.”6

Teva Pharmaceuticals also clarifies the distinction between the “factual” and “legal” determinations underlying the claim construction process. Citing Markman, the Supreme Court reaffirmed that the ultimate question in claim construction—the meaning of a claim term in a patent—is a question of law and will continue to be reviewed de novo.7 Likewise, when a district judge reviews only evidence intrinsic to the patent (the claims, specifications, and prosecution history) in construing a claim term, this amounts to solely a legal determination that will also be reviewed de novo.8 When a trial judge, however, must look beyond the intrinsic evidence to extrinsic evidence such as expert opinion on the general meaning of a certain term of art at the time of the invention, the trial judge’s findings on that matter are factual findings that, under Rule 52, can only be reviewed for “clear error.”9

In summary, the Supreme Court in Teva Pharmaceuticals has held that the Federal Circuit must review factual determinations made by a trial judge during claim construction for “clear error.” A trial judge’s ultimate claim interpretation, however, is a legal determination. On appeal, this ultimate determination remains subject to de novo review. But now, subsidiary factual findings underlying a trial judge’s claim construction may only be overturned if “clearly erroneous.”10