Phillips v. AWH Corp.
Phillips is the Federal Circuit's foundational en banc statement on how to read a patent claim. The court restored the specification to its central role in claim construction, ranked the sources of meaning as intrinsic before extrinsic, and rejected the dictionary-first approach that had taken hold in the years after Markman.
Holding
The Federal Circuit, sitting en banc, held that claim terms are given the ordinary meaning they would have to a person of ordinary skill in the art at the time of the invention, read in the context of the entire patent. Intrinsic evidence — the claims, the specification, and the prosecution history — controls. Extrinsic evidence such as dictionaries, treatises, and expert testimony may be consulted but is secondary. The court rejected the methodology of Texas Digital Systems, Inc. v. Telegenix, Inc., 308 F.3d 1193 (Fed. Cir. 2002), which had elevated dictionaries to a primary role.
Procedural posture and facts
Edward Phillips owned U.S. Patent No. 4,677,798, directed to modular vandalism-resistant building panels suitable for use in correctional facilities. The patent's claims recited "internal steel baffles" extending inwardly from the steel shell walls. AWH Corp. produced a competing panel system. The infringement question turned on whether the term "baffles" required a structure positioned at an angle other than 90 degrees relative to the shell wall, or whether perpendicular baffles fell within the claim.
The district court construed "baffles" to require an angle other than 90 degrees, drawing on figures in the specification that depicted angled baffles, and granted summary judgment of noninfringement. A Federal Circuit panel affirmed in Phillips v. AWH Corp., 363 F.3d 1207 (Fed. Cir. 2004), but the full court vacated the panel decision and took the case en banc to address the methodology of claim construction itself.
The en banc court issued an order with seven specific questions, ranging from the role of dictionaries to the weight of the specification to the scope of de novo review. The 2005 opinion answered those questions through a sustained discussion of how to perform claim construction after Markman.
The court's reasoning
Judge Bryson's opinion organized claim construction around a single principle: the words of the claim are read from the perspective of a person of ordinary skill in the art, in the context of the patent as a whole. From that principle the court derived a hierarchy of evidence.
The claims themselves
Claims are the starting point. The same term used in different claims is presumed to have the same meaning, and differences in claim language — especially through the doctrine of claim differentiation — can illuminate the scope of any particular claim. Dependent claims that add a limitation imply that the independent claim does not include that limitation.
The specification as the "single best guide"
The court called the specification the "single best guide to the meaning of a disputed term." A patent is, by statute, a written instrument that includes a written description of the invention. 35 U.S.C. § 112(a). The applicant chooses the terms used in the claims and may act as her own lexicographer, defining a term in a particular way; she may also disclaim subject matter. The court rejected, however, the routine practice of importing limitations from the specification into the claims. The challenge in any close case is "to read the specification in light of its purpose without unduly importing limitations from the specification into the claims."
Prosecution history
The prosecution history is also intrinsic evidence. It records the dialogue between the applicant and the examiner and may reveal disclaimers or narrowing constructions that bind the patentee. Because the prosecution history reflects the negotiated scope of the patent, it can supply important context. But the court warned that prosecution history often lacks the polish of the issued specification and "often lacks the clarity" of the issued specification, requiring careful interpretation.
Extrinsic evidence in its place
Dictionaries, treatises, expert testimony, and inventor testimony are extrinsic evidence. The court did not banish them; they may be useful for understanding technology, providing background, and establishing how a person of ordinary skill would understand a term. But extrinsic evidence is "less reliable than the patent and its prosecution history in determining how to read claim terms." The principal danger of starting with a dictionary is that the abstract dictionary meaning may diverge from the meaning the inventor and the patent itself intended.
Rejection of Texas Digital
Texas Digital had announced a methodology in which the dictionary supplied the presumptive meaning of a claim term, displaced only if the specification clearly redefined the term or disclaimed it. Phillips reversed the priority. The dictionary's place is supportive; the specification's place is central. "The main problem with elevating the dictionary to such prominence," the court explained, "is that it focuses the inquiry on the abstract meaning of words rather than on the meaning of claim terms within the context of the patent." Dictionaries also vary among themselves and frequently provide multiple definitions, leaving courts to pick one without an anchor in the patent.
The framework Phillips produced
After Phillips, the doctrinal hierarchy is settled:
- Claims: the words of the claims themselves, read in the context of the entire claim set.
- Specification: the written description and figures, including any explicit lexicography or disclaimer.
- Prosecution history: the file wrapper, including amendments, arguments, and examiner statements that shed light on scope.
- Extrinsic evidence: dictionaries, treatises, expert testimony, and other materials, used to inform the court's understanding without contradicting the intrinsic record.
The framework also assigns roles to the participants. The judge construes the claim, applying the framework as a matter of law, consistent with Markman. Subsidiary factual findings about how a skilled artisan would understand a term in light of extrinsic evidence are made by the judge as factfinder and reviewed for clear error after Teva Pharmaceuticals USA, Inc. v. Sandoz, Inc., 574 U.S. 318 (2015). The legal conclusion that follows from those facts is reviewed de novo.
Subsequent application
Phillips is now the operating instruction for every Markman hearing. District courts open their claim construction orders by quoting Phillips's hierarchy, and parties' briefs are organized around the four-step structure. The Federal Circuit applies the same standard in reviewing district court constructions and Patent Trial and Appeal Board determinations in inter partes review and post-grant review. The PTAB now uses the Phillips standard rather than the broadest-reasonable-interpretation standard for claim construction, aligning Board and court methodology.
Phillips's specific warnings have proved durable. The "single best guide" framing is repeated in nearly every claim-construction opinion. The instruction not to import limitations from the specification into the claims is a recurring point of contention; panels divide regularly on whether a particular embodiment in the specification narrows the claim or merely illustrates one example. The court's caution about dictionaries has held: a litigant who leads with Webster's typically loses to one who leads with the patent.
Phillips also has the practical consequence that literal infringement and anticipation turn on a record assembled at the Markman stage. A construction tracking the specification will often be claim-narrow; a construction privileging dictionary breadth will be claim-broad. Defendants generally prefer narrow constructions for noninfringement and broad constructions for invalidity, and Phillips channels the dispute through the intrinsic record rather than through extrinsic battles.
Open questions and pressure points
Three lines of difficulty remain. First, the line between "reading the claim in light of the specification" and "importing a limitation from the specification" is inherently judgment-bound. The Federal Circuit's case law swings, panel by panel, between treating embodiments as illustrative and treating them as limiting. Phillips itself acknowledged that this line is the central challenge of claim construction.
Second, the role of extrinsic evidence under Teva remains a live question. Phillips placed extrinsic evidence in a secondary position, and Teva said that subsidiary factual determinations from extrinsic evidence get clear-error deference. Panels have not always treated such determinations as Rule 52(a)(6) findings requiring deference; sometimes they are folded back into the legal conclusion and reviewed de novo.
Third, the role of post-Phillips materials — for example, statements made by the patentee during inter partes review at the PTAB — has emerged as a pressure point. Disclaimers made during IPR may bind the patentee in subsequent district court litigation, importing a Phillips-style intrinsic record analysis into the post-grant proceeding. This intersection between district court and Board records continues to generate doctrine.
Finally, Phillips did not resolve the meaning of "ordinary skill in the art" itself. The level of skill, the date of measurement, and the breadth of the relevant art are all factual questions that affect both claim construction and downstream issues such as obviousness and enablement.
Citation and record
Formal citation: Phillips v. AWH Corp., 415 F.3d 1303 (Fed. Cir. 2005) (en banc).
Below: The earlier panel decision, 363 F.3d 1207 (Fed. Cir. 2004), was vacated when the court took the case en banc.
Author: Judge Bryson for the en banc court. Judges Mayer and Newman dissented in part on issues unrelated to the central methodology.
Vote alignment: En banc majority on the methodology of claim construction; partial dissents on related questions.
See also
- Markman v. Westview Instruments, Inc.The Supreme Court decision that allocated claim construction to the court.
- Claim constructionThe overarching doctrine that Phillips structured.
- Markman hearingsThe procedural setting in which Phillips is applied.
- Prosecution history estoppelA separate but related doctrine that draws on the file wrapper.
- Inter partes reviewPTAB now uses the Phillips standard for claim construction.
- DefinitenessConstruction methodology informs whether a claim term is sufficiently definite under § 112(b).
- Title 35 referenceStatutory framework for claims and specification under § 112.
Last reviewed: 2026