10.5.1 Claim construction
The construction of patent claims is central to the evaluation of infringement and validity and can affect or determine the outcome of other significant issues, such as unenforceability, enablement and remedies. The Supreme Court’s decision in Markman v. Westview Instruments96 laid the groundwork for modern U.S. claim construction practice. That decision, reinforced by Teva Pharmaceuticals USA, Inc. v. Sandoz, Inc.,97 declared that “the construction of a patent, including terms of art within its claim, is exclusively within the province of the court.”98
The Federal Circuit’s decision in Phillips v. AWH Corp.99 stands as the most authoritative synthesis of the claim construction doctrine. A “bedrock principle” of patent law is that “the claims of a patent define the invention to which the patentee is entitled the right to exclude.”100 The “objective baseline” for construing patent claims is determining “how a person of ordinary skill in the art understands a claim term” “at the time of the invention, i.e., as of the effective filing date of the patent application.”101 “That starting point is based on the well-settled understanding that inventors are typically persons skilled in the field of the invention and that patents are addressed to and intended to be read by others of skill in the pertinent art.”102 Often, other evidence will provide context for characterizing the person having ordinary skill in the art. The “effective filing date” is the earlier of the actual filing date or the filing date of an application from which priority is accorded. The skilled artisan “is deemed to read the words used in the patent documents with an understanding of their meaning in the field, and to have knowledge of any special meaning and usage in the field.”103 Interpreting patent claims thus requires the court to consider “the same resources as would that person, viz., the patent specification and the prosecution history.”104
The proper definition of a claim term is context-dependent. The patent and its prosecution history “usually provide the technological and temporal context to enable the court to ascertain the meaning of the claim to a person having ordinary skill in the art at the time of the invention.”105 Thus, patent claims are to be interpreted in light of this “intrinsic” evidence (i.e., the patent specification and its prosecution history) as well as pertinent “extrinsic” evidence (i.e., evidence showing the usage of the terms in the field of art, such as in dictionaries, treatises, and inventor and expert testimony), but extrinsic evidence cannot contradict or override intrinsic evidence. The Federal Circuit explained why extrinsic evidence is inherently less reliable than intrinsic evidence:
First, extrinsic evidence by definition is not part of the patent and does not have the specification’s virtue of being created at the time of patent prosecution for the purpose of explaining the patent’s scope and meaning. Second, while claims are construed as they would be understood by a hypothetical person of skill in the art, extrinsic publications may not be written by or for skilled artisans and therefore may not reflect the understanding of a skilled artisan in the field of the patent. Third, extrinsic evidence consisting of expert reports and testimony is generated at the time of and for the purpose of litigation and thus can suffer from bias that is not present in intrinsic evidence […] Fourth, there is a virtually unbounded universe of potential extrinsic evidence of some marginal relevance that could be brought to bear on any claim construction question […] Finally, undue reliance on extrinsic evidence poses the risk that it will be used to change the meaning of claims in derogation of the “indisputable public records consisting of the claims, the specification and the prosecution history,” thereby undermining the public notice function of patents.106