The U.S. Court of Appeals for the Federal Circuit is currently considering en banc the level of deference to which a district court’s interpretation of patent claims is entitled in Lighting Ballast Control v. Philips Electronics North America, No. 2012-1014.1 Undoubtedly, a lot will be written on the implications of that decision, and it will inform how practitioners craft their claim construction arguments going forward. The Federal Circuit’s decision in Lighting Ballast, however, will not resolve a growing uncertainty about the proper methodology for construing patent claims in the first place. Establishing a consistent, predictable approach to claim construction is perhaps of even more importance than the standard of appellate review applied to a district court’s construction.2 After all, “claim construction is the single most important event in the course of a patent litigation. It defines the scope of the property being enforced, and is often the difference between infringement and non-infringement, or validity and invalidity.”3
Claim Construction Methodology in ‘Phillips’
After the Supreme Court held in Markman v. Westview Instruments4 that claim construction was a task for the court, a split developed in the Federal Circuit over whether it was proper to interpret patent claims in view of the description of the invention in the patent specification or to rely on the “ordinary” meaning of claim language as derived from dictionaries, expert testimony, and other extrinsic source. The Federal Circuit resolved that split in its 2005 en banc decision in Phillips v. AWH.5
