BROAD CLAIM CONSTRUCTIONS —Be Careful What You Ask For

In a recent Federal Circuit decision, the court once again illustrated the dangers associated with seeking unduly broad claim constructions.  In MagSil,[1] the plaintiff had a claim which required a change in resistance of at least 10 percent at room temperature.  The specification showed examples up to 11.8 percent, but no greater.  During litigation, however, the plaintiff sought a claim construction that would encompass from 10 percent to infinity.  The district court granted summary judgment to the defendants that such an interpretation was invalid as lacking enablement under 35 U.S.C. §112.

In upholding the determination of invalidity, the Federal Circuit noted that the enablement doctrine exists to prevent both “inadequate disclosure of an invention and overbroad claiming that might otherwise attempt to cover more than was actually invented.”  Here, the patent in suit was filed in 1995, and the plaintiff sought to cover recent developments which allowed for resistance changes of 600 percent.  The court noted that enablement is an inquiry that is conducted based on the specification and the knowledge at the time of filing, and future developments cannot be used to assist in enabling claims.

In cases such as these, where older patents are used against new technologies, defendants need to recognize that the enablement doctrine can serve as a useful shield against a patentee’s attempt to broaden claim scope beyond what was actually invented.


[1] MagSil v. Hitachi, 2011-1221 (Fed. Cir. 2012)