The interpretation of patent claims differs among jurisdictions within the World Intellectual Property Organization (WIPO). Countries such as Germany, Ireland, Switzerland, the United Kingdom, and the United States use the doctrine of equivalents to evaluate patent claims. Typically, patent claims for infringement include either literal or non-literal claims for infringement. Literal patent infringement entails the need for all patent elements (“limitations”) to exactly match in order to incur liability for patent infringement. The concept of non-literal infringement means that one or more of the patented invention claims fall outside of the scope of the claims of the patented invention. Winans v. Denmead, 56 U.S. 330, 340, 343 (1854) (with regard to an infringement claim on the shape of a railway car (octagonal vs. round) as infringing).

The doctrine of equivalents refers to non-literal patent infringement. Under the doctrine of equivalents, a patent infringement claim may be levied against an entity even if not all of the parts of the claimed invention are an identical match. The doctrine of equivalents has been used to reference similar function of a patented device. Graver Tank & Mfg. Co. v. Linde Air Products Co., 339 U.S. 605, 606, 609 (1950) (where substitution of a similar ingredient resulted in a similar functional result in a mechanical process). Thus, Graver outlined criteria for establishing equivalence among elements of patent claims. These included (as previously stated) similar or identical performance of function, identical activity, and identical outcome or result as recognized by a person with ordinary skill in the art (PHOSITA). Id.

Image: Circe Offering the Cup to Odysseus. 1891. John William Waterhouse (1849 – 1917). British. Public Domain.

Warner-Jenkinson Co. Inc. v. Hilton Davis Chemical Co. introduced the concept of the “all elements” rule. 520 U.S. 17 (1997). The “all elements” rule means that each element of a claim must be considered on an individual basis for equivalence. 35 U.S.C. § 282. Specifically, “[a] claim of infringement under the doctrine of equivalents modifies th[e] second step [of the infringement analysis, i.e., the comparison step,] by requiring that the fact finder determine whether differences between particular elements of the accused device and the asserted claims are insubstantial.” Cybor Corp. v. FAS Technologies, Inc., 138 F.3d 1448, 1467 (Fed. Cir. 1998) (en banc).

Additional considerations for the doctrine of equivalents are the significance of the discovery (invention) as determined by the PHOSITA and the extent of the scope of rights conferred through language of equivalence. This is of particular concern when examining claim scope with regard to prior art. Wilson Sporting Goods Co. v. David Geoffrey & Associates, 904 F. 2d 677 (Fed Cir.), cert denied, 498 U.S. 992 (1990) (where a hypothetical claim that covers prior art is not considered infringement).

Overall, the doctrine of equivalents allows some flexibility when considering patent claims while maintaining a balance between clarity of the patent claims and infringement of the patent.