• The doctrine evolved to prevent parties from evading liability for patent infringement by making trivial changes to avoid the literal language of the patent claims. Graver Tank & Mfg. Co. v. Linde Air Prods. Co., 339 U.S. 605, 70 S.Ct. 854 (1950). In determining whether infringement exists under the doctrine, the court must first determine whether “the accused product or process contain[s] an element identical or equivalent to each claimed element of the patented invention.” Warner-Jenkinson Co. v. Hilton Davis Chem. Co., 520 U.S. 17, 39–40, 117 S.Ct. 1040, 1054 (1997). If it does, it infringes on the patent if the differing element performs substantially the same function in substantially the same way to get the same result as the patented product or process. Prosecution-history estoppel is not an absolute bar to a patentee who seeks to invoke the doctrine of equivalents to prove infringement on a claim that was voluntarily amended. Festo v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722, 122 S.Ct. 1831 (2002).
— Also termed equivalents doctrine; doctrine of equivalence; doctrine of equivalency; doctrine of substantial equivalents; nonliteral infringement. Cf. literal infringement under INFRINGEMENT. [Cases: Patents 237. C.J.S. Patents §§ 425–426.]
