The U.S. Supreme Court case Festo Corporation v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., et al., 2001, revolved around the issue of patent infringement and the doctrine of equivalents - a legal rule that allows a court to hold a party liable for patent infringement even if the infringing device or process does not fall within the literal scope of a patent claim, but nevertheless is equivalent to the claimed invention. The Supreme Court held that when an inventor narrows his or her claims during prosecution in order to obtain issuance of their patents (a practice known as "prosecution history estoppel"), it doesn't necessarily mean they surrender all rights to equivalents for those amended claims. However, such amendments create presumptions about what was surrendered which can be rebutted by showing reasons why an equivalent could not have been reasonably contemplated at time of amendment.

The dissenting opinion in the case of Festo Corporation v. Shoketsu Kinzoku Kogyo Kabushiki Co., Ltd., argued that the majority's ruling was too rigid and could potentially stifle innovation. The dissent, led by Justice Kennedy, disagreed with the majority's decision to limit patent protection only to those inventions that were exactly as described in a patent claim (the "literal infringement" rule). They believed this approach ignored the reality of technological progress and would unfairly penalize inventors who made minor modifications or improvements on existing patents. Instead, they advocated for a more flexible doctrine known as "equivalents," which would allow some degree of variation from an original patent while still providing legal protection against infringement. This view held that such flexibility is necessary to encourage creativity and advancement in technology.