In the case of T.H. Symington Company v. National Malleable Castings Company et al., 1918, the U.S Supreme Court was tasked with determining whether a patent for car couplers held by T.H. Symington Co., a railway supplies manufacturer, had been infringed upon by National Malleable Castings Co and other defendants involved in manufacturing similar products. The lower court had ruled in favor of Symington, finding that their patent was valid and had indeed been violated. However, on appeal to the Supreme Court, this decision was reversed based on an analysis of prior patents and existing technology at the time when Symington's patent application was filed. The justices concluded that there were no new or novel elements present in their design which would warrant exclusive rights under patent law; instead it represented merely an improvement over previous designs using known techniques. The ruling emphasized that while improvements are important for technological progress they do not necessarily meet criteria for obtaining a patent unless they introduce some distinct innovation or discovery beyond what is already known within industry practices.

In the dissenting opinion for T.H. Symington Company v. National Malleable Castings Company et al., the justice disagreed with the majority's decision that Symington had not infringed on National Malleable's patent rights, arguing that there was indeed infringement of patent in this case. The dissenting justice believed that Symington’s use of a similar process to create railway car couplers constituted an infringement upon National Malleable’s patented method, even if it wasn't identical but only substantially equivalent to it. This view is based on the doctrine of equivalents which provides protection against unscrupulous copying of a patented invention by making minor changes while retaining its essence. The dissenter held that such conduct should be considered as infringing activity and therefore liable for damages under patent law.