Benson v. McMahon was a United States Supreme Court case that addressed the issue of whether a patentee could assign a patent to another party without assigning the right to sue for infringement. The case was brought by William Benson, who had obtained a patent for a machine for making and cutting screws. Benson had assigned the patent to the defendant, John McMahon, but had not assigned the right to sue for infringement. The Supreme Court held that the patentee could assign the patent without assigning the right to sue for infringement. The Court reasoned that the patentee had the right to assign the patent without assigning the right to sue for infringement because the patentee had the exclusive right to make, use, and sell the invention, and the right to sue for infringement was a separate right that was not included in the patent. The Court also held that the patentee could assign the right to sue for infringement separately from the patent. The Court concluded that the patentee had the right to assign the patent without assigning the right to sue for infringement, and that the defendant had the right to sue for infringement.

Justice Field delivered the dissenting opinion in Benson v. McMahon, arguing that the majority's decision was contrary to established precedent and would lead to an absurd result. He argued that a patentee should not be able to claim exclusive rights over something which had already been invented by another person prior to the issuance of his own patent. The Patent Act of 1836 provided for patents on inventions made after its passage, but did not provide any protection for those who had previously invented such things before it was passed into law. Justice Field noted that if this ruling were allowed to stand, then anyone could obtain a patent on something already known or used and thus gain exclusive control over it despite having no part in its invention or development - an outcome he found unacceptable under existing laws and principles of equity.