In the 1946 case of MacGregor v. Westinghouse Electric & Manufacturing Co., the United States Supreme Court addressed a patent dispute. The plaintiff, MacGregor, claimed that Westinghouse had infringed on his patented invention for an automatic circuit breaker. However, the court ruled in favor of Westinghouse, stating that there was no infringement because their product did not use or incorporate any novel elements from MacGregor's patent claim. Furthermore, it was found that MacGregor’s patent lacked novelty and therefore could not be enforced against others who independently developed similar products without copying his design. This decision reinforced principles regarding what constitutes as a valid patent and how they can be legally protected under U.S law.

In the dissenting opinion for MacGregor v. Westinghouse Electric & Manufacturing Co., it was argued that the majority's decision to uphold a patent on an invention that had been in public use for more than two years prior to its application was inconsistent with established legal principles and precedent. The dissent emphasized that under U.S. law, any invention must be patented within two years of its first public use or else it becomes part of the public domain, free for anyone to use without infringement. By allowing this exception, they believed the court undermined this important safeguard against monopolies and stifled competition by granting exclusive rights over something already publicly available.