Duff v. Sterling Pump Company was a United States Supreme Court case that addressed the issue of whether a contract between two parties was valid. The case involved a contract between the plaintiff, Duff, and the defendant, Sterling Pump Company. Duff had contracted with Sterling Pump Company to purchase a steam engine and boiler for his business. The contract stated that the engine and boiler would be delivered within a certain time frame and that Duff would pay for the items upon delivery. When the engine and boiler were delivered, Duff refused to pay for them, claiming that the contract was invalid because it had not been signed by both parties. Sterling Pump Company then sued Duff for breach of contract. The Supreme Court held that the contract was valid and enforceable, even though it had not been signed by both parties. The Court reasoned that the contract was valid because it was clear that both parties had agreed to the terms of the contract and that the contract was supported by consideration. The Court also noted that the contract was supported by the fact that Duff had accepted delivery of the engine and boiler. As a result, the Court held that Duff was liable for breach of contract and ordered him to pay Sterling Pump Company for the items.

Justice Field delivered the dissenting opinion in Duff v. Sterling Pump Company, arguing that the majority had incorrectly interpreted the patent law of 1836 and failed to consider evidence from prior cases. He argued that a machine could be patented if it was novel and useful, even if its parts were not new inventions themselves. In this case, he believed that the pump created by Duff was both novel and useful because it combined existing elements into a single device with an improved purpose - namely pumping water more efficiently than other pumps at the time. Furthermore, Justice Field argued that there was no reason for Congress to have intended otherwise when they passed patent laws in 1836; thus he concluded that Duff should have been granted his patent on his invention as it met all requirements under current law at the time.