Mellen v. Moline Malleable Iron Works was a United States Supreme Court case that addressed the issue of whether a contract between two parties was valid. The plaintiff, Mellen, had entered into a contract with the defendant, Moline Malleable Iron Works, to purchase a certain amount of iron. The contract stated that the iron was to be delivered within a certain time frame, and that Mellen would pay for the iron upon delivery. However, when the iron was delivered, Mellen refused to pay for it. The Supreme Court held that the contract was valid and enforceable. The Court reasoned that the contract was clear and unambiguous, and that Mellen had agreed to pay for the iron upon delivery. The Court also noted that Mellen had not raised any defenses to the contract, such as fraud or mistake, and that Mellen had not provided any evidence that the contract was invalid. Therefore, the Court held that Mellen was obligated to pay for the iron as agreed.

Justice Field delivered the dissenting opinion in Mellen v. Moline Malleable Iron Works, arguing that the majority's decision was incorrect and should be reversed. He argued that a contract between two parties is only binding if it is made with full knowledge of all relevant facts and circumstances, which he believed did not exist in this case. The defendant had been unaware of certain facts regarding the plaintiff's title to land when they entered into their agreement; thus, Justice Field concluded that there was no valid contract between them. Furthermore, he argued that even if there had been a valid contract at one point, it would have become void due to subsequent events such as changes in ownership or other material alterations to the terms of the agreement. In conclusion, Justice Field asserted that since there was no enforceable contract between these two parties at any time during their dispute over land rights and titles, then neither party could claim legal entitlement to those rights or titles under existing law.