Dunphy v. Sullivan was a United States Supreme Court case that dealt with the issue of whether a state court could enforce a contract that was made in violation of a state statute. The case involved a contract between two parties, Dunphy and Sullivan, in which Dunphy agreed to pay Sullivan a certain amount of money for the use of a certain piece of property. The contract was made in violation of a state statute that prohibited such contracts. The Supreme Court held that the state court could not enforce the contract because it was made in violation of the state statute. The Court reasoned that the state statute was a valid exercise of the state's police power and that the state had the right to protect its citizens from contracts that were made in violation of the law. The Court also noted that the state had the right to protect its citizens from contracts that were made without proper consideration. The Court's decision in Dunphy v. Sullivan established that state courts could not enforce contracts that were made in violation of state statutes. This decision has been cited in numerous cases since then and has been used to support the idea that state courts should not enforce contracts that are made in violation of the law.

Justice Field delivered the dissenting opinion in Dunphy v. Sullivan, arguing that the majority's decision was contrary to both precedent and common sense. He argued that a contract between two parties should be enforced as written, regardless of any subsequent changes in law or circumstances. In this case, he noted that the plaintiff had agreed to pay an annual rent for his land lease with no provision for adjustment due to inflation or other economic factors; thus, it would be unfair and unjust to allow him relief from such payment on those grounds. Furthermore, Justice Field pointed out that if courts were allowed to modify contracts based on changing laws or conditions outside of their control then there would be little incentive for parties entering into agreements since they could not rely upon them being upheld by the court system. Ultimately he concluded that while sympathy may lie with one party over another in certain cases like this one, justice must prevail over emotion when interpreting contracts according to established legal principles and precedents set forth by prior decisions of higher courts.