Seymour v. Freer was a United States Supreme Court case that dealt with the issue of whether a state court had the authority to issue a writ of habeas corpus to a prisoner held in a federal prison. The case arose when the state of New York issued a writ of habeas corpus to a prisoner held in a federal prison in New York. The prisoner, Seymour, argued that the state court did not have the authority to issue the writ because the federal government had exclusive jurisdiction over the prison. The Supreme Court disagreed, ruling that the state court had the authority to issue the writ. The Court reasoned that the writ of habeas corpus was a fundamental right that could not be denied by the federal government. The Court also noted that the writ was necessary to protect the rights of individuals held in federal custody. The Court concluded that the state court had the authority to issue the writ of habeas corpus to the prisoner held in the federal prison.

In the case of Seymour v. Freer, the Supreme Court was asked to decide whether a contract between two parties could be enforced when it had been made in violation of an existing statute. The majority opinion held that such contracts were unenforceable and thus granted judgment for the defendant. However, Justice Field dissented from this decision, arguing that while statutes should generally be respected and followed, they do not always trump all other considerations. He argued that if a contract is otherwise valid under common law principles then it should still be enforceable even if it violates a statute; he reasoned that allowing enforcement would promote fairness by preventing one party from taking advantage of another's ignorance or lack of legal knowledge regarding applicable laws. Furthermore, he noted that enforcing such contracts would also help maintain public confidence in contractual arrangements as well as encourage people to enter into them without fear of being taken advantage of due to their lack of understanding about relevant laws.