Hoyt v. Sprague 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 who was being held in a federal prison. The case arose when a prisoner, William Hoyt, was held in a federal prison in Massachusetts. He sought a writ of habeas corpus from the state court, claiming that he was being held in violation of the Constitution. The state court granted the writ, and the federal government appealed the decision to the Supreme Court. The Supreme Court held that the state court did not have the authority to issue a writ of habeas corpus to a prisoner held in a federal prison. The Court reasoned that the writ of habeas corpus was a federal remedy, and that the state court did not have the power to interfere with the federal government's authority to imprison individuals. The Court also noted that the writ of habeas corpus was a remedy that could only be used to challenge the legality of a person's detention, and not to challenge the conditions of the detention. The Court's decision in Hoyt v. Sprague established that state courts do not have the authority to issue writs of habeas corpus to prisoners held in federal prisons. This decision has been cited in numerous subsequent cases, and it remains an important precedent in the area of federal-state relations.

In the case of Hoyt v. Sprague, the Supreme Court was asked to decide whether a contract between two parties that involved an illegal act could be enforced by law. The majority opinion held that such contracts were unenforceable and thus not valid under the law. However, in his dissenting opinion Justice Field argued that while it is true that contracts involving illegal acts are generally void and unenforceable, this should not always be so when both parties have acted in good faith and with no intention to violate any laws or public policy. He further argued that if one party has already performed their part of the agreement then they should still receive compensation for their efforts even if there was some illegality associated with it as long as there was no intent on either side to break any laws or do anything wrong. In conclusion he stated “The rule which denies all relief upon a contract founded upon an immoral consideration does injustice where none is intended”