Shepherd v. May 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, Shepherd, was held in a federal prison in the state of Virginia. Shepherd sought a writ of habeas corpus from the state court, claiming that he was being held in violation of his constitutional rights. 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 authority to interfere with the federal government's power 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. In conclusion, 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 authority to interfere with the federal government's power to imprison individuals.

Justice Field delivered the dissenting opinion in Shepherd v. May, arguing that the majority's decision was an incorrect interpretation of a contract between two parties. He argued that when interpreting contracts, courts should look to what is written and not consider extrinsic evidence such as prior negotiations or understandings between the parties. In this case, he believed there was no ambiguity in the language of the contract and thus it should be interpreted according to its plain meaning without considering any other factors outside of what is written on paper. Furthermore, Justice Field argued that if one party had intended for something else to be included in their agreement then they would have made sure it was explicitly stated within their document rather than relying on external sources for clarification. Ultimately, he concluded by stating his belief that allowing extrinsic evidence into consideration could lead to confusion and uncertainty regarding contractual obligations which could ultimately undermine public confidence in private agreements going forward.