Final answer:
A contract for medical services provided by John, who is only licensed in Michigan, may not be enforceable if he provided those services in another state where he is not licensed, such as Oxford.
Step-by-step explanation:
The question "John will be able to enforce the contract he made with Isaac for medical services relying on his Michigan medical license after he retired to Oxford?" deals with the enforceability of contracts and professional licensing. The enforceability of a contract for medical services provided by a retired physician depends on the licensing laws of the state where the services were provided. If John provided medical services in Oxford without the proper state medical license, despite being licensed in Michigan, the contract may not be enforceable. This is because most states require medical practitioners to be licensed in the state where they practice, and providing medical services without a required license can be illegal and subject to penalties. Consequently, John's Michigan medical license would not be sufficient for him to legally practice medicine or enforce a contract for medical services in another state unless there is a reciprocity agreement or other exception under local laws.