In Lessee of John Mercer, and Mary Scott Mercer, His Wife v. William Cary Selden, the Supreme Court was tasked with determining whether a deed that conveyed land to two individuals as tenants in common could be revoked by one party without the consent of the other. The Mercers argued that they had purchased an estate from Selden under a deed which gave them joint tenancy over it; however, when Selden later attempted to revoke his grant and reclaim ownership of the property for himself without their consent or knowledge, they sued him for trespass on their rights as co-tenants. The court ultimately held that while each tenant has certain exclusive rights within a tenancy in common arrangement such as those enjoyed by the Mercers here - including possession and enjoyment of all parts of it - no single tenant can unilaterally revoke or alter any part thereof without permission from all parties involved. As such, since Selden's attempt at revoking his grant did not have unanimous agreement among all tenants in this case (the Mercers), he was found liable for trespass against them.

In this case, the Supreme Court was asked to decide whether a contract between two parties could be enforced if it violated a state law. The plaintiffs argued that the contract should be enforced because they had relied on its terms and acted in good faith. However, the defendant argued that since the contract violated state law, it was void and unenforceable. The majority of justices agreed with the defendant's argument and held that contracts which violate public policy are not enforceable under any circumstances. Justice McLean dissented from this opinion arguing that while contracts which violate public policy may not always be enforceable, there were certain cases where enforcing such contracts would still serve justice by preventing one party from taking advantage of another who has acted in good faith reliance on their agreement. He concluded by stating his belief that this particular case fell into such an exception as both parties had entered into their agreement without knowledge or intent to break any laws and thus should have been allowed to stand despite violating public policy.