Smith v. McCool was a United States Supreme Court case that was decided in 1872. The case involved a dispute between two parties over a contract for the sale of a horse. The plaintiff, Smith, had agreed to purchase a horse from the defendant, McCool, for $100. Smith paid McCool $50 as a down payment and agreed to pay the remaining $50 at a later date. However, Smith failed to pay the remaining $50 and McCool sued him for breach of contract. The Supreme Court held that Smith was liable for breach of contract. The Court reasoned that Smith had agreed to pay the remaining $50 and had failed to do so. The Court also noted that McCool had not waived his right to receive the remaining $50 and that Smith had not offered any valid excuse for his failure to pay. Therefore, the Court held that Smith was liable for breach of contract and ordered him to pay the remaining $50 to McCool.

In Smith v. McCool, the Supreme Court was tasked with determining whether a contract between two parties could be enforced when one of them had died before it was fully executed. The majority opinion held that such contracts were not enforceable because they lacked consideration and mutuality of obligation, but Justice Field dissented from this decision. He argued that the contract should be upheld as valid because there had been an offer made by one party and accepted by another in good faith; thus, consideration existed even though only part of the agreement had been completed at the time of death. Furthermore, he noted that public policy favored enforcing agreements to which both parties consented rather than allowing them to become void due to unforeseen circumstances like death or incapacity. Ultimately, Justice Field's dissent did not prevail and his view on this issue has since been rejected by subsequent courts; however, his dissenting opinion still serves as an important reminder about how contractual obligations can sometimes be affected by unexpected events outside either party's control.