Evariste Blanc was the plaintiff in error in a case brought before the United States Supreme Court. He argued that George W. Lafayette and John Hagan had wrongfully taken possession of his property, which he claimed to have acquired through legal title from the Spanish government prior to Louisiana's admission into the Union as a state. The defendants argued that they were entitled to possess it by virtue of their having purchased it from another party who held valid title under Louisiana law. The court ultimately found for Lafayette and Hagan, ruling that since Blanc had not obtained any rights or privileges under either Spanish or American laws at the time of his purchase, he could not claim ownership over land located within an area now part of Louisiana State territory.

In this case, the Supreme Court was asked to decide whether a contract between two parties could be enforced when it had been made without consideration. The majority opinion held that the contract was not enforceable because there had been no consideration given for its formation. However, in his dissenting opinion Justice McLean argued that although there may have been no consideration given at the time of making the agreement, subsequent events such as part performance or reliance on promises can provide sufficient grounds for enforcing an otherwise unenforceable contract. He further noted that if contracts were only enforceable when supported by some form of consideration then many agreements would never be fulfilled and justice would suffer as a result. Therefore he concluded that courts should consider all relevant circumstances before deciding whether to uphold an agreement even if it lacked initial considerations upon which it was based.