Justification and excuse are different defenses in criminal cases in the United States. Both defenses admit that the defendant committed an act proscribed by law. The proscribed act has justification if the act had positive effects that outweigh its negative effects, or is not wrong or blameworthy. The proscribed act is excused if the defendant's violation was not entirely voluntary, such as if they acted under duress or under a false belief. Martin v. Ohio (1986) established that states may make justification an affirmative defense, placing the burden of proof on defendant. Patterson v. New York (1977) established that states may make excuses, such as involving mental state, an affirmative defense, rather than part of the mens rea element the prosecution must prove beyond a reasonable doubt.