The Constitution prohibits Congress and state legislatures from passing bills of attainder or ex post facto laws. A bill of attainder is a law that legislatively determines guilt and inflicts punishment on an identifiable individual or group without a judicial trial. An ex post facto law retroactively imposes criminal liability or punishment for actions that were legal when taken.
The Framers included these prohibitions to prevent legislatures from bypassing the judicial system to punish political enemies, a practice British Parliament had used against colonists. These protections ensure the separation of powers by reserving to courts—not legislatures—the power to determine guilt and impose punishment.
Courts apply a three-part test for bills of attainder: the law must specify affected persons, impose punishment, and lack a judicial trial. For ex post facto laws, courts examine whether a law increases punishment for past acts, changes the legal consequences of actions already taken, or deprives someone of a defense available when they acted.
These prohibitions protect the separation of powers by preventing legislatures from taking on judicial functions. They ensure that punishment comes through courts, not political processes, which protects unpopular minorities from legislative vengeance.
People often think these prohibitions only apply to obvious cases. Modern laws can violate them too: legislation targeting a specific named individual or retroactively changing penalties for past conduct violates these principles.
These prohibitions protect the separation of powers by preventing legislatures from taking on judicial functions. They ensure that punishment comes through courts, not political processes, which protects unpopular minorities from legislative vengeance.
People often think these prohibitions only apply to obvious cases. Modern laws can violate them too: legislation targeting a specific named individual or retroactively changing penalties for past conduct violates these principles.