“Ex post facto” is a Latin term meaning “after the fact” in English. In legal contexts, it refers to a law or regulation that retroactively changes the legal consequences or status of actions that were committed before the enactment of the law.
Many legal systems disallow the ex post facto principle because it violates the basic principles of fairness and justice. Retroactively criminalizing an action or increasing the punishment for an offense after it has been committed is seen as unfair. Individuals should be aware of the legal consequences of their actions at the time they engage in them.
In constitutional law, many jurisdictions explicitly prohibit ex post facto laws to protect individuals from arbitrary and unjust treatment by the legal system. The prohibition against ex post facto laws is often found in the constitutions or legal frameworks of democratic societies to uphold the principle of the rule of law.
