Ex post facto laws
Ex post facto laws are legal provisions that apply retroactively, penalizing individuals for actions that were not illegal at the time they were committed. In the United States, these laws are prohibited by the Constitution, specifically in Article I, where Congress and state legislatures are barred from enacting such measures. Historically, the prohibition against ex post facto laws was established to protect individuals from potential government overreach and arbitrary punishment. The Supreme Court has clarified the scope of this prohibition through various landmark cases, determining that it primarily applies to criminal laws, preventing the imposition of harsher penalties or changes in evidentiary rules after the fact. Notably, cases like Calder v. Bull and Beazell v. Ohio have shaped the understanding of what constitutes an ex post facto law, with the Court allowing certain civil regulations that may have retroactive effects. Overall, the concept of ex post facto laws reflects a commitment to fairness and due process in the legal system, emphasizing the importance of predictable and transparent legal standards. Understanding these laws is crucial for comprehending the broader principles of justice and individual rights within the U.S. legal framework.
Ex post facto laws
Description: Statutes that render an act committed in the past illegal, although that act was legal when it took place.
Significance: The Supreme Court examined the extent of the restriction against ex post facto laws, which are banned by the Constitution, prohibiting their use in criminal but not civil law.
Ex post facto laws, regarded as tools of oppression when the U.S. Constitution was written, were banned in Article I, section 9, of the Constitution, where they are excluded from the powers of Congress, and in Article I, section 10, where the exclusion is applied to state legislatures.

The Supreme Court specified the extent and meaning of this restriction on the powers of U.S. government. Its principal interpretation came in Calder v. Bull (1798), where plaintiffs challenged the right of a state legislature to legislate against their interests in a civil case. Justice Samuel Chase ruled, however, that the ex post facto exclusion applied only to criminal not to civil law.
Besides laws criminalizing actions that were committed before the law was passed, Chase’s decision excluded laws that make crimes greater or subject to more severe punishments than when committed and laws that alter rules of evidence, making conviction easier.
Later Court cases extended the ex post facto restriction. In the Test Oath Cases (1867), the court voided laws requiring oaths regarding past loyalties that disqualify individuals from holding office or practicing certain professions. In Beazell v. Ohio (1925), changes in laws regarding evidence that “operate only in a limited and unsubstantial manner to [the defendant’s] disadvantage, are not prohibited.” In Weaver v. Graham (1981), the Court held that laws that reduce a prisoner’s “good time” credits, thereby extending punishment, are prohibited, but those acting to defendants’ benefit are allowed. The Court has also held that deportation of aliens and the denial of a passport are not banned as ex post facto because they are not criminal punishments.