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Ex post facto law

An ex post facto law (Latin for "from a thing done afterward"), also known as a retrospective law, is a law that is retroactive, i.e. that affects facts or legal relationships that have existed prior to the enactment of the law. Ex post facto is a term from the Latin and means "after the deed." In reference to criminal law, it is an attempt to criminalize an action that was not a crime at the time it was committed. A law may have an ex post facto effect without being technically ex post facto. For example, when a law that repeals another law, the repealed legislation will no longer apply to situations even when those situations arose before the law was repealed. The principle of prohibiting these kinds of laws is also known as Nullum crimen, nulla poena sine praevia lege poenali.

Generally speaking, ex post facto laws are seen as a violation of the rule of law as it applies in a free and democratic society. Most common law jurisdictions do not permit retrospective legislation, though some have suggested that judge-made 'law' is retrospective as a new precedent applies to events that happened prior to the judicial decision. In some nations that follow the Westminister system of government, such as the United Kingdom, ex post facto laws are technically possible as parliamentary supremacy allows the parliament to pass any law it wishes. However, in a nation with an entrenched bill of rights or written constitution this may prohibit ex post facto legislation.

Ex post facto laws internationally

• France - any ex post facto criminal law may only be applied if it benefits the accused person (for instance, if weaker sentences are now applicable but were not previously applicable); otherwise, prohibited by the Declaration of the Rights of Man and of the Citizen.

• United Kingdom - Ex post facto laws are permitted under the doctrine of the 'sovereignty of parliament'; in criminal law, however, ex post facto laws are prohibited by article 7 of the European Convention on Human Rights.

• United States - Prohibited by Article I section 9 (applying to federal law) and section 10 (applying to state law) of the U.S. Constitution. Over the years, when deciding ex post facto cases, the United States Supreme Court has referred repeatedly to its ruling in the Calder v. Bull case of 1798, in which Justice Chase established four categories of unconstitutional ex post facto laws.

• Republic of Ireland - Prohibited by Article 15.5.1 of the Constitution of Ireland.

• Sweden - Retroactive penal sanctions and other retroactive legal effects of criminal acts, and retroactive taxes or charges due the State are prohibited by chapter 2, article 22, point 5 of the Instrument of Government (Regeringsformen).