Retroactive

Having reference to things that happened in the past, prior to the occurrence of the act in question.

A retroactive or retrospective law is one that takes away or impairs vested rights acquired under existing laws, creates new obligations, imposes new duties, or attaches a new and different legal effect to transactions or considerations already past. Common-law principles do not favor the retroactive effect of laws in the majority of cases, and canons of legislative construction presume that legislation is not intended as retroactive unless its language expressly makes it retroactive.

Retroactive criminal laws that increase punishment for acts committed prior to their enactments are deemed Ex Post Facto Laws and are unenforceable because they violate Article I, Section 9, Clause 3, and Section 10, Clause 1, of the U.S. Constitution and comparable provisions of state constitutions.

---

retroactive adj. referring to a court's decision or a statute enacted by a legislative body, which would result in an application to past transactions and legal actions. In criminal law, statutes which would increase penalties or make criminal activities which had been previously legal are prohibited by the Constitutional ban on ex post facto laws (Article I, Section 9). Most court decisions which change the elements necessary to prove a crime or the introduction of evidence such as confessions are usually made non-retroactive to prevent a flood of petitions of people convicted under prior rules. Nor can statutes or court decisions take away "vested" property rights or change contract rights. However, some decisions are so fundamental to justice they may have a retroactive effect, depending on the balance on stability of the law balanced against the public good. Retroactive is also called "retrospective." (See: ex post facto)