This word is usually applied to those acts of the legislature, which are made to operate upon some subject, contract or crime which existed before the passage of the acts, and they are therefore called retrorospective laws. These laws are generally unjust and are, to a certain extent, forbidden by that article in the Constitution of the United States, which prohibits the passage of ex post facto laws or laws impairing contracts.
The right to pass retrospective laws, with the exceptions above mentioned, exists in the several states, according to their own constitutions, and become obligatory if not prohibited by the latter. An instance may be found in the laws of Connecticut. In 1795, the legislature passed a resolve, setting aside a decree of a court of probate disapproving of a will and granted a new hearing; it was held that the resolve not being against any constitutional principle in that state, was valid. 386. And in Pennsylvania a judgment was opened by the act of April 1, 1837, which was holden by the supreme court to be constitutional. Laws should never be considered as applying to cases which arose previously to their passage, unless the legislature have clearly declared such to be their intention.