Looking backwards. 2. 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 retrospective 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. 3. 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… See Ex Post Facto.