A change made that is then applied to a previous point in time and rolled forward as if that change was made in the past. Typically this refers to statutes or rulings that will have an impact prior to the date of enaction. In most instances, such laws are prohibited, e.g. the increase of criminal penalties to take effect as if promulgated one year earlier is unconstitutional and an unlawful ex post facto law. has the same meaning as “retrospective,” (q. v.)