Ex post facto law
One which (1) makes an action done before the passing of the law and which was innocent when done criminal, and punishes such action; or (2) aggravates a crime or makes it greater than it was when committed; or (3) Which damages the punishment and inflicts a greater punishment than the law annexed to the crime when it was committed; or (4) Which alters the legal rules of evidence and receives less or different testimony than the law required at the time of the commission of the offense in order to convict the defendant; or 5) assumes to regulate civil rights and remedies only but in effect imposes a penalty or deprivation of a right which when done was lawful; or 6) deprives a person accused of a crime some lawful protection to which he has become entitled, such as the protection of the former conviction or acquittal, or a proclamation of amnesty.
The first four of the enumeration were provided in Mekin vs. Wolfe,<ref>G.R. No. 1251, 27 March 1903</ref> while the last two were added in In re: Kay Villegas Kami, Inc.<ref>G.R. No. L-32485, 22 October 1970</ref>
Prohibition and coverage
Ex post facto laws are prohibited under the Constitution (Art. III, Sec. 22). The prohibition against ex post facto laws applies only to criminal or penal, and not to civil matters.<ref>De la Paz vda. De Ongsiako vs. Gamboa, G.R. No. L-1867, 8 April 1950</ref>