Definitions from Black's Law Dictionary: 2nd Edition and Ballentine's Law Dictionary as are available for each term in each dictionary.
  • Ballentine's Law Dictionary

    One which augments the punishment or alters the rules of evidence to the prisoner’s disadvantage, after the commission of the crime. See 45 Am. Rep. 544, note.

  • Black's Law Dictionary: 2nd Edition

    A law passed after the occurrence of a fact or commission of an act, which retrospectively changes the legal consequencos or relations of such fact or deed. By Const. U. S. art. 1, § 10, the slates are forbidden to pass "any ex post facto law." In this connection the phrase has a much narrower meaning than its literal translation would justlfy, as will appear from the extracts given below. The phrase "ex post facto," in the constitution, extends to criminal and not to civil cases. And under this head is included:
    (1) Every law that makes an action, done before the passing of the law, and which was innocent when done, criminal, and punishes such action.
    (2) Every law that aggravates a crime, or makes it greater than it was when committed.
    (3) Every law that changes the punishment, and inflicts a greater punishment than the law annexed to the crime when committed.
    (4) Every law that niters 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 offender. All these, and similar laws, are prohibited by the constitution. But a law may be ex post facto, and still not amenable to this constitutional inhibition ; that is, provided it mollifies, instead of aggravating, the rigor of the criminal law. Boston v. Cummins, 16 Ga. 102, 60 Am. Dec. 717 ; Cummings v. Missouri, 4 Wall. 277, 18 L. Ed. 356; U. S. v. Hail, 2 Wash. C. C. 366, Fed. Cas. No. 15,285; Woart v. Winnick, 3 N. H. 473, 14 Am Else. 384; Calder v. Bull, 3 Dali. 390, 1 L. Ed. 648 ; 3 Story, Const. 2l2. An ex post facto law is one which renders an act punishable, in a manner in which it was not punishable when committed. Such a law may inflict penalties on the person, or pecuniary penalties which swell the public treasury. The legislature is therefore prohibited from passing a law by which a man's estate, or any part of it, shall be seized for a crime, which was not declared, by some previous law, to render him liable to such punishment Fletcher v. Peck, 6 Cranch, 87, 138, 3 In Ed. 162. The plain and obvious meaning of this prohibition is that the legislature shall not pass any law, after a fact done by any citizen, which shall have relation to that fact, so as to punish that which was innocent when done; or to add to the punishment of that which was criminal; or to increase the malignity of a crime; or to retrench the rules of evidence, so as to make conviction more easy. This definition of an ex post facto law is sanctioned by long usage. Strong v. State, 1 Blackf. (Ind.) 196 The term "ex post facto law," in the United States constitution, cannot be construed to include and to prohibit the enacting any law after a fact, nor even to prohibit the depriving a citizen of a vested right to property. Calder v. Bull, 3 Dall. 386, 1 In Ed. 648. "Ex post facto" and "retrospective" are not convertible terms. The latter is a term of wider signification than the former and includes it. All ex post facto laws are necessarily retrospective, but not e converso. A curative or confirmatory statute is retrospective, but not ex post facto. Constitutions of nearly ali the slates contain prohibitions against ex post facto laws, but only a few forbid retrospective legislation in specific terms. Black, Const. Prohib. §§ 170, 172, 222. Retrospective laws divesting vested rights are impolitic and unjust; but they are not "ex post facto laws," within the meaning of the constitution of the United States, nor repugnant to any other of its provisions ; and, if not repugnant to the state constitution, a court cannot pronounce them to be void, merely because in their judgment they are contrary to the principles of natural justice. Albee v. May, 2 Pnine, 74, Fed. Cas. No. 134. Every retrospective act is not necessarily an ex post facto law. That phrase embraces only such laws as impose or affect penalties or forfeitures. Locke v. New Orleans, 4 Wall. 172, 18 In Ed. 334. Retrospective laws which do not impair the obligation of contracts, or affect vested rights, or partake of the character of ex post facto laws, are not prohibited by the constitution. Bay v. Gage, 36 Barb. (N. Y.) 447.