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Ex Post Facto Law

Ex Post Facto Law Definition

A statute which would render an act punishable in a manner in which it was not punishable when it was committed. (…). A law made to punish acts committed before the existence of such law, and which had not been declared crimes by preceding laws. Dec. Rights Mass. pt. 1, § 24; Dee. Eights Md. art. 15. One which, in its operation, makes that criminal or jjenal which was not so at the time the action was performed, or which increases the punishment, or, in short, which, in relation to the offense or its consequences, alters the situation of the party to his disadvantage. (…). Laws under the following circumstances are to be considered ex post facto laws, within Const, art. 1, § 10:

  • Every law that makes an act done before the passing of the law, and which was innocent when done, criminal, and punishes such action.
  • Every law that aggravates a crime, or makes it greater than it was when committed.
  • Every law that changes the punishment, and inflicts a greater punishment than the law annexed to the crime when committed, though it would be otherwise of a law mitigating the punishment. 3 Story, Const. 212.
  • Every law that 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 offender, though it might be otherwise of a law merely modifying the remedy or mode of procedure. 3 DalL (U. S.) 386; 16 Ga. 102.
  • A fifth class has been suggested, to cover some exceptional cases, viz., laws that, in relation to the offense or its consequences, alter the situation of the party to his disadvantage. (…)

As, for example, where, after a crime was committed, the law was so changed that’ a conviction of a lower degree was no longer a bar, on a new trial being granted, to a conviction of a higher degree. 107 U. S. 22L A law mitigating the punishment of previously committed crimes is not ex post facto, within the meaning of the constitution. (…). Nor is a statute which regulates only mode of procedure. 110 U. S. 574; 137 U. S. 483.

There is a distinction between ex post facto laws and retrospective laws. Every ex post facto law must necessarily be retrospective, but every retrospective law is not an ex post facto, law; the former only are prohibited. It is fully settled that the term ex post facto, as used in the constitution, is to be taken in a limited sense as referring to criminal or penal statutes alone, and that the policy, the reason, and the humanity of the prohibition against passing ex post facto laws do not extend to civil cases, to cases that merely affect the private property of citizens. Some of the most necessary acts of legislation are, on the contrary, founded upon the principle that private rights must yield to public exigencies. (1)

Practical Information

Any retroactive legislation that has the effect of substantially prejudicing the rights of the accused or convicted party in a criminal proceeding. An example of an ex post facto law is one that designates an act as criminal after it has been committed. Another example is the passage of a law that would increase the penalty for a crime already committed. The Constitution denies to both Congress and the states the right to pass ex post facto laws. (Revised by Ann De Vries)

What is Ex Post Facto Law?

An ex post facto law (a law passed after the fact) has three features. It

  • is a criminal law, one defining a crime or providing for its punishment;
  • applies to an act committed before its passage; and
  • works to the disadvantage of the accused.

Neither Congress nor the State legislatures may pass such laws. Article I, Sections 9 and 10. The phrase ex post facto is from the Latin, meaning “after the fact.”

For example, a law making it a crime to sell marijuana cannot be applied to someone who sold it before that law was passed. Or, a law that changed the penalty for murder from life in prison to death could not be applied to a person who committed a murder before the punishment was changed.

Ex post facto cases do not come along very often. The Court decided its most recent one, Carmell v. Texas, in 2000. There, the Court overturned a man’s sexual abuse conviction because of a change in State law. That change had made it easier for the prosecution to prove its charge than was the case when the abuse was committed.

Retroactive civil laws are not forbidden. Thus, a law raising income tax rates could be passed in November and applied to income earned through the whole year.

For a meaning of it, read Ex Post Facto Law in the Legal Dictionary here. Browse and search more U.S. and international free legal definitions and legal terms related to Ex Post Facto Law.


Notes and References

  1. This definition of Ex Post Facto Law is based on The Cyclopedic Law Dictionary

See Also

Retrospective Law

Further Reading


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  • Article Name: Ex Post Facto Law
  • Author: Johannes Maule
  • Description: Ex Post Facto Law Ex Post Facto Law Definition A statute which would render an act punishable in a manner in which it was [...]

This entry was last updated: June 17, 2017

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