Ex Post Facto
Literal meaning: “From after the fact.”
What does the Latin term "Ex Post Facto" mean in law?
An ex post facto law is one that retroactively criminalizes conduct that was legal when performed, increases the punishment for a crime after it was committed, reduces the evidence required to convict, or otherwise disadvantages a defendant by changing the legal consequences of acts already completed. The U.S. Constitution explicitly prohibits both Congress (Article I, Section 9) and state legislatures (Article I, Section 10) from enacting ex post facto laws. The prohibition applies only to criminal and penal statutes, not to civil laws, although a law labeled 'civil' may be struck down if its purpose or effect is punitive.
Source: Criminal · Legal Latin
Legal Definition
An ex post facto law is one that retroactively criminalizes conduct that was legal when performed, increases the punishment for a crime after it was committed, reduces the evidence required to convict, or otherwise disadvantages a defendant by changing the legal consequences of acts already completed. The U.S. Constitution explicitly prohibits both Congress (Article I, Section 9) and state legislatures (Article I, Section 10) from enacting ex post facto laws. The prohibition applies only to criminal and penal statutes, not to civil laws, although a law labeled 'civil' may be struck down if its purpose or effect is punitive.
How It's Used
Ex post facto is used in constitutional law and criminal law when analyzing whether retroactive legislation violates the constitutional prohibition. It arises in discussions of sentencing enhancements, sex offender registries, and other laws applied retroactively.
Example Sentences
The court struck down the statute as an ex post facto law because it retroactively increased the mandatory minimum sentence for offenses committed before its enactment.
Applying the new sentencing guidelines to crimes committed before their adoption would violate the Ex Post Facto Clause.
The sex offender registration requirement was challenged as an ex post facto law, but the court found it regulatory rather than punitive.