ex post facto

An ex post facto law operates on acts done before it was made. Article 20(1) of the Constitution forbids such laws only in criminal matters: no person shall be convicted of an offence except for violation of a law in force at the time of the act, nor subjected to a penalty greater than that which might have been inflicted under the law in force at that time.

Article 20(1) bars conviction and sentence under retrospective criminal laws, not trial under a new procedure, and it does not prevent a later law that reduces punishment from benefiting the accused. Civil and tax laws may be made retrospective, subject to other constitutional limits. The phrase is also used for an approval or sanction given after the act (ex post facto sanction).

Example

A 2025 amendment raising the punishment cannot be applied to an offence committed in 2023, as Article 20(1) bars ex post facto penal laws.

In Indian law

• Article 20(1), Constitution of India

See also

double jeopardy · due process of law · doctrine of eclipse

Read more in the study notes

• Control of delegated legislation: parliamentary, procedural and judicial (Administrative Law)
• Article 13: pre- and post-constitutional laws, severability, eclipse and waiver (Constitutional Law I)
• Article 14: equality before law and the new doctrine of arbitrariness (Constitutional Law I)
• Article 20: rights of the accused (Constitutional Law I)
• Specific performance of contracts (Contract I)
• Relations of partners to third parties (Contract II)