A law that operates retrospectively to make an act a crime that was not a crime when committed, or to increase the penalty for an act after it was done. The Constitution prohibits this in criminal matters under Article 20(1).
- Article 20(1): no person shall be convicted of any offence except for violation of a law in force at the time of the act, nor be subjected to a penalty greater than that prescribed when the offence was committed.
- The protection covers conviction and enhanced penalty only; it does not bar a retrospective reduction of punishment, and a beneficial change can be claimed.
- The bar applies to criminal laws; civil liabilities and taxes may be imposed retrospectively (the prohibition is specific to penal consequences).
- It does not prevent preventive detention or trial under procedures changed after the offence, only the substantive penalising of past conduct.
- Article 20 as a whole (including this clause, concept double jeopardy and protection against concept self incrimination) cannot be suspended even during a national emergency (Article 359 after the 44th Amendment, 1978).
Article 20(1) is a standard Fundamental Rights recall item, and the emergency-proof nature of Articles 20 and 21 is a frequently tested point.
The ban is on retrospective criminal liability and increased penalty only; a law reducing punishment can apply retrospectively, and civil or tax laws may be retrospective.
Article 20(1): no conviction or heavier penalty under a law made after the act; protection against retrospective criminal law.