Review : “Lex retro non agit”

The term "lex retro non agit" translates to "the law does not act retroactively." This principle is fundamental in legal systems, particularly in criminal law. It asserts that laws should not apply to actions that occurred before the law was enacted. This rule protects individuals' autonomy and helps maintain legal certainty, ensuring that people are not punished for actions that were not illegal at the time they were committed.

This principle is commonly applied in various areas of law, including:

• Criminal Law: Prevents individuals from being prosecuted for acts that were legal when committed.
• Civil Law: Ensures that changes in laws do not affect past transactions or agreements.

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·       Main GoalsLegal Certainty: Ensuring that individuals can know for certain which actions are legal and illegal before they do them.Individual Protection: Preventing someone from being punished for an act that when committed was not considered a violation of the law

 

The principle of non-retroactive application of law first emerged in Roman law, where it took the form of a rule against punishing an individual in the absence of a specific rule prohibiting certain conduct when committed.⁴ Its application has become particularly controversial as states adopt stricter environmental regulations to tackle climate change.⁵ The retroactive effect of these and other regulations has been challenged in international courts and tribunals. However, outside the context of criminal law, the principle of non-retroactivity has received little attention in comparative and international law literature. Its poor understanding leads to statements about its universal nature and confusing it with other legal concepts such as legality, legal certainty, fair and equitable retreatment and res judicata, and has resulted in an increasing number of disputes.

Major ExceptionsIn practice, the principle of lex retro non agit has very important exceptions, especially in criminal law. New legal rules that are more lenient in sentencing for defendants can be applied retroactively (known as the principle of lex favorabilis or lex benignior retro agit).

The principle of non-retroactivity was first clearly articulated in Roman law, where already by the end of the second century B.C. it applied in both criminal and civil law to protect the existing legal order and economic interests.¹⁷ The Roman statesman Cicero explained the importance of the principle of non-retroactivity. According to him, individuals should be able to rely on laws in the expectation that the state will not afterwards interfere with individuals’ rights.¹⁸ This expectation helped to ensure equality of all before the law guarding predictability and legal certainty.¹⁹

Roman law made a distinction between natural or unwritten law (called ius) and laws adopted by the legislator (called lex). Unlike lex, ius existed long before the foundation of Rome with its roots in antiquity.²⁰ Cicero explained the limits of non-retroactivity, such as in situations when the grievous nature of committed actions resulted in an assumed positive duty not to commit them, even in the absence of positive law expressed in a statute. Ius came from fundamental moral values and the law of nature which are not necessarily expressed in lex. Rather than creating a new law and applying it retroactively the judge was considered to facilitate concrete determination of legal rules.²¹ Therefore, the principle of non-retroactivity did not affect ius, which usually covered only serious crimes or offences.²²

It is important to distinguish the principle of non-retroactivity from res judicata, which literally means ‘a matter that has been adjudicated.’ New judgements cannot invade on procedurally ‘concluded’ acts, and final judgments preclude completely or create legal barriers to relitigation between the same parties in respect of the same object and within the same jurisdiction.²³ In Roman law, the res judicata principle served as a ‘supreme guarantor of the social order,’ protecting from invasions of the past by a new judgment.²⁴ The principles of res judicata and non-retroactive application of law both aim at ensuring legal certainty. While res judicata concerns court judgements, non-retroactivity applies to legislation.