What legal principle states that laws cannot be applied retroactively?

The legal principle that states laws cannot be applied retroactively is known as the non-retroactivity of law. This principle is a fundamental concept in legal systems that ensures individuals are not penalized under laws that were enacted after their actions took place. It guarantees that individuals can rely on the legal standards that were in effect at the time of their conduct, promoting fairness and stability in the legal system.

This principle is rooted in the idea that people should have the ability to understand and predict the consequences of their actions based on the laws that are in existence at that time. By preventing retroactive application of laws, the legal system respects the rights of individuals and upholds justice by ensuring that new laws do not disrupt the established legal environment unfairly.

The presumption of innocence pertains to criminal law and the idea that a defendant is considered innocent until proven guilty, which does not directly relate to the question of retroactive law. The rule of law emphasizes that law should govern a nation, as opposed to arbitrary decisions by individual government officials, but it does not specifically address the retroactivity issue. Proportionality relates to ensuring that legal measures are appropriate and not excessive in relation to their aims, which also does not involve retroactivity.