Legal Definitions - Nullum crimen sine lege

Nullum crimen sine lege is a fundamental principle in criminal law, Latin for "no crime without law."

This principle means that an individual cannot be found guilty of a crime, nor can they face criminal punishment, unless the act they committed was clearly defined as a crime by a specific law before they performed the act. It ensures that laws are not applied retroactively and that criminal statutes are clear, precise, and publicly known. Essentially, people must have fair warning about what conduct is prohibited before they can be held accountable for it. This concept is also often referred to as the "legality principle."

Here are some examples illustrating this principle:

• Example 1: New Technology and Unregulated Behavior

  Imagine a new online platform emerges where users can create and share highly realistic deepfake videos. While some of these videos might be misleading or offensive, there is no existing law specifically prohibiting the creation or sharing of deepfakes for non-malicious purposes at the time. If a person creates and shares such a video, they cannot be prosecuted for a crime related to deepfakes until a specific law is passed that clearly defines and criminalizes such actions. The principle of nullum crimen sine lege dictates that without a pre-existing law, there is no crime.

• Example 2: Retroactive Application of New Laws

  A country's legislature passes a new law making it illegal to possess certain types of cryptocurrency, effective immediately. Before this law was enacted, possessing that cryptocurrency was perfectly legal. The government cannot then prosecute individuals who legally owned and possessed that cryptocurrency *before* the new law came into effect. To do so would violate nullum crimen sine lege, as the act was not a crime at the time it was committed.

• Example 3: Vague or Undefined Offenses

  Consider a local ordinance that states, "It is unlawful to engage in any activity that is generally considered 'disruptive to public order'." A person is arrested for loudly singing in a public park, and the authorities attempt to charge them under this ordinance. However, the term "disruptive to public order" is extremely vague and does not clearly define what specific actions are prohibited. Because the law does not provide clear notice of what constitutes a crime, the individual cannot be convicted under such an ambiguous statute, upholding the requirement of nullum crimen sine lege for clear and precise legal definitions.