An act of legislature to have force of law must be intelligibly expressed and when too vague is a nullity.

Explanation

(English-origin maxim.) A statute so vague that a reasonable person cannot determine its meaning violates due process of law and is void — the legislature must express its commands with sufficient intelligibility to be obeyed.

Where this applies

• A state legislature passes a criminal statute so vague that citizens cannot tell what conduct is prohibited — the court strikes it down as void for vagueness.
• A city ordinance bans 'inappropriate behavior in public' without defining what that means — a defendant challenges the law because no reasonable person can know what it forbids.
• A regulation requires businesses to maintain 'adequate' safety measures but never defines what 'adequate' means — the rule is struck down as unconstitutionally vague.