Constitutional Law
Vagueness Doctrine
Definition
The vagueness doctrine, rooted in the Due Process Clause, requires that laws provide fair notice of what conduct is prohibited and include sufficient standards to prevent arbitrary enforcement. A law is void for vagueness if a person of ordinary intelligence cannot understand what it prohibits or if it encourages arbitrary and discriminatory enforcement by officials. Vagueness challenges are particularly potent in the First Amendment context, where imprecise laws may chill protected expression.
Example
A city ordinance bans 'loitering in a suspicious manner.' Without clear standards for what is 'suspicious,' the ordinance is likely void for vagueness.