Glossary

Void for vagueness

The rule that a law is unconstitutional if it is so unclear that ordinary people cannot know what it forbids.

Also called: vagueness doctrine

The void-for-vagueness doctrine holds that a criminal law, or a law imposing serious penalties, violates due process if it fails to define the offense with enough clarity that ordinary people can understand what conduct is prohibited, or if it invites arbitrary and discriminatory enforcement.

The doctrine serves two purposes: giving fair notice to citizens and preventing police, prosecutors and juries from filling in the gaps with their own preferences. Courts apply it more strictly to laws that reach protected speech or impose criminal penalties. Recent examples include Johnson v. United States (2015), which struck down the "residual clause" of the Armed Career Criminal Act, and Sessions v. Dimaya (2018), which invalidated a similar clause in an immigration statute. United States v. Davis (2019) did the same for part of a gun-crime statute.

The doctrine links to the rule of law ideal that laws be knowable and applied equally, and to separation-of-powers concerns, since a vague law effectively delegates lawmaking to enforcers. Its use has produced unusual cross-ideological coalitions among justices. It affects the application of mandatory minimum sentence sentencing statutes.

Last reviewed November 8, 2026

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Related terms

Procedural due process The constitutional requirement that government use fair procedures, such as notice and a hearing, before depriving a person of life, liberty or property. Rule of law The principle that everyone, including government, is subject to publicly known laws that are applied equally and fairly. Nondelegation doctrine The principle that Congress may not hand its lawmaking power to agencies or others without clear limits on how it is used. Mandatory minimum sentence A law setting a minimum prison term that a judge must impose for a specific crime, regardless of circumstances.