Maxims, axioms & idioms · a browsable collection

Legal maxims, political axioms, and the idioms that carry them into everyday argument — each with a plain-English gloss and where it comes from. We state what a maxim means and where it's from; we do not tell you it is right. Open any maxim to see the case law that cites or applies it — curated landmark cases plus a live search of the public record. The legal maxims cross-reference the same categories as our case law.

Legal maxims Political axioms Idioms & mottos All

Ignorantia juris non excusat legal · Latin

“Ignorance of the law excuses not”

You are bound by the law whether or not you know it exists.

Provenance: Roman-law maxim; standard in common-law systems.

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Actus reus non facit reum nisi mens sit rea legal · Latin

“An act does not make one guilty unless the mind is also guilty”

Most crimes require both a wrongful act and a guilty mental state.

Provenance: Coke; foundational to Anglo-American criminal law.

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Nemo judex in causa sua legal · Latin

“No one should be a judge in his own cause”

A decision-maker must not have a personal stake in the matter — the rule against bias.

Provenance: Natural-justice maxim; Dr. Bonham's Case (1610).

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Audi alteram partem legal · Latin

“Hear the other side”

No one should be condemned unheard — the core of due process.

Provenance: Roman/natural-justice maxim.

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Stare decisis legal · Latin

“To stand by things decided”

Courts follow prior rulings — the engine of case law.

Provenance: Common-law doctrine of precedent.

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Respondeat superior legal · Latin

“Let the superior answer”

An employer is liable for torts an employee commits within the scope of employment (vicarious liability).

Provenance: Common-law agency doctrine.

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Nulla poena sine lege legal · Latin

“No penalty without a law”

You can only be punished under a law that existed when you acted (anti-ex-post-facto).

Provenance: Enlightenment penal principle; Feuerbach.

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Ei incumbit probatio qui dicit, non qui negat legal · Latin

“The burden of proof is on the one who asserts, not the one who denies”

The party making a claim must prove it.

Provenance: Roman law (Digest).

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Res ipsa loquitur legal · Latin

“The thing speaks for itself”

Some accidents so obviously imply negligence that the fact of them is evidence.

Provenance: Byrne v. Boadle (1863).

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De minimis non curat lex legal · Latin

“The law does not concern itself with trifles”

Courts won't act on trivial matters.

Provenance: Common-law maxim.

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Habeas corpus legal · Latin

“That you have the body”

A court order requiring a jailer to justify holding a prisoner — the great writ against unlawful detention.

Provenance: English common law; U.S. Const. art. I, §9.

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Cui bono legal · Latin

“To whose benefit?”

Ask who profits — a guide to motive.

Provenance: Cicero, quoting Cassius.

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Fiat justitia ruat caelum legal · Latin

“Let justice be done though the heavens fall”

Justice must be done regardless of consequence.

Provenance: Roman maxim; Somerset v Stewart (1772).

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