Definition
The petit jury is the trial jury: the body of citizens assembled to hear evidence in a civil or criminal case and return a verdict on disputed questions of fact. It is distinguished from the grand jury, which does not decide guilt or liability but instead determines whether sufficient evidence exists to bring charges.
At common law, the petit jury consisted of twelve members, and a valid verdict required unanimity. Modern practice has modified both requirements in some contexts — federal courts retain the twelve-person, unanimous standard in criminal trials, while state courts and civil proceedings operate under varying rules.
The petit jury sits as the factfinder. Its role is to evaluate testimony and evidence, apply the law as instructed by the judge, and return a verdict. It does not make legal rulings, interpret statutes, or determine what law governs — those functions belong to the court.
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Common Language
Modern common usage (Wiktionary): A regular trial jury, assembled to determine criminal or civil liability.
Historical common usage (Webster's 1913): Webster's 1913 treats "petit jury" as a legal term of art and does not assign it a separate common-language meaning distinct from its legal definition.
The term "petit" — French for small or lesser — is familiar in ordinary English but carries no independent legal weight here. The word functions solely as a contrast to "grand," distinguishing the trial jury from the indicting body. Researchers encountering "petty jury" in older sources should treat it as an exact synonym; the spelling variation is common through the nineteenth century and into the early twentieth.
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Common Confusion
PETIT JURY vs. GRAND JURY: The two bodies are frequently conflated by non-specialists and occasionally by historical sources that treat "jury" without qualification. The grand jury accuses; the petit jury decides. Grand jury proceedings are secret and ex parte; petit jury proceedings are open, adversarial, and governed by rules of evidence. The constitutional right to a jury trial — as applied in criminal cases — refers to the petit jury, not the grand jury.
PETIT JURY vs. SPECIAL JURY: Historical sources, including nineteenth-century treatises and some early American practice, distinguish the common or ordinary jury (petit jury) from a special jury summoned for particular cases involving technical subject matter or called by special writ. The distinction has largely collapsed in modern American practice but may appear in older English materials and early state court records.
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Why It Matters in Research
The term is stable in meaning but not in form. Researchers using historical sources will encounter "petty jury," "petit jury," and simply "jury" used interchangeably, sometimes within the same document. Keyword searches that rely on a single spelling will miss material.
The twelve-person unanimity rule, which Black's Law Dictionary treats as definitional, is no longer universally required. The Supreme Court held in *Apodaca v. Oregon* (1972) that state criminal convictions could stand on non-unanimous verdicts, a position that produced a fractured precedent litigated for decades before *Ramos v. Louisiana* (2020) required unanimity in serious criminal cases under the Sixth Amendment. Researchers examining twentieth-century state criminal procedure must account for this shift; sources from the interim period may reflect rules that are no longer good law.
Civil petit jury practice diverges significantly from criminal practice. Federal Rule of Civil Procedure 48 permits juries of as few as six in civil cases and allows verdicts without unanimity if the parties stipulate. State civil rules vary further. Historical sources that define the petit jury by its twelve-person composition are accurate for criminal proceedings but should not be applied wholesale to civil jury research.
The petit jury's constitutional dimension runs through the Sixth Amendment (criminal) and Seventh Amendment (civil) jury trial rights. These are distinct guarantees with different incorporation histories and different doctrinal frameworks. Research touching on the right to a jury trial — as opposed to the mechanics of jury composition — should track those constitutional provisions separately.
Rapalje & Lawrence's entry offers no independent definition, redirecting to the general JURY entry. This is typical of that dictionary's treatment of compound terms and is not an indication that the term lacks significance — it is a reminder that nineteenth-century dictionaries often consolidated jury doctrine under a single heading rather than treating subtypes as standalone entries.
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Historical Dictionary Support
Black's Law Dictionary defines the petit jury as "the ordinary jury of twelve men for the trial of a civil or criminal action," emphasizing the twelve-person, unanimous-verdict standard. The definition reflects the common-law baseline accurately for its period and remains a useful starting point, but the word "ordinary" quietly carries significant weight — it signals that the definition describes the default rule, not a constitutional floor that is invariant across jurisdictions and case types.
Rapalje & Lawrence redirects to the general JURY entry, consistent with that dictionary's practice of treating the petit jury as the default meaning of "jury" rather than a distinct subcategory requiring separate treatment. Researchers using Rapalje & Lawrence for jury doctrine should go directly to the JURY entry.
Neither dictionary addresses the constitutional underpinnings of the petit jury right in any depth, which is characteristic of late-nineteenth-century legal dictionaries generally. For constitutional doctrine on jury trial rights, these sources must be supplemented with treatise and case law research.
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Jurisdictional Note
Federal criminal practice requires twelve jurors and a unanimous verdict for serious offenses. State practice varies: jury size in civil cases, the unanimity requirement, and the definition of which offenses trigger the jury trial right all differ by jurisdiction and have shifted over time. Researchers should not assume that the common-law twelve-person unanimity standard applies in any state civil or misdemeanor proceeding without checking current rules.
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Encyclopedia Cross-Reference
The Law Mind Criminal Law Encyclopedia — Mistrial and Hung Jury (directly relevant to petit jury deadlock and verdict requirements)
The Law Mind Criminal Law Encyclopedia — Grand Jury: Fifth Amendment in Grand Jury Proceedings (essential contrast with petit jury function and constitutional basis)
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