Definition
A commission of nisi prius was a formal royal authority issued to judges — typically justices of the court at Westminster — empowering them to travel into the counties to try civil jury cases that had been initiated in the central courts but could not practically be heard there. The commission authorized designated judges to sit locally and take verdicts, after which the record would return to the central court for final judgment.
In English legal history, the commission formed one of the mechanisms by which the common law courts at Westminster extended their reach across the realm. Rather than requiring parties to transport witnesses, jurors, and evidence to London, the commission brought the court's authority to the locality. The judges riding circuit under such a commission sat with the authority of the central court itself, not merely as local magistrates.
The name derives from the Latin phrase nisi prius — "unless before" — which appeared in the original writ summoning jurors to Westminster at a fixed date, unless before that date a royal justice came into the county. The commission formalized the "unless before" mechanism into a standing authority.
Common Confusion
The commission of nisi prius is frequently conflated with the assize commissions — particularly the commission of oyer and terminer and the commission of gaol delivery — which also authorized judges to ride into the counties. The distinction is functional: the commission of nisi prius was directed at civil jury trials originating in the central common law courts (principally the Court of Common Pleas and later the King's Bench), while the assize commissions addressed criminal matters and felony cases. In practice, the same judges often held multiple commissions simultaneously on a single circuit, which compounds the confusion in older sources that use "assizes" loosely to describe all circuit business. A researcher encountering "nisi prius" in a historical record should treat it as a signal pointing toward civil litigation, not criminal proceedings.
Why It Matters in Research
This term carries heavy historical freight and has essentially no modern operational meaning in English or American law. Researchers will encounter it most commonly in three contexts: (1) pre-nineteenth-century English procedural materials, where it describes the mechanism by which civil jury trials were conducted outside Westminster; (2) American colonial and early republic materials, where the commission structure was transplanted in modified form and the phrase "court of nisi prius" sometimes designated a trial court of first instance as distinct from an appellate court; and (3) treatise and form-book literature, particularly from the seventeenth through nineteenth centuries, where "nisi prius" appears as a near-synonym for the trial stage of a civil action.
The critical research trap is anachronism of vocabulary. By the mid-nineteenth century, English procedural reforms — culminating in the Judicature Acts of 1873–1875 — dismantled the old commission structure. American jurisdictions, which had adopted various versions of the system, similarly reformed their court organizations at different times. A source dated 1820 using "nisi prius" may mean something procedurally precise; a source dated 1890 using the same phrase may be deploying archaic language as shorthand for "trial court" without the technical machinery behind it.
Researchers working in equity records should note that the commission of nisi prius was a common law instrument. Equity proceedings before the Chancellor or in equity courts did not proceed under this commission and will not use this terminology.
The Burrill entry's reference to "five [now four]" classes of commission reflects a mid-nineteenth-century editorial update, signaling that even within the historical dictionary literature this term was understood to be a moving target undergoing reform.
Historical Dictionary Support
Burrill's Law Dictionary identifies the commission of nisi prius as one of a small class of English commissions — originally five, reduced to four at the time of Burrill's writing — issued to authorize judicial circuit work. This places the commission of nisi prius within a formal taxonomy of royal commissions alongside the commissions of oyer and terminer, gaol delivery, the peace, and assize. Burrill's truncated entry (the source material provided is incomplete) was characteristic of how mid-nineteenth-century American legal dictionaries treated English procedural antecedents: as historical background requiring acknowledgment but no longer demanding full operational exposition.
Earlier English legal writers, including Blackstone in his Commentaries on the Laws of England (Book III), treated the nisi prius system with considerably more depth, describing the practical mechanics of how writs, commissions, and circuit schedules operated together. Blackstone remains the more useful source for understanding the institution in its full working form. Burrill's entry, by contrast, reflects the perspective of an American compiler working as the old commission structure was being actively reformed in England — useful for confirming that the term belonged to a recognized formal category, less useful for explaining what that category actually did.
No significant divergence exists among historical dictionaries on the basic meaning. The variation is one of depth, not disagreement.
Jurisdictional Note
In American usage, "nisi prius" survived the commission structure itself and was used in many states through the nineteenth century to denote a trial court or the trial level of a court system, as distinguished from an appellate court sitting en banc. The phrase appears in this looser American sense in statutory materials, court rules, and reported decisions from jurisdictions that never formally adopted the commission mechanism. Researchers must distinguish between the technical English commission and the American colloquial usage.