Definition
Si non omnes (Latin: "if not all") is a writ used in English legal practice to authorize a subset of appointed justices to proceed with judicial business when the full commission cannot assemble on the appointed day. Rather than requiring every justice named in a commission to be present before proceedings could begin, the writ permitted two or more of the commissioners to act on behalf of the whole, ensuring that judicial business was not indefinitely delayed by the absence of one or more members.
The writ functioned as a practical safety valve within the English commission system, under which groups of justices were formally appointed by name to conduct specific judicial tasks — such as gaol delivery, oyer and terminer, or assize proceedings. Without a si non omnes provision, the absence of any single named commissioner could theoretically paralyze the entire commission. The writ resolved that problem by building in a quorum-style authorization at the outset.
Why It Matters in Research
This term is primarily of historical significance and will appear almost exclusively in English legal sources predating the nineteenth century. Researchers encountering it should understand it as a procedural instrument within the old English commission system — not a substantive legal doctrine with continuing application.
The term surfaces most often in records of commissions of oyer and terminer, gaol delivery, and assize, where multi-justice panels were the norm. If a researcher is tracing the procedural history of a particular commission or trying to understand how a court proceeded with fewer justices than originally named, si non omnes is the controlling mechanism to identify.
One navigational trap: the writ should not be confused with modern quorum rules in legislative or administrative bodies, which operate under entirely different frameworks. The commission-based structure of early English judicial administration has no direct modern counterpart in American courts, so the term will rarely appear in American legal materials. Researchers working in colonial American legal records may encounter it, as early colonial courts borrowed heavily from English commission structures.
The references to Fitzherbert's Natura Brevium and the Registrum Omnium Brevium (Reg. Orig.) in the historical dictionaries are the authoritative starting points for anyone pursuing deeper research into the writ's formal operation.
Historical Dictionary Support
Black's Law Dictionary (both the first and second editions) and Burrill's Law Dictionary are in complete agreement on this term: all three define it identically as a writ of association allowing two or more justices to proceed when the full commission cannot meet. The definitions are essentially verbatim across sources, suggesting the term had a fixed and uncontested meaning by the time these dictionaries were compiled.
Burrill's entry adds citations to the Registrum Omnium Brevium at pages 202 and 206, and to Fitzherbert's Natura Brevium at both 111 C and 186 A, providing slightly richer bibliographic grounding than Black's. None of the historical dictionaries discuss the writ's origins, its relationship to other writs of association, or its eventual disuse — gaps a researcher would need to fill through primary sources or specialized histories of English judicial administration.
The historical dictionaries treat this as a purely English practice term, and there is no indication in any of the sources that the writ was adopted or adapted in other common law jurisdictions in any formal way.
Jurisdictional Note
Si non omnes is exclusively an English legal practice term. It has no recognized equivalent in American federal or state court procedure. Researchers working in Scottish, Irish, or colonial legal records should not assume the writ applied without confirming that the relevant jurisdiction operated under the English commission framework.