Definition
A rule nisi is a conditional court order that commands a party to show cause why a particular act should not be required of them, or why a particular legal consequence should not be enforced against them. The order takes effect automatically and becomes absolute — a rule absolute — unless the opposing party appears and demonstrates sufficient cause why it should not. The term derives from the Latin nisi, meaning "unless," which captures the order's conditional character: it stands as a final command unless good cause is shown to the contrary.
In practice, a rule nisi is typically obtained ex parte, on motion, without advance notice to the opposing party. Once issued, it is served on the party against whom it runs, who then has the opportunity to contest it. The hearing that follows proceeds like an ordinary motion, with one procedural distinction: the party who obtained the rule nisi opens, but the party showing cause against it is entitled to open and reply. If no cause is shown, or if cause shown is insufficient, the court makes the rule absolute.
Common Confusion
Rule nisi should not be confused with a show cause order, though the two are functionally similar and often used interchangeably in modern practice. Technically, a show cause order affirmatively directs a party to appear and explain why relief should not be granted, while a rule nisi is framed as a provisional command that will become absolute unless contested. In modern American practice, the distinction has largely collapsed; courts and practitioners routinely treat them as equivalent. In historical sources, particularly English and early American authorities, the rule nisi form is more precisely observed and the distinction carries procedural weight.
Rule nisi is also distinct from a rule absolute, which is its end state. The two appear in historical sources as a pair: a rule nisi is the provisional stage, the rule absolute is the conclusive one. Researchers encountering only one term in a historical record should look for the companion entry.
Why It Matters in Research
The phrase appears throughout English and early American procedural records in contexts that modern researchers may not immediately recognize as equivalent to contemporary motion practice. Courts employed rule nisi routinely in matters ranging from mandamus proceedings, to compelling sheriffs to return writs, to contempt enforcement, to mortgage foreclosure procedures. A researcher encountering "rule nisi granted" in a nineteenth-century case report is reading what a modern court would express as "motion granted provisionally pending response" or "order to show cause issued."
The Latin construction caused the term to persist in formal legal writing long after plain-English equivalents were available. As procedural reform movements — particularly the merger of law and equity under codes of civil procedure and later the Federal Rules — streamlined motion practice, the rule nisi as a named procedural form faded from American usage. It remains more alive in Commonwealth jurisdictions. Researchers working in pre-twentieth-century American sources, particularly in equity, common law certiorari, mandamus, and contempt proceedings, will encounter it frequently. It is largely absent from twentieth-century American federal practice.
The Rapalje & Lawrence entry cross-references rather than defines, directing users back to the general entry for RULE. This is a reliable signal that the term was sufficiently familiar to contemporary practitioners to require no independent explanation — but it is a trap for modern researchers who begin their search with the sub-entry and find only a redirect.
One procedural detail worth noting for corpus researchers: the hearing-procedure rule that the party showing cause against a rule nisi gets to open and reply (noted in Bouvier's) is a reversal of the usual order. This asymmetry occasionally matters when reading accounts of historical arguments and trying to reconstruct who bore what burden at which stage.
Historical Dictionary Support
The four source dictionaries are in close agreement on substance. Black's, Bouvier's, and Burrill's all define the term as a provisional rule to show cause that becomes absolute unless good cause is shown — essentially the same formulation in slightly different words. All three identify the conditional character (the Latin nisi meaning "unless") as definitionally central.
Bouvier's adds the most procedural texture, noting the ex parte origin, the service requirement, and the reversal of hearing order. Burrill's adds the useful concrete illustration of ruling a sheriff to return a writ, grounding the abstract procedural form in a specific historical application. Black's is the most compressed, but its formulation — "will become imperative and final unless cause be shown against it" — is the clearest single-sentence statement of the concept.
Rapalje & Lawrence's cross-reference without definition is editorially significant: it signals that the term was treated as a sub-species of the general concept of a "rule" rather than a freestanding doctrine, which reflects how English common law procedure organized this material.
What the historical sources collectively omit: any account of the term's decline, its relationship to equity practice versus common law practice, or guidance on how it maps to modern procedural equivalents. Researchers need to supply that context themselves.
Jurisdictional Note
Rule nisi remains in active use in some Commonwealth jurisdictions, particularly in constitutional and administrative law contexts (habeas corpus, certiorari, mandamus), where courts still issue a rule nisi before making an order absolute. In the United States, the form has been substantially absorbed into show cause practice and is rarely invoked by name in federal courts. Some American state courts — particularly in the South — retained the terminology longer than others, and it continues to appear in older state procedural statutes and rules.