Definition
A writ of conspiracy was a common law procedural remedy directed against persons who had unlawfully combined to harm the plaintiff — specifically by procuring a false indictment against him for treason or felony. The writ enabled the injured party to seek redress directly against those who conspired to use the criminal process as a weapon. It is an obsolete form of action, long since superseded by the action on the case, which provided a broader and more flexible remedy covering the same and wider ground.
The writ was narrow in scope. At common law, it lay only when the conspiracy took the specific form of procuring a false accusation of treason or felony against the plaintiff. Combinations to injure a person in other ways — through fraud, interference with trade, or other unlawful concert — were not remediable by this writ. Those cases were handled from early on as actions on the case, which became the dominant and eventually exclusive vehicle for conspiracy-based civil claims.
---
Common Confusion
WRIT OF CONSPIRACY vs. CONSPIRACY (as a modern tort or crime): These are distinct concepts across distinct eras. The writ of conspiracy was a specific medieval procedural form, technically confined to malicious-prosecution-style combinations. Modern conspiracy — both criminal and civil — is a vastly expanded doctrine that does not require a prior false indictment and is not tied to any writ form. Researchers encountering "conspiracy" in older sources must determine whether the author means the ancient writ, an early action on the case sounding in conspiracy, or a modern criminal or civil conspiracy claim. The same word spans all three, and conflating them distorts the history of both the substantive doctrine and the procedural forms.
---
Why It Matters in Research
The writ of conspiracy is a tracing point, not a living tool. Its chief research value is genealogical: understanding it is necessary to follow how conspiracy doctrine evolved from a narrow, writ-bound remedy into a general common law cause of action and ultimately into modern criminal conspiracy law.
Several traps await researchers working in historical sources. First, early English treatises and year books use "conspiracy" almost exclusively to mean the writ or the action on the case that replaced it — not a general doctrine of unlawful combination. Modern conspiracy doctrine's breadth is a later development, and reading it back into pre-18th century materials produces anachronism. Second, the line between the writ proper and the action on the case in conspiracy was not always clearly drawn by early writers, and some sources use the terms interchangeably for the pre-writ period. Third, American sources such as the New York case cited by Bouvier (7 Hill N.Y. 104) adopted the English framework but in an American procedural context where the writ forms were already giving way to code pleading; researchers using such cases as authority for substantive conspiracy doctrine must be careful about what the court was actually deciding.
For researchers tracing the history of malicious prosecution, the writ of conspiracy is also a direct ancestor. The overlap between conspiracy-to-falsely-indict and what became the tort of malicious prosecution is significant, and some historical sources treat them as closely related or effectively identical in their core application. Cross-referencing both lines of development is necessary for a complete picture.
The writ has no operational role in modern practice. Any researcher encountering a reference to it in a contemporary context is likely looking at historical argument, academic treatment, or an error.
---
Historical Dictionary Support
Black's and Bouvier's agree on the essential points: the writ is ancient, it is obsolete, and it was superseded by the action on the case. Bouvier adds the critical doctrinal precision that Black's omits — namely, that at strict common law, the writ lay only where the conspiracy was to indict the plaintiff of treason or felony. All other conspiracy cases in the books, Bouvier notes, were actions on the case, not true writs of conspiracy. This distinction matters: it means that the broader common law treatment of unlawful combinations was never writ-based in the first place, and the writ was always the narrow exception rather than the general rule.
Bouvier's citation to Fitzherbert's Natura Brevium (260) is the standard reference for the writ's formal common law description. Fitzherbert's work, a 16th-century treatise on the forms of writs, is the principal historical source for understanding what the writ required and what it did not reach. Researchers working on the early history of conspiracy doctrine should consult Fitzherbert alongside the Year Book materials to understand how courts and practitioners actually understood the writ's limits.
What neither dictionary addresses — and what researchers need to source elsewhere — is the question of how and when the action on the case in conspiracy expanded beyond the false-indictment scenario to encompass general unlawful combinations in restraint of trade and labor. That development, largely an 18th and 19th century story, is where modern conspiracy doctrine actually originates, and it post-dates the period either dictionary is primarily describing.
---
Jurisdictional Note
The writ was an English common law form and, as such, formed part of the received common law in American jurisdictions. American courts and treatise writers acknowledged it but almost universally noted its obsolescence, treating the action on the case as the operative vehicle. The shift to code pleading in the mid-19th century further dissolved any remaining procedural relevance. No American jurisdiction retained the writ as a living procedural form into the modern era.
---
Encyclopedia Cross-Reference
Coram Nobis and Other Extraordinary Writs (The Law Mind Criminal Law Encyclopedia) — for context on the historical writ system and the displacement of writ forms by modern procedural remedies.
Drug Conspiracy (The Law Mind Criminal Law Encyclopedia) — represents the modern terminal point of the doctrinal line that begins with the writ; useful for understanding the distance traveled.
---