Definition
Rationalibus divisis (Law Latin: "of reasonable boundaries") was an abolished common law writ used to settle disputed boundary lines between adjacent lordships or seigniories lying in different townships. The writ lay at the suit of a lord who found that his land had been gradually encroached upon by a neighboring lord, allowing him to compel a rectification of their common bounds. It was a remedy of boundary, not of title — its purpose was to fix and correct the dividing line between two adjoining estates held in seigniory, not to determine which party owned the underlying fee.
Why It Matters in Research
This term surfaces almost exclusively in historical English common law sources. Researchers encountering it in period materials — particularly those dealing with feudal land tenure, manorial records, or boundary disputes predating modern surveying law — should understand several things.
First, this writ belongs to a family of abolished real actions. Its abolition followed the broader elimination of the old real and mixed actions in England under the Real Property Limitation Act 1833 and, more comprehensively, the Common Law Procedure Act 1860. American jurisdictions largely never adopted it, having shed the feudal seigniorial framework that gave the writ its function. Finding rationalibus divisis cited in American sources is rare and usually antiquarian.
Second, the writ's mechanism was incremental encroachment — it responded to boundary creep over time rather than a single discrete act of trespass. Researchers comparing this writ to related boundary remedies should note this distinguishing feature. It is not simply a variant of trespass quare clausum fregit, which addressed discrete entries; rationalibus divisis addressed the slow erosion of an established boundary through repeated small encroachments.
Third, the term appears in secondary sources, form books, and abridgments of English law without deep procedural elaboration, because it was already largely obsolete by the time systematic common law treatises became standard. Coke, Fitzherbert, and Cowell touch on it, but none provide extended procedural treatment. Researchers should not expect substantial case law development — the writ left a thin documentary trail.
Fourth, in the Law Mind corpus, this term connects most directly to materials on real actions, feudal tenure, manorial courts, and the history of English land law. Cross-referencing entries on perambulation, metes and bounds, and the history of real actions will provide the necessary surrounding context.
Historical Dictionary Support
Black's Law Dictionary, both the first and second editions, carry substantially identical entries: a brief definition identifying the writ as abolished, its purpose (rectifying encroached boundaries between lords of adjoining seigniories in divers towns), and a single citation to Cowell. John Cowell's The Interpreter (1607) is the primary authority both editions rely upon, and neither Black's entry adds procedural or historical depth beyond Cowell's brief description.
The agreement between both editions is complete, suggesting the entry was carried forward without revision or independent research. Neither edition notes the writ's English abolition, which is a meaningful omission for researchers trying to understand its historical shelf life. Neither edition situates it within the broader family of abolished real actions. For a term already archaic when Blackstone was writing, the thin treatment is unsurprising but should prompt researchers to look beyond Black's to primary sources in the English abridgments — particularly Fitzherbert's Natura Brevium and Rolle's Abridgment — for any procedural detail.
The Cowell citation is genuine and appropriate, though Cowell himself treats the writ briefly. No American authority is cited in either edition, consistent with the writ's inapplicability in the American legal system.
Jurisdictional Note
This writ was exclusively English in origin and operation. It presupposed the feudal structure of seigniorial landholding and was never transplanted into American law. Researchers working in any American jurisdiction will find it relevant only as historical background to the development of boundary dispute remedies, not as operative law at any period.