Definition
De rationabilibus divisis (Latin: "for reasonable boundaries") is a now-obsolete common law writ used to settle disputed boundary lines between lands belonging to different proprietors situated in different towns or townships. The writ was brought by one landowner against another when one party complained of encroachment across an uncertain or contested boundary. Its purpose was to compel a legal determination of where the boundary rightfully lay — not to recover land already lost, but to fix the dividing line prospectively.
The writ was a form of real action, belonging to that broad category of early English proceedings concerned with rights in land rather than personal obligations.
Why It Matters in Research
This term appears almost exclusively in historical English legal sources and antiquarian treatments of the common law real actions. Researchers are unlikely to encounter it in American case law or modern statutes; its primary value is as a navigational marker when working through old English plea rolls, Fitzherbert's Natura Brevium, or Reeve's History of English Law.
The critical research point is context of obsolescence. The real actions — including de rationabilibus divisis — were progressively displaced in England by ejectment and then abolished wholesale by the Real Property Limitation Act 1833 and subsequent reforms. In American jurisdictions, most real actions were never adopted or were abandoned very early, replaced by statutory boundary proceedings, quiet title actions, or actions at law for trespass. A researcher finding this writ cited in an American source is almost certainly encountering a historical reference or a treatise tracing the ancestry of modern boundary dispute remedies.
When tracing the lineage of boundary dispute law, this writ connects to the broader corpus of real actions alongside writs such as perambulation and the writ of right. Researchers working in land title history, early American property law reception, or the history of equitable boundary relief should be aware that modern quiet title and boundary-by-acquiescence doctrines are the functional successors to what de rationabilibus divisis once addressed procedurally.
Fitzherbert's Natura Brevium is the authoritative source cited by both Bouvier and Black for the mechanics of this writ. Researchers needing the full procedural account should consult Fitzh. N.B. 128, M directly. Reeve's History of English Law (vol. 3) provides additional historical context on the writ's place within the real actions system.
Historical Dictionary Support
Bouvier and Black agree on essentials: the writ lay to determine boundaries between lands of different proprietors in different towns, initiated by the aggrieved party complaining of encroachment. Both cite the same primary sources — Fitzherbert's Natura Brevium and Reeve's History of English Law — suggesting neither entry was independently developed but rather reflects the settled antiquarian understanding of the writ.
Black's entry adds a reference to Roscoe's Real Actions (Rosc. Real Act. 31) and the Registrum Omnium Brevium (Reg. Orig. 157b), providing a slightly fuller procedural grounding. The note in Black's entry that the writ lay where one party "complained of encroachment" sharpens the functional picture: this was a reactive remedy, not a preventive one. A landowner who believed a neighbor had pushed the boundary line into his territory could invoke this writ to have the line properly established.
Neither dictionary treats the writ's internal procedure in any depth, and neither addresses how the boundary was actually determined once the writ issued — presumably by jury or commissioners, consistent with practice in other real actions. Researchers needing procedural detail must go to the primary sources cited. Both dictionaries reflect the conventional nineteenth-century treatment of the real actions as a closed historical category, with no suggestion that the writ retained any practical vitality at the time of writing.
Jurisdictional Note
This writ was a creature of English common law and has no direct American procedural counterpart. American states developed their own statutory mechanisms for resolving boundary disputes, and the formal English real actions, including de rationabilibus divisis, were generally not carried over upon reception of the common law. Any American reference to this writ is historical or comparative in nature.