Definition
Latin: "in the case provided." An obsolete writ of entry in old English real property practice, created by the Statute of Gloucester (6 Edw. I, c. 7). The writ lay for the benefit of the reversioner — the person entitled to receive property back after a life estate ended — when a tenant in dower unlawfully alienated the land in fee simple or for life without authority to do so. The writ ran against the alienee (the person who received the improper conveyance) and could be brought only during the lifetime of the tenant in dower. Once the dower tenant died, the reversion fell naturally to the reversioner, eliminating the need for the writ.
In plain terms: a widow holding land as dower could not permanently convey that land away, because she held only a life interest. If she tried, the person entitled to the land after her death could use the casu proviso to recover it immediately, without waiting for her death.
Common Confusion
Casu proviso should not be confused with the broader Latin term casus, meaning chance or accident (as in casus fortuitus, an act of God or unforeseeable event). Burrill's and Rapalje & Lawrence both define casus-related terms in the same entry, which can create the impression of a connection. The writ takes its name from the statutory phrase "in the case provided" — a reference to the specific case addressed by the Statute of Gloucester — and has nothing to do with the concept of accidental or fortuitous events.
Why It Matters in Research
This term appears almost exclusively in historical English real property sources and has no modern procedural equivalent. Researchers encountering it should treat it as a marker of pre-modern dower law and the writ system, not as anything with continuing legal force.
The writ is tightly bound to a now-abolished bundle of concepts: dower rights as a form of life tenancy, the reversion as a distinct possessory interest, and the writ of entry as the procedural vehicle for recovering land wrongfully held. Researchers working in pre-1833 English land law — before the Real Property Limitation Act and subsequent reforms dismantled the old writ system — will find this term in treatises on writs of entry and in Fitzherbert's Natura Brevium (cited by multiple sources as F. N. B. 205), which remains the primary practical guide to the old writ forms.
The key research trap is the secondary definition that appears in Rapalje & Lawrence and Burrill under the same entry: both slip in a definition of "casual" (that which happens accidentally) immediately after defining casu proviso, without clearly marking the transition. Burrill further notes the related term casus fortuitus (a chance event or accident) in the same entry. Researchers skimming these sources may conflate the writ with the broader Latin concept of casus (chance, accident, case). They are unrelated. The writ casu proviso takes its name from the statutory phrase — "in the case provided" by the Statute of Gloucester — not from the general Latin meaning of casus as an accidental event.
Jurisdictional note: American legal sources carry this term only by inheritance from English common law dictionaries. It was never enacted or applied as operative law in the United States. Any American appearance is historical or academic.
Historical Dictionary Support
The four source dictionaries agree on all substantive points: the writ originates in the Statute of Gloucester (6 Edw. I, c. 7); it protects the reversioner; it is triggered by a dower tenant's unauthorized alienation in fee or for life; and it runs against the alienee during the dower tenant's lifetime. Burrill's entry is the most technically precise, specifying that the writ lay "during the life of the tenant in dower" — a limitation the other sources imply but do not state as explicitly. Rapalje & Lawrence correctly labels the writ "obsolete," which neither Black's edition does explicitly, though the historical framing makes the obsolescence clear.
All sources cite Fitzherbert's Natura Brevium at page 205, and Burrill additionally cites Termes de la Ley and the Institutes (Inst. 4.3.3) for the secondary casus meaning. None of the sources provides meaningful doctrinal analysis beyond the basic elements; this writ was already a historical artifact by the time these dictionaries were compiled. Researchers needing deeper treatment should go directly to Fitzherbert and to early English real property treatises such as Littleton's Tenures and Coke upon Littleton for the underlying law of dower and reversion that gave the writ its context.