Definition
De rationabili is a Latin phrase meaning "of reasonable" or "of a reasonable share," appearing in several distinct medieval and early common law writs and doctrines. The term functions primarily as a prefix or component in specific writ names rather than as a freestanding legal concept. Its principal appearances are:
1. De rationabili parte — A writ of reasonable part (or reasonable share), lying at common law to compel a father or other ancestor to make a fair division of his personal estate among his children or next of kin. In some usages, this writ enabled a widow or children to recover their proportional share of a deceased's movable goods, rooted in the ancient custom that a man's personal estate was divided into three equal parts: one for the widow, one for the children, and one freely disposable by the deceased.
2. De rationabili modus — A related phrase appearing in the context of tithe law and prescriptive customs, describing a claim grounded in a "reasonable manner" of payment or obligation. Here the term attaches to prescriptive modes of tithing, signaling that the customary arrangement has a defensible basis in reasonableness and long usage.
3. De rationabili parte bonorum — The formal writ name for the action to recover a reasonable part of goods or chattels from an estate, used historically in ecclesiastical courts as well as common law courts before statutory reforms curtailed testamentary freedom claims.
The unifying thread across these usages is the assertion of a legally cognizable entitlement grounded in reasonableness and custom rather than express grant or statute.
Common Confusion
The Rapalje & Lawrence entry associated with this term slides into a discussion of modus decimandi — the prescriptive custom of tithing in a particular manner — which is a related but distinct concept. De rationabili as applied to modus describes the reasonableness standard that legitimizes a prescriptive tithe arrangement. Researchers encountering the phrase in tithe litigation contexts should not assume they are reading about the writ of reasonable part; the two applications share Latin roots and doctrinal logic but operate in entirely different procedural settings. Additionally, de rationabili parte should not be confused with the dower right (de dote), though both protect surviving family members' interests in a decedent's property.
Why It Matters in Research
This term is a navigational hazard in historical source research for several reasons.
First, the phrase appears in multiple distinct writ contexts, and historical dictionaries — including Rapalje & Lawrence — often address only one application while silently assuming the reader understands the others. The Rapalje & Lawrence entry reproduced here addresses the modus decimandi context almost exclusively, leaving the writ of reasonable part, which was the more prominent common law action, underexplained.
Second, the writ de rationabili parte bonorum had significant jurisdictional complexity in England: it was cognizable in both ecclesiastical courts (over personal estate distribution according to church custom) and common law courts (over chattel claims), and the overlap generated competing proceedings well into the early modern period. Researchers working in probate records, ecclesiastical court files, or Year Book materials will encounter this writ in forms that look procedurally different depending on the forum.
Third, for researchers in the tithe law context, the phrase de rationabili modus signals a prescriptive exemption claim grounded in reasonableness — not total exemption from tithes (which would be non decimando), not a fixed monetary substitution (a modus decimandi proper), but a defensible customary arrangement. The distinction matters because the legal tests for defeating each type of tithe claim differed, and early sources sometimes conflate them.
Fourth, the abolition of customary shares of personal estate in England (effectively accomplished through a series of statutes culminating in the late seventeenth and eighteenth centuries) rendered the writ of reasonable part largely obsolete. Researchers working in American colonial records should be alert to whether local jurisdictions adopted or rejected the English custom, as reception varied considerably by colony and early state.
Historical Dictionary Support
Rapalje & Lawrence address de rationabili only indirectly, in the context of modus decimandi and prescriptive tithe claims. Their treatment emphasizes that the "de rationabili" qualifier signals a prescription by spiritual persons or corporations — a claim that their customary mode of tithing is reasonable and therefore legally defensible. This is a narrower window than the full scope of the term warrants.
Older English law dictionaries, including Jacob's Law Dictionary and Tomlin's Law Dictionary, give fuller treatment to de rationabili parte as a writ of right over movable property, tracing it to the ancient tripartite custom of estates. Those sources are more useful for researchers approaching the term from probate or family law angles.
What the historical dictionaries collectively tend to miss is the procedural history of forum competition between ecclesiastical and common law courts over these claims — a gap that matters for understanding why the writ appears in such varied archival contexts.
Jurisdictional Note
The writ de rationabili parte bonorum and the underlying custom of reasonable shares were never uniformly received in American law. Some colonial jurisdictions, particularly in the mid-Atlantic and Southern colonies, rejected the tripartite custom in favor of testamentary freedom. Researchers should not assume that the presence of this phrase in an American source reflects the same doctrinal content as its English antecedent.