Definition
The plural of month, used in law to define periods of time measured in monthly increments. Because "month" carries more than one legal meaning, "months" as a unit of measurement in a contract, statute, or pleading requires careful interpretation to determine which type of month is intended.
Two primary legal meanings apply:
1. Lunar months. Each consisting of twenty-eight days, with thirteen lunar months comprising a year. This was the default meaning at common law for temporal matters.
2. Calendar months. Months of unequal length as fixed by the standard calendar, with twelve calendar months comprising a year. This is the default meaning for ecclesiastical matters under the common law, and the dominant meaning in modern statutory and contractual usage.
Common Language
Modern common usage (Wiktionary): Plural of month — the twelve named divisions of the calendar year (January through December), each ranging from 28 to 31 days.
Historical common usage (Webster's 1913): The common understanding tracked the calendar month — one of the twelve portions of the year as fixed by the Gregorian calendar — while also acknowledging the lunar month as a distinct astronomical unit.
Editorial note: Ordinary English has always defaulted to calendar months. The legal divergence is significant: at common law, a document using "months" in a temporal legal context could be construed as referring to lunar months of twenty-eight days each — a result entirely contrary to what a modern reader, or even most historical laypeople, would expect. This gap between legal and common meaning has caused genuine interpretive disputes and is the central trap for researchers working with older documents.
Common Confusion
The most persistent confusion is between lunar months and calendar months when neither the document nor the governing rule makes the choice explicit. Under strict common law, "months" in a deed, bond, or legal process meant lunar months in temporal matters — thirteen to the year, each exactly twenty-eight days — while the same word in an ecclesiastical instrument meant calendar months. Modern statutes have largely resolved this by defining "month" as a calendar month, but the resolution is not universal or retroactive. A researcher reading a nineteenth-century contract or pleading cannot assume that "three months" meant what it means today.
Why It Matters in Research
The common law rule — lunar months for temporal matters, calendar months for ecclesiastical matters — creates a significant interpretive hazard in historical documents. A lease, a bond, a notice period, or a limitations period expressed in "months" in an eighteenth- or nineteenth-century instrument may not mean what modern readers assume. The shift from lunar to calendar months as the legal default occurred primarily through statutory intervention, and the timing of that shift varies by jurisdiction and subject matter.
Researchers working with older statutes of limitation must be alert: a limitations period of "six months" under an early American or English statute may have been calculated as 168 days (six lunar months) rather than the varying 181–184 days of six calendar months. The difference is modest in isolation but can determine whether a claim was timely.
In corpus searches, expect inconsistency. Older legal texts, especially pre-1850, often use "month" or "months" without qualification, relying on the reader's knowledge of the common law default. Later texts increasingly specify "calendar months" precisely because the default was no longer universally understood. The presence or absence of the qualifier "calendar" or "lunar" is itself a meaningful signal about the period and drafting conventions of a document.
Cross-reference to statutes of limitation, notice requirements, and time-computation rules is essential, as these are the contexts where the months question most frequently generates litigation.
Historical Dictionary Support
Rapalje & Lawrence provide the foundational statement: months are either lunar (twenty-eight days, thirteen per year) or calendar (unequal length per the almanac, twelve per year), with the common law defaulting to lunar months in temporal matters and calendar months in ecclesiastical matters. The entry cites 1 Stephen's Commentaries 283, which reflects the established English rule.
What Rapalje & Lawrence do not address — and what researchers need — is the subsequent statutory displacement of the lunar month default. By the mid-to-late nineteenth century, American and English legislatures had largely codified calendar months as the operative unit, but the historical dictionaries were slow to reflect this transition fully. Researchers relying solely on Rapalje & Lawrence for period-accurate interpretation should verify whether applicable statutes in the relevant jurisdiction had already overridden the common law default at the time the document was drafted.
Jurisdictional Note
England codified the calendar month as the default legal meaning through the Interpretation Act 1850 and later the Interpretation Act 1978. American states followed varied paths; many enacted general construction statutes defining "month" as a calendar month, but the dates of those enactments differ. In jurisdictions and periods where no such statute applied, the common law lunar-month default remained operative for temporal legal matters.
Encyclopedia Cross-Reference
Law Mind Encyclopedia — Time Computation
Law Mind Encyclopedia — Statutes of Limitation
Law Mind Encyclopedia — Interpretation of Statutes