Definition
Old Style (abbrev. O.S.) refers to the Julian calendar system of date reckoning that was in use in England and its territories prior to 1752, and in most Roman Catholic countries of continental Europe prior to 1582. Under Old Style reckoning, the year began on March 25 (Lady Day) rather than January 1, and leap years occurred every four years without exception. It was superseded by the Gregorian calendar — termed New Style (N.S.) — which corrected accumulated calendar drift by adjusting the leap year formula to 97 leap years in every 400 years and resetting the new year to January 1.
In legal documents, the designation "Old Style" or "O.S." signals which calendar system governs a stated date. A date between January 1 and March 24 is particularly susceptible to ambiguity: under Old Style reckoning, those dates fell in the prior year; under New Style, they fall in the new year. Documents from the transitional period frequently employ a dual-date notation (e.g., "February 10, 1648/49") to eliminate ambiguity across both systems.
Common Language
Modern common usage (Wiktionary): The Julian calendar system, especially with reference to Russia, where it continued in use until the early 20th century; a dating system in which March 25 is New Year's Day.
Historical common usage (Webster's 1913): [The term was understood in ordinary usage as referring to the pre-Gregorian calendar, consistent with the legal meaning.]
The common and legal meanings are closely aligned, but the legal significance runs deeper than calendar trivia. In legal instruments — deeds, wills, court records, indictments, and contracts — an incorrectly interpreted Old Style date can misplace an event by an entire year. The common usage tends to treat Old Style as a historical curiosity; the legal usage treats it as a precision problem with real consequences for document interpretation.
Common Confusion
Old Style is frequently conflated with the eleven-day discrepancy correction that accompanied England's 1752 adoption of the Gregorian calendar. These are related but distinct issues. The year-start shift (March 25 to January 1) creates the year-ambiguity problem for dates in January through March. The eleven-day correction (September 2, 1752 was followed by September 14) creates a separate day-count discrepancy affecting any date calculation that spans the 1752 transition. Both must be accounted for when working with pre-1752 English legal documents, but they require different analytical approaches.
Why It Matters in Research
Researchers working with English legal records before 1752 — and with records from colonial American jurisdictions that followed English practice — must treat every date between January 1 and March 24 as potentially ambiguous. A deed dated "February 5, 1700" in an Old Style document is what a New Style calendar would call February 5, 1701. Failure to recognize this can misplace documents in chronological sequence, misread the order of events in a dispute, or incorrectly calculate deadlines, ages, or limitations periods.
The Gregorian reform was not instantaneous or universal. Scotland shifted its legal new year to January 1 in 1600, predating England by 152 years. Most of continental Europe converted in 1582. Russia did not adopt the Gregorian calendar until 1918. Researchers encountering documents from correspondence or transactions crossing jurisdictional lines during transitional periods must determine which calendar system each party was using — a document drafted in London in 1650 and one drafted in Amsterdam on the same day may carry nominally different dates under their respective systems.
In the Law Mind corpus, Old Style is most likely to surface in connection with property records, probate documents, colonial charters, ecclesiastical records, and criminal indictments from the pre-1752 English legal tradition. Any corpus search involving date ranges that span the 1752 transition should be constructed to account for both calendar conventions. The Bouvier entry's tangential reference to indictment date-formatting requirements (year numerals, "A.D." notation) reflects how courts of the period treated date precision as a substantive pleading matter — not mere formality.
Historical Dictionary Support
The historical dictionaries agree on the core definition: Old Style denotes the pre-Gregorian Julian calendar, with year commencement on March 25, superseded in England in 1752. Black's (both editions) and Bouvier offer substantively identical definitions. Rapalje & Lawrence simply cross-references New Style, offering no independent content — a reminder that the two terms are mirror images and should be researched together.
Bouvier adds the most useful historical texture, noting the leap year correction formula (97 in 400 years under New Style, versus every fourth year under Old Style) and the earlier 1582 continental adoption. The Bouvier entry's digression into indictment date requirements is not directly about Old Style but reflects the period's broader anxiety about date precision in legal instruments — a useful contextual signal for researchers.
What none of the historical dictionaries address adequately is the dual-date notation convention, the Scotland exception, or the practical challenges for cross-jurisdictional documents. Researchers should not rely on these sources alone when navigating complex transitional-period dating problems.
Jurisdictional Note
England and its colonies adopted New Style in 1752 under the Calendar (New Style) Act 1750. Scotland had already moved its legal new year to January 1 in 1600, creating an intermediate system. Continental European legal documents generally follow New Style from 1582 onward. Researchers working across these jurisdictions in any single matter must identify the governing calendar for each document individually rather than assuming uniformity.
Encyclopedia Cross-Reference
See Law Mind Encyclopedia — Calendar Reform; Date Reckoning in Legal Documents; Colonial Legal Records