Why should the latter year in a double-date be used in date fields?

Question

N.B. - This is not intended to be a discussion of whether wikitree should or should not accept double-dates in date fields! That would more properly appear in the WikiTree Tech category of G2G, and has been discussed there previously.

You may run across references which have dates indicated, for example, as:

"25 Jan 1678/9"
"25 Jan 1678/79"
"25 Jan 1678-9"
"25 Jan 1678-79"

Those are commonly called "double-dates," most likely occurring in references other than original sources such as vital or church records. The example dates are a commonly accepted way of indicating dates for two different calendars - the Julian calendar (1678 in the examples above) and the Gregorian (or Common Era) calendar (1679 in the examples above). The references preceding and following provide information on the why, when and where calendar changes were made, and why double-dates are used at all.

See also:
Professional Genealogy : A Manual for Researchers.., Elizabeth Shown Mills. Genealogical Pub. Co., Baltimore. © 2001. p. 8 (books.google.com), and The 1752 Calendar Change

What's a good reason to use the latter (Gregorian calendar) year from a double-date in profile date-fields, rather than the Julian year indicated in original records?

EDIT - 1. That's the convention recommended on wikitree ("Julian vs. Gregorian Calendar").

2. Using the second of two years indicated in a double-date permits the direct comparison of dates.

E.g., North American colonial records may indicate that a child was born April, 1701, and another child Feb, 1701. Those are very likely Julian dates. Because March was the first month of the year prior to ~1752, the child born Feb, 1701, was born after April, 1701, some 10 months after April of the same (Julian calendar) year. In their profiles, the birthdates in the datefields should be recorded as April, 1701, and February, 1702, clearly indicating (by comparison) the order of their birth. The biography for the latter could then indicate that the child was born "February, 1701/2" or "February, 1701/02" for accuracy purposes, citing and providing a quotation from the source.

Comments

Geez, I did not even know this!  (About the first month of the year being March)  Thank you for posting!!

---

It is correct to use the 'second year' of a double date for the date field.  So and Old Style Julian date of 1715, would be double dated as 1715/6 in the biography, and properly recorded as 1716 in the date field.

However, what you have written and what wikitree's help page says is not quite correct.  Changing 1 February 1715 to 1 February 1715/6 is NOT a switch to the Gregorian calendar.  The Gregorian calendar date was 12 February 1716.  It is shift from Julian calendar Old Style dating to Julian calendar New Style dating.

Note that you can find online calculators that make the calculation for changing a Julian date to a Gregorian date.  They should NEVER be used.  The date (day and month) should remain as found in a document, even if we change the year to New Style.

Answer 1

Unfortunately some have not understood the facts of the matter and use double dates all year long, Most don't realize that only in a certain span of years does this apply, and that different spans occur in different places.

At one time I tried to change to the latter year, but realize that I don't know enough to do this accurately.  I now copy the dates as they are presented, 3 Feb 1782-3, or whatever, leaving accuracy to one who knows.

I understand that dates like 23/11/1743 in the Julian calender is 23/1/1744 in the Gregorian calender, but only in the place where the calender was changed at that time.

Comments

 Exactly! That's the reason I was rather equivocal about when and where, and spoke only to "when you run into a date that looks like.." To be sure, one has to be very careful, and cite sources and provide quotations.

Answer 2

The old Julian calendar began the new year on March 25.  So, for example, 24 March 1451 was followed the next day by 25 March 1452.  March was also considered the first month of the year. Old parish records commonly didn’t name the month but gave a month number.  So, for example, a parish record of a baptism dated 16day 2mo: 1515 was 16 April 1515.  It is very common to see conflicting dates off by 2 months as the result of people not understanding how the months were numbered.

The Gregorian calendar was introduced by Pope Gregory XIII in October 1582, and introduced two reforms:

1. The first day of the new year was moved from March 25 to January 1.
2. Ten days were dropped so that the Julian calendar day of Thursday, 4 October 1582 was followed by the first day of the Gregorian calendar, Friday, 15 October 1582.

This new calendar was primarily adopted by the catholic countries (France, Italy, Portugal, and Spain) in 1582, but not by the protestant countries, including the British Empire, until much later.  England and her colonies switched to the new calendar in 1752.

Within England and her colonies, however, there was still a partial shift to the Gregorian calendar, and dates were sometimes recorded as if the year started on March 25 (Old style) and sometimes as if the year had started on January 1 (New style).  Note this is NOT a shift to the Gregorian calendar as there was no 10 day shift in dates.  So it was very common for parish records to begin the practice of double dating for dates between January 1 and March 25.

It also became a standardization for historians (and genealogists) to record the date “New style” as if the year began on January 1 even for records which occurred long before the Gregorian calendar was introduced.  This was actually to avoid confusion, not create more. 

As a Data doctor I commonly run into situations where on one child was born say September 1689, and the next child was born say January 1690.  Obviously, this is impossible.  The answer and the correction though is that the second child was born January 1690/1 and we properly record the date as January 1691.  These sorts of confusions in the timeline would happen continuously throughout history if we did not standardize a year start date of January 1.

So in history or genealogy we use the following rules:

Rule 1: We use the day and month found on the document. This may seem like obvious common sense, however, shifting from one calendar to another can also cause a shift in the days - don't do it.

Rule 2: We assume the year started on January 1st. This does mean we often have to change the year found in a document.

Wikitree suggestion:  Anytime a date is written Old style in a document (e.g.1715), but is recorded New Style in a date field (e.g. 1716), it is smart to use the double date in the biography to make this clear (e.g. 1715/6).

Answer 3

I starting to include the following text in the Research Notes section of profiles to ensure clarity on this topic:

The Julian calendar was in use in <insert location> during this period. Each year began on 25 March, in the spring. Dates between 1 January and 24 March in the Julian calendar are represented in the text portion of this profile with double dating notation, e.g., 11 February 1503/4. However, the same date recorded in an event date field in this profile is recorded as 11 February 1504. This ensures that date mathematics works correctly. For reference, this example date on the Gregorian calendar is 21 February 1504. Julian dates are not converted to Gregorian on this profile.

Feedback welcome.

Answer 4

With the following info 

   25 Jan 1678/79 would be 25 Jan 1679 + 10 days or 5 Feb 1679

And

25 Feb 1739/40 would be 6 Feb 1740 (11 days were added)

See Also:

This page uses content from the English Wikipedia. The original article was at Old Style and New Style dates. The list of authors can be seen in the page history. As with the Calendar Wikia, the text of Wikipedia is available under Creative Commons License. See Wikia:Licensing.

Conversion of Julian to Gregorian dates

Time period (from March 1 of first year to February 29 of last year)	Сorrection, days
400–500	+1
500–600	+2
600–700	+3
700–900	+4
900–1000	+5
1000–1100	+6
1100–1300	+7
1300–1400	+8
1400–1500	+9
1500–1700	+10
1700–1800	+11
1800–1900	+12
1900–2100	+13

Old Style or OS is a designation indicating that a date conforms to the Julian calendar, formerly in use in many countries, rather than the Gregorian calendar, currently in use in most countries.

"Old Style" (OS) and "New Style" (NS) are sometimes added to dates to identify which system is used in the British Empire and other countries that did not immediately change to the Gregorian calendar. In Britain it is usual to map most dates from the Julian year onto the Gregorian year without converting the day and month. However because the start of the Julian year was not always January 1 (see New Year's Day section in the Julian calendararticle), OS/NS is particularly relevant for dates which fall between the start of the Gregorian year (January 1), and the start of the Julian year which was March 25 in England. Great Britain did not adopt the Gregorian calendar until September 14, 1752 and it was not until that year that England officially adopted January 1 as the start of the calendar year. 

For example, according to the English calendar of the day, King Charles I was executed on Tuesday January 30, 1648. This date is usually written in modern histories as January 30, 1649, showing merely the modernised end of year. In fact a full conversion of the date into the Gregorian calendar is February 9, 1649, the date by which his contemporaries in some parts of continental Europe would have recorded his execution.^[1]

Contents

• 1 Possible date conflicts
• 2 Countries that used lunisolar calendars
  • 2.1 Japan
  • 2.2 Korea
  • 2.3 China
• 3 See also
• 4 Further reading
• 5 Footnotes