When a modern historian is writing about European history in the English language, I know it is customary to use either the Julian or Gregorian calendar, whichever was in force in the time and place being written about.

But what about non-European countries that went directly from an indigenous calendar to the Gregorian calendar, and never used the Julian calendar? For example, Japan switched from a traditional luni-solar calendar to the Gregorian calendar in 1873. So if an English-speaking historian were writing about Japan, would she use the Gregorian calendar for events as recent as 15 October 1582, and the Julian calendar before that? Would the Gregorian calendar be used even before it was officially created when writing about events in Japan?

Any references to accepted sources on how historians should write would be appreciated.

  • 1
    Various historians do it differently, depending on the purpose of their text. It is a question of convenience in each separate case. Some give dual dates.
    – Alex
    Mar 13, 2016 at 13:34
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    I've seen Japanese history given in traditional reckoning or Gregorian backdating; I'm not sure it's ever been converted to Julian (outside of contemporary documents), though.
    – Semaphore
    Mar 13, 2016 at 14:06

1 Answer 1


A modern secondary historical paper or book should always use the Gregorian Calendar and the era of Exiguus. For pre-Gregory dates the proleptic calendar should be used. The reason for this is so that the exact distance between two dates can always be calculated easily and so that all books are using the same time scale so that dates in one book can easily be compared to those in other books.

In cases where a date from a source document is being used, then that date should be given verbatim, as it appears in the source document with no interpretation or conversion, along with the era and calendar being used so far as it is known, followed by the believed Gregorian equivalent. For example,

...according the MSS, the battle occurred a fortnight from Michaelmas, 1143 (AD, Julian), which is 14 October (Gregorian),...

The reason why you find Julian dates in many history books is because the historian is simply copying the date from the source without further comment, and in many cases without identifying the source, which often may be some other secondary source whose author is, in turn, doing the same thing. Because of this, most history books are littered with chronological mistakes of various kinds.

If you are drawing a date from such a book and using it, you should identify what calendar you believe the author to be using.

...the naval engagement occurred on 15 March 1743 (Julian?)[1]...

So, in this case did the author of the book you are reading translate the date to "new style" or is it an "old style" (Julian) date? You make your best guess (Julian?) and footnote the source. Sometimes you will see ("o.s.") in books, indicating that they are using an old style date.

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    "American National Biography" published in 1999 by Oxford U. Press adopts the convention, stated on page xxi, that dates are usually given in either Julian or Gregorian, whichever was in force at the time and place of the event (virtually all the people described were Americans or Europeans). However, the year is held to begin on January 1, even though England and Whales held it to begin on March 25 until 1752. So I am skeptical that modern historians use the Gregorian calendar to describe events that occurred when and where the Julian calendar was in force. Mar 14, 2016 at 13:52

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