|Benjamin Franklin on the facade of the Brooklyn Historical Society|
On January 17, 1706, Benjamin Franklin -- printer, author, inventor, statesman, Postmaster General, and ladies' man -- was born.
Or was it January 6, 1705?
While it is not unusual to have people shave off a few years to appear younger -- or add a year or two when they are young to give themselves more gravitas (see also: Alexander Hamilton) -- the discrepancy in Franklin's birth date isn't vanity.
Franklin was, in fact, born on January 6, 1705, according to what is now termed the "old style" calendar. When Franklin was born, Great Britain and its colonies still followed the Julian calendar. In 1752, when the British finally moved to the Gregorian system, everything was bumped forward by eleven days. Many people born prior to the shift kept their old birthdays, but Franklin happily shifted his forward as a sign that he was in favor of the move. (Most of the rest of Europe had been on the Gregorian calendar since the 16th century; Protestant England's distaste for all things "popish" was one reason they stayed behind.)
However, the switch in 1752 from January 6 to January 17 doesn't explain the discrepancy in Franklin's birth year.
That, too, is a result of the calendar change. Prior to the adoption of the Gregorian system, New Year's Day in Britain was March 25, which roughly coincides with the first day of Spring (and which is also the date of the Feast of the Annunciation, when the angel Gabriel revealed to Mary that she was going to give birth to Jesus Christ).
With the switch to new calendar, the first day of the year was moved back to January 1. Thus anyone born in the period January 1-March 25 under the Julian system also had the year of their birth retroactively bumped forward a year, and Franklin's January 6, 1705, birth date was transformed to January 17, 1706.