From Sir Gawain and the Green Knight through English Common Law until 1996, 'a year and a day' seems to have be a common unit of time measurement.
How exactly did this come to be? Why not simply a year? And where and when did the phrase/notion originate from?
Thanks!
The concept is to some extent a correct way of saying "a year from now." Counting 365 days from today, March 27, and including today, lands us on March 26, 2020. Well, OK, 2020 is a leap year, so 366 days in this case, but the sense is technically correct. The anniversary of today marks the beginning of a new annual cycle. We say "a year from today" to mean the anniversary of today, but counting specific days and including today, a full year is completed one morning short of today's anniversary.