The Cultural Tutor

In any case, that's the story of why October 4th 1582 was followed by October 15th. That days can be removed from (or added to) the calendar is a wonderful reminder of our strange relationship with time, of how some things which seem permanent — like the date — really aren't. https://t.co/tqdvkw3KHy

For example, William Shakespeare was born on 23rd April 1564 according to the Julian Calendar — but on 3rd May according to the (retrospectively applied) Gregorian Calendar. When the Gregorian Calendar is extended backward in time it is called the "Proleptic Gregorian Calendar".