Draw a number line and imagine that it represents what most people referred to as AD (Anno Domini) and BC (Before Christ) but some now refer to as CE (Common Era) and BCE (Before the Common Era)
Two rays extending laterally from a common point of origin, one to the right, one to the left. Hashmarks are added and labeled 1, 2, 3, 4 to the right and -1, -2, -3, and -4 to the left, etc.
It quickly appears obvious: There IS NOT and NEVER WAS a YEAR ZERO. Year 1 AD extends from the origin one unit to the right. Year 1 BC extends from the origin one unit to the left. And so on.
Think about it. It makes no sense for there to have been a year that was both an AD year and a BC year, or a year that stood on its own as being neither an AD year nor a BC year. Every year in time falls neatly into one or the other category, AD or BC.
And before anyone asks, yes, this is something that has been sticking in my craw.
Among the things that this exercise of drawing a simple number line can show, to even the least mathematically inclined person willing to take a little bit of time and exercise a modicum of thought, is the following: The nineteenth century ended at midnight on December 30, 1900 (an event understantably trumpeted by the New York Times in its edition of January 1, 1901 which contained many pages of retrospective stories/articles about the nineteenth century just ended and many prospective stories/articles about what might transpire in the twentieth century that had just begun), and the twentieth century ended at midnight on January 1, 2001 (an event that inexplicably passed entirely unnoticed by the now math-incompetent New York Times, as the content of its edition of January 1, 2001 edition clearly reveals, since it contained absolutely no retrospective or prospective articles/stories commemorating the massively important transition, not only between separate centuries, but between the second and third millenia!).
And yes, it’s official: Prince and his admirers jumped the gun and partied exactly one year too early. (But admittedly, it was fun.)
Oops. That is, rather, “...at midnight on December 31, 1900...”. (”Thirty days hath September, April, June, and November. February has 28 alone, And all the rest have 31.”) Okay—mnemonicization complete! :-)