Beginnings, endings and continuing on

Count to ten: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10.

We start with one and end with zero, as we would counting to twenty or thirty or any ten count. So, coming to January first what decade is it? Is it the last year of the decade of the teens, the 2011 decade ending? Or is it the first year of the 2020s, starting the third decade in this century?

There is not universal agreement on when decades start and therefore when decades end. It is not like gravity or the speed of light: “186,000 miles per second per second is not just a good idea, it’s the law.” A decade’s start is not a fact, undisputable.

As...