At the end of 1999, some people declared that we were about to embark on the 21st century. Those people were mistaken. The 21st century did not begin until 2001. There was no year zero A.D. The first year was 1 A.D.; thus, the first century was 1-100; the second century was 101-200; and the 20th century was 1901-2000. The 21st century didn’t start until 2001, and will last through 2100.
Everyone knows this now, and the people who thought the 21st century would begin in 2000 have accepted their error. You live and you learn. Unfortunately, some people have taken this idea beyond its bounds and declared that the current decade, the 2010s, is NOT about to end. They say it won’t end until Dec. 31, 2020.
Here is the problem: We are talking about two different things. The logic used with centuries doesn’t apply to decades because we don’t number our decades the way we number our centuries. Technically, this is the 202nd decade A.D. But we don’t call it that. We call it the ’10s. The ’10s are, by definition, the years that have “1” as their next-to-last digit: 2010-2019. Likewise, the ’80s were, by definition, the years that had “8” as their next-to-last digit: 1980-1989. The year 1990 was obviously not part of “the 1980s.” Try saying “1990” out loud. Did you say “eighty” at any point? No? Then it’s not part of “the eighties,” is it?
Now, if we did refer to this as the 202nd decade, you would be absolutely correct that it won’t end until the end of 2020. The years 1-10 were the first decade; 11-20 were the second decade; 2001-2010 were the 201st decade; and 2011-2020 are the 202nd decade.
But we don’t refer to our decades that way. The people who said “the century” was ending in 1999 were right — the “century” of The Nineteen-Hundreds was indeed ending. They were only mistaken when they said “the 20th century” was ending. “The 20th century” is specific and defined, and can only mean the years 1901-2000.
In common parlance, when we talk about what “decade” it is, we’re talking about which digit is next-to-last in the year number. If that digit is a 9, that year was part of the ’90s. If that digit is a 0, it’s part of the ’00s. Most of the time, when we talk about the “decade,” that’s the criteria we’re using. The whole “there was no year zero” thing has nothing to do with it. That would only matter if we were counting the number of decades, which we don’t do. That’s why you’re seeing “best of the decade” lists now, at the tail end of 2019: because 2020 will be part of a new “decade,” the ’20s. Get it? Now shut up and leave me alone.