It occurred to me today that it had always bothered me when people insisted that the 21st Century and the new millennium started on January 1st, 2000 (when, in fact, the previous millennium and century both continued for another year after that1), yet I am not bothered at all with the commonly-accepted notion that a new decade starts in a year that ends with 0. Must have something to do with “decade” being oftentimes used to mark any statistically or historically significant stretch2, whereas “century” or “millennium” seem to always be used with specific boundaries in mind.
This deep thought is all I’m going to offer today.
1 If someone wants to re-visit that tired argument, please do me a favor first. Imagine yourself turning 2000 years old on January 1st, 2000. Count back 2000 years to come up with the day you had to be born. Use all of the tools in your disposal to determine whether year 0 AD ever existed. Try to accept that the first day of Anno Domini was January 1st, 1 AD (at least, as expressed within our modern-day Gregorian conventions). Add two thousand years to that to determine on which exact day you would turn 2000 if you were born on 01/01/0001. You can also add in increments of 100 to determine each century’s boundaries.
If you still want to pick up that argument with me after that, please don’t expect me to hold your mental abilities in high esteem.
2 I see passages like “over the following decade” appearing very frequently in bios and historical notes, preceded by an event occurring in a not-multiple-of-ten year.