To the editor:
Does a century end with the year ‘99 and the next one begin then with the year ‘00? Or is the last year of the century ‘00 and the next year, in the new century, ‘01? (Editor’s Notes, Jan. 15-28.)
The answer is really not that difficult.
To start with, let’s put labels with numbers on exactly 2,000 boxes in a warehouse. On the first box we write #1, on the second one #2, until we reach the last box and write #2000 on it. Now we will put numbers on the same number of years—two thousand of them or, as we call it, two Millennia of years. The first year we call year number 1 (same as with the boxes) and the last one number 2000. Notice: The LAST one 2000! So, after that , the third Millennium starts with the year 2001.  In other words, the 20th Century did not end on the 31st of December 1999 because that Century was “not full yet”! It ended only on the 31st of December 2000!
The same goes for a Decennium, a period of 10 years. A Decennium starts with 1, 11, 21,31 etc. and ends with 10, 20, 30, etc. The last Decennium of a Century is’91 up to including ‘00 so the last Decennium of the 20th Century was 1991 up to including  2000. The Decennium we’re in now started on the 1st of January 2001 and will end on the 31st of December 2010. It’s as simple as counting the fingers on your two hands. You don’t start with finger number zero! You start with number one and the last one is number 10!
So, it’s not really that complicated!
Willem Hoogstraten, Buckhead

To the editor:
Nah. You are forgetting the concept of  zero: Is a baby not alive until he celebrates his first birthday? Has he not lived a decade when he celebrates his tenth birthday? See?
“The Sixties” (a decade) started in 1960, as in Jan. 1, 1960. Ditto all the decades we refer to – the ‘70s, the ‘80s, and so on.
This is actually too tiresome to worry about. We have mortgages to pay, so let’s just get on with the fresh new decade and hope for better days ahead.
Karen Klare, Buckhead

To the editor:
If you transfer the decade argument to the life of a child, it will make sense.  If a child is born on Jan. 1, 2010, he will be 1 year old on Jan 1, 2011, 2 on 1/1/12, 3 on 1/1/13, 4 on 1/1/14, 5 on 1/1/15, 6 on 1/1/16, 7 on 1/1/17, 8 on 1/1/18, 9 on 1/1/19 and 10 on 1/1/20 … and a new decade begins.  Tell a kid, whose birthday is celebrated each year, that when he has lived 10 years, he has to wait until 1/1/2011 to celebrate his 10th birthday [and] sparks will fly and that will end the ‘argument.’
Ruth James