Originally Posted by jhausner
Technically and factually speaking, decades start at the 0 so that means January 1st, 2010 was the start of a new decade much like December 31st, 1990 wasn't the end of the 80s, December 31st 1989 was.
So the end of the last decade was really December 31st, 2009.
The more you know...
However... the beginning of the year 10 C.E. marked the end of the 9th year since the end of the 1st year B.C.E.
(Say that aloud). The First decade in the Common Era started 2009 years ago, at the beginning of the year 1 C.E.
In Western culture, when you're born, you're 0 years old ( We don't include the first 9 months because most people don't record the day their child was conceived)
In that sense, the end of your 9th year or beginning of your 10th year marks being alive for one decade.
This is cardinal counting and is how modern mathematics counts.
However, some cultures (Korean is one) use the ordinal counting system to count years.
This is why we live in the 2000s but in the 21st century. It's all because of that pesky 0 that the hindus invented.
I guess I should be thankful... it would've sucked to have to add MDCCLXVI + MDCCCLXXXVII in school.