# When does the new decade begin?

There has been some discussion among some people around my office as to when the new decade begins: January 1, 2010, or January 1, 2011. Someone finally asked me… they probably gave up on getting a simple, short answer that would persuade them, so they went to mister have-you-got-five-minutes. Here’s my disquisition:

Q. What was the first year AD? Zero or one?

A. AD 1. Before that was 1 BC.

Q. Why does that matter?

A. Well, so what was the first decade AD? One, two, three, four… A decade is ten years. The first ten years were completed at the end of the year AD 10. The first century was completed at the end of the year AD 100. The second millennium – the end of two thousand years since the point at which we started counting forward – was the end of AD 2000.

Of course, a lot of people thought that the turning of the millennium was when it turned from 1999 to 2000. And no surprise that they did: aside from the obvious change-over of the numbers, the way we count years of age is just the opposite. When’s your first year of life? Why, the year before you turn 1. Once you turn 1 you’ve finished your first year. Once you turn 2 you’ve finished your second year. When you’re 39 you’re in your 40th year.

So here’s this great irony: people keep saying someone who’s 40 is in their 40th year, which is wrong, but they also keep thinking that, for instance, the second millennium AD ends at the beginning of AD 2000, not the end, which is also wrong for the exactly converse reason. So we number years the way we count objects: the first one is 1, from beginning to end; the second, starting right after that, is 2; and so on. But we measure age the way we measure other things: you don’t get to 1 until you actually have a whole one.

Q. OK, fine, but just say it: when is the start of a new decade?

A. If you’re counting decades since the beginning of the counting of years, each decade ends at the end of the -0 year and begins at the beginning of the -1 year. So the current decade, if you’re making stacks of 10 like poker chips starting with AD 1, ends at the end of 2010.

So in the end, it really depends on what your purpose is. The real truth, as I said, is that a new decade starts whenever you want it to. The time starting exactly now and ending in exactly 10 years is a decade. So pick your frame of reference. If you want to refer to a decade such as we usually think of them in our culture, the ’20s, ’40s, ’70s, etc., then 2010 starts a new decade. If you want to play little gotcha-games, you can say, “Oh, no, the first decade of the third millennium isn’t over until the end of 2010!” Both are true.

### 11 responses to “When does the new decade begin?”

1. Wilson Fowlie

Jesus wasn’t born in AD 1 or 1 BC anyway. It’s now thought he was born 4 or 6 years earlier.

There is actually a growing body of evidence to suggest that he wasn’t born at all.

• You might find The Jesus Dynasty by James Tabor an interesting read. Tabor is a religious studies scholar of some stature, not a Bible-thumper or an unqualified crank, so he proceeds from good research and historical basis. His conclusions are not exactly mainstream, but on the other hand they’re not on the order of “no such dude.” One thing one comes to recognize is that Jesus was somewhat different from the standard conceptions. And, of course, there is as you say the ongoing debate as to his existence. There’s also ongoing debate as to whether his literal human existence matters one way or the other. It’s a heck of an area for unbounded discussion and debate (best served by sidestepping dogma an invective on either side), but I’ll try for the most part to tiptoe around it on this blog, which I’ll try to keep focused on language…

2. Wilson Fowlie

Glad to hear it! Merry Christmas, in any case.

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5. Further backup on what I’m saying about the meaning of decade: In the January 2011 issue of National Geographic, I see the following on page 60: “In a single decade beginning in the early 1990s, the fertility rate fell from three to around two.”

Now, are all the cranks going to line up and sneer, “Well, it must have been beginning on January 1, 1991, because that’s the only decade beginning in the early 1990s – and, by the way, the 1990s were not a decade, in case you thought they were!”?

Of course, the 1990s were a decade, but more than that, National Geographic is here obviously using decade in an even slightly looser way, in that it doesn’t appear to mean ten years to the day, but just a period of ten years with a sensible fudge margin. And that period does not necessarily start on January 1, 1991. Nor is National Geographic the only place you’ll see this usage. Of course.

• And in the latest issue of B&W magazine, there’s the article headline “The Golden Decade: 1945–1955.”

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7. ZMarko

Fantastic article on how we count time. Not a simple thing!

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