I have seen a lot of questions involving a "decade":

How does Politics SE here define a fixed time period of a decade/century/millennium?

Some users and I have been in a conversation on this question:

  • Me: 2021 is a different decade! (Current decade: 2011-2020, next decade: 2021-2030)

  • User45266: Most people define a decade as starting with the year ending in a zero: The Sixties started in 1960 (duh), and therefore 1970 was part of the Seventies, not the Sixties. The (20)'20s will include the year 2020.

  • JJ: well, I'd invite "most people" to take a look here. On English (the site), many regard the year ending with zero as the end of a decade / century / millennium. It's quite interesting.

  • User45266: Whoa! I can feel my horizons broadening! I never knew that that was even up for debate. Although with decades, I've never heard anyone argue that 1990 was part of the '80s. It's probably the same thing as saying "the 1900's" versus "the 20th century". I bet this is going to blow up in the media with people taking both sides once New Year's Eve rolls around... you heard it here first :)

  • JJ: Well I wouldn't recommend posting a happy new decade post on the ELU Meta site at the end of this year. :p

  • M69: Actually this was a big thing when billions of idiots celebrated the start of the new millennium in the year 2000.

  • User45266: But would they have been wrong in celebrating the start of the 2000s? I have a hard time believing that the year 2000 was part of the 1900s, but I could maybe see it being part of the 20th century... Ultimately, does it even matter?

  • BSMP: 0 = 10 not 1. If you asked someone to organize a bunch of sticks in bundles of 10, would you expect them to put the 10th stick in the 2nd bundle? The first bundle would only have 9 sticks. A group of 10 includes the 10th thing. (For 0 to be 1 there’d have to be a year 0 and there isn’t.)

BSMP and some other users tried to correct User45266. But instead of accepting the truth and moving on, User45266 would only decline and escalate from there.

  • User45266: Okay, but take those same ten sticks (actually, let's make it a hundred - you'll see why), label them 0-99 and spread them out on a table. Now, if I asked you to take all the "forties" out, would you grab stick number fifty (and leave out stick forty)? To me, that's ridiculous.

  • User45266: Now, we do have words like "century" and "decade" that are specifically tied to the chronological system we use, and to me it's fine to define a "decade", "century", or "millenium" as "one-indexed" (first ordinal number is one) rather than "zero-indexed", since our calendar system excludes a year zero. But to take a word like "the two thousands" and include "three (!) thousand" is illogical; it goes against the very meaning of the number two thousand.

And now, he/she reaches into a massive climax where I would have completely fainted.

  • User45266: To take this to an extreme, what if the number of things in a group is only one? Example: Is the year 2179 part of the "two thousands"? Of course. Is the year 2179 part of the "twenty-one hundreds"? Yup. Is the year 2179 part of the "seventies" (2170s)? Duh. But is the year 2179 part of the "nines"? I think it clearly should be! You can't possibly argue that it's part of the "eights", can you?

  • User45266: If you want to argue that the year 2179 will actually be the 2,178th "monoyear" (?) or something, be my guest, but you can't tell me that 2179 will be a part of the 2178th year.

Does Politics SE here define a "fixed" decade / century / millennium as '1-'0 or '0-'9? I would argue to follow the '1-'0 method. This is a more accurate method, since the first year was marked as year I, not nulla. (I and nulla = 1 and 0) In this view, the 0s (the first decade) ran from year 1-10. Note that the year 10 is not part of the 10's. In this view, the current year is 2020 and is part of the 2010s (2011-2020). "Most people" (?) would define the current decade (2020s) as 2020-2029 and not 2021-2030, according to what User45266 had said. So does Politics SE generally define the "last decade" as 2001-2010 or 2010-2019?

In general, does this site define a decade/century/millennium as '1-'0/'01-'00/'001-'000 or as '0-'9/'00-'99/'000-'999?

This is how I define the current peroid:

  • Year: 2020
  • Decade: 2010s (2011-2020)
  • Century: 21st century (2001-2100)
  • Millennium: 3rd millennium (2001-3000)
  • 1
    2020.0 to 2030.0 - Boundaries are at midnight local time so Jan 1st 2030 at 12:00:01 AM is a new decade. – SurpriseDog Feb 24 '20 at 19:50
  • 3
  • @SurpriseDog Jan 1st 2031, not 2030. You are saying it is 2020-2029. 0 is 10 not 1. For 0 to be 1 there should be a "year 0" and there was no "year 0". The first year was in fact year 1 and not 0. BSMP is correct. – user25526 Feb 28 '20 at 9:12
  • @Machavity Ok, it seems like a moderator should come here and tell the truth. – user25526 Feb 28 '20 at 9:14
  • 2
    @Yubin-chan Well the denizens of year 1 are free to complain about their decade being short changed, lol. – SurpriseDog Feb 28 '20 at 14:38
  • 3
    Obviously, I'm biased, but I think the key quote in the comment discussion you referenced is "Ultimately, does it even matter?" – user45266 Feb 28 '20 at 19:41
  • @user45266 yes. – user25526 Mar 5 '20 at 6:07
  • @user45266 0 is 10, not 1. The first "decade" (?) is marked as 0's, but there is no "year 0". We usually start counting from 1 and not 0. A decade is a period of 10 years. So 0's will include the years 1-10. – user25526 Mar 14 '20 at 2:44
  • How about centuries / millenniums? – user25526 Mar 15 '20 at 6:35

I think any distinction you make between the two would be hard pressed to find a notable difference, as such in questions where there is ambiguity (in other words where it actually makes a difference), I propose we either ask the questioner to specify, or answerers can make a determination as to which range they wish to use and provide a good answer.

This may lead to having multiple good answers on individual questions, but I for one would be pretty interested to see them both. Having both possibilities may provide insight on such questions which may not be available if only a single rule is strictly enforced.

  • I edited my question. Please edit this answer accordingly, too. – user25526 Mar 16 '20 at 5:27

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