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A great-great-great grandmother thought to be the oldest person in the world has died in Japan aged 117.

Nabi Tajima, who was born August 4, 1900, became the world's oldest seven months ago after the death of 117 year old Jamaican Violet Brown.

Ms Tajima, who was thought to be the last person born in the 19th century, had seven sons, two daughters and reportedly more than 160 descendants, including great-great-great grandchildren.

ITV News 22 april 2018

Was Nabi Tajima born in the 19th Century or the 20th Century ?

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    Unless something very strange happened after 4th August 1900 for the rest of the year, I suspect ITV News mean that she's thought to be the last living person born in the 19th Century. Commented Apr 23, 2018 at 8:52
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    @NigelJ So when did you start the second decade of you life? In year 10 or in year 11 of your life? The first year of your life was year one, not year zero.
    – oerkelens
    Commented Apr 23, 2018 at 10:25
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    @oerkelens When we say "I'm in my thirties", we mean "I am between 30 and 39 inclusive", not "between 31 and 40 inclusive"; that is the 4th decade of your life (after 0-9, 10-19, and 20-29). Similarly, "the 1930s" would widely be recognised as "between 1930 and 1939", not "between 1931 and 1940", and that is the 4th decade of the 20th Century. So it is perfectly logical to call "1900 to 1999" the "20th Century".
    – IMSoP
    Commented Apr 23, 2018 at 11:18
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    @oerkelens The more I think about it, the more I disagree with your comment and agree with Nigel's. The first year of your life was the one leading up to your first birthday; your age during that year was zero. Your "11th year" started on your 10th birthday, which also marked the beginning of your second decade.
    – IMSoP
    Commented Apr 23, 2018 at 11:54

3 Answers 3

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In the Western calendar system based on the Gregorian calendar, the year zero does not exist. That means we started counting with year 1.

That means that the first decade, the first century and the first millennium all started in the year 1, not in the year zero.

From there it follows that the second century started in the year 101, and the 20th century in the year 1901.

However, a lot of people like round numbers, and a lot of people celebrated the beginning of the third millennium on January 1st, 2000, instead of 2001.

Technically, Nabi was indeed born in the 19th century, because the 20th century didn't begin until January 1901. In common usage most people will however consider 1900 the start of the 20th century.

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    Is that not GR? en.wikipedia.org/wiki/19th_century And what has that to do with the English language and its usage anyway?
    – Kris
    Commented Apr 23, 2018 at 9:22
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    @Kris "Is that not GR?" - what is "GR"? Commented Apr 23, 2018 at 11:20
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    @DaveBoltman it's just EL&U jargon, GR stands for "general reference", an defunct reason for closing questions. We now have "lack of research" in its place.
    – Mari-Lou A
    Commented Apr 23, 2018 at 12:17
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    Oerkelens, you say "In common usage most people will however consider". I think that is sidestepping the issue of correctness. People who do that are factually incorrect. It's a very easy mistake to make, and I'm going to celebrate the party when all the digits change too, but it is still a terminological mistake.
    – Mitch
    Commented Apr 23, 2018 at 14:06
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    @Mitch This is where this question touches on English usage. In reality, people use the expression "20th century" when they mean the period that started on 1/1/1900 and ended 31/12/1999. Whether that is actually "correct" according to people who look at the calendar is not very relevant in everyday usage.
    – oerkelens
    Commented Apr 23, 2018 at 14:30
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Ms Tajima was born in the 19th Century. That is, between 1st January 1801 and 31st December 1900. I think if you were a mathematician you would like to argue that the calendar should have began at 0, however it didn't it began at 1 which means that each following century began at 101, 201 and so on.

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    Mathematicians would not have a problem with something being ℕ and not ℕ0. Personally I find that people with less knowledge of maths have the biggest problem with centuries starting with 1. Your answer is correct though.
    – Bent
    Commented Apr 23, 2018 at 8:02
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    It is not a matter of mathematics (or plain arithmetic). It seems to be a matter of convention. I would be interested to know who decided this convention and whether the general populace had any say in the matter.
    – Nigel J
    Commented Apr 23, 2018 at 9:42
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    @NigelJ You can't have a year nought. It's either before Christ (BC or ante Christum natum) or in the Year of Our Lord (AD). If you're going to ask about whether the people had a choice, there wasn't really a choice to make since a year nought made absolutely no sense.
    – JDF
    Commented Apr 23, 2018 at 10:59
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    You can't say "should have began". That's not grammatical.
    – tchrist
    Commented Apr 23, 2018 at 11:07
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    @Pakk: of course you can have a year zero. Just use the proleptic Gregorian calendar with astronomical year numbering. Look - you're dealing with dates. Dates are actually quite mutable. There is nothing special about them. Many people say that today is "April 23rd, 2018", but it's all just a matter of convention. And not everyone goes along with it. Consider, for example, all the other calendrical systems which are also in use worldwide. Really, you can have today be whatever day you want. The trick is to get others to agree. :-) Commented Apr 23, 2018 at 11:37
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The year 1900 is more properly referred to as 1900 A.D. (or 1900 C.E.) which is itself an abreviated form of "The 1900th year of our Lord" (a.k.a. "The 1900th year of the Common Era")

Because we are ordering years rather than counting them, we use Ordinal numbers instead of Cardinal numbers. For example, once you are born you are 0 years old - but it is the 1st year of your life. The 12 months leading up to that point are the 1st year before you were born (or, arguably, the last, but that makes counting backwards rather awkward). This means that the Year is 1-indexed rather than 0-indexed, so the 1st decade ran from 1 A.D. to 10 A.D., and the 1st century from 1 A.D. to 100 A.D.

An Ordinal number starts at 1, and can have a vector/direction, but not a sign (it is always positive): The 1st dog to your left is not the -1st dog to your right, and there is no 0th dog in any direction.

(Unless you are a dog - but who would know?)

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  • A.D. is traditionally prepended at the start of a data. That is, AD 2018. It's usually expressed fully as 'the Year of our Lord Two Thousand and Eighteen'.
    – JDF
    Commented Apr 24, 2018 at 0:03

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