As I was studying vocabulary today, I happened to come across the titular 十干
which are as follows:

> [甲]{こう} • [乙]{おつ} • [丙]{へい} • [丁]{てい} • [戊]{ぼ} • [己]{き} • [庚]{こう} • [辛]{しん}
> • [壬]{じん} • [癸]{き}

There's a somewhat lengthy definition near the middle of [this
page.](http://ginjo.fc2web.com/117obikyuu/obikyuu.htm)

I happened across this while looking up the word へい（塀 - wall), and the first
entry in my プログレッシブ dictionary was 丙（へい）- showing the definition as "3rd rank"
or a "grade of C (in school)". I proceeded to find that 甲 and 乙 are also used
to mean a grade of A and B respectively.

My questions are:  

  * Are these used in modern Japanese for ranking things??? If so, all of them, or just like the first 3??? And what kinds of things are ranked this way???
  * Is this a part of 尺貫法 or is it something completely separate???

_[Side note: would anyone be interesting in making/helping to make a community
wiki on 尺貫法? I find it strangely fascinating for some reason.]_
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2011-06-22T19:37:31.573
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usage kanji history etymology
History of 十干（じっかん）and modern uses
I use 甲 and 乙 when writing business-to-business **contracts** , meaning first
party, second party.
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2011-06-23T07:40:47.123
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1. Sorry for that I'm sure the answer because of I can't find any references. However, as I know, it's not modern in Japanese ranking.
  2. This system is not a 尺貫法. It is a sequence. It comes from Chinese: 天干 [(Celestial stem)](http://en.wikipedia.org/wiki/Celestial_stem).
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2011-06-23T08:30:56.253
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They used to be used to express (mathematical) variables until the western
influence changed the custom to use western characters instead. It is still
used where the tradition remains.

  * You can find them in traditional mathematics called 和算 especially on [算額](http://ja.wikipedia.org/wiki/%E7%AE%97%E9%A1%8D).
  * The cases that Nicolas mentions is actually a special case of the variable use. In contract, you do not use `甲乙` out of the blue. They do not mean first party, second party. They are preceded by a definition like: `賃借人 (以下甲とする)`.

Other than as variables, it is used to mention some kind of orderings. Grading
as you mentioned is one example.
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2012-03-17T23:45:45.557
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In addition to what others have stated, below are three areas where I
regularly see and use these:

1: In Old Japanese, there were syllables that phonemically contrasted with
each other such as ki1 / ki2, me1 / me2 etc. This is called 上代特殊仮名遣, and the
distinction essentially vanished at the start of Early Middle Japanese. In
practice, the subscript 1 type is called 甲類 (kō-rui: type A or type 1) and the
subscript 2 type is called 乙類 (otsu-rui: type B or type 2).

2: Reading of classical Chinese texts has a long history in Japan. This is
called kambun (漢文). Due to syntax and grammatical difference, the order must
be changed for a text to be read as Japanese. The primary ordering marks are
一二点 (ichini-ten) and レ点 (re-ten). In the former, one places numbers beside the
characters to know how to read it. In more complex clauses, secondary,
tertiary, and even quanternary marks are used to clarify the order. Secondary
is 上・中・下 (上下点, jōge-ten), and tertiary is 甲・乙・丙・丁… (甲乙点, kōotsu-ten). While
quite rare, in the most complex texts, a qunternary level using 天・地・人 called
天地点 is also used.

3: Old documents used a sexagenary cycle (干支 kanshi or eto) borrowed from
China to record days and years. This system combines the above 十干 (jikkan
甲・乙・丙・丁・戊・己・庚・辛・壬・癸) with 十二支 (jūnishi 子・丑・寅・卯・辰・巳・午・未・申・酉・戌・亥). This produces
60 pairs, each with a given order. For example, the 『続日本紀』 (Shoku-nihongi)
begins at 丁酉年 (hinototori or teiyū). This is number 34, and means any western
year that when divided by 60 results in a remainder or 37 (34 + 3). Hence,
517, 577, 637, 697, 757, 814, 877 etc. In this case, it is the year 697.
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2012-03-18T04:05:57.463
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