# History of 十干（じっかん）and modern uses

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}

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.]

I use 甲 and 乙 when writing business-to-business contracts, meaning first party, second party.

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.
• 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.

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.

• Very interesting answer. But for part #3, I'm missing how that is 60 pairs and not 120 pairs (10x12?). – istrasci Mar 19 '12 at 20:08
• While it is possible to make 120 pairs, notice that the order is (十干, 十二支), not (十二支, 十干). This will reduce the count in half, i.e. 60. Thus, for an example, I gave 丁酉, but there is no 酉丁. Just like seconds and minutes, a sexagenary cycle has 60 units. – Dono Mar 20 '12 at 1:00
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).
• Cannot understand the very first sentence: “Sorry for that I'm sure the answer because of I can't find any references.” Maybe you omitted “not” or something similar somewhere? – Tsuyoshi Ito Jun 23 '11 at 15:50