The dictionary I'm using lists two common pronunciations of 「九」: 「きゅう」 and
「く」. I've usually heard it as 「きゅう」 before, but when saying 「９時」, it always
seems to be 「くじ」. Is there a rule to this?
CC BY-SA 3.0
2014-12-14T09:08:26.987
20881
2014-12-15T14:40:23.473
2014-12-14T16:28:36.680
3275
7946
question
pronunciation readings numbers
Pronunciation of 九
> Is there a rule to this?

Yes! The rule is **9時 is always くじ**. (And similarly, 9月 "September" is always
くがつ. Cf. 9ヶ月 きゅうかげつ "nine months".)
CC BY-SA 3.0
2014-12-14T12:47:12.507
20882
2014-12-14T12:47:12.507
1628
20881
answer
A single Kanji usually has several different readings, and numbers 1-10 are
probably some of the most salient examples of this. The readings can vary
wildly. For example,

九｛きゅう｝ (nine) 九本｛きゅうほん｝ (nine bottles) 九番{きゅうばん} (problem number 9) 九時｛くじ｝
(nine o'clock) 九月｛くげつ｝ (September -- 9th month) 九日｛ここのか｝ (the 9th day of the
month) 九つ｛ここの｝ (nine objects that are either round or of no discernible shape)

I can't really think of a general rule, unfortunately. I can say, however,
you'll eventually get used to all the exceptions.
CC BY-SA 3.0
2014-12-14T16:37:34.670
20885
2014-12-14T16:37:34.670
7207
20881
answer
Generally speaking, there is no hard rule to decide which reading of a _kanji_
is used for a given word or compound. To be certain, you need to look it up in
a dictionary and remember each word on a case-by-case basis.

However, there are certain _tendencies_ that allow you to guess, better than
by random guessing, which reading to use for a certain _kanji_. To put it
another way, you can use your feeling for the language to come up with an
educated guess for a new word, and need to remember only the exceptions,
reducing the required mental load and capacities.

Another point I believe is worth mentioning, you need to learn each word
anyway, be there _kanji_ or not. By `learning a word`, I am referring to the
association between meaning and sound. You need to do that for any other
language as well. And once you _know the word_ , all you need to do when
reading a text with kanji is identifying the word in question, and you will
know its pronunciation. For example, if you have learned the word `kuji = `,
and you see `九時` in some written text, your knowledge that `九 = 9, 時 = time`
together with the context allows you to conclude that `九時 = `. Therefore, even
without remembering which reading to use for each word, you know that `九時 =
kuji`.

Tendencies include the following:

ON/KUN reading:

  * ON, in _kanji_ compounds, eg. 芸者【げいしゃ】, 恍惚【こうこつ】
  * ON reading if it has become an individual word on its own*, eg. 肉【にく】, 秒【びょう】, 魔【ま】, 豹【ひょう】, 雹【ひょう】, 生【せい】, 僕【ぼく】, 本【ほん】, 印【いん】
  * KUN reading if there are _okurigana_ forcing it, eg. 頂【いただ】きます, 行【おこな】う, 躊躇【ためら】う (cf. 躊躇【ちゅうちょ】), 話【はな】し
  * KUN for individual kanji whose ON reading is not an individual words, especially if it is a noun with the _okurigana_ of the 連用形 omitted, eg. 神【かみ】, 鏡【かがみ】, 話【はなし】, 歌【うた】, 鉈【なた】
  * words consisting of multiple words etymologically are prone to mixed readings, especially when the ON reading exists as a word, or it contains pre/suffixes: 取調室【とりしらべしつ】, 秒読み【びょうよみ】, 消印【けしいん】, 団子【だんご】, 客間【きゃくま】, 時代物【じだいもの】
  * Words referring to cultural activities, rituals, objects, food, clothing, medicine, plants, weaponry etc. tend to use irregular readings, and you had better look them up, eg. 八咫烏【やたがらす】, 地謡座【じうたいざ】, 栴檀板【せんだんのいた】, 上四方固【かみしほうがため】, 天照大神【あまてらすおおみかみ】, 剪定鋏【せんていばさみ】

Some compound words without _okurigana_ read KUN: 子守唄【こもりうた】, 神々【かみがみ】,
素直【すなお】, 取引【とりひき】. Note that there are some mixed ON/KUN compounds (cf. 湯桶読み,
重箱読み).

Different ON readings:

  * Most _kanjis_ have got one ON reading that is much more common in contemporary Japanese. Often, this is the KAN (漢音) reading. Some of the more frequent _kanjis_ have got more common readings, but the rarer, the less irregular, and most kanji are infrequent**. Eg., 植【しょく】, 衛【えい】, 療【りょう】, 恥【ち】, 攪【かく】, 命【めい】, 焉【えん】, 集【しゅう】. Words with other readings are not so common: 命終【みょうじゅう】, 駢植【へんち】, 兵衛【ひょうえ】, 結集【けちじゅう】, 攪拌【こうはん】
  * GO (呉音) reading for Buddhistic vocabulary, and common words of Buddhistic origin: 薬師 **如** 来【やくしにょらい】, お経【きょう】, **涅** 槃【ねはん】, **解** 脱【げだつ】,八 **正** 道【はっしょうどう】, **精** 進【しょうじん】, 名色【みょうしき】, **怨** 憎 **会** 苦【おんしょうえく】, 不動 **明** 王【ふどうみょうおう】
  * Some older (Heian/Kamakura - Edo) words use TOU/SOU (唐宋音), eg. 椅 **子** 【いす】, 杏 **子** 【あんず】, **行** 灯【あんどん】, 箪 **笥** 【たんす】, 九時【くじ】

* * *

(*) Often, these words are used only as part of some larger sentence and might
be unintelligible if used in isolation. For example, `この世に生をうける` is
understandable, but saying `せい` without context is not.

(**) Some less frequent _kanji_ with a reading different than what their
structure (semantic-phonetic compound) suggests have acquired a new ON reading
corresponding to the phonetic element. This is called 慣用音, eg. 消耗【しょうもう】
instead of the original 消耗【しょうこう】.
CC BY-SA 3.0
2014-12-14T18:47:19.993
20887
2014-12-14T18:47:19.993
3275
20881
answer
Today, きゅう is the default (i.e. productive) _on-yomi_ pronunciation of 九 (or
9) for counting most things, and only a small portion of words requires く.

Always:  
**hours** (o'clock) (`9時`, `19時`), **dates** (`19日`, `29日`), **month name**
(`9月`)

Preferred or alternative to きゅう:  
**hours** (duration) (`9時間`, `19時間`...), **years** (`9年(間)`, `2009年`...),
**people** (`9人`, `19人`...), **degree** (`29度`, `39度`...), **bare double-
figure numbers** (`19`, `29`, `1029`...), **-fold, -ple** (`9重`, `19重`...),
followed by **次** (`第9次`, `9次元`...)

Sporadic traditional or euphonic examples (Google it for details):  
`九段`, `九十九里`, `四十九日`, `九分九厘`, `九条`, `九九`, `九曜`, `第九`, `月9` (= 月曜9時) etc.  
(There are far more old words; historically く had been the prevailing
pronunciation until it was replaced because of its homophony with 苦{く}
"anguish".)
CC BY-SA 3.0
2014-12-15T09:49:35.727
20895
2014-12-15T14:40:23.473
2014-12-15T14:40:23.473
7810
7810
20881
answer