The primary reason Japanese kanji have multiple readings is that the Japanese language developed far before kanji came into use. True to the name (the literal meaning of the word “kanji” is “Chinese letters”), kanji were imported into Japan from China, beginning between the fifth and sixth centuries AD. However, they did not come to be used in Japan as they are today until several hundred years later. At the time that kanji came to Japan, Japan had no writing system of its own, but it did have an established spoken language; which resulted in the development of multiple readings for kanji: readings based on the meaning of the character (kun-yomi), and readings based on the character’s original Chinese pronunciation (on-yomi).
It should be noted that the on-yomi of Japanese kanji do not necessarily correspond precisely with the way said character is pronounced in a given dialect of modern Chinese (e.g. Mandarin or Cantonese). This is partially because different on-yomi were adopted at different points in history, and partially because most Chinese dialects have sounds which are not completely replicable through the Japanese alphabet. A good example of this is the word “preparation,” which in Japanese is pronounced “junbi” and in Mandarin Chinese is pronounced “zhunbei.” There is no combination of kana in the Japanese alphabet which can quite equate to the Chinese “zhun,” and so the sound has become “jun.”
What's the Difference Between On-Yomi and Kun-Yomi? Why is it Important to Learn Both?
While many kanji have just one on-yomi and one kun-yomi, some kanji have multiple on- and/or kun-yomi and some kanji only have one or the other. However, when there are multiple on- or kun-yomi oftentimes certain readings will be more common than others. When first learning kanji, it is good to learn at least one of the most common on-yomi and one kun-yomi (if the character has both) for each character you are studying, as this will allow you to make educated guesses a greater percentage of the time when you encounter that kanji. Additional readings can be learned as you progress in your studies. One way to determine which readings are the most commonly used is to do a quick search of that kanji in electronic dictionaries such as the Imi Wa? app, and see how the character is pronounced in the top ten or so results.
Many of the simplest and most common kanji unfortunately have the largest number of potential readings. This may partially be due to the fact that many simple kanji express very basic concepts (up, down, living, etc) and thus after being imported into the Japanese language were applied to a variety of different already-existing words. The kanji for “up” (上), for instance, has more than 15 potential readings if on-yomi, kun-yomi, and nanori readings are all counted; although before you panic it should be noted that many of these are rather uncommonly used and okurigana will sometimes let you know which reading is being used (see below).
Note: Along with the kun-yomi and the on-yomi, there is a third type of reading for kanji called the nanori. Nanori are irregular readings primarily used in given names and surnames (although on-yomi and kun-yomi can be used in names also). Nanori readings are not frequently applicable aside from in reading names, so learning nanori is not as emphasized when studying kanji as learning on- and kun-yomi is.
How Can I Use On-Yomi and Kun-Yomi / How Can I Differentiate Them in a Text?
As is unfortunately often the case in any language, there are few rules that apply unequivocally. If you feel unsure of a kanji or kanji compound’s pronunciation, it is still best to look it up. However, here are a few rules of thumb which you can generally use to help determine which readings are most likely to apply to a particular word:
1) When the kanji is by itself (e.g. 猫, neko, “cat”) or paired with okurigana* (e.g. 食べる, taberu, to eat) it is likely to be read with a kun-yomi. This may be because single kanji as well as kanji with okurigana often represent common or simple words or ideas (cat, white, to talk, etc) which both do not require more than one kanji to express and probably had a word in the Japanese language before the introduction of kanji.
2) When the kanji is in a compound word comprising of two or more kanji, it is likely to be read with an on-yomi (e.g. 勉強, benkyou, “studies”). Many kanji compounds, especially if they are comprised of more than two kanji, express more complex ideas than single characters (hydropower, museum, etc).
3) If the kanji is part of a compound word with another kanji but has attached kana (e.g., 生け花 (ikebana, “flower arranging”) or 髪飾り(kamikazari, “hair decorations”)), it is more likely to be read with kun-yomi. The other kanji in that compound is also more likely to be read with kun-yomi, but may not be. It should be noted that this rule does not apply to kanji pairs that have been turned into a verb by being followed by する (suru, “to do”). Though する may look like okurigana, する-verbs that use kanji compounds (勉強する, benkyou suru, “to study”) often still follow rule #2.
4) If the kanji is part of a surname** or place name, it is likely to be read with a kun-yomi even if it comprises of two or more kanji. Similarly to rule #1, this is probably because many surnames and place names were in existence before the adoption of kanji, and names made later followed old patterns. When it comes to names, it is a good idea to ask the person in question (in the case of a surname) or a local (in the case of a place name) for confirmation of pronunciation. Sometimes even common surnames or place names can have multiple potential readings (e.g., 上野 can be read both “Ueno” and “Kamino”).
*Okurigana are kana that are attached to a kanji. Okurigana will often provide an indication of which kun-yomi is being used, for example in the two verbs 入る (hairu, “to enter,” which has only “ru” as okurigana) and 入れる (ireru, “to put in,” which has “reru” as okurigana).
**First names tend, especially in recent decades, to be read creatively (and thus irregularly) and frequently do not follow any rules at all. For example, parents may give their child a name with foreign origins but still write it in kanji of their choosing, or apply unusual kanji to a name typically written with common kanji.
Note that every one of these rules has exceptions! However, in general, following them will give you a relatively good idea of whether an on-yomi or a kun-yomi applies in a given situation.
3 Examples of On-Yomi vs Kun-Yomi
Example 1: Watashi wa yoku shokudou de taberu.
私はよく食堂で食べる。
- 私 “Watashi” stands alone with no other kanji attached to it, and so is pronounced with a kun-yomi (rule #1).
- 食堂 “Shokudou” has no okurigana and is a two-kanji compound, and so both its kanji use an on-yomi (rule #2).
- 食べる “Taberu” uses the same kanji as the first kanji of “shokudou,” but has no other kanji attached to it and is followed by okurigana. It is pronounced with a kun-yomi (rule #1).
Example 2: Tanaka-san wa Nagasaki no chuushinchi ni sundeiru.
田中さんは長崎の中心地に住んでいる。
- 田中 “Tanaka” is a kanji compound, but is also a surname; and so is pronounced using kun-yomi (rule #4). The same goes for Nagasaki because it is a place name.
- 中心地 “Chuushinchi” uses one of the same kanji as Tanaka, but is not a surname or place name and so follows rule #2.
- 住んでいる “Sundeiru” has no other kanji attached to it and is followed by okurigana, and so is pronounced with a kun-yomi (rule #1).
Example 3: Densha no noriba ni wa, joukyaku ga ippai narandeiru.
電車の乗り場には、乗客がいっぱい並んでいる。
- 電車 “Densha” is a two-kanji compound word with no attached kana, and so is read with on-yomi (rule #2).
- 乗り場 “Noriba” is a two-kanji compound word but the “ri” in between indicates that the first kanji is pronounced “nori,” a kun-yomi. The second kanji is not necessarily also pronounced with kun-yomi, although in this case it is (rule #3).
The first kanji of 乗客 “joukyaku” is the same as the first kanji of “noriba,” but joukyaku has no kana between it and its attached second kanji, and so is pronounced with on-yomi (ruule #2).
Just as with the other verbs in examples 1 and 2, “narandeiru” follows rule #1.
