First off: on'yomi and kun'yomi don't matter at all. Not in the least. Nope. Nothing. You might as well close this page right now and forget about kun'yomi and on'yomi because they will help you in exactly nothing. Just pretend they are the same thing and you'll be OK.
Readings and KanjiNow, to elaborate my point, let's remember how words and kanji work: one word is made up of one or more kanji and kana. Each kanji has multiple ways it can be read, but when its used in a word it's always read the same way.
So, basically, if suugaku 数学 means "mathematics," kazu 数 means "number," and manabu 学ぶ means "to study," you will always see suugaku 数学 read as suugaku, never as kazumana 数学. This is because kazumana isn't a real word, I just made it up from the readings of the kanji found in other words.
Some words, however, can be read with either kun'yomi and on'yomi. These are very rare so we won't really talk about them.
Now, why is suu 数 read as suu in suugaku 数学, suunin 数人, suubyou 数秒, etc. but has a very different reading in kazu 数 and kazoeru 数える? Simply put, the suu reading is the 数 kanji on'yomi, while the kazu reading is its kun'yomi.
Likewise, gaku is the on'yomi of 学 and mana is the kun'yomi of 学.
Telling Kun'yomi and On'yomi ApartNow we know that suugaku 数学 is always read suugaku, in on'yomi, but how do you tell if in another word the kanji is read with kun'yomi or on'yomi? Sure there is a way?
Yeah, well, maybe. Sort of.
The best way is always to have furigana 振り仮名 to help you, but f that isn't the case, then, generally speaking, with as many exceptions as there are useless protagonists in anime, the following rules apply:
First, words with only one kanji are read with kun'yomi. Examples:
- sakana 魚
- ishi 石
- inochi 命
- koto 事
- toki 時
- aida 間
Second, words with more than one kanji are read with on'yomi. Examples:
- kakkou 格好
- shokuji 食事
- hadouken 波動拳
- unmei 運命
- kingyo 金魚
- jikan 時間
Third, verbs ending in suru or jiru are read with on'yomi. Examples:
- kekkon suru 結婚する
- ai suru 愛する
- kan-jiru 感じる
- mei-jiru 命じる
To order. To command.
Fourth, verbs non-suru are read with kun'yomi. Examples:
- tabe-ru 食べる
- hako-bu 運ぶ
- mana-bu 学ぶ
- ugo-ku 動く
Like I said, there are many exceptions. To the very first rule, ai 愛, "love," is an one-kanji word read with on'yomi. For the second, monogoto 物事, "things," is read with kun'yomi. The third, tojiru 閉じる, "to close," is kun'yomi. And the fourth... I can't really think of a word but it probably exists.
Mixing Kun'yomi and On'yomi
The problem with trying to tell kun'yomi and on'yomi apart really starts when you have mixed reading words. Words with kanji having on-on readings are common, kun-kun, also common, so when the little rarer kun-on and on-kun show up they might catch you by surprise.
Perhaps the most fitting example I could have for this article is the very word on'yomi 音読み. The on of on'yomi is an on'yomi reading, but the yomi is a kun'yomi reading. Also, the kun of kun'yomi is an on'yomi reading.
So both kun'yomi and on'yomi are on-kun words, but why are they on-kun words? What led Japan to create this monstrosity? This mix of complete opposites? This entangling of things that shouldn't be tangled? Well, pretty much it: they mixed two words.
In this case, yomi 読み means "reading," and comes from yomu 読む, "to read." So all this time we have been saying "on'yomi reading" we have been saying "on reading reading."
In other cases... who knows? If you see two unknown kanji and a kana or more together it could be a single word, two words, three words, even. And this fact brings me back to my original point.
The Kanji Reading Doesn't Matter
When you encounter an unknown word, save for the fact the kanji can only be in a few ways, all else is uncertain.
It could be on readings, kun readings, a mix of the two, multiple, separate words, whatever. The fact is that in a given Japanese text you don't even know where a word starts and the other ends half of the time, so trying to guess how to read it based on whether it's supposed to be kun'yomi or on'yomi is not only impossible, it's pointless.
Even if by some divine miracle you are able to read the word correctly, like, after 4 or more guesses, that won't change the simple fact that you still don't know what the word means. It will be like reading some book from decades past, finding the word "enjoin" on it, and wondering what the hell did the author mean.
In summary: if you encounter a word you don't know to read in Japanese, you will check the dictionary anyway, and on that dictionary you will find the right reading. So knowing which reading is it in an unknown word doesn't really matter.
The Word Reading Matters
An alternative, which in my humble opinion is for the best, is to learn the readings of words instead of the readings of kanji.
Like we have discussed in the first part of this article: one kanji has multiple readings, but one word always have the same single reading.
Therefore, remembering that 数学 is read suugaku and only suugaku is far easier than remembering each kun and on'yomi of both kanji and trying to figure out on spot if whether it's kazugaku, kazumana, suumana, etc.
On and Kun in The Dictionary
By the way, in case you have ever wondered: when you encounter the words on 音 or kun 訓 randomly placed around a dictionary, they mean on'yomi 音読み and kun'yomi 訓読み.
I just thought it was important to note in case you were wondering what the on and kun meant in your Japanese dictionary.
Origin of On'yomi and Kun'yomi
One last thing important noting are the origins of on'yomi and kun'yomi. After all, why the fuck does this madness exists? Who came up with this shit? It's absolute non-sense and only makes everything more difficult to learn than it was before!
(take it with a Sahara of Salt because I don't actually study Japanese history and I don't think I have any authority about these things.)
Kanji Gets Into Japan
Basically, long, long, very long ago. In a date I don't know for sure and won't bother googling it up. Japan didn't have kanji.
Obviously, they had words, they spoke, talked to each other in some archaic version of Japanese, but nope, no kanji. After all the kanji 漢字 are literally "Chinese characters," they weren't invented in Japan, they were imported from China.
And thus it happened: they imported the hanzi 漢字 from China! (then, later on, Japan would make hiragana and katakana from the kanji they imported)
Japan only had one little... tiny... minuscule problem. Japan had words already. The kanji had meanings already. And those kanji also had their Chinese ways of being read already.
So what they did was, for example, taking the word sakana, which means fish, take the kanji 魚, which meant fish, IN CHINA, and just start writing sakana as 魚, because why not?
Except that sakana 魚 was read (something like) gyo 魚 in Chinese. So now they ended up with two different ways of reading the same kanji.
So what Japan did then was to make it so that when the kanji was read in their own way, the reading based on a native Japanese word, it would be called a kun'yomi. And when it was its original Chinese reading, that would be the on'yomi.
Of course that after thousands of years the on'yomi of kanji 漢字 no longer matches the modern Chinese pronunciations of the same hanzi 漢字. Who knows if it even matched it back then? But that's basically the gist of it.
On'yomi, Kun'yomi and Suru Verbs
If you haven't noticed, this also explains why verbs suru are usually on'yomi and non-suru kun'yomi.
When Japan associated their native words with kanji, the verbs, such as a-geru 上げる, had the part which was conjugated left in hiragana so it could be conjugated according to Japanese grammar: agaranai 上がらない.
On the other hand, if you make a word up from on'yomi readings of kanji, it doesn't end in something that can be conjugated. The word kekkon 結婚 isn't kekkon-geru 結婚げる. You can't conjugate kanji, so it needs to be appended the suru verb so it works in Japanese grammar.