Some on'yomi and kun'yomi patterns I've noticed. Help me confirm?

I’ve been noticing certain patterns regarding kun’yomi and on’yomi readings. I’m not too sure of these, but they almost seem true. What do you guys think? Yay or nay? Here they come:

  • Most on’yomi readings tend to be pretty short, to the point that if it’s less than 3 kanas, I’m almost certain its an on’yomi reading.
  • On the contrary, most kun’yomi readings tend to be pretty long. Most of them, not all of them. Also, if there’s okurigana, it’s a kun’yomi reading.
  • Following up on that, most non-する verbs tend to be a kum’yomi reading.
  • する verbs are pretty much a grab bag. They can either be kun, on, or even a foreign word so there’s not much of a pattern there.
  • I’m almost 100% sure that all い-adjectives are kun’yomi readings. Whereas な-adjectives, like する verbs, are pretty random. (I’ve seen ファンキーな as in funky, funky music. I’m sure it’s my favorite な-adjective.)

I think that’s pretty much it. What do you guys think? I could be wrong. What patterns have you noticed?

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The opposite is more useful. If it’s more than two mora it is definitely a kun’yomi reading. I say mora because きょ (etc.) is considered a single mora.


Disclaimer: some oversimplification.

Kunyomi readings are usually “Yamato kotoba” (words from Old Japanese). Old Japanese had a fairly strict CVCVCV… pattern (C=consonant, V=vowel).
Just look at the term “Yamato kotoba” itself to see this pattern.
It was also a polysyllabic language so most words used multiple syllables, which is why most kunyomi readings are multiple kana.
Onyomi readings are usually based on borrowings from Chinese. Older variants of Chinese are monosyllabic languages, where each character is one syllable is one word. (Chinese has now become polysyllabic, basically using a lot of compound words from older words)
However, chinese syllables are more complicated than Japanese mora.
E.g. 王 was pronounced “hjwang” in Middle Chinese.
The Japanese couldn’t pronounce this so they adapted it into two mora わう which later became the おう reading now used today.
All the small kana features (ゃ, っ, etc.) are actually Chinese influences that didn’t exist in older Japanese.
(However you still see them in modern kunyomi readings as a result of sound changes. When Japanese adopted these features they didn’t hesitate to retrofit them into the words they already had, e.g. けふ became きょう over centuries of sound changes)

Some obvious exceptions to this pattern are “fake” kunyomi/onyomi readings.
Sometimes a reading is arbitrarily declared a kunyomi or an onyomi even though it didn’t come from Old Japanese or Chinese, respectively.
I don’t think they’re many examples of this, though.

Suru-verbs and na-adjectives are nouns at the core.
Someone took a noun and added “suru” to make a verb or added “na” to make an adjective.
Non-suru-verbs and i-adjectives, on the other hand, have been handed down from Old Japanese (with very few exceptions).
They’ve been adapted and changed, but there have been very very few completely new addition into these classes.
(Linguists say they form a “closed” class).
When the Japanese borrowed heavily from Chinese, they borrowed almost only nouns, converting them into verbs and adjectives using “suru” and “na” if needed, which is why those are the only classes that will contain onyomi readings.
I suspect the reason is something like this: With true verbs and i-adjectives, you need to worry about the conjugation and, in general, conjugating a completely foreign word just sounds wrong. And since there is an easy way out with suru / na, there is no need to bother.

Note, that there are ways to make a new verb, by slight of hand. The first is to give a special meaning to a conjugated form (e.g. the passive or the causative), e.g. 合わせる is technically the causative of 合う.
The second is compounding, e.g. 走り回る is a compound of 走る and 回る.
There is an awful lot of compound verbs as a result of this.


I had no idea the word “mora” existed, which is even extra confusing considering it’s spanish for “berry”, and I’m a native spanish speaker, but it certainly makes sense. Thank you for pointing that out!

Usually on’yomis are either one syllable long or the second syllable is an u sound like くor つ.

こう、かい、きゅう、かん、こく、かつ etc.

Mora is actually Latin, literally means “duration of time”. Japanese is most “properly” pronounced with each mora taking the exact same amount of time, hence the name.

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Very interesting. It even makes me wonder what impact would knowing chinese have on japanese studies. Tofugu has some great articles out there on the origin of words, and it coincides with a lot of the points you’re listing here.

I’ll look up some of the things you’ve listed here. Thank you!

I found “Classical Chinese for Everyone” to be fun to work through. It’s a short intro to Classical Chinese, which is the Chinese of Confucius and his contemporaries. Just watch out that the character meanings and forms often don’t really match modern kanji. I didn’t really bother to revise any the vocabulary since I was just curious how the language works on a basic level (it’s actually very different from Japanese, for the most part; they didn’t really bother adopting much grammar, if any).

I don’t know if it’s actually useful for Japanese studies to study this kind of stuff, but it’s certainly very interesting.

(Actually the first section is quite interesting even if you don’t care about Chinese, as it explains how kanji were made)

It seems to me that apart from foreign loan words written in katakana, most する verbs are onyomi. So I’d say that’s a pattern. (And same with な adjectives.)

Another pattern I’ve noticed is that most words with an おう (or こう,しょう,とう) are onyomi. Most kunyomi words use a short お or are written with おお rather than おう. Of course there are exceptions such as 妹(いもうと) and 弟(おとうと) which from what I read historically had the final うと morph from the original ひと. But there are also others such as 設ける(もうける) and I don’t know the history behind that one.

I don’t know about this one. Yes, the long ones are all kunyomi, but I think the average is still quite short.

All non-する verbs use kun’yomi. It’s the one shining exception to the “all rules in Japanese have exceptions” rule. The trick to remember is that verbs with ~じる endings (like 感じる, 信じる and so forth) are also する verbs. And then there’s 略す, which (amusingly, given its defition) is 略する with an abbreviation.

Adjectives with attached okurigana always use kun’yomi also.

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The verb kun’yomi readings are particularly short often since they exclude the ending.
上げる is a three mora word but the kanji is only used for the first mora.

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Yeah, that’s what I was thinking of.

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