On'yomi vs Kun'yomi: When to Use Each Kanji Reading
Open a kanji dictionary and most characters list two kinds of reading. Which one do you use? 山 alone is やま, but 登山 is とざん. The choice isn’t random. There’s a reliable rule of thumb that gets you most of the way.
Two Kinds of Reading
On'yomi (音読み) is the reading borrowed from Chinese when the kanji was imported. Kun'yomi (訓読み) is the native Japanese word that was matched to the character's meaning.
So 山 carries the meaning “mountain.” Its kun'yomi is the native word やま; its on'yomi is the Chinese-derived サン.
The Rule of Thumb
- Kanji standing alone, or with okurigana → usually kun'yomi. 山 = やま, 学ぶ = まなぶ.
- Two or more kanji together (a compound) → usually on'yomi. 登山 = とざん, 学校 = がっこう.
It's a tendency, not a law. There are exceptions, and jukujikun ignore it entirely, but it predicts the majority of cases.
Examples
Why Some Kanji Have Multiple On'yomi
The single on'yomi you meet most often for a given kanji isn't always the only one. Japan borrowed Chinese pronunciations in several waves over centuries, from different regions and periods of Chinese, and often kept more than one layer rather than replacing the old one. That is why a character can carry two distinct on'yomi that both still show up in real words today.
You don't need to track which historical layer a reading came from. The practical takeaway is simpler: if a compound's on'yomi doesn't match the one you already memorized for that kanji, don't assume you learned it wrong. Check whether the kanji simply has more than one on'yomi in circulation.
Where Kun'yomi Ends and Okurigana Begins
食べる looks like one unit, but the kun'yomi of 食 is actually just た; べる is okurigana, the conjugating tail that changes with tense and politeness (食べます, 食べない, 食べた). Mixing these up is a common source of confusion when a dictionary entry lists a kun'yomi that looks shorter than the word you actually see in a sentence.
A quick check: if part of the reading changes depending on the verb form, that part is okurigana, not the kanji's reading. The part that stays fixed across all conjugations is the true kun'yomi.
How to Study
- Learn both readings with example words, not in isolation: 山 (やま) and 登山 (とざん) together.
- Use the compound-vs-standalone rule as your first guess, then confirm.
- Watch for jukujikun (今日, 大人) that follow neither reading, so learn those as whole words.
Teacher's Note
Don't drill readings on bare kanji cards. You'll memorize sounds with no anchor. Always learn a kanji inside a word. The reading then comes with context, and the on/kun choice takes care of itself.
Learn kanji inside real words
Nihongo Pass teaches every kanji with example vocabulary, so on'yomi and kun'yomi come with context, not as a guessing game.