By the intermediate stage you will meet kanji you have never formally studied — and you cannot look every one up. The reassuring truth, largely hidden from beginners, is that kanji readings are far more predictable than they first appear. Most characters carry a built-in phonetic hint, and a couple of simple heuristics tell you whether to reach for the on-reading or the kun-reading. This page gives you three tools: the phonetic-component principle, the compound-vs-standalone rule, and a warning system for the irregular readings that break every rule.
Tool 1 — The phonetic component
The overwhelming majority of kanji are phono-semantic compounds (形声文字（けいせいもじ）, keisei moji): one part signals meaning (the semantic element, usually the radical) and another part signals sound. Once you know this, kanji stop being arbitrary pictures. When several characters share the same phonetic element, they very often share an on'yomi.
The classic teaching example is the 青 (sei/shō, "blue/green") family. Take 青 as the phonetic element, bolt on different radicals, and the on-reading rides along:
| Kanji | On'yomi | Radical (meaning) | Sample word |
|---|---|---|---|
| 青 | せい (sei) | — (blue) | 青年（せいねん, seinen, youth) |
| 清 | せい (sei) | 氵 water (clear) | 清潔（せいけつ, seiketsu, cleanliness) |
| 晴 | せい (sei) | 日 sun (fine weather) | 晴天（せいてん, seiten, clear skies) |
| 請 | せい (sei) | 言 speech (request) | 請求（せいきゅう, seikyū, a claim/bill) |
| 精 | せい (sei) | 米 rice (refined) | 精神（せいしん, seishin, spirit) |
明日は一日中、晴天になるでしょう。
ashita wa ichinichi-jū, seiten ni naru deshō
Tomorrow will be clear skies all day.
手術の前に、手を清潔にしてください。
shujutsu no mae ni, te o seiketsu ni shite kudasai
Before the operation, please make your hands clean.
The same trick works with the 寺 (ji) family and the 反 (han) family:
| Phonetic | Shared on'yomi | Members |
|---|---|---|
| 寺 (ji) | じ (ji) | 時 (time), 持 (hold), 侍 (samurai) — all ji |
| 反 (han) | はん (han) | 飯 (meal), 版 (edition), 販 (sell), 坂 (slope) — all han |
| 工 (kō) | こう (kō) | 江 (bay), 紅 (crimson), 攻 (attack), 功 (merit) — all kō |
この時計は時間がとても正確です。
kono tokei wa jikan ga totemo seikaku desu
This clock keeps very accurate time.
毎朝、必ずご飯を食べます。
maiasa, kanarazu gohan o tabemasu
I always eat rice every morning.
Honest limits of the phonetic principle
Be clear-eyed: this is a strong prior, not a guarantee. The on-readings were borrowed from Chinese over many centuries and from different regions, and pronunciations drifted. So the 寺 family is mostly ji — but 詩 (poem) is shi and 待 (wait) is tai. The 主 (shu) family shifts toward chū/jū (注 chū, 住 jū). Treat the phonetic component as a bet that pays off well over half the time, verify when it matters, and never assume the hint is infallible.
彼女は詩を書くのが上手です。
kanojo wa shi o kaku no ga jōzu desu
She's good at writing poetry.
Tool 2 — On or kun? The compound-vs-standalone heuristic
The phonetic component tells you a sound; this heuristic tells you which reading applies. The rule of thumb:
- Kanji inside a multi-kanji compound → on'yomi. (See Jukugo.)
- Kanji standing alone, especially with a kana tail (送り仮名, okurigana) → kun'yomi.
Watch the same character switch readings depending on its company:
| Kanji | Standalone (kun) | In a compound (on) |
|---|---|---|
| 食 | 食べる（たべる, taberu, to eat） | 食事（しょくじ, shokuji, a meal） |
| 生 | 生きる（いきる, ikiru, to live） | 生活（せいかつ, seikatsu, daily life） |
| 行 | 行く（いく, iku, to go） | 旅行（りょこう, ryokō, travel） |
昨日、友達と久しぶりに食事をしました。
kinō, tomodachi to hisashiburi ni shokuji o shimashita
Yesterday I had a meal with a friend for the first time in a while.
毎晩、家族みんなで晩ご飯を食べます。
maiban, kazoku minna de bangohan o tabemasu
Every evening the whole family eats dinner together.
Like Tool 1, this is a default with real exceptions — mixed 重箱読み / 湯桶読み compounds break it, and some single kanji standing alone take on'yomi (愛（あい）, ai, "love"; 本（ほん）, hon, "book"). But as a first guess it is right the large majority of the time.
Tool 3 — The rule-breakers: jukujikun
Now the honest warning. Some words attach a reading to a whole cluster of kanji at once, with no per-character logic at all. These are jukujikun (熟字訓（じゅくじくん）): the reading belongs to the word, not to the characters. Neither the phonetic component nor the on/kun heuristic will save you — you simply memorize them as wholes, the way English speakers memorize that "colonel" is pronounced "kernel."
| Word | Reading | Meaning | Why it's irregular |
|---|---|---|---|
| 明日 | あす / あした (asu / ashita) | tomorrow | Not meinichi; whole-word reading |
| 今日 | きょう (kyō) | today | Not konnichi here; assigned to the pair |
| 大人 | おとな (otona) | adult | Neither 大 nor 人 is read this way alone |
| 果物 | くだもの (kudamono) | fruit | Reading spans both characters |
| 一人 / 二人 | ひとり / ふたり (hitori / futari) | one/two people | Irregular counter readings |
| 上手 / 下手 | じょうず / へた (jōzu / heta) | skilled / unskilled | Idiomatic pair readings |
明日の朝、時間がありますか。
ashita no asa, jikan ga arimasu ka
Do you have time tomorrow morning?
今日はいい天気なので、散歩に行きましょう。
kyō wa ii tenki na node, sanpo ni ikimashō
The weather's nice today, so let's go for a walk.
大人になったら、その気持ちが分かりますよ。
otona ni nattara, sono kimochi ga wakarimasu yo
When you grow up, you'll understand that feeling.
デザートに新鮮な果物を用意しました。
dezāto ni shinsen na kudamono o yōi shimashita
I've prepared fresh fruit for dessert.
A worked example
Suppose you meet 清流 for the first time. Apply the tools in order:
- Phonetic component: 清 contains 青 → bet sei. 流 contains a phonetic that gives ryū.
- Compound-vs-standalone: two kanji together → on'yomi. So sei
- ryū → せいりゅう (seiryū).
- Meaning from parts: 清 (clear) + 流 (stream) → "a clear stream." Correct on all counts.
Now try 清い alone: standalone with okurigana → kun'yomi → きよい (kiyoi), "pure/clear." Same kanji, different company, different reading — and the heuristics predicted both.
Common mistakes
❌ 全ての漢字を部分の読みから組み立てられると思う
subete no kanji o bubun no yomi kara kumitaterareru to omou
Incorrect — assuming every kanji word can be built up from its parts' readings.
✅ 明日（あす）のような熟字訓は丸ごと覚える
asu no yō na jukujikun wa marugoto oboeru
Correct: whole-word readings like 明日 must be memorized as units.
❌ 詩 を、寺の仲間だから「じ」と読む
shi o, ji no nakama da kara 'ji' to yomu
Incorrect — forcing 詩 to be 'ji' just because it's in the 寺 family.
✅ 詩 は例外で「し」
shi wa reigai de 'shi'
Correct: 詩 is an exception in the family — it's read 'shi'.
❌ 食事 の 食 を「たべ」と読む
shokuji no shoku o 'tabe' to yomu
Incorrect — using the standalone kun'yomi inside a compound.
✅ 熟語の中では 食 は「しょく」
jukugo no naka de wa shoku wa 'shoku'
Correct: inside a compound, 食 takes the on'yomi 'shoku'.
❌ 今日 をいつも「こんにち」と読む
kyō o itsumo 'konnichi' to yomu
Incorrect — always reading 今日 as 'konnichi'.
✅ 「今日は暑い」の 今日 は「きょう」
'kyō wa atsui' no kyō wa 'kyō'
Correct: in 'it's hot today' 今日 is read 'kyō', the jukujikun.
The through-line: the phonetic component and the compound rule are accelerators, not certainties. Lean on them, expect them to be right most of the time, and keep a mental flag raised for the small, high-frequency set of jukujikun that ignore all logic.
Key takeaways
- A shared phonetic component (青, 寺, 反, 工…) usually predicts a shared on'yomi — a genuine reading accelerator, reliable well over half the time.
- Compound → on'yomi; standalone with okurigana → kun'yomi. A strong first guess, with named exceptions.
- Jukujikun (明日, 今日, 大人, 果物…) attach a reading to the whole word and must be memorized as units — but they cluster in everyday vocabulary, so they come quickly.
Now practice Japanese
Reading grammar gets you part of the way. The exercises are where it sticks — free, no signup needed.
Start learning Japanese→Related Topics
- Radicals (部首): The Building Blocks of KanjiN4 — How kanji decompose into recurring components — semantic radicals that hint at meaning and phonetic components that hint at the reading — and why two-thirds of kanji are phono-semantic compounds you can partly predict.
- Jukugo: Kanji Compound WordsN4 — How two or more kanji combine into compound words read with on'yomi — the four main structural patterns, and how to guess a new compound's meaning from its parts.
- On'yomi and Kun'yomiN5 — Why almost every kanji has two reading families — the Chinese-derived on'yomi used in compounds and the native kun'yomi used alone — plus a reliable heuristic for choosing between them.