The short version: dictionaries only store the dictionary form (辞書形). To get there from any conjugated verb: (1) strip the ending, (2) use the ない-test to decide godan or ichidan, (3) if the form ends in て or た, reverse the sound change — った←う/つ/る, んだ←ぬ/ぶ/む, いた←く, いだ←ぐ, した←す.
It happens in the same way every time. You are reading something real — a manga panel, a caption, the back of a packet — and you meet a word:
読まなかった
You type it into a dictionary. Nothing. You try without the kanji. Nothing. You are certain you know this verb, and the dictionary is telling you it does not exist.
It does exist. It is just not stored anywhere. Japanese dictionaries list only the 辞書形 — the plain non-past form, the one that ends in an う-row syllable. Every other form in the language is built by replacing that ending, and none of those built forms gets its own entry. A conjugated verb is not a word; it is a word plus instructions.
Which means that between you and the dictionary sits a skill nobody teaches directly: un-conjugation. Textbooks drill forwards — here is 読む, now make 読みました. Real reading runs backwards, and the backwards direction has traps the forwards direction never shows you.
The mental model: stem plus ending
Every Japanese verb form is two pieces welded together. A part that carries the meaning, and a part that carries the grammar:
English does the same thing with far less material — walk / walked / walking — so the English reader's instinct is to look for a short suffix. Japanese endings are longer, and they stack: polite + negative + past is a single six-kana tail. That length is what makes the word look unrecognisable, and it is also the good news, because the endings come from a small closed set. There are perhaps twenty of them. Once you can name the tail, everything in front of it is the verb.
Strip the ending
Find the tail in this table and cut it off. Note what kind of stem it leaves behind — that is what step 2 works on.
| Ending you see | What it means | Leaves you with | Example |
|---|---|---|---|
| 〜ます | polite non-past | ます-stem | 読みます → 読み |
| 〜ました | polite past | ます-stem | 食べました → 食べ |
| 〜ません | polite negative | ます-stem | 行きません → 行き |
| 〜ませんでした | polite past negative | ます-stem | 飲みませんでした → 飲み |
| 〜ない | plain negative | ない-stem | 読まない → 読ま |
| 〜なかった | plain past negative | ない-stem (via ない) | 食べなかった → 食べない |
| 〜た / 〜だ | plain past | た-form | 買った → step 3 |
| 〜て / 〜で | connective, requests | て-form | 読んで → step 3 |
| 〜ています | ongoing state | て-form | 待っています → 待って |
| 〜てください | please do | て-form | 見てください → 見て |
| 〜たい | want to do | ます-stem | 行きたい → 行き |
| 〜たら | if / when | た-form | 読んだら → 読んだ |
| 〜ながら | while doing | ます-stem | 歩きながら → 歩き |
| 〜ば | conditional | え-row base | 読めば → 読め |
| 〜れる / 〜られる | passive / potential | あ-row or stem | 読まれる → 読ま |
| 〜せる / 〜させる | causative | あ-row or stem | 読ませる → 読ま |
| 〜よう / 〜おう | let's / intention | え/お-row base | 行こう → 行こ |
Note the useful shortcut in rows four and six: なかった always reduces to ない first, and every polite ending reduces to the ます-stem. Four different-looking tails, one destination.
Decide the class with the ない-test
This is the fork the whole method turns on, and the ない-form is the cleanest way through it, because it separates the two classes visibly.
If ない attaches to an あ-row syllable → godan.
読ま·ない · 買わ·ない · 待た·ない
Move that あ-row syllable to the う-row: ま→む, わ→う, た→つ. Result: 読む · 買う · 待つ
If ない attaches straight to the stem → ichidan.
食べ·ない · 見·ない · 起き·ない
Add る: 食べる · 見る · 起きる
Why not use the ます-form for this? Because it hides the fork. 読みます and 起きます both end in an い-sound stem, but one is godan and the other ichidan. There is one thing the ます-form does tell you for certain: a stem ending in an え-sound is always ichidan — 食べます, 寝ます, 教えます — because no godan verb produces an え-row ます-stem.
And there are exactly two irregular verbs in the entire language: 来る (きます, きて, こない, きた) and する (します, して, しない, した). Compound verbs ending in する — 勉強する, 電話する — follow する.
So it is 帰らない and 帰った, never 帰ない or 帰た. No rule predicts these — it is a list, and it is short enough to learn in one sitting. The full picture is in Godan vs Ichidan.
Reverse the て / た sound change
This is where most learners get stuck, because it is the only step that is genuinely many-to-one. The て and た forms compress the original ending — 音便, euphonic change — and compression loses information. Here is the reversal, complete:
| You see | It came from | Examples |
|---|---|---|
| 〜った / 〜って | う · つ · る | 買った←買う · 待った←待つ · 取った←取る |
| 〜んだ / 〜んで | ぬ · ぶ · む | 死んだ←死ぬ · 遊んだ←遊ぶ · 読んだ←読む |
| 〜いた / 〜いて | く | 書いた←書く |
| 〜いだ / 〜いで | ぐ | 泳いだ←泳ぐ |
| 〜した / 〜して | す | 話した←話す |
| stem + た / て | ichidan る | 食べた←食べる · 見た←見る |
How to resolve the three-way ambiguity: look at the kanji. 買った carries 買, so it is 買う. 待った carries 待, so it is 待つ. 読んだ carries 読, so it is 読む. The kanji does not only mean something — it eliminates two of your three candidates before you have finished reading the word. This is the same reason kanji make unspaced Japanese readable at speed.
Eight worked chains
Follow the arrows. Every one of these is a word you will genuinely meet.
Adjectives un-conjugate too
| You see | Reduce to | Meaning |
|---|---|---|
| 高かった | 高い | was expensive |
| 高くない | 高い | is not expensive |
| 高くなかった | 高い | was not expensive |
| よかった | いい | irregular — was good. Also よくない, not いくない. |
| 静かでした | 静か | な-adjective — the tense sits on です, the word itself never changes |
Practise the reversal both ways — free, in your browser
We built a Japanese verb conjugator and drill for exactly this: pick any of 120 N5–N4 verbs and see the complete table (辞書形, ます, ません, ました, ませんでした, ない, なかった, て, た, たい, potential, volitional, conditional), with the class and every sound change labelled. Then switch to drill mode and answer them under time. No signup, nothing to install.
Open the free verb conjugator →Why this skill matters more than it looks
Un-conjugation is not a dictionary trick. It is the gate between studying Japanese and reading Japanese. Textbook sentences are conjugated in the forms you were just taught; real sentences are conjugated in whatever the speaker felt like. Until the reversal is automatic, every unfamiliar tail stops you dead — and stopping dead, five times a page, is what makes people conclude they are “not ready” for real material when the truth is that they are missing one mechanical skill.
Two things accelerate it. First, drill backwards, not forwards: given 読んで, produce 読む — that is the direction reading actually demands, and almost no textbook practises it. Second, meet conjugated verbs in real material with the answer one tap away, so the reversal is confirmed instead of guessed. Pointing the OCR scanner at a page, or pasting a link into learn-from-a-video and seeing each sentence split into words with furigana and level marks, gives exactly that: hundreds of live examples with immediate confirmation, which is how a mechanical skill becomes reflex.
Reference summary
- Why the lookup fails
- Dictionaries store only the 辞書形 (dictionary form). Conjugated forms have no entry of their own.
- Step 1
- Strip the ending. All polite endings (ます/ました/ません/ませんでした/たい/ながら) reduce to the ます-stem; なかった reduces to ない first.
- Step 2 — the ない-test
- ない on an あ-row syllable = godan (読まない → 読む). ない on the bare stem = ichidan (食べない → 食べる). An え-sound ます-stem is always ichidan.
- Step 3 — sound-change reversal
- った ← う/つ/る · んだ ← ぬ/ぶ/む · いた ← く · いだ ← ぐ · した ← す · stem+た ← ichidan る.
- The one exception
- 行った comes from 行く, not from a う/つ/る verb.
- Nine fake-ichidan godan verbs
- 帰る · 入る · 走る · 切る · 知る · 要る · 限る · 滑る · 減る.
- Two irregular verbs
- する (します/して/しない/した) and 来る (きます/きて/こない/きた).
- Adjectives
- かった and くない both reduce to い. Irregular: いい → よかった, よくない.
Related Reading on Kanjijo
Frequently Asked Questions
Dictionaries store only the dictionary form (辞書形) — the plain non-past that ends in an う-row syllable. Every other form is that word plus an ending, and none of them gets its own entry. You have to reverse the conjugation before the word is searchable.
なかった is the past of ない, so first reduce to 食べない. Then apply the ない-test: ない attaches directly to the stem 食べ with no あ-row syllable, which means ichidan — so add る to get 食べる. Compare 読まなかった → 読まない, where ない sits on the あ-row ま, marking godan, so ま moves to the う-row: 読む.
Three possible endings: う (買った ← 買う), つ (待った ← 待つ) and る (取った ← 取る). The kanji resolves it instantly. The same three-way pattern applies to んだ ← ぬ/ぶ/む. いた ← く, いだ ← ぐ, した ← す. The only irregular is 行った, which comes from 行く.
帰る, 入る, 走る, 切る, 知る, 要る, 限る, 滑る and 減る. They end in いる or える but conjugate as godan, so it is 帰らない and 帰った, never 帰ない. No rule predicts them — memorise the nine.
い-adjectives: かった is past and くない is negative, so 高かった, 高くない and 高くなかった all reduce to 高い. The irregular is いい → よかった / よくない. な-adjectives never inflect — the tense lives on です, so 静かでした reduces to 静か.
Stop losing the thread at every unfamiliar ending
Kanjijo covers the full N5–N1 grammar bank, every conjugation pattern with example sentences in furigana, and exclusive mnemonics for every kanji and every vocabulary word. An SRS engine keeps verbs from fading, home, lock screen and interactive test widgets drill them between sessions, and the OCR scanner plus learn-from-a-video let you meet conjugated verbs in real material with the reading and meaning one tap away. Plus JLPT reading and listening practice, full mock tests, conversation, shadowing and dictation. Free on iPhone.
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