The plain form (常体（じょうたい）, also called the "dictionary style") is the grammatical bedrock of Japanese. It is the register of close friends and family, but far more importantly it is the form the language builds on: relative clauses, quotations, conditionals, embedded thoughts, and dozens of grammar patterns all attach to plain verbs, not polite ones. There are exactly four plain cells you conjugate for tense and polarity — dictionary (書く), negative (書かない), past (書いた), and past-negative (書かなかった) — and this page lays all four out across every class, each paired with its polite counterpart.
The four cells, anchored on 書く
Think of every verb as a two-by-two grid: non-past vs past, crossed with affirmative vs negative. Filling the grid for 書く（かく, "to write"）gives you the model you copy for everything else.
| Affirmative | Negative | |
|---|---|---|
| Non-past | 書く (kaku) — write / will write | 書かない (kakanai) — don't write |
| Past | 書いた (kaita) — wrote | 書かなかった (kakanakatta) — didn't write |
Two things to notice. First, the negative and past-negative share the same あ-row stem (書か-); the past-negative is just the negative ない reshaped into its own past (ない → なかった, exactly like an い-adjective). Second, the past 書いた carries the same 音便（おんびん）softening as the te-form 書いて — that machinery lives on the te/ta chart, and the negatives on the ない page. This table just shows you where they all sit together.
時間がないから、今日は日記を書かない。
jikan ga nai kara, kyō wa nikki o kakanai
I've got no time, so I'm not writing in my diary today.
返事、まだ書いてない。ごめん。
henji, mada kaitenai. gomen
I haven't written the reply yet. Sorry.
The full plain paradigm across classes
| Plain cell | 書く (godan) | 食べる (ichidan) | する | 来る |
|---|---|---|---|---|
| Dictionary (non-past) | 書く (kaku) | 食べる (taberu) | する (suru) | 来る (kuru) |
| Negative 〜ない | 書かない (kakanai) | 食べない (tabenai) | しない (shinai) | 来ない (konai) |
| Past 〜た | 書いた (kaita) | 食べた (tabeta) | した (shita) | 来た (kita) |
| Past-negative 〜なかった | 書かなかった (kakanakatta) | 食べなかった (tabenakatta) | しなかった (shinakatta) | 来なかった (konakatta) |
The two irregulars are worth staring at: 来る shifts its reading in every plain cell — 来る kuru, but 来ない konai, 来た kita, 来なかった konakatta. The kanji 来 stays put while the reading walks く→こ→き. する is cleaner: し for both negatives, した for the past.
疲れてて、昨日はどこにも行かなかった。
tsukarete te, kinō wa doko ni mo ikanakatta
I was worn out, so I didn't go anywhere yesterday.
あの店、先週は開いてたけど、今日は来なかったの?
ano mise, senshū wa aiteta kedo, kyō wa konakatta no
That shop was open last week — did the owner not come in today?
Every plain form has a polite twin
The plain and polite systems are two parallel tracks. This is the map between them — the same four verbs, the plain cell on the left and the polite ます form it corresponds to on the right.
| Plain (常体) | Polite (敬体) |
|---|---|
| 書く (kaku) | 書きます (kakimasu) |
| 書かない (kakanai) | 書きません (kakimasen) |
| 書いた (kaita) | 書きました (kakimashita) |
| 書かなかった (kakanakatta) | 書きませんでした (kakimasendeshita) |
週末、何した?
shūmatsu, nani shita
What did you do this weekend? (plain — to a friend)
週末、何をしましたか。
shūmatsu, nani o shimashita ka
What did you do this weekend? (polite — to an acquaintance)
The insight: register is chosen at the sentence, but plain form lives inside every sentence
Here is the point that saves learners months of confusion. Politeness is decided once, at the end of the sentence — the final verb is either ます (polite) or plain (casual). But almost every grammatical structure that reaches inside a sentence demands the plain form regardless of how polite you are being. A relative clause, a quotation with と, a reason with から or ので, a nominalizer こと／の — all of these take a plain verb even in the most formal speech.
昨日買った本は、もう読みました。
kinō katta hon wa, mō yomimashita
I already read the book I bought yesterday.
Look closely: 買った is plain (it is inside the relative clause modifying 本), while 読みました at the end is polite. That is correct and normal. You do not say ×昨日買いました本. The politeness lives only on the sentence-final verb; everything embedded is plain.
雨が降ると思いますが、傘は持っていきません。
ame ga furu to omoimasu ga, kasa wa motte ikimasen
I think it'll rain, but I'm not taking an umbrella.
Here 降る (before と) is plain, 思います and 持っていきません (sentence-final) are polite — a completely ordinary polite sentence with two plain verbs inside it.
Common mistakes
❌ 昨日買いました本を読みました。
Wrong — the verb before a noun (relative clause) must be plain: 買った本, not 買いました本. Only the final verb carries the polite ます.
✅ 昨日買った本を読みました。
kinō katta hon o yomimashita
I read the book I bought yesterday.
❌ 手紙を書きない。
Wrong — the plain negative is built on the あ-row (書か), not the ます-stem (書き): 書かない.
✅ 手紙を書かない。
tegami o kakanai
I don't write letters.
❌ 昨日は行かないでした。
Wrong — plain verbs form their own past-negative as なかった, not ×ないでした (that pattern is for です/adjectives, not plain verbs).
✅ 昨日は行かなかった。
kinō wa ikanakatta
I didn't go yesterday.
❌ きない
kinai
Careless slip — the plain negative of 来る is 来ない, read konai (こ-row), not ×kinai. The kanji 来 hides the vowel shift.
✅ 来ない
konai
doesn't come / won't come
Key takeaways
- Every verb has four plain cells: dictionary, 〜ない, 〜た, 〜なかった — model them on 書く／書かない／書いた／書かなかった.
- The two negatives share the あ-row stem, and the past-negative なかった conjugates like an い-adjective.
- 来る shifts its reading across cells (kuru / konai / kita / konakatta); the kanji stays but the vowel walks.
- Politeness is chosen once at the sentence end; every embedded clause — before a noun, before と・から・ので・こと・の — takes the plain form even in formal speech.
- Use this page as the reference for the plain column that feeds relative clauses, casual speech, and the wider grammar system.
Now practice Japanese
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Start learning Japanese→Related Topics
- ます-Form: Conjugation TableN5 — The complete polite ます-family across every verb class — present, negative, past, past-negative, and volitional — all built on the い-row 連用形 stem.
- Negative ない: Formation TableN4 — How to build the plain negative 〜ない across every class — the 五段 あ-row stem (with the わ trap), 一段 drop-る, the irregulars, and the suppletive ある → ない.
- Past た-Form: Conjugation TableN5 — The plain past た across every class — built exactly like the te-form but with た／だ, so the same 音便 map (including the voicing) applies throughout.
- Plain vs Polite RegisterN5 — The register axis every Japanese sentence sits on — plain 食べる for intimates and writing versus polite 食べます for strangers and superiors — and why it is decided only at the sentence's final verb.
- Switching Registers & Register MismatchN2 — Moving between plain and です・ます mid-conversation is itself a message — a drop into plain form signals warmth or excitement, a sudden climb into keigo signals distance or displeasure — so the goal is controlled switching, not rigid uniformity.