Chapter 12 — Plain Forms: ない-Form and た-Form

Every verb form you have learned so far ends in ます, ません, ました, or ませんでした. These are polite forms. They are safe, correct, and appropriate for any situation where you would speak politely to another person. But they are not the base forms of Japanese verbs. The base forms — the forms that appear in dictionaries, in casual speech, inside subordinate clauses, and before dozens of grammatical patterns you have not yet encountered — are the plain forms.

This chapter teaches you to produce all four plain forms of any verb: non-past affirmative (the dictionary form, which you already know), non-past negative (the ない-form), past affirmative (the た-form), and past negative (the なかった-form). It also covers the plain forms of adjectives and the copula. When you finish this chapter, you will have the complete conjugation foundation for Japanese verbs. Every grammar pattern from this point forward depends on it.

12.1 Why Plain Forms Matter

You have been using ます-forms since they were introduced. They work. Why learn another system?

Because ます-forms can only appear in one place: at the end of a sentence directed at someone you are being polite to. That is it. They cannot appear inside sentences. They cannot be used before most grammar patterns. They cannot express thought, intention, hearsay, conditionality, or any of the constructions that make Japanese expressive. Plain forms can.

Here is a concrete preview. To say "I think it will rain," you need to embed the verb "rain" inside the sentence as a clause before と思う. That embedded verb must be in its plain form:

あめが ふると 思います。

You cannot say あめが ふりますと 思います. It is ungrammatical. The embedded clause requires a plain form. This pattern repeats across Japanese grammar: つもりだ (intention), ことができる (ability), まえに (before doing), あとで (after doing), と (conditional), から (because) — all of these require plain forms. Without them, you are locked out of intermediate Japanese entirely.

Plain forms are also the forms of casual speech. When Japanese speakers talk to close friends, family members, or people younger than them in informal situations, they use plain forms at the end of sentences. You will hear them constantly in any Japanese media — anime, dramas, films, songs, social media.

To summarize: ます-forms are for polite sentence endings. Plain forms are for everything else.

12.2 The ない-Form (Plain Negative)

The ない-form is the plain non-past negative of a verb. It means "do not [verb]" or "will not [verb]." Where ません is the polite negative, ない is the plain negative.

たべません (polite) → たべない (plain) "do not eat"

The formation rules depend on the verb class.

一段 verbs (る-verbs)

Drop る. Add ない.

This is completely regular. No exceptions exist within the 一段 class.

五段 verbs (う-verbs)

Change the final vowel sound from the う-row to the あ-row of the same consonant column, then add ない.

What this means concretely: every 五段 verb ends in an う-row sound (う, く, す, つ, ぬ, ぶ, む, る, ぐ). To form the ない-form, you shift that ending to the corresponding あ-row sound (あ, か, さ, た, な, ば, ま, ら, が) and then attach ない.

Here is the full table:

Study this table until the pattern is automatic. The shift is always the same: う→あ, く→か, ぐ→が, す→さ, つ→た, ぶ→ば, む→ま, る→ら. There is one exception, described next.

The う-ending exception: かう → かわない

Look at the う row in the table above. The verb かう ("to buy") becomes かわない, not かあない. This is the single irregularity in the 五段 ない-form system, and it applies to every verb ending in う: あう (to meet) → あわない, うたう (to sing) → うたわない, つかう (to use) → つかわない.

The reason is historical. These verbs originally had a -w- consonant before the final vowel: かう was underlyingly kaw-u. In modern Japanese, the -w- has disappeared before every vowel except -a. So in the dictionary form, kaw-u surfaces as かう (the w is silent). But when you shift to the あ-row, the -w- reappears: kaw-a-nai surfaces as かわない. The w was always there — it just hides in most forms.

You do not need to memorize the linguistics. Just remember: verbs ending in う form their ない-form with わ, not あ. かう → かわない. No other ending has this irregularity.

Irregular verbs

These must be memorized. する drops its vowel entirely and attaches しない. くる changes its stem vowel: く → こ.

ある → ない (suppletive)

The verb ある ("to exist," inanimate) has a completely irregular negative: ない. Not あらない. Just ない — the same word that is the negative suffix for other verbs.

This is a suppletive form, meaning the negative is a completely different word from the affirmative, the way English "go" becomes "went" rather than "goed." You already know this form from い-adjective negation and from じゃない. The word ない is deeply embedded in the Japanese negative system. The verb ある simply uses it directly as its own negative.

へやに ねこが いない。 (いる → いない — regular) つくえの うえに ほんが ない。 (ある → ない — suppletive)

Practice: identify the ない-form

Cover the right column and test yourself.

If you got every one correct, you understand the ない-form. If you missed any う-ending verb or the irregulars, review those sections.

12.3 The た-Form (Plain Past)

The た-form is the plain past affirmative. It means "[verb]-ed" or "did [verb]." Where ました is the polite past, た is the plain past.

たべました (polite) → たべた (plain) "ate"

You already know how to form this. The た-form follows exactly the same consonant-change pattern as the て-form you learned in Chapter 10, but with た/だ in place of て/で.

一段 verbs

Drop る. Add た.

五段 verbs

The same sound changes as the て-form:

The one exception you already know: いく → いった (not いいた).

Irregular verbs

Relationship to the て-form

If you can produce the て-form of any verb, you can produce the た-form. Replace て with た. Replace で with だ. That is the entire rule. There are no exceptions.

かいて → かいた のんで → のんだ たべて → たべた して → した

12.4 The Full Four-Form Plain Paradigm

Every verb in Japanese has four plain forms. Here they are for representative verbs from each class:

五段 verbs

一段 verbs

Irregular verbs

How the past negative works

Look at the past negative column. Every form ends in なかった. This is not a new conjugation to memorize. It follows from a fact about ない itself: ない conjugates like an い-adjective.

You already know that い-adjectives form their past by dropping い and adding かった:

たかい → たかかった

The negative suffix ない is the same:

かかない → かかなかった たべない → たべなかった しない → しなかった

The process is: form the ない-form, then conjugate ない as an い-adjective into its past form. Drop the final い from ない, add かった. That gives you なかった. This is completely regular and works for every verb without exception.

Here is the full picture of ない behaving as an い-adjective:

You will not need the "negative of the negative" forms (かかなくない) in practice, but seeing them confirms the pattern: ない follows い-adjective rules in every respect.

12.5 Plain Forms of Adjectives and Nouns

Verbs are not the only words with plain and polite forms. Adjectives and noun-copula sentences do as well. Since several upcoming grammar patterns require plain forms of all predicate types, here is the complete picture.

い-adjectives

い-adjectives are already plain in their base form. You have been using their plain forms inside sentences since Chapter 8. The polite versions simply add です at the end.

The plain forms are the ones on the left. They are the forms that appear before grammar patterns like と思う:

このほんは たかいと 思います。 "I think this book is expensive."

きのうは さむかったと 思います。 "I think yesterday was cold."

Full paradigm for いい (good) — recall that いい is irregular:

な-adjectives

な-adjectives use the copula だ in their plain forms. Remember: な-adjectives cannot stand alone as predicates — they need the copula.

Note that the plain non-past affirmative is しずかだ, not just しずか. The だ is the plain copula — the same だ mentioned briefly in Chapter 5.

Additional examples:

Nouns with the copula

Noun predicates follow the exact same pattern as な-adjectives, because both use the copula:

Summary of all predicate types in plain form

This table is one of the most important reference points in the entire book. Every grammar pattern that requires "the plain form" means one of these sixteen cells, depending on the predicate type and the tense/polarity you need. Return to this table whenever a new grammar point says "attach to the plain form."

12.6 Recognizing Casual Speech

Now that you know plain forms, you can begin to understand casual Japanese. In informal situations — between friends, family members, or in internal monologue — plain forms replace ます-forms at the end of sentences.

Polite:

あした、えいがを みますか。 "Will you watch a movie tomorrow?"

Casual:

あした、えいがを みる？ "Watching a movie tomorrow?"

Polite:

きのう、なにを たべましたか。 "What did you eat yesterday?"

Casual:

きのう、なにを たべた？ "What'd you eat yesterday?"

Features of casual speech

Questions drop か. In casual speech, questions are marked by rising intonation alone. In writing, a question mark is often used instead of か:

これ、たべる？ (Do you eat this?) もう、でた？ (Did you already leave?)

Adding か to a plain-form sentence can sound blunt or even aggressive in some contexts, particularly with male speakers. At this stage, simply be aware that casual questions usually lack か.

Particles are often dropped. In casual speech, は, を, and sometimes other particles are frequently omitted when the meaning is clear from context:

ごはん たべた？ (を dropped — "Did you eat?") これ いい？ (は dropped — "Is this okay?")

This does not mean particles are optional in Japanese. They are grammatically required. But in fast casual speech, speakers rely on context and shared knowledge to fill in the gaps. You should not drop particles in your own speech at this stage. You should recognize that missing particles are normal in casual Japanese, not errors.

だ sometimes drops after な-adjectives and nouns in certain contexts. In casual questions and some sentence-final positions, the copula だ may be absent:

あした ひま？ (= ひまだ？ — "Are you free tomorrow?") あれ、なに？ (= なにだ？ — "What's that?")

Again, recognize this pattern. Do not worry about producing it yet.

Common contractions (recognition only)

Japanese casual speech compresses certain て-form constructions into shorter forms. You will encounter these constantly in media. You do not need to produce them, but you need to recognize what they are.

Examples:

なにを してる？ (= している — "What are you doing?") もう たべちゃった。 (= たべてしまった — "I already ate it all.") べんきょう しとく。 (= しておく — "I'll study in advance.") みてない。 (= みていない — "I haven't seen it.")

These contractions are pervasive. The ている → てる contraction in particular is so common that many speakers use it even in semi-polite speech. You will learn to produce these naturally over time. For now, when you hear てる, know that it is ている. When you hear ちゃった, know that it is てしまった.

12.7 Chapter Summary

This chapter gave you three things:

First, the ない-form — the plain non-past negative of verbs. 一段 verbs drop る and add ない. 五段 verbs shift to the あ-row and add ない (with the special う → わ rule). する becomes しない, くる becomes こない, ある becomes ない.

Second, the た-form — the plain past affirmative. It follows the same sound changes as the て-form, with た/だ replacing て/で. If you know the て-form, you know the た-form.

Third, the complete plain paradigm for all predicate types: verbs, い-adjectives, な-adjectives, and noun-copula sentences. The past negative of verbs works by conjugating ない as an い-adjective (なかった). This system is fully regular once you know the ない-form.

You now have every tool needed to form and recognize the four basic conjugations of any Japanese verb. The chapters that follow will put these forms to work — embedding them in clauses, attaching them to grammar patterns, and using them to express ideas that polite sentence-ending forms alone cannot reach.

12.8 Reading Passage — しゅうまつの けいかく

ゆうこさんと けんさんが はなしています。

ゆうこ：けんくん、しゅうまつ なにする？

けん：うーん、どようびは ともだちと えいがを みると おもう。あたらしい にほんの えいがが ある んだ。

ゆうこ：へえ、いいね。どんな えいが？

けん：よく しらない。でも、ともだちが おもしろいと おもうって いってた。ゆうこは？

ゆうこ：わたしは どようびに かいものに いく。あたらしい ふくが ほしい んだ。にちようびは なにも しない。うちで ゆっくりする。

けん：にちようびに いっしょに ごはんを たべない？えきの ちかくに あたらしい みせが できた。

ゆうこ：いいね！いく いく！なんじ？

けん：じゅうにじごろは どう？

ゆうこ：うん、だいじょうぶ。たのしみ！

Translation

Yuko and Ken are chatting.

Yuko: Ken, what are you doing this weekend?

Ken: Hmm, on Saturday I think I'll watch a movie with a friend. There's a new Japanese movie.

Yuko: Oh, that's nice. What kind of movie?

Ken: I don't really know. But my friend said he thinks it's interesting. How about you, Yuko?

Yuko: On Saturday I'm going shopping. I want new clothes. On Sunday I'm not doing anything. I'll relax at home.

Ken: Want to eat together on Sunday? A new restaurant opened near the station.

Yuko: Sounds great! I'll go, I'll go! What time?

Ken: How about around noon?

Yuko: Yeah, that works. I'm looking forward to it!

Notes on the Passage

なにする？ — "What are you doing?" Casual form of なにを しますか. The を particle is often dropped in casual speech.

みると おもう — "I think I'll watch." と おもう with a plain form verb expresses what the speaker thinks.

ある んだ — "there is (you see)." んだ (casual form of んです) adds explanation or emphasis.

おもしろいと おもうって いってた — "said he thinks it's interesting." って is a casual quotation marker. いってた is a casual contraction of いっていた (was saying).

なにも しない — "not doing anything." なにも with a negative verb means "nothing."

たべない？ — "Won't you eat?" / "Want to eat?" A negative plain form used as a casual invitation.

できた — "opened" / "was made." The た-form of できる (to be completed / to come into existence).

Vocabulary

New words introduced in this chapter: