Nai-Form Japanese: How to Make Any Verb Negative

To say ‘I don’t eat,’ ‘She doesn’t go,’ or ‘Don’t touch that’ in Japanese, you need the ない form (nai-form). It’s the foundation of all Japanese negation — and once you learn the pattern, you can negate almost any verb in seconds.

How to Make the Nai-Form

Group 2 (ru-verbs): replace る with ない

Group 1 (u-verbs): change the u-sound to a-sound + ない

⚠️ Special rule: verbs ending in う (u-sound alone) add a わ before ない. 買う → 買わない (not 買あない).

Group 3 (Irregular)

Yuka

The 買う → 買わない rule surprised me. I thought it’d be 買あない — but that’s impossible to say! The わ is inserted to make it pronounceable. All う-ending verbs that end in う-alone follow this pattern.
(歌う → 歌わない, 使う → 使わない — they all add わ.)

Rei

For Group 1, my mnemonic: change the final ‘u-row’ kana to its ‘a-row’ partner, then add ない. く → か, む → ま, す → さ, つ → た, ぐ → が. Each is just one row up in the hiragana chart.
(The a-row substitution works for every u-verb except the う-alone ones.)

Key Nai-Form Patterns You Need

~ないでください — Polite negative request

ここで写真を撮らないでください。
(Please don’t take photos here.)

静かにしてください → 騒がないでください
(Please don’t make noise.)

~なくてもいい — You don’t have to

To make this: nai-form → remove い → add くてもいい

食べなくてもいい。
(You don’t have to eat.)

急がなくていいよ。
(You don’t have to hurry.)

~なければならない / ~ないといけない — Must (obligation)

These use the nai-form base to express obligation (double negative = positive).

早く起きなければならない。
(I have to wake up early.)

宿題をしないといけない。
(I have to do my homework.)

~ないうちに — Before it becomes the case

忘れないうちにメモしておこう。
(Let’s make a note before I forget.)

Yuka

I always got confused by なければならない because it’s such a mouthful. My shortcut: in casual speech, everyone says なきゃ or なきゃいけない. 行かなきゃ means ‘I gotta go’ — much more natural in everyday conversation!
(なきゃ is the casual contracted form of なければ.)

Rei

In formal business Japanese, you use なければなりません (not ならない). The difference: ならない is plain form, なりません is polite. At work I say 提出しなければなりません — it’s formal and shows responsibility.
(ならない = plain; なりません = polite — choose by register.)

Negative Past: なかった

Simple: take the nai-form, drop い, add かった.

昨日、宿題をしなかった。
(I didn’t do my homework yesterday.)

Quick Quiz

1. What is the nai-form of 飲む?

→ 飲まない (nomanai)

2. How do you say ‘Please don’t run’ using ～ないでください?

→ 走らないでください (hashiranai de kudasai)

3. What is 買う in nai-form? (Watch for the special rule!)

→ 買わない (kawanai) — わ is inserted

4. Fill in: 宿題をし___もいい。(You don’t have to do homework.)

→ なくて (しなくてもいい)

5. What is the nai-form past of 行く?

→ 行かなかった (ikanakatta)

Which nai-form pattern trips you up most? The obligation forms, or the negation itself? Let us know in the comments!

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