What is the Nai Form?
The ない form is how you say "don't do" or "won't do" in casual Japanese. It's the plain negative. The casual counterpart of ません.
You'll hear it constantly in everyday conversation, and it also shows up inside grammar patterns even when the overall sentence is polite. Things like ～なければならない (must do), ～ないでください (please don't), and ～ないほうがいい (better not to) all build on the nai-form. The ない ending also appears in たい form when you want to say you don't want to do something (たくない).
Conjugation Rules
U-verbs (Group I)
For verbs ending in う: replace う with わ, then add ない.
| Dictionary | Nai-Form |
|---|---|
| 買う (kau) | 買わない |
| 会う (au) | 会わない |
For all other u-verbs: change the final う-row sound to its あ-row equivalent, then add ない.
| Dictionary | Nai-Form |
|---|---|
| 書く (kaku) | 書かない |
| 話す (hanasu) | 話さない |
| 待つ (matsu) | 待たない |
| 飲む (nomu) | 飲まない |
| 遊ぶ (asobu) | 遊ばない |
| 泳ぐ (oyogu) | 泳がない |
| 帰る (kaeru) | 帰らない |
The pattern: う→わ, く→か, す→さ, つ→た, む→ま, ぶ→ば, ぐ→が, る→ら. Always shifting to the あ-row.
Ru-verbs (Group II)
Drop る, add ない. Same simplicity as always with ru-verbs.
| Dictionary | Nai-Form |
|---|---|
| 食べる (taberu) | 食べない |
| 見る (miru) | 見ない |
| 起きる (okiru) | 起きない |
Irregular Verbs
| Dictionary | Nai-Form |
|---|---|
| する | しない |
| 来る (kuru) | こない |
| ある | ない |
Note: ある → ない is a special case. The negative of "to exist" is just ない by itself. No あらない.
Hidden Use: Casual Invitations
One cool trick: the nai-form with rising intonation becomes a casual invitation. It's like saying "won't you...?" in a friendly way:
- 一緒に食べない？ = Won't you eat together? (casual invite)
- 映画見ない？ = Wanna watch a movie?
This is softer than a direct command and sounds natural among friends.