Japanese derivative forms are grammatical structures that modify verbs to express concepts like desire, obligation, ability, prohibition, permission, and more.

Unlike core verb conjugations, derivative forms are constructed by attaching additional grammar to verbs rather than altering the verb root itself.

Most derivative forms are built using:

• Masu-stem of the verb
• Te-form of the verb
• Plain form (dictionary or past form)

Many derivative forms act like adjectives or require auxiliary verbs (like いる, なる, こと).

1. Tai -たい (Desiderative Form)

Used to express desire for an action.

How to Form:

• Take the ます-stem of a verb and add たい.
• Works like an い-adjective (たい → たくない for negative).

Example Sentences:

ラーメンを食べたい。
Rāmen o tabetai. → I want to eat ramen.

日本に行きたい！
Nihon ni ikitai! → I want to go to Japan!

水を飲みたくない。
Mizu o nomitakunai. → I don’t want to drink water.

💡 Note:

たい is only for first-person (I) or asking about someone’s desire. To talk about someone else’s desires, use たがる (e.g., 彼はゲームをしたがる → "He wants to play a game").

2. E -え / Ro -ろ (Imperative / Command Form)

Used to command or order someone to do something. It is often used in military, sports, or very casual/rude speech.

How to Form:

• Group 1 (う-verbs): Change the う sound to the え sound
• Group 2 (る-verbs): Replace る with ろ
• Irregular verbs:
  • する → しろ / せよ
  • くる → こい

Example Sentences:

もっと食べろ！
Motto tabero! → Eat more!

早く行け！
Hayaku ike! → Hurry up and go!

黙れ！
Damare! → Shut up!

💡 Note:

The imperative form sounds very strong and can be rude unless used in the right context, like military training, sports, or casual speech with close friends.
For a softer or more polite command, use ～なさい instead (e.g., 食べなさい！ → Eat!).

3. Te Iru -ている / Teru -てる  (Progressive / Continuous Form)

The Progressive form, also called Continuous form is used to describe:

• An ongoing action (like "I am eating").
• A habitual action (like "I usually take the train").
• A resulting state (like "The door is open" → It is still open after being opened).

How to Form:

Take the て-form of the verb and add いる (or just る in casual speech).

Example Sentences:

今、ラーメンを食べている。
Ima, rāmen o tabete iru. → I am eating ramen now.

彼は毎日ゲームをしている。
Kare wa mainichi gēmu o shite iru. → He plays games every day.

ドアが開いている。
Doa ga aite iru. → The door is open (state resulting from opening).

💡 Note:

The progressive form is not always equivalent to the English present continuous (e.g., 行っている means "I went and am there now," not "I am going").

4. Te (ha) ikenai -てはいけない (Prohibitive Form)

Used to express rules, prohibitions, or warnings.

How to Form:

• Take the て-form of a verb and add はいけない.
• In polite speech, say ～てはいけません.

Example Sentences:

ここでタバコを吸ってはいけません。
Koko de tabako o sutte wa ikemasen. → You must not smoke here.

この部屋に入ってはいけない！
Kono heya ni haitte wa ikenai! → You must not enter this room!

テスト中に話してはいけません。
Tesuto-chū ni hanashite wa ikemasen. → You must not talk during the test.

5. Rareru / Koto ga dekiru -られる / -ことができる (Potential / Ability Form)

Used to express ability (being able to do something).

How to Form:

Potential Form 1 ~られる / ～える (More casual)

• Group 1 (Godan verbs) → Change う → え-line + る
• Group 2 (Ichidan verbs) → Drop る, add られる
• する → できる (Exception)

Potential Form 2 ～ことができる (More explicit / Formal / Final)

• Take the dictionary form of a verb, add ことができる.

Example Sentences:

私は日本語が話せる。
Watashi wa nihongo ga hanaseru. → I can speak Japanese.

ここでお酒を飲むことができる。
Koko de osake o nomu koto ga dekiru. → You can drink alcohol here.

泳げる？
Oyogeru? → Can you swim?

6. Ta koto ga aru -たことがある (Experiential Form)

Used to express past experiences (something you have done before).

How to Form:

• Take the past tense (た-form) of a verb and add ことがある.

Example Sentences:

日本に行ったことがある。
Nihon ni itta koto ga aru. → I have been to Japan before.

寿司を食べたことがある？
Sushi o tabeta koto ga aru? → Have you ever eaten sushi?

フランス語を勉強したことがありません。
Furansugo o benkyō shita koto ga arimasen. → I have never studied French.

💡 Note:

• To say "I have never done it", use ～たことがない / ありません.

7. Te mo ii -てもいい (Permission / Allowed to Do Form)

Used to express permission or that it is okay to do something.

How to Form:

1. Take the て-form of the verb.
2. Add もいい at the end.

Example Sentences:

ここで写真を撮ってもいいです。
Koko de shashin o totte mo ii desu. → You may take photos here.

もう帰ってもいいですか？
Mō kaette mo ii desu ka? → May I go home now?

このペンを使ってもいい？
Kono pen o tsukatte mo ii? → Can I use this pen?

💡 Note:

• To make it polite, use です at the end (e.g., "行ってもいいです").
• To soften the expression, you can say もかまわない (mo kamawanai), which also means "It's okay if...".

8. Nakutemoii -なくてもいい (Not Necessary / Don't Have to Do Form)

Used to express that something is not necessary or that it is okay not to do something.

How to Form:

1. Take the negative form of the verb (ない-form).
2. Replace ない with なくてもいい.

Example Sentences:

明日は学校に行かなくてもいいよ。
Ashita wa gakkō ni ikanakute mo ii yo. → You don’t have to go to school tomorrow.

全部食べなくてもいいですよ。
Zenbu tabenakute mo ii desu yo. → You don’t have to eat everything.

この書類は書かなくてもいいです。
Kono shorui wa kakanakute mo ii desu. → You don’t have to write this document.

💡 Note:

• To make it polite, use です at the end (e.g., "行かなくてもいいです").
• To soften the expression, you can say なくても大丈夫 (nakutemo daijōbu), which means "It's okay not to...".

9. Tsumori つもり (Intention / Plan Form)

Used to express intention or plans for the future.

How to Form:

1. Take the dictionary form of the verb for affirmative intention.
2. Take the negative (ない-form) of the verb for negative intention.
3. Add つもりだ / つもりです at the end.

Negative Intention:

Example Sentences:

来年、日本に行くつもりです。
Rainen, Nihon ni iku tsumori desu. → I plan to go to Japan next year.

今日、映画を見ないつもりです。
Kyō, eiga o minai tsumori desu. → I don't plan to watch a movie today.

会社を辞めるつもりはありません。
Kaisha o yameru tsumori wa arimasen. → I don’t have any plans to quit my job.

💡 Note:

• To make it polite, use つもりです instead of つもりだ.
• To express a stronger intention, you can add は (e.g., "行くつもりはない" → "I have no intention of going").