In short

Two て-form patterns cover almost everything: 〜てもいいです 〜te mo ii desu (“you may”) and 〜てはいけません 〜te wa ikemasen (“you must not”). The blunt 命令形 (imperative: 行け ike, 食べろ tabero) exists, but it lives on signs, in sports and in anger - as a learner you read it far more often than you say it.

The rule

Japanese does not have one “imperative” the way English does. It has a ladder, and choosing the wrong rung is a social error, not a grammatical one. Learn the polite middle first, and the harsh bottom as recognition.

Step 1 - Permission: て-form + も + いいです. The particle も (“even”) is the key: “even if you do it, it is fine.”

• Asking: 〜てもいいですか 〜te mo ii desu ka - 帰ってもいいですか kaette mo ii desu ka (“may I go home?”).
• Granting: 〜てもいいですよ 〜te mo ii desu yo, or simply どうぞ dōzo (“go ahead”).
• Two other granting variants: 〜てもかまいません 〜te mo kamaimasen (“I don’t mind if you …”, a shade more formal) and the friendlier 〜ても大丈夫です 〜te mo daijōbu desu (“it’s fine if you …”).

Refusing a request for permission is rarely done with いけません - that is what a police officer says. In real life people trail off: すみません、ちょっと……。Sumimasen, chotto…… (“sorry, that’s a bit …”).

Step 2 - “No need to”: ない-form, with ない -> なくて, + もいいです. Build it on the ない-form, not the ます-stem: 行かない -> 行かなくて -> 行かなくてもいいです ikanakute mo ii desu (“you don’t have to go”). This is the opposite of forbidding - it removes an obligation. Keep it strictly apart from Step 3.

Step 3 - Prohibition: て-form + は + いけません. Here the particle is は (pronounced and romanized wa): “as for doing that, it won’t do.”

• 〜てはいけません 〜te wa ikemasen - the standard rule-stating prohibition (teacher, sign, regulation).
• 〜てはだめです 〜te wa dame desu - softer and more personal, common in speech and to children.
• Noun + は禁止されています N wa kinshi sarete imasu (”… is prohibited”) - the wording of official notices. Take it as a set phrase for now; its passive form belongs to a later lesson.

Contractions (casual only). In speech 〜ては shrinks to 〜ちゃ and 〜では to 〜じゃ: 食べてはだめ -> 食べちゃだめ tabecha dame, 飲んではいけない -> 飲んじゃいけない nonja ikenai, 行っては -> 行っちゃ itcha. Friends and family only - never in writing, never to a teacher or a customer.

Step 4 - The polite negative request: 〜ないでください. From lesson 17: ない-form + でください - 撮らないでください toranaide kudasai (“please don’t take photos”). It is a request, not a rule. 〜てはいけません states what the regulations say; 〜ないでください asks this person, now to stop. Signs use the first, people use the second.

Step 5 - The imperative 命令形. One bare word, no politeness at all. Formation is regular:

• Group I (五段): change the final -u to -e. 書く kaku -> 書け kake, 行く iku -> 行け ike.
• Group II (一段): drop る, add ろ (spoken) or よ (written, formal). 食べる taberu -> 食べろ tabero ／ 食べよ tabeyo.
• Irregulars: する -> しろ shiro ／ せよ seyo, 来る -> 来い koi.

Its registers are narrow and you should be able to name them: signs and slogans (止まれ tomare “stop”, 頑張れ ganbare “go for it”), sports and drills (走れ hashire “run”), anger, rough male casual speech, and quoted commands - 行けと言われました ike to iwaremashita (“I was told to go”), where the harsh form is reported, not uttered by you. Never aim it at a superior, a customer or a stranger.

Step 6 - Prohibitive な. Attach な directly to the dictionary form: 行く -> 行くな iku na (“don’t go”), 見る -> 見るな miru na. It is the negative twin of 命令形 and shares its registers exactly. It cannot be made polite - ×行くなでください does not exist; the polite version is 行かないでください.

Step 7 - ます-stem + なさい. Take the ます-stem (書きます -> 書き) and add なさい: 書きなさい kakinasai. It is a soft command from someone with authority: parents to children, teachers to pupils, and above all exam papers - 答えなさい kotaenasai (“answer”), 選びなさい erabinasai (“choose”). Using it with an adult peer sounds condescending.

The ladder, bottom to top: 命令形 -> plain て -> 〜てください -> 〜てくださいませんか -> お〜ください. The top rung is honorific and belongs to the keigo lessons; 〜てください is your safe default. 〜なさい (Step 7) stands beside the ladder rather than on a rung: it marks authority, not a level of politeness.

Forms & patterns

Permission and prohibition - the particle does the work.

命令形 (imperative) by verb group.

Negative command な and the なさい command.

One verb, the whole ladder.

Examples

Common mistakes

• 食べてもいけません。 (Tabete mo ikemasen.) -> 食べてはいけません。 (Tabete wa ikemasen.) - the particle and the ending are a fixed pair: も goes with いい (permission), は goes with いけません／だめ (prohibition). You cannot take one half from each.
• 行きなくてもいいです。 (Ikinakute mo ii desu.) -> 行かなくてもいいです。 (Ikanakute mo ii desu.) - なくてもいい is built on the ない-form (行かない), never on the ます-stem.
• 部長、これを見ろ。 (Buchō, kore o miro.) -> 部長、これを見てください。 (Buchō, kore o mite kudasai.) - 命令形 is never aimed upward. To a boss, teacher or customer the floor is 〜てください.
• ここで写真を撮るなでください。 (Koko de shashin o toru na de kudasai.) -> ここで写真を撮らないでください。 (Koko de shashin o toranaide kudasai.) - な cannot be politened. The polite negative request is a different pattern entirely.
• 食べりなさい。 (Taberinasai.) -> 食べなさい。 (Tabenasai.) - なさい attaches to the ます-stem: 食べます -> 食べ -> 食べなさい. Compare 飲みます -> 飲みなさい.

Tips

• Read the particle, not the verb. も = “even if you do it, fine” -> permission. は = “as for doing it, no” -> prohibition. も and いいです always travel together, は and いけません always travel together: 帰ってもいいです versus 帰ってはいけません.
• “Don’t have to” is not “must not”. English learners routinely map both onto one Japanese pattern. 行かなくてもいいです removes an obligation; 行ってはいけません creates one. Drill the pair together.
• 命令形 is a reading skill. You will meet it on road signs (止まれ), at stadiums (頑張れ), in manga and in quoted speech, and you should parse it instantly - but in your own mouth 〜てください is almost always the right choice. The same goes for 〜な and for the ちゃ／じゃ contractions.
• なさい carries a power gradient. It is warm from a parent and neutral on an exam paper, but saying it to a colleague implies you outrank them. When in doubt, 〜てください.