～てもいい / ～てはいけない: How to Ask Permission and State Prohibition in Japanese

Knowing ～てもいい / ～てはいけない gives you both sides of one yes/no question: is an action allowed? ～てもいい grants the action ("you may"), and ～てはいけない denies it ("you must not").¹² Both attach to the same て-form. Once you can build the て-form, you can build either answer.²¹

Overview

One axis: permission yes, prohibition no

～てもいい and ～てはいけない answer one question: "is doing X all right?" One grants the action, and the other denies it.¹²

Both use the same V-て (the て-form): permission is V-て + も + いい, and prohibition is V-て + は + いけない.¹²

The textbook Genki I teaches the two together in one lesson, precisely as a permission/denial pair: the negative answer to a ～てもいいですか request is the ～てはいけません prohibition.³⁴

These patterns span several course levels rather than one fixed point. The basic ～てもいいです permission and ～てはいけません prohibition are elementary building blocks. The casual contractions and the いけない/ならない/だめ ending ladder bring the unit up to the N4 tier used in this article.⁵⁶

The level span is curriculum-based

Common course sequences such as Genki introduce the plain permission and prohibition forms early, then add the casual contractions and the ending ladder later. This N4 article treats the whole permission/prohibition axis as one unit that points back to those earlier building blocks.³⁵⁶

Why it builds on the て-form

Both patterns are て-form + particle + predicate. The て-form is the shared conjugation base. If you can form V-て, you can build both without learning a new stem.²¹

The literal mechanics depend on the て-form acting like a clause that the following particle modifies: も "even" for permission, and は "as for" for prohibition.² The dedicated construction article covers て-form conjugation, so it is not re-derived here.²

Form and construction

Permission: て-form + も + いい

The slot is V-て + も + いい(です). いい is the い-adjective meaning "good," so the whole phrase literally reads "even doing X is good."¹⁶

The polite ending です attaches to いい, giving ～てもいいです. In casual speech, も is often dropped (食べていい? for 食べてもいい?), and the も form sounds slightly more modest.⁷

テレビを見みてもいいです。⁶
"You may watch TV."

明日あしたは休やすみを取とってもいいですよ。⁶
"As for tomorrow, you may take the day off."

大おおきな声こえで騒さわいでもいいですよ。⁶
"You may make noise in a loud voice."

The sentence-final よ softens the grant in conversation. It signals reassurance rather than a bare statement.⁶

Asking permission: ～てもいいですか

Add the question particle か to turn the grant into a request: V-て + も + いい + ですか, meaning "may I do X?"⁴⁶

The casual request drops です and uses rising intonation on いい: 食べてもいい? ("can I eat this?").⁷

教科書きょうかしょを見みてもいいですか。⁴
"May I look at the textbook?"

ここに座すわってもいいですか。⁶
"May I sit here?"

To speak more politely to a superior, replace いい with the formal adjective よろしい, giving ～てもよろしいですか. The よろしい form is markedly formal and suits a superior or a customer.⁷

写真しゃしんを撮とってもよろしいですか。⁷
"Would it be all right for me to take a photo?"

Prohibition: て-form + は + いけない

The slot is V-て + は + いけない. Here は is the contrastive particle, written は but read "wa."⁴⁸

いけない is the negative potential of いく ("to go"), so the construction literally reads "as for doing X, it will not do." Its polite form is いけません, giving ～てはいけません.²⁴

ここで写真しゃしんを撮とってはいけません。⁴
"You must not take photographs here."

人ひとの物ものを盗とってはいけない。⁵
"You must not steal other people's things."

知しらない人ひとについて行いってはいけない。⁸
"You must not go off following strangers."

The は is not droppable here

Unlike the も of permission, the は of prohibition stays. Without it, いけない would read as the second verb in an ordinary て-form sequence ("do X and then it doesn't go"), not as prohibition.⁸

The negation logic

～てはいけない looks affirmative: the verb is in plain て-form, with no ない on the action. Even so, it means "must not." The negative sits in the predicate いけない, not on the action itself.²

The literal parse is "as for doing X (V-ては), it won't do (いけない)." The contrastive は singles out the action, and the negative predicate rejects it.²⁸

The clearest way to see the pattern is to place the four related forms side by side. は marks the topic and a negative predicate rejects it. も marks the topic with "even," and いい accepts it. Swap the action between affirmative (V-て) and negative (V-なくて), and swap the predicate between accept (いい) and reject (いけない), and you get the whole set.⁵

Pattern	Action	Predicate	Literal reading	Meaning
～てもいい	affirmative (V-て)	いい (accept)	"even doing X is good"	permission1
～てはいけない	affirmative (V-て)	いけない (reject)	"as for doing X, it won't do"	prohibition2
～なくてもいい	negative (V-なくて)	いい (accept)	"even not doing X is good"	"you don't have to"5
～なくてはいけない	negative (V-なくて)	いけない (reject)	"as for not doing X, it won't do"	obligation ("you must do")5

The register ladder: いい vs かまわない, いけない vs ならない vs だめ

Permission endings: いい, かまわない, 大丈夫

いい is the neutral default, meaning "it's good" or "it's fine." It works in both speech and writing.⁶

大丈夫 is colloquial reassurance, meaning "it's all right" or "no problem." It is a casual substitute for いい.⁶

ここに座すわっても大丈夫だいじょうぶですか。⁶
"Is it okay if I sit here?"

かまわない / 構いません means "I don't mind" or "no objection." It is the more formal, deferential neighbor you will hear in formal or written contexts. The 構いません form adds a humble sense of "would it trouble you if…"⁹

かまわない sits one level up

構いません is a more formal, higher-tier alternative, not a core elementary point. Treat it as a register-ladder neighbor to recognize, not as a form to drill at the same level as てもいい.⁹

写真しゃしんを撮とっても構かまいませんか。⁹
"Would you mind if I took a photo?"

So ～てもいいですか is the friendly, everyday default. ～ても構いませんか is the cautious, deferential version for formal or customer-facing contexts.⁹

Prohibition endings: いけない, ならない, だめ

The three prohibition endings differ by formality and typical setting. This is a qualitative register ranking that references agree on, not a count of corpus frequencies.⁵

Ending	Register	Typical setting
だめ(だ)	blunt, casual	almost exclusively spoken5
いけない	neutral	everyday default, speech and writing5
ならない	formal	mostly written; rules and regulations5

ここで遊あそんではだめだ。⁵
"You can't play here."

廊下ろうかを走はしってはいけない。⁵
"You must not run in the hallway."

ここでタバコを吸すってはならない。⁵
"Smoking is not permitted here."

ならない carries an impersonal, rule-book authority that fits signage and law. だめ is the bluntest and reads as a direct, personal "no."⁵

Polite vs plain across the ladder

Each ending has a polite and a plain form: いけません / いけない, なりません / ならない, だめです / だめ. Permission likewise pairs いいです with いい.⁴⁵⁶

This polite/plain split is the same です/ます-versus-だ system that governs sentence endings generally. Choosing いけません over いけない is the same register decision as choosing です over だ. The dedicated polite-versus-plain article covers that system, so it is not re-derived here.⁴⁵

入はいってはいけません。⁴
"You must not enter." (polite)

入はいってはだめだよ。⁵
"Hey, you can't go in." (blunt, casual)

The same prohibition moves up and down the politeness scale by swapping only the predicate: だめだよ to a child or close friend, いけない as the neutral default, ならない for written rules.⁵

Casual contractions: ちゃ / じゃ

ては → ちゃ, では → じゃ

In casual speech, the prohibition particle string contracts: ては becomes ちゃ, and では becomes じゃ. The contracted forms are easier to say.⁸

Which contraction you get follows the て-form's voicing. A verb whose て-form is voiceless (ends in て) takes ちゃ: 食べて + は becomes 食べちゃ. A verb whose て-form is voiced (ends in で, such as the ぬ/ぶ/む group) takes じゃ: 飲んで + は becomes 飲んじゃ.⁸

So 食べてはいけない becomes 食べちゃいけない or 食べちゃだめ. 飲んではいけない becomes 飲んじゃいけない or 飲んじゃだめ.⁸

ここに落書らくがきしちゃだめだよ。⁸
"Don't scribble graffiti here."

そんなにお酒さけを飲のんじゃいけないよ。⁸
"You shouldn't drink that much."

The contraction comes from the contrastive ては / では, so ちゃ / じゃ inherit the same prohibition force. They are simply casual.⁸

Where it lands: speech register and who uses it

ちゃ / じゃ contractions are casual and essentially spoken-only. They are common in everyday conversation and in casual written dialogue, such as manga and chat, but not in formal writing.⁸⁵

ちゃだめ / じゃだめ is the everyday spoken prohibition a parent or friend uses. The full ～てはいけません stays for formal or written contexts.⁵⁸

ここで遊あそんじゃだめ。⁸
"Don't play here."

ならない does not contract this way in practice. Its formality clashes with the casual contraction.⁵

ちゃだめ stacks two casual choices

Both the contraction (ちゃ / じゃ) and the bluntest predicate (だめ) are casual, so ちゃだめ is the most informal prohibition on the ladder. Reserve it for close, familiar settings.⁵⁸

Nuance and usage contexts

Permission granted vs permission sought

The same form does both jobs: ～てもいいですよ grants permission ("go ahead"), and ～てもいいですか asks for it ("may I?"). Only the final particle (よ versus か) and the intonation differ.⁴⁶

Japanese often drops the subject, so context tells you whether the sentence means "may I" or "you may." In a question it is normally "I," and in an answer normally "you."⁴

A: 教科書きょうかしょを見みてもいいですか。 B: はい、見みてもいいですよ。⁴
A: "May I look at the textbook?" B: "Yes, you may."

A bare はい、いいですよ or はい、どうぞ grants permission without repeating the verb. It is the natural conversational answer to a ～てもいいですか request.³⁴

はい、どうぞ。³
"Yes, please do."

Refusing and softening

A negative answer to a permission question becomes a prohibition: いいえ、…てはいけません or だめです.⁴

A: ここで写真しゃしんを撮とってもいいですか。 B: いいえ、だめです。⁵
A: "May I take a photo here?" B: "No, you may not."

Flatly stating ～てはいけない to refuse can be too blunt face-to-face. In practice, speakers often hedge with ちょっと… (今はちょっと…) rather than issue the bare prohibition.¹⁰

すみません、ここはちょっと…。¹⁰
"Sorry, here is a bit… (not allowed)."

The trailing ちょっと… leaves the prohibition implied. It is a polite, face-saving way to say no without the flat てはいけない.¹⁰

Rules, signs, and laws

～てはいけない and the more formal ～てはならない appear in written rules, regulations, and laws. The ならない variant is more formal and carries an authoritative, rule-stating tone. That is why it reads as an impersonal "one must not."¹¹

This is the "impersonal must not" reading: a standing rule that applies to everyone, rather than a direct command aimed at the listener in front of you.¹¹²

芝生しばふに入はいってはいけません。⁴
"Keep off the grass." (lit. "You must not enter the lawn.")

許可きょかなく立たち入いってはならない。¹¹
"No entry without permission."

ならない frames the prohibition as a standing rule rather than a personal "you, stop." Its formal, rule-stating register is why written rules and regulations favor it over いけない or だめ.¹¹

Good to know

The は is "wa", and it is contrastive, not topic-neutral

A common pitfall is reading the は in てはいけない as "ha." It is the particle は, which is always read "wa." So 食べてはいけない is read tabete wa ikenai, never tabete ha ikenai.⁴⁸

食たべてはいけない。⁸
"You must not eat (it)."

This は is the contrastive topic particle, the same は that marks a topic. It singles out "as for doing THAT." It is not droppable here, because without it いけない reads as an ordinary sequential て-form verb instead of as prohibition.⁸

Do not confuse てはいけない (must not do) with なくてはいけない (must do)

A classic N4 trap is treating the affirmative-looking form as obligation. Reading 行ってはいけない as "you must go" is wrong. It means "you must NOT go."²⁵

行いってはいけない。²
"You must not go."

The affirmative-looking V-てはいけない is prohibition, while the negative-looking V-なくてはいけない is obligation. The negative on the action (なくて) flips "must not" into "must." The obligation "you must go" is 行かなくてはいけない or 行かなければならない, which belongs to its own pattern.⁵

だめ is blunt: choose the ending to fit the listener

だめ is the bluntest, most casual prohibition and is almost exclusively spoken. It fits a child or a close friend. To a superior, it reads as rude.⁵

いけない is the neutral default and is safe in most situations. ならない is the form for written rules. When in doubt with someone above you, choose いけません rather than だめ.⁵

Why "even if" (も) softens a permission

The も in ～てもいい is the concessive も ("even"), not the additive "also." V-ても means "even if you do X," so V-てもいい literally says "even if you do X, it is good."¹²⁷

That "even if" frame can sound grudging in English, but it became the neutral, everyday permission form in Japanese. It also explains why the particle is も rather than something else.¹²⁷

"Even-if-good" vs "as-for-no-go"

Two short glosses keep the も/は choice and the good/no-go predicate straight. Link permission to "even if you do it, it's GOOD" (V-て + も + いい), and prohibition to "as for doing it, it WON'T GO" (V-て + は + いけない).¹²

See also

• The Te-Form in Japanese: Construction Rules
• ～なくてもいい / ～なくていい: How to Say "You Don't Have To" in Japanese
• ～なければならない / ～なきゃ: How to Say "I Have To" or "Must" in Japanese
• ～たほうがいい / ～ないほうがいい: How to Give Advice ("You Should" / "You Shouldn't") in Japanese
• The Japanese Imperative Form (命令形): Plain Commands and Prohibitions
• Polite vs. Plain Japanese: です/ます vs. だ (丁寧体・普通体)

References

Footnotes

1. Makino, Seiichi, and Michio Tsutsui. A Dictionary of Basic Japanese Grammar. The Japan Times, 1986. Entry "～te mo ii." The construction V-te + mo + ii expresses permission ("may / it is all right if"). ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸

2. Makino, Seiichi, and Michio Tsutsui. A Dictionary of Basic Japanese Grammar. The Japan Times, 1986. Entry "～te wa ikenai." The construction V-te + wa + ikenai expresses prohibition ("must not / may not / cannot"). ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵

3. Banno, Eri, Yoko Ikeda, Yutaka Ohno, Chikako Shinagawa, and Kyoko Tokashiki. Genki I: An Integrated Course in Elementary Japanese. The Japan Times. Lesson 6 grammar: "～てもいいです (permission)" and "～てはいけません (prohibition)," taught together on the て-form. https://wp.stolaf.edu/japanese/grammar-index/genki-i-ii-grammar-index/temoiidesu-tewaikemasen-genki-i-chapter-6/ ↩ ↩² ↩³ ↩⁴

4. Banno, Eri, et al. Genki I, Lesson 6. Permission request きょうかしょをみてもいいですか and the responses はい、みてもいいですよ / いいえ、きょうかしょをみてはいけません. は in てはいけません is read "wa." https://wp.stolaf.edu/japanese/grammar-index/genki-i-ii-grammar-index/temoiidesu-tewaikemasen-genki-i-chapter-6/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶

5. Wasabi. "How to Express Prohibition and Obligation: だめだ, いけない, and ならない." Wasabi Japanese magazine. Register ranking: だめだ casual/conversational, いけない neutral, ならない formal/written. https://wasabi-jpn.com/magazine/japanese-grammar/how-to-express-prohibition-and-obligation/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷ ↩¹⁸ ↩¹⁹ ↩²⁰ ↩²¹ ↩²² ↩²³ ↩²⁴ ↩²⁵ ↩²⁶ ↩²⁷

6. Wasabi. "How to Express Permission and Advice: …てもいい and …方がいい." Wasabi Japanese magazine. Formation V-te + も + いい(です); か for asking; いい may be replaced by 大丈夫 or 構わない. https://wasabi-jpn.com/magazine/japanese-grammar/how-to-express-permission-and-advice/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴

7. Tofugu. "〜てもいい for Permissions." (limitation) Explanation of も as the emphatic/concessive "even if"; literal reading "is it good even if I do X"; てもよろしいですか polite lift; も optionally dropped in casual speech. https://www.tofugu.com/japanese-grammar/temoii/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

8. Maggie Sensei. "How to Use ては / では ( = tewa / dewa)." (limitation) Contraction rules ては→ちゃ, では→じゃ; casual/spoken register; は in ては is contrastive. https://maggiesensei.com/2017/11/01/how-to-use-%E3%81%A6%E3%81%AF-%E3%81%A7%E3%81%AF-tewa-dewa/ ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷ ↩⁸ ↩⁹ ↩¹⁰ ↩¹¹ ↩¹² ↩¹³ ↩¹⁴ ↩¹⁵ ↩¹⁶ ↩¹⁷

9. Coto Academy. "JLPT N3 Grammar ～てもかまわない." てもかまわない / 構いません is more polite and deferential than てもいい; 構いません used in formal settings and written language. https://cotoacademy.com/jlpt-n3-grammar-temokamawanai-japanese-english/ ↩ ↩² ↩³ ↩⁴

10. Tofugu. "Chotto: A Little Japanese Word with 7 Different Meanings." (limitation) Meaning #7 ("I'd Rather Not Say… / Ambiguity"): "This ちょっと is also used as a way to avoid a direct refusal," with the trailing 今日はちょっと… ("today is a bit…") example, declining an invitation without stating いいえ. https://www.tofugu.com/japanese/chotto/ ↩ ↩² ↩³

11. Bunpro. "てはならない (JLPT N2)." Grammar-point reference. てはならない is "slightly more formal and therefore more often found in the written language, such as in rules or regulations," and carries "an authoritative tone, as if stating a rule." https://bunpro.jp/grammar_points/%E3%81%A6%E3%81%AF%E3%81%AA%E3%82%89%E3%81%AA%E3%81%84 ↩ ↩² ↩³ ↩⁴

12. Makino, Seiichi, and Michio Tsutsui. A Dictionary of Basic Japanese Grammar. The Japan Times, 1986. Entry "mo." The particle も has a concessive use ("even") in conditional / ～ても environments, distinct from its additive "also, too" use. ↩ ↩²