Japanese Must Should and Have To: Obligation Grammar

🗣️ Obligation grammar is the part of Japanese you need at speed, in the moment you are already flustered — leaving a party, missing a train, asking a manager for something. SoraSpeak gives you unscripted spoken practice with AI Japanese teachers, plus instant corrections on grammar, particles and politeness explained in simple English. Free daily tier, in your browser. Start a free speaking session →

Here's the short version: must is 〜なければなりません, which in real speech becomes 〜なきゃ or 〜ないと. Must not is 〜てはいけません, casually 〜ちゃだめ. May is 〜てもいいです. Do not have to is 〜なくてもいいです. Should as advice is 〜ほうがいい, should as duty is 〜べき, and should as expectation is 〜はず. Nine patterns, and between them they cover most of what an adult says in a day.

Two things make this cluster harder than it looks. First, Japanese builds obligation out of double negatives — "if I do not go, it will not do" — so the textbook forms are long and awkward to say. Second, spoken Japanese chops those long forms down to two syllables, and nobody teaches the chopped versions first even though they are what you will hear. This guide fixes both, in speaking order.

In this guide: how obligation works · must and have to · what people really say · must not · permission and not having to · the three shoulds · cheat sheet · boss versus friend · mistakes · drills · bottom line

How obligation works in Japanese

English has dedicated words — must, should, may. Japanese has none of those. It builds the same meanings out of conditionals stacked on negatives, and once you see the machine you can generate every form in this article from one starting point.

Everything starts from the ない form. Take 行く, make it 行かない, then drop the final い to get the stem 行かな. Everything else bolts onto that stem:

• 行かな + ければなりません → 行かなければなりません — "I have to go."
• 行かな + くてはいけません → 行かなくてはいけません — "I have to go."
• 行かな + くてもいいです → 行かなくてもいいです — "I do not have to go."
• 行かな + いと → 行かないと — "I have to go." (casual)

The literal logic of the first one is "if I do not go, it will not become" — a double negative that lands as obligation. It is a strange machine, but it is a regular one, and that is the good news: there are no irregular verbs here beyond the ones you already know from the ない form itself (する → しない, 来る → こない).

The permission and prohibition side runs off the て form instead:

• 行って + もいいです → 行ってもいいです — "You may go."
• 行って + はいけません → 行ってはいけません — "You must not go."

Two stems, six endings, most of the cluster. If the て form or the ない form is still slow for you, that is the thing to fix first — everything below is one syllable away from a conjugation you already know.

Must and have to the full forms

There are four full-length ways to say "have to", and they differ mostly in formality and in whether the obligation comes from a rule or from the situation.

• 〜なければなりません (nakereba narimasen) — the most formal. Rules, contracts, announcements, written Japanese. 11時までにチェックアウトしなければなりません (jūichi-ji made ni chekku auto shinakereba narimasen) — "You have to check out by eleven."
• 〜なければいけません (nakereba ikemasen) — polite spoken, slightly more personal. 薬を飲まなければいけません (kusuri o nomanakereba ikemasen) — "I have to take my medicine."
• 〜なくてはいけません (nakute wa ikemasen) — polite spoken, situational obligation. 今日は早く帰らなくてはいけません (kyō wa hayaku kaeranakute wa ikemasen) — "I have to go home early today."
• 〜ないといけません (nai to ikemasen) — polite but softer and very common in conversation. もう行かないといけません (mō ikanai to ikemasen) — "I have to get going."

The rough division that native speakers feel: ならない points at a rule that exists whether you like it or not, while いけない points at this situation, for you, now. It is a tendency rather than a law, and no listener will misunderstand you for picking the other one.

This machine runs on adjectives and nouns too, which surprises people:

• もっと安くなければなりません (motto yasuku nakereba narimasen) — "It has to be cheaper."
• 会員でなければなりません (kaiin de nakereba narimasen) — "You have to be a member."

Three conjugations to check yourself on, because they are the ones learners fumble aloud: する → しなければ / しなきゃ, 来る → こなければ / こなきゃ, 食べる → 食べなければ / 食べなきゃ.

What people actually say nakya nakucha and naito

Here is the part most courses bury in a footnote. In ordinary conversation the full forms above are rare. They are correct, they are what you write, and they are what you say to a client — but between friends, and in your own head, Japanese chops them in half and usually deletes the ending altogether.

• なければ → なきゃ. 行かなきゃ (ikanakya) — "I have to go."
• なくては → なくちゃ. 行かなくちゃ (ikanakucha) — "I have to go."
• ないと(いけない) → ないと. 行かないと (ikanai to) — "I have to go."

All three routinely end there, with いけない or だめ simply dropped. もう行かなきゃ (mō ikanakya) — "I have to go now" — is a complete, natural sentence, and it is what you will actually say when you are leaving.

More of them, out loud:

• 早く寝なきゃ (hayaku nenakya) — "I have to get to bed."
• 明日までに終わらせなくちゃ (ashita made ni owarasenakucha) — "I have to finish it by tomorrow."
• 電話しないと (denwa shinai to) — "I have to make that call."
• 買い物に行かなきゃいけない (kaimono ni ikanakya ikenai) — "I have to go shopping." (contraction with the ending kept)

A register note that matters: なきゃ and ないと are the neutral casual choices, while なくちゃ sounds a touch softer and is heard more from women and when talking to children. None of the three belongs in an email or a meeting.

Must not the prohibition forms

Prohibition is built on the て form, and it also has a spoken contraction that learners hear long before they are taught it.

• 〜てはいけません (te wa ikemasen) — the standard. 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."
• 〜てはなりません (te wa narimasen) — very formal, legal or written. Rare in speech.
• 〜ちゃだめ (cha dame) — the casual contraction of てはだめ. 食べちゃだめ (tabecha dame) — "You must not eat that."
• 〜じゃだめ (ja dame) — the same contraction after a て form that ends in で. 飲んじゃだめ (nonja dame) — "Do not drink that."
• 〜ないでください (nai de kudasai) — "Please do not." 写真を撮らないでください (shashin o toranai de kudasai) — "Please do not take photos."

The difference between the last one and the rest is worth its own sentence. 〜てはいけません states a rule; 〜ないでください makes a request. A sign in a museum uses the first. A person asking you personally uses the second, and it is far more common in ordinary conversation because most of the time you are asking rather than legislating.

The contraction rule is mechanical: if the て form ends in て, it becomes ちゃ; if it ends in で, it becomes じゃ. 見て → 見ちゃだめ. 遊んで → 遊んじゃだめ. Same rule as てしまう → ちゃう, which is why 忘れちゃった sounds familiar.

Permission and not having to

Permission runs on 〜てもいい.

• ここに座ってもいいですか (koko ni suwatte mo ii desu ka) — "May I sit here?"
• 写真を撮ってもいいですか (shashin o totte mo ii desu ka) — "Is it OK to take photos?"
• もう帰ってもいいですよ (mō kaette mo ii desu yo) — "You can head home now."
• 〜てもかまいません (te mo kamaimasen) — "I do not mind if you…", politer and slightly more distant.
• 〜てもよろしいでしょうか — the formal version for a client or a manager.
• 〜ていい — the casual clip. 見ていい？ (mite ii?) — "Can I look?"

Not having to runs on 〜なくてもいい, off the same ない stem as the obligation forms.

• 来なくてもいいですよ (konakute mo ii desu yo) — "You do not have to come."
• 心配しなくてもいいよ (shinpai shinakute mo ii yo) — "You do not have to worry."
• 予約しなくても大丈夫です (yoyaku shinakute mo daijōbu desu) — "You do not need a reservation."

The trap here is an English-shaped one. In English, "must not" and "do not have to" look like near neighbours; in Japanese they are built on different stems and mean opposite things. 来てはいけません is "you must not come". 来なくてもいいです is "you do not have to come". Saying the wrong one to someone waiting for your answer is the kind of error that does not get politely parsed around.

The three should forms hazu beki and hou ga ii

English "should" does three separate jobs, and Japanese uses a different word for each. This is the highest-value section in the article, because the mix-up survives for years otherwise.

Hou ga ii is advice

〜ほうがいい: it would be better if you… This is the everyday one, the one you want in ninety percent of conversations.

• 病院に行ったほうがいいですよ (byōin ni itta hō ga ii desu yo) — "You should go to the doctor."
• 早く寝たほうがいいよ (hayaku neta hō ga ii yo) — "You should get to bed early."
• 無理しないほうがいいです (muri shinai hō ga ii desu) — "You should not overdo it."

Note the asymmetry, which is genuinely odd and genuinely standard: the affirmative normally uses the plain past form (行った ほうがいい), while the negative uses the plain non-past ない form (行かない ほうがいい). 行くほうがいい also exists but reads as a neutral comparison between two options rather than as advice.

Adding よ aims the advice squarely at the listener. Leaving it off makes it a general observation.

Beki is duty

〜べき attaches to the dictionary form and means ought to, as a matter of principle.

• 謝るべきです (ayamaru beki desu) — "You should apologise."
• もっと早く言うべきでした (motto hayaku iu beki deshita) — "I should have said something sooner."
• そんなことをするべきではない (sonna koto o suru beki de wa nai) — "You should not do that."
• する has two accepted forms: するべき and the more formal すべき.

Warning, because learners over-reach for this word: べき is heavy. It invokes duty, principle, right and wrong. Aimed at a person it can sound like a lecture, and aimed at someone senior it is a genuine social misstep. Reserve it for principles and for talking about yourself in hindsight — べきでした is a graceful way to admit a mistake.

Hazu is expectation

〜はず means it should logically be the case, based on evidence, a schedule or a promise. It is not advice at all.

• 田中さんは3時に来るはずです (Tanaka-san wa san-ji ni kuru hazu desu) — "Tanaka should be here at three."
• 彼は知っているはずだ (kare wa shitte iru hazu da) — "He should know."
• 明日は休みのはずです (ashita wa yasumi no hazu desu) — "Tomorrow should be a day off." (noun takes の)
• 元気なはずです (genki na hazu desu) — "He should be fine." (な-adjective takes な)
• 来るはずがない (kuru hazu ga nai) — "There is no way he is coming." Stronger than 来ないはずです, which is simply "he should not be coming".
• 来るはずだったのに (kuru hazu datta noni) — "He was supposed to come, but…"

The classic error: using べき for a train. 電車は3時に着くべきです says the train has a moral duty to be punctual. You want 着くはずです. The test that always works — if you can swap "should" for "is expected to", it is はず; if you can swap it for "ought to", it is べき; if you are giving a person friendly advice, it is ほうがいい.

はず also belongs to the certainty ladder covered in our guide to saying it seems like in Japanese: かもしれない, then でしょう, then はず, then に違いない.

The obligation cheat sheet

The politeness ladder from boss to friend

Same meaning, four social distances. Say each column out loud and you will hear how much of Japanese politeness lives in the ending rather than in the words.

Two rules that will keep you out of trouble. First, do not give a superior advice with ほうがいい. Even with ですよ attached it positions you as the one who knows better. 〜たらいかがでしょうか (tara ikaga deshō ka) — "how would it be if you…" — is the safe form, and 〜てはいかがですか works the same way.

Second, obligation about yourself is always safe. Telling a manager 5時に出なければならないので (go-ji ni denakereba naranai node) — "because I have to leave at five" — is polite, factual and blames a schedule rather than a person. Obligation aimed at someone else is where the register minefield is. There is more on this in our business Japanese conversation guide.

Mistakes at conversation speed

1. Must not versus do not have to. ×来てはいけません when you meant "you do not have to come" → ○来なくてもいいです. Opposite meanings, similar English shapes, and the most consequential error in this article.

2. べき for a schedule. ×電車は3時に着くべきです → ○着くはずです. Trains have timetables, not consciences.

3. ほうがいい to a superior. Grammatically fine, socially wrong. Use 〜たらいかがでしょうか.

4. Forgetting the past form in ほうがいい. ×行くほうがいいですよ as advice → ○行ったほうがいいですよ. The past form is what makes it advice rather than comparison.

5. Putting the past form in the negative half. ×行かなかったほうがいい → ○行かないほうがいい. Affirmative takes た, negative takes ない. This asymmetry is real and worth drilling.

6. Missing の and な before はず. ×休みはず → ○休みのはず. ×元気はず → ○元気なはず. Nouns take の, な-adjectives take な.

7. Using なきゃ in a work email. The contractions are speech only. In writing, go back to なければなりません.

8. The ちゃ / じゃ split. ×飲んちゃだめ → ○飲んじゃだめ. If the て form ends in で, the contraction is じゃ.

9. Over-conjugating out loud. Learners often freeze mid-word building 行かなければなりません and lose the sentence entirely. In casual speech, say 行かなきゃ. Two syllables of obligation beat eight syllables you never finish.

Say it out loud three drills

Drill one, the contraction ladder. Take one verb — 行く. Say the same idea five times, formal to casual, without pausing: 行かなければなりません、行かなくてはいけません、行かないといけません、行かなきゃいけない、行かなきゃ. Then do it with する, 来る, 食べる and 帰る. This is the single most useful five minutes in the article, because it drills conjugation and register at the same time.

Drill two, the three shoulds. Take one situation — a friend is ill. Say all three: 病院に行ったほうがいいよ (advice), 医者に相談するべきだ (duty, notice how much heavier it sounds), 薬が効くはずだ (expectation). Hearing the weight difference in your own voice is what stops the mix-up for good.

Drill three, the permission pair. Pick five things you might ask about today — sitting, photographing, borrowing, leaving early, using someone's charger. Ask each twice: 〜てもいいですか to a colleague and 〜てもよろしいでしょうか to a manager. Then answer yourself both ways: どうぞ and すみません、ちょっと…. The trailing ちょっと is how refusals actually sound, and it is worth practising as a whole phrase. The daily Japanese conversation phrases list has more of these ready-made frames.

Drills like these are where a speaking partner earns their keep, because obligation errors are invisible from the inside — なくてもいい and てはいけない feel equally fluent in your mouth and mean opposite things to the listener. SoraSpeak exists for that loop: you speak in the browser, an AI Japanese teacher answers in natural Japanese with subtitles, and every grammar and politeness correction comes back in simple English while you still remember what you were reaching for. Being honest about it: it is a new product, it complements real conversation rather than replacing it, and no software fully replaces a good teacher. For the specific job of saying twenty obligation sentences and finding out which register you got wrong, it is lower-friction than waiting for a class.

The bottom line

Must is 〜なければなりません, spoken as 〜なきゃ or 〜ないと. Must not is 〜てはいけません, spoken as 〜ちゃだめ. May is 〜てもいい. Do not have to is 〜なくてもいい. Advice is 〜ほうがいい, duty is 〜べき, expectation is 〜はず. Everything above is elaboration on those seven lines.

Two things to take away if you take nothing else. Learn the contractions early, because なきゃ and ないと are what Japanese people actually say and the full forms will not come out of your mouth fast enough in the moment you need them. And keep the three shoulds separate: advice for people, duty for principles, expectation for trains.

For seeing these forms in real sentences rather than exercise sentences, NHK News Web Easy is free and furigana-supported, and news writing is dense in なければなりません and はず because reporting is largely about rules and expectations. The Japan Foundation publishes learner materials built around communicative use, and the official JLPT site shows which of these appear at each level — worth knowing that it tests reading and listening only, so a form you can recognise is not yet a form you can say.

Related grammar in the same series: sou, rashii and mitai for saying it seems like covers the certainty ladder that はず sits on, the particles guide handles the layer underneath every sentence here, and the beginner conversation guide gives you patterns to attach these endings to.

🗣️ Say the contraction, get the register checked, fix it the same minute. Practise speaking Japanese free →

SoraSpeak is an independent Japanese speaking-practice app. Example sentences are written for learners; natural usage can vary by context and region.

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