Obligation and Permission in Japanese

When a Japanese speaker says must

Japanese speakers reach for the obligation pattern when a duty comes from outside: a deadline, a rule, a doctor's instruction, a train timetable. Ashita wa hayaku okinakereba narimasen states that early rising is required by circumstances, not that you want it. The pattern is also the standard way to excuse yourself, because mō ikanakereba narimasen sounds like the world is pulling you away rather than you choosing to leave.

That is why the form is so often about the speaker. Telling another adult what they must do is blunt, so advice to someone else usually softens to hō ga ii, and rules for someone else usually come as a request with kudasai. Keep must for your own duties and for stating general rules, and you will already sound more natural than a learner who translates every English must directly.

The double negative behind must

Every obligation form is two negatives in a row. The first is the nai form of the verb, turned into a condition: nakereba, if you do not. The second is a judgement that the result is unacceptable: narimasen, it does not become right, or ikemasen, it will not go. Together they read if you do not do it, that will not do, and Japanese treats that as the plain statement of necessity. The permission and prohibition forms use the same judgement words with the te form instead, which is why the table below lines them up together.

Forming the nai stem from the dictionary form

The whole family hangs off the nai form, so the derivation is the nai form plus a fixed ending. Godan verbs change the final u sound to a and add nai, with one trap: a verb ending in the vowel u alone takes wa, so kau becomes kawanai, not kaanai. Ichidan verbs drop ru and add nai. Suru becomes shinai and kuru becomes konai, with the vowel change in kuru that catches everyone the first time.

From nai, replace the final i with kereba to get nakereba, exactly as any i-adjective forms its ba conditional, or replace it with kute to get nakute. Then add narimasen, ikemasen, or wa ikemasen. The verb-conjugation guide has the full nai form table; the rows below are enough to check any new verb against.

The contracted forms you will hear: nakya and nakucha

In casual speech nobody says the full nakereba narimasen. Nakereba squeezes to nakya, nakute wa squeezes to nakucha, and the judgement word at the end is usually dropped altogether, so ikanakya on its own means I have to go. Nai to survives as it is, again with the ending dropped: hayaku kaeranai to, I need to get home soon. When the ending is kept, it is the plain ikenai or dame, giving ikanakya ikenai and ikanakucha dame.

These are casual forms, so they belong with friends, family, and colleagues you already speak to in plain form. Saying ikanakya to a manager is a register mistake, not a grammar mistake, and it is one of the most common ways a learner sounds younger than they mean to. With anyone you address in masu, use nakereba narimasen or nai to ikemasen in full.

Hō ga ii for advice that does not command

When the duty is your opinion rather than a rule, Japanese switches to hō ga ii: the side of doing it is better. The verb goes into its plain past form for positive advice, itta hō ga ii desu, and into the nai form for negative advice, ikanai hō ga ii desu. The past form is not about time; it is the standard shape of concrete advice, and the dictionary form in this slot sounds vaguer and more general.

The minimal pair shows the contrast. Byōin ni ikanakereba narimasen tells a friend they are obliged to go to the hospital, which sounds like a doctor or a parent. Byōin ni itta hō ga ii desu yo tells them you think they should, and the yo makes it friendly. A natural reply is sō desu ne, sō shimasu, you are right, I will. Advice to someone else almost always wants hō ga ii; obligation about yourself wants nakereba narimasen.

Asking permission with te mo ii desu ka

Permission is the te form plus mo ii desu ka: even if I do this, is it fine? Koko ni suwatte mo ii desu ka asks whether you may sit here, and it works in shops, offices, and homes alike. The te-form guide covers the derivation; what matters here is the reply, because Japanese rarely refuses with a plain no. A grant sounds like hai, dōzo or ii desu yo. A refusal usually sounds like sumimasen followed by a reason, or the trailing chotto that leaves the sentence unfinished.

Learners often miss the refusal because they are listening for dame or ikemasen, which a stranger will almost never say to your face. If you hear chotto and a pause, that is a no. Reply with wakarimashita, understood, and drop it. Pressing on after chotto is the one thing that turns a polite refusal into an awkward one.

Nakute mo ii: you do not have to

Swap the te form for the nakute form and permission flips into freedom from obligation. Konakute mo ii desu means you do not have to come; it grants an exemption rather than an action. This is the answer to a must question, so when someone asks ikanakereba narimasen ka, must I go, the kind reply is iie, ikanakute mo ii desu yo. Learners mix it up with te wa ikemasen, but the two are opposites: one removes a duty, the other imposes a ban.

The cleanest way to keep the family straight is to say all three with one verb. Konakereba narimasen, you must come. Konakute mo ii desu, you need not come. Kite wa ikemasen, you must not come. Only the middle of the word changes, and the three meanings are far enough apart that mixing them can cause a real misunderstanding at work.

Prohibition: te wa ikemasen and the signs that use it

The te form plus wa ikemasen forbids: koko de shashin o totte wa ikemasen, you must not take photos here. It is strong, so in speech it comes from people with authority, a teacher, a guard, a parent, and learners mostly need to recognise it rather than say it. If you have to stop someone yourself, the softer request naide kudasai, please do not, is the form a polite adult uses. The casual version compresses te wa to cha or ja, giving tabecha dame and nonja dame.

Signs carry the same prohibition in two characters: kinshi, forbidden. Tachiiri kinshi is no entry, satsuei kinshi is no photography, chūsha kinshi is no parking, and dosoku kinshi means no outdoor shoes. Reading a sign aloud as a te wa ikemasen sentence is a useful habit, because it turns the noun on the wall into a verb you can use when explaining the rule to someone else.

Asking permission at three levels of politeness

The same request changes shape with the listener. To a friend, drop desu ka and let the intonation carry the question: kore tsukatte mo ii, can I use this. To a colleague or teacher you speak to in masu, use the full te mo ii desu ka. To a manager, a client, or anyone whose permission carries weight, replace ii desu ka with yoroshii deshō ka, or switch to the humble causative sasete itadakemasen ka, which asks to be allowed rather than asking whether it is fine.

The replies scale too. A friend says ii yo or dame. A colleague says ii desu yo or chotto. A manager who agrees says ii desu yo or dōzo, and one who declines will often give a reason such as kyō wa chotto kibishii desu ne, today is a little tight, rather than a direct refusal. Answering a manager's chotto with hai, wakarimashita and a fallback plan shows you understood the refusal without forcing them to say it.

Mistakes that mark a learner

• Saying nakereba narimasen to tell another adult what they should do, when hō ga ii or kudasai is what a native speaker would choose.
• Forming kau as kaanai instead of kawanai, so that kawanakereba comes out wrong before the ending is even reached.
• Using nakya or nakucha with a manager or a customer, which is a register slip rather than a grammar error.
• Answering a must question with te wa ikemasen when the intended message is nakute mo ii, you need not.
• Waiting for dame after a permission question, and missing the chotto that was the actual refusal.
• Attaching hō ga ii to the dictionary form for specific advice, which sounds vaguer than the past form itta hō ga ii.