Must Grammar in Japanese: Have To, Should, Needn't

Obligation: “if I don’t, it won’t do”

なりません sounds like a general rule; いけません sounds more like a personal need. Both mean “must”.

Short answer: Japanese says “must” with a double negative: 行かなければなりません, literally “if I don’t go, it won’t do”. Take the ない form, change ない to なければ, and add なりません or いけません. In conversation this shrinks to 行かなきゃ, 行かなくちゃ or just 行かないと, often with the end left off.

Forming it

Start from the ない form of any verb, adjective or noun.

Must	Meaning	From
ikanakereba narimasen	must go	行かない
tabenakereba narimasen	must eat	食べない
shinakereba ikemasen	must do	しない
konakereba ikemasen	must come	来ない
yasukunakereba narimasen	must be cheap	安くない
nihongo de nakereba narimasen	must be in Japanese	日本語でない

Rules and personal needs

The full forms are polite and common in rules, instructions and careful speech.

明日あしたashitatomorrow早くはやくhayakuearly起きなければなりませんおきなければなりませんokinakereba narimasenmust get up

Ashita hayaku okinakereba narimasen.“I have to get up early tomorrow.”Why: Personal need.

パスポートpasupōtopassportをo(object)見せなければいけませんみせなければいけませんmisenakereba ikemasenmust show

Pasupōto o misenakereba ikemasen.“You have to show your passport.”Why: A rule for anyone.

薬くすりkusurimedicineをo(object)飲まなければなりませんのまなければなりませんnomanakereba narimasenmust take

Kusuri o nomanakereba narimasen.“I have to take my medicine.”Why: Medicine is “drunk” in Japanese: 薬を飲む.

In conversation

These mean exactly the same; the ending (いけない) is understood. ないと is the most neutral.

あaohもうmōalready九時くじku-jinine帰らなきゃかえらなきゃkaeranakyagotta go home

A, mō ku-ji. Kaeranakya. · “Oh, it’s nine already. I’ve got to go home.”なきゃ: short for なければ.

宿題しゅくだいshukudaihomeworkもmoalsoやらなくちゃyaranakuchagotta do

Shukudai mo yaranakucha. · “I’ve got homework to do too.”なくちゃ: short for なくては. やる is casual する.

じゃあjāthen急がないといそがないとisoganai toneed to hurry

Jā, isoganai to. · “Better hurry, then.”ないと alone means “must”.

Casual short forms

In speech, the long obligation forms shrink.

Casual	Meaning	Full form
ikanakya	gotta go	行かなければ
ikanakucha	have to go	行かなくては
tabenakya dame	you must eat	食べなければだめ
shinakute ii	no need to do	しなくてもいい
ikanai to	I need to go	行かないといけない

Should: べき and はず

べき is a moral “should”; はず is an expectation, “should be (by all logic)”.

約束やくそくyakusokupromisesはwa(topic)守るまもるmamorukeepべきbekishouldですdesuis

Yakusoku wa mamoru beki desu.“You should keep your promises.”Why: べき: what is right.

彼かれkareheはwa(topic)もうmōalready着いたついたtsuitaarrivedはずhazushouldですdesuis

Kare wa mō tsuita hazu desu.“He should have arrived by now.”Why: はず: logical expectation.

そんなsonnasuchはずhazuexpectationはwa(topic)ないnaiisn’t

Sonna hazu wa nai.“That can’t be right.”Why: Negative はず: impossible by all logic.

Advice: 方がいい

た form + 方がいい gives friendly advice; ない form + 方がいい advises against.

Check yourself

Say each one in Japanese, then open the answer to check and hear it.

I must go to work tomorrow.
Show answer
Ashita shigoto ni ikanakereba narimasen.
You don’t have to come.
Show answer
Konakute mo ii desu.
Gotta study! (casual)
Show answer
Benkyō shinakya!
You should see a doctor.
Show answer
Byōin ni itta hō ga ii desu yo.

Don’t have to

The opposite uses なくてもいい: “it’s fine even if not”. Japanese never says “don’t must”.