Japanese Modal Expressions: Can, Must, Should, May in Japanese (2026)
Japanese does not have modal verbs the way English does. There is no single word equivalent to "can," "must," or "should" that attaches to a base verb. Instead, Japanese expresses these meanings through grammatical patterns — typically suffixes, auxiliary expressions, or conjugated verb forms added to the verb stem.
The challenge is that most modal meanings have multiple Japanese equivalents at different formality levels. The English word "must," for example, maps onto at least five Japanese patterns — all grammatically correct, but very different in nuance and register. This article covers each modal meaning with a clear formality comparison table and natural example sentences.
1. Ability — Can (できる, potential verbs)
Japanese expresses "can" in two main ways: the verb できる, and the potential form of the verb itself.
できる — general ability with nouns and する verbs
できる (can do, be able to) is used with nouns and with する compound verbs. It indicates that the ability or possibility exists.
- 日本語ができます。— I can speak Japanese. (literally: Japanese exists as an ability)
- 料理ができます。— I can cook.
- それはできません。— I cannot do that.
- 明日来ることができますか。— Can you come tomorrow? (formal)
Potential verb forms — specific action ability
To express "can [verb]" for a specific action, Japanese uses the potential form:
| Dictionary form | Potential form | Meaning | Example |
|---|---|---|---|
| 食べる (to eat) | 食べられる | can eat | 辛いものが食べられません。(I cannot eat spicy food.) |
| 飲む (to drink) | 飲める | can drink | お酒が飲めます。(I can drink alcohol.) |
| 話す (to speak) | 話せる | can speak | 英語が話せますか。(Can you speak English?) |
| 書く (to write) | 書ける | can write | 漢字が書けます。(I can write kanji.) |
| 見る (to see/watch) | 見られる | can see/watch | 富士山が見られます。(You can see Mt. Fuji.) |
| 来る (to come) | 来られる | can come | 今日来られますか。(Can you come today?) |
| する (to do) | できる | can do | 何でもできます。(I can do anything.) |
Note: In casual speech, the ら in 〜られる is often dropped — 食べれる instead of 食べられる. This is called ら抜き言葉 (ら-dropping) and is very common in conversation, though considered non-standard in formal writing.
2. Obligation — Must, Have to
Japanese has multiple patterns for expressing obligation, each at a different formality level. All three below mean "must do" or "have to do."
| Pattern | Example | Register | Nuance |
|---|---|---|---|
| 〜なければならない | 行かなければならない。(I must go.) | Formal / Written | External rule or duty; sounds formal in speech |
| 〜なければいけない | 行かなければいけない。(I have to go.) | Neutral | General obligation; common in speech and writing |
| 〜ないといけない | 行かないといけない。(I've gotta go.) | Casual / Spoken | Most natural in everyday conversation |
| 〜なきゃ (short form) | 行かなきゃ。(Gotta go.) | Very casual | Contraction of なければ; colloquial shorthand |
| 〜ねばならない | 改善せねばならない。(It must be improved.) | Very formal / Literary | Old-fashioned; found in literature and formal documents |
Formation: Take the negative て-form or ない-form of the verb, then add the obligation pattern. For 食べる: 食べなければならない → must eat.
3. Prohibition — Must Not, Cannot
Prohibition in Japanese is expressed with the て-form of the verb followed by a prohibition marker.
| Pattern | Example | Register | Nuance |
|---|---|---|---|
| 〜てはいけない | ここで食べてはいけない。(You must not eat here.) | Neutral | Standard prohibition; rules and instructions |
| 〜てはならない | 法律を破ってはならない。(You must not break the law.) | Formal / Written | Stronger; moral or legal prohibition |
| 〜てはだめ | 走ってはだめ。(You can't run here.) | Casual | Used by parents, teachers; can sound emotional |
| 〜禁止 | 撮影禁止。(Photography prohibited.) | Written / Signs | Noun form; used on signs and official notices |
| 〜ないでください | ここで電話しないでください。(Please do not use your phone here.) | Polite | Polite request not to do something; softer than prohibition |
4. Permission — May, Can (permission)
To ask or grant permission, Japanese uses the て-form followed by a permission marker.
| Pattern | Example | Register | Nuance |
|---|---|---|---|
| 〜てもいい | ここに座ってもいいですか。(May I sit here?) | Neutral / Casual | Most common permission expression |
| 〜てもかまわない | 使ってもかまいません。(I don't mind if you use it.) | Neutral / Formal | "I don't mind if" — slightly more formal than いい |
| 〜ても構わない | 遅れても構いません。(It doesn't matter if you are late.) | Formal / Written | Formal version; 構う written in kanji |
| 〜てよい | 退出してよい。(You may leave.) | Formal / Written | More formal than いい; used in official statements |
| 〜ていい (casual) | 食べていいよ。(You can eat it.) | Very casual | Casual spoken grant of permission |
5. Recommendation — Should, Had Better
Japanese has three common patterns for giving recommendations or advice. They differ in how strong the recommendation is and whether it implies moral duty or practical benefit.
| Pattern | Example | Register | Strength | Nuance |
|---|---|---|---|---|
| 〜べきだ | 謝るべきだ。(You should apologise.) | Formal / Neutral | Strong | Moral/logical duty; implies it's the right thing |
| 〜べきではない | 嘘をつくべきではない。(You should not lie.) | Formal / Neutral | Strong negative | Negative recommendation; morally wrong |
| 〜ほうがいい | 早く寝たほうがいい。(You had better sleep early.) | Neutral / Casual | Moderate | Practical advice; "it would be better if" |
| 〜たらいい / 〜といい | 医者に行ったらいいと思う。(I think you should go to the doctor.) | Casual | Soft | Gentle suggestion; often followed by と思う |
| 〜ことをお勧めします | 早めに申し込むことをお勧めします。(I recommend applying early.) | Formal / Business | Polite | Professional recommendation; customer service language |
Key distinction: べきだ is present/future oriented — you cannot use it to say what someone should have done (use べきだった for past regret: 謝るべきだった = "I should have apologised").
6. Possibility — Might, May, Probably
Japanese distinguishes different levels of certainty through different modal expressions. Choosing the wrong one can make you sound either too certain or too uncertain.
| Pattern | Certainty | Example | Register |
|---|---|---|---|
| 〜かもしれない | ~50% | 雨が降るかもしれない。(It might rain.) | Neutral |
| 〜かもしれません | ~50% | 間違いかもしれません。(It may be a mistake.) | Polite |
| 〜だろう | ~70–80% | 彼は知っているだろう。(He probably knows.) | Neutral / Casual |
| 〜でしょう | ~70–80% | 明日は晴れるでしょう。(It will probably be sunny tomorrow.) | Polite / Formal |
| 〜と思う | Personal opinion | 彼女は来ると思います。(I think she will come.) | Neutral |
| 〜に違いない | ~90%+ | 彼が犯人に違いない。(He must be the culprit.) | Neutral |
| 〜はずだ | ~85%+ (expectation) | もう着いているはずだ。(He should have arrived by now.) | Neutral |
Master reference table — all modals by formality
| Modal meaning | Casual | Neutral | Formal / Written |
|---|---|---|---|
| Can (ability) | 〜れる/〜える (ra-dropped) | 〜られる / できる | 〜ことができる |
| Must / Have to | 〜なきゃ / ないといけない | 〜なければいけない | 〜なければならない / 〜ねばならない |
| Must not | 〜てはだめ | 〜てはいけない | 〜てはならない / 〜禁止 |
| May (permission) | 〜ていい | 〜てもいい | 〜てもかまわない / 〜てよい |
| Should (recommendation) | 〜たらいい | 〜ほうがいい / 〜べきだ | 〜べきである / ことをお勧めします |
| Might / Maybe | 〜かも | 〜かもしれない / だろう | 〜でしょう / 〜と考えられる |
Common mistakes with Japanese modal expressions
Mistake 1: なければならない in casual conversation
✗ 今日、早く帰らなければなりません。(Grammatically correct but stiff for casual speech)
✓ 今日、早く帰らないといけない。(Natural in conversation)
✓ 今日、早く帰らなきゃ。(Very casual, natural shorthand)
Mistake 2: べきだ for past regret (missing だった)
✗ もっと勉強するべきだ。(Means "I should study more" — present/future)
✓ もっと勉強するべきだった。(Means "I should have studied more" — past regret)
Mistake 3: Using かもしれない when you are actually fairly certain
✗ 彼はもう着いたかもしれない。(Implies only 50% certainty)
✓ 彼はもう着いているはずだ。(Implies expectation based on schedule/reason)
✓ 彼はもう着いているだろう。(Implies fairly confident estimate)
Modal expressions are one of the most error-prone areas of Japanese grammar because register misjudgments are easy to make. Use ZISTICA MOJIIQ's free grammar checker to get real-time feedback on whether your modal expressions sound natural and are at the right formality level for your context.
Frequently asked questions
How do you say "can" in Japanese?
There are two main ways to express "can" in Japanese: (1) できる — used with nouns and する verbs: 日本語ができます (I can speak Japanese), 料理ができます (I can cook); (2) Potential verb form — change the verb ending: 食べられる (can eat), 話せる (can speak), 書ける (can write). The potential verb form is slightly more specific about the action; できる is slightly more general.
What is the difference between なければならない and なければいけない in Japanese?
Both mean "must" or "have to," but なければならない is slightly more formal and often implies a rule or external obligation. なければいけない is more neutral and commonly used in speech. In casual conversation, ないといけない is the most natural. All three are grammatically correct; choosing between them is about register and context.
What is the difference between べきだ and ほうがいい in Japanese?
べきだ ("should") expresses a stronger moral or logical obligation — it implies the action is the right thing to do based on principles or duty. ほうがいい ("had better," "it would be better to") is softer advice based on practical benefit. Use べきだ for strong recommendations; use ほうがいい for friendly advice.
How do you express "might" or "may" in Japanese?
The main expressions for possibility in Japanese are: かもしれない (maybe, might — about 50% certainty), だろう / でしょう (probably — about 70–80% certainty), と思う (I think — expresses personal opinion), and に違いない (must be, no doubt — very high certainty). かもしれない is the closest equivalent to English "might" or "may."
How do you say "must not" in Japanese?
Japanese has three main expressions for "must not": てはいけない (must not — general prohibition), てはならない (must not — stronger, more formal, often rules/laws), and てはだめ (must not — casual, can sound childish or emotional). For signs and official instructions, ～禁止 (きんし, prohibited) is also commonly used.