Chinese Formal Commands: Must, Should, and Advisable (宜, 当, 须)
Grammar Rule in 30 Seconds
Use {宜|yí}, {当|dāng}, and {须|xū} to express formal obligation, propriety, or necessity in high-register Chinese writing and speech.
- {须|xū} indicates absolute necessity: {你须|nǐ xū} {遵守|zūnshǒu} {规则|guīzé}.
- {当|dāng} denotes moral duty or propriety: {人当|rén dāng} {自强|zìqiáng}.
- {宜|yí} suggests advisability or suitability: {此地|cǐdì} {宜|yí} {静|jìng} {不宜|bùyí} {闹|nào}.
Overview
Ever noticed how a simple 'should' on a sign in Shanghai feels like a gentle suggestion, while another 'must' feels like a command from the heavens? You've likely bumped into the world of literary imperatives. These single-character powerhouses—宜 (yí), 当 (dāng), and 须 (xū)—are survivors from Classical Chinese.
They are the linguistic equivalent of wearing a sharp suit to a Zoom call. While you won't use them to ask your roommate to pass the milk, you will see them everywhere in professional life. They appear in legal contracts, app 'Terms of Service,' formal notices, and even poetic social media captions.
Think of them as the 'VIP versions' of their modern two-character cousins. Using them correctly doesn't just make you sound fluent; it makes you sound authoritative. It's the difference between saying 'You should probably do this' and 'It is decreed that this be done.' If you've ever wanted to sound like a high-level executive or a character in a historical drama, this is your toolkit.
Just don't use them at a dive bar, or people might think you've time-traveled from the Ming Dynasty. We're talking about high-stakes communication here, where every character carries the weight of a thousand years of tradition. Get these right, and you’ll navigate Chinese bureaucracy and high literature like a pro.
It’s all about that 'literary' flavor that adds gravitas to your speech.
How This Grammar Works
应该 for 'should' or 必须 for 'must.' But in literary Chinese, brevity is king. These three characters—宜 (yí), 当 (dāng), and 须 (xū)—act as monosyllabic modal verbs.宜 is the 'gentle advisor'—it suggests what is fitting or appropriate.当 is the 'moral compass'—it points to what you ought to do as a matter of duty or logic. 须 is the 'enforcer'—it tells you what is absolutely required, no questions asked. When you use these, you are stripping away the 'filler' of modern speech to get straight to the point.不宜, which is the polite way of saying 'Don't even think about doing this here.' You'll find these characters embedded in four-character idioms (成语) or standing alone in formal lists. They don't change form; they don't care about tense.须, reach for your pen—it’s mandatory. If you see 宜, it’s more of a 'best practice.' Understanding these nuances is key to grasping the 'hidden' tone of formal Chinese writing.Formation Pattern
宜): 此地 (this place) + 宜 (is suitable for) + 安宁 (peace). 'This place should be peaceful.'
当): 人 (one) + 当 (ought to) + 自强 (strive for self-improvement). 'One should always strive to improve.'
须): 游客 (tourists) + 须 (must) + 持证 (hold a permit) + 入内 (enter). 'Tourists must have a permit to enter.'
不): Just slap a 不 in front. 不宜 (not suitable), 不当 (not proper), 不须 (not necessary). Note: 不须 is often used like 'no need to.'
玩 (play) or 吃 (eat). Pair them with formal, often two-character literary verbs to keep the style consistent. You wouldn't wear flip-flops with a tuxedo, right? Same logic applies here. Use 进食 instead of 吃饭 when using 宜 or 须.
When To Use It
- Legal & Business: Contracts are full of
须and当. 'The parties须fulfill the agreement.' It sounds much more 'binding' than the daily必须. - Public Notices: Signs in parks or museums.
草坪 不宜 踩踏(The grass should not be stepped on). It's a classy way to tell you to stay off the lawn. - Health & Lifestyle Advice: Traditional Chinese Medicine (TCM) or wellness blogs.
冬季 宜 温补(Winter is suitable for warming supplements). It sounds like ancient wisdom rather than just a tip from a TikToker. - Social Media & Poetry: When you want your Instagram caption to look deep.
人生 当 如 蜡烛(Life should be like a candle). It adds that 'intellectual' vibe that gets the likes. - App Interfaces: Next time you change your password, look for
须 包含 数字(Must contain numbers). It's short, efficient, and fits perfectly on a phone screen. - Workplace Communication: In a formal report to your boss or a memo to the department. It shows you have a high command of the language and respect the professional atmosphere.
Common Mistakes
- Mixing Registers: Using
须with super casual slang. '你 须 给 我 打 call' (You must support me) sounds like a confused robot. Keep the whole sentence formal. - Overusing them: If you use
宜,当, and须in every sentence of a casual chat, you'll sound like you're reading from a 500-page law book. Use them sparingly for emphasis. - Misunderstanding the 'Strength': Using
宜when you actually mean须. If a fire exit '宜' remain clear, that's a safety hazard! It '须' (must) remain clear. - The '
不须' Trap: Some learners think不须is a strong 'must not.' Actually, it often means 'no need to' or 'need not.' For 'must not' in a formal sense, we usually use禁止or严禁. - Tone Deafness: Using
当to boss around your friends. Unless you're trying to be funny/ironic, it comes off as incredibly arrogant or stiff. Imagine telling your friend 'You ought to reflect on your actions' using当. Yikes.
Contrast With Similar Patterns
宜vs应该:应该is your everyday 'should.'宜is the 'it is fitting' version.应该is a suggestion;宜is an aesthetic or situational recommendation.当vs应当: They are basically the same, but当is the literary, single-character version.应当is used in speech and standard writing;当is reserved for slogans, idioms, and high-level prose.须vs必须:必须is emphatic and common.须is cold, hard, and formal.必须is what your mom says;须is what the law says.须vs得:得is super casual and Northern-sounding. '你 得 走 了.' Never replace须with得in a formal document unless you want the CEO to think you're a street vendor.宜vs合适:合适is an adjective ('This is suitable').宜is a verb/auxiliary ('It is suitable to [do something]'). You can't say '这 个 很 宜,' but you can say '此 事 不宜 再 提' (This matter should not be mentioned again).
Quick FAQ
Are these only used in writing?
Mostly, yes. But you'll hear them in formal speeches, news broadcasts, or historical TV shows.
Which one is the most common?
宜 is very common in health and lifestyle contexts. 须 is everywhere in tech and law.
Can I use them in an HSK exam?
Absolutely. Using these correctly in the writing section is a one-way ticket to a high score. It shows you've mastered the 'literary' side of Chinese.
Does 当 always mean 'should'?
No, 当 has many meanings (like 'to be' or 'when'), but in this modal context, it's 'ought to.' Context is everything!
Is 宜 related to IKEA?
Fun fact: IKEA's Chinese name is 宜家, meaning 'suitable for the home.' Now you'll never forget it!
Can I use these with the particle 了?
Generally, no. These literary markers describe states of necessity or appropriateness, not completed actions.
Modal Verb Usage Table
| Modal | Meaning | Register | Example |
|---|---|---|---|
|
须
|
Must/Necessary
|
Formal
|
须遵守
|
|
当
|
Ought to/Duty
|
Formal
|
当自强
|
|
宜
|
Advisable/Suitable
|
Formal
|
宜静养
|
|
不须
|
Not necessary
|
Formal
|
不须多言
|
|
不当
|
Ought not
|
Formal
|
不当如此
|
|
不宜
|
Not advisable
|
Formal
|
不宜久留
|
Meanings
These are formal modal verbs used to express varying degrees of obligation, moral duty, and situational suitability, primarily found in written, legal, or literary contexts.
Absolute Necessity (须)
Indicates a strict requirement or mandatory action.
“{入|rù} {此|cǐ} {门|mén} {须|xū} {脱鞋|tuōxié}.”
“{会议|huìyì} {须|xū} {准时|zhǔnshí} {开始|kāishǐ}.”
Moral Duty (当)
Expresses what is right, proper, or expected by social/moral standards.
“{君子|jūnzǐ} {当|dāng} {言出必行|yánchūbìxíng}.”
“{吾辈|wúbèi} {当|dāng} {为|wèi} {国|guó} {效力|xiàolì}.”
Advisability (宜)
Suggests that an action is appropriate, suitable, or recommended.
“{此|cǐ} {药|yào} {宜|yí} {饭后|fànhòu} {服用|fúyòng}.”
“{今日|jīnrì} {宜|yí} {出行|chūxíng}.”
Reference Table
| Form | Structure | Example |
|---|---|---|
|
Affirmative
|
Subj + Modal + Verb
|
你须遵守
|
|
Negative
|
Subj + 不 + Modal + Verb
|
你不宜去
|
|
Interrogative
|
Modal + Subj + Verb + 吗?
|
当他去吗?
|
|
Advice
|
Subj + 宜 + Verb
|
此宜静
|
|
Requirement
|
Subj + 须 + Verb
|
须签名
|
|
Duty
|
Subj + 当 + Verb
|
人当自立
|
Formality Spectrum
君须往。 (Command)
你必须去。 (Command)
你得去。 (Command)
快去！ (Command)
Modal Hierarchy
Necessity
- 须 Must
Duty
- 当 Ought to
Advice
- 宜 Suitable
Examples by Level
{须|xū} {走|zǒu}.
Must walk.
{宜|yí} {吃|chī}.
Should eat.
{当|dāng} {做|zuò}.
Ought to do.
{不宜|bùyí} {去|qù}.
Not suitable to go.
{你|nǐ} {须|xū} {学习|xuéxí}.
You must study.
{这|zhè} {宜|yí} {早|zǎo} {睡|shuì}.
It is best to sleep early.
{人|rén} {当|dāng} {诚实|chéngshí}.
People ought to be honest.
{不须|bùxū} {担心|dānxīn}.
No need to worry.
{会议|huìyì} {须|xū} {准时|zhǔnshí}.
The meeting must be on time.
{此|cǐ} {法|fǎ} {不宜|bùyí} {推广|tuīguǎng}.
This method is not suitable for promotion.
{吾辈|wúbèi} {当|dāng} {努力|nǔlì}.
We ought to work hard.
{须|xū} {注意|zhùyì} {安全|ānquán}.
Must pay attention to safety.
{凡|fán} {会员|huìyuán} {须|xū} {遵守|zūnshǒu} {章程|zhāngchéng}.
All members must follow the bylaws.
{此|cǐ} {地|dì} {宜|yí} {静|jìng} {不宜|bùyí} {闹|nào}.
This place is suitable for quiet, not for noise.
{君子|jūnzǐ} {当|dāng} {有所为|yǒusuǒwéi} {有所不为|yǒusuǒbùwéi}.
A gentleman ought to know what to do and what not to do.
{须|xū} {知|zhī} {其|qí} {难|nán}.
Must know its difficulty.
{此|cǐ} {项|xiàng} {决策|juécè} {宜|yí} {慎重|shènzhòng}.
This decision should be made cautiously.
{当|dāng} {以|yǐ} {民|mín} {为|wéi} {本|běn}.
Ought to take the people as the foundation.
{须|xū} {经|jīng} {审批|shěnpī} {方可|fāngkě} {执行|zhíxíng}.
Must be approved before execution.
{不当|bùdāng} {如此|rúcǐ} {行事|xíngshì}.
Ought not to act this way.
{凡|fán} {有|yǒu} {志|zhì} {者|zhě} {当|dāng} {自强|zìqiáng}.
Those who have ambition ought to strive for self-improvement.
{此|cǐ} {药|yào} {宜|yí} {空腹|kōngfù} {服用|fúyòng}.
This medicine is best taken on an empty stomach.
{须|xū} {知|zhī} {天外有天|tiānwàiyǒutiān}.
Must know that there is always someone better.
{不宜|bùyí} {操之过急|cāozhīguòjí}.
It is not advisable to be overly hasty.
Easily Confused
Learners think they are interchangeable.
Both mean 'should'.
Both suggest options.
Common Mistakes
Wǒ xū chīfàn
Wǒ yào chīfàn
Tā bù yào xū qù
Tā bù xū qù
Yīnggāi xū zuò
Xū zuò
Xū le zuò
Xū zuò
Sentence Patterns
凡___者，须___。
此地宜___，不宜___。
人当___，不当___。
___须___。
Real World Usage
乙方须按时付款。
此药宜饭后服。
吾辈当为民请命。
员工须佩戴工牌。
今日宜出行。
研究者当保持客观。
Context is Key
Don't Over-conjugate
Conciseness
Literary Flair
Smart Tips
Replace 'yào' with '须' to sound more professional.
Use '宜' instead of 'yīnggāi' for a more refined tone.
Use '当' to emphasize moral duty.
Use '须' for mandatory items.
Pronunciation
Tones
Ensure the fourth tone of 须 and the first tone of 宜 are clear.
Formal Declarative
Subject + Modal + Verb ↓
Conveys authority and finality.
Memorize It
Mnemonic
Remember 'X-D-Y': X (须) is a cross (must), D (当) is duty, Y (宜) is 'yes' (advisable).
Visual Association
Imagine a judge (须) with a gavel, a soldier (当) standing guard, and a doctor (宜) holding a prescription.
Rhyme
须是必须不可违，当是应当守道义，宜是适宜好建议。
Story
In a formal court, the judge (须) says 'You must follow the law.' The citizen (当) says 'I ought to do my duty.' The advisor (宜) whispers 'It is advisable to stay calm.'
Word Web
Challenge
Write three sentences using 须, 当, and 宜 regarding your daily routine.
Cultural Notes
Used heavily in official government notices.
Common in herbal prescriptions.
Used in poetry and essays.
These characters derive from Classical Chinese where they functioned as auxiliary verbs.
Conversation Starters
你认为学生当做什么？
这药宜怎么吃？
我们须遵守什么规则？
什么情况下不宜出门？
Journal Prompts
Common Mistakes
Test Yourself
公民___遵守法律。
Which is most formal?
Find and fix the mistake:
他须了去。
Arrange the words in the correct order:
All words placed
Click words above to build the sentence
It is advisable to sleep early.
Answer starts with: 宜早睡...
Match each item on the left with its pair on the right:
Can you use 'le' with 须?
A: 怎么处理这事? B: ___.
Score: /8
Practice Exercises
8 exercises公民___遵守法律。
Which is most formal?
Find and fix the mistake:
他须了去。
宜 / 此 / 药 / 服 / 饭后
It is advisable to sleep early.
Match: 须, 当, 宜
Can you use 'le' with 须?
A: 怎么处理这事? B: ___.
Score: /8
Practice Bank
10 exercises须 | 参会人员 | 提前 | 签到
One should be honest.
Match the pairs:
感冒初期，___ 饮用姜茶。
Which sentence is correct?
防火通道不宜堆放杂物。
不宜 | 晚间 | 咖啡 | 饮用
You must strictly keep the secret.
职员办事，___ 秉公处理。
Pick the most literary sounding sentence:
Score: /10
FAQ (8)
Generally no. They will make you sound overly formal or like you are reading a legal document.
须 is more concise and formal; 必须 is the standard modern compound.
They are modal verbs, not main verbs. They express mood, not aspect.
Yes, 'bù' is the standard negation for these modals.
Yes, they are used in formal writing across all Chinese-speaking regions.
No, they are different characters/meanings. '当' as a modal means 'ought to'.
宜 is most common for medical/lifestyle advice.
Yes, but these are the most common for C2 learners.
Scaffolded Practice
1
2
3
4
Mastery Progress
Needs Practice
Improving
Strong
Mastered
In Other Languages
deber
Chinese modals are more register-specific.
devoir
Chinese modals don't conjugate.
müssen/sollen
German modals conjugate for person.
beki/hitsuyou
Japanese uses particles.
yajib
Arabic has complex gender/number agreement.
yào/gāi
Register is the main difference.
Learning Path
Prerequisites
Learn These First
Chinese Modal Verbs: How to say 'Should' (应该 yīnggāi)
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Formal Chinese Modals: Duties and Commands (应当, 理应, 务必)
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