Must and Should in Chinese: 應該, 必須, 得, 需要

Chinese spreads “must” across a scale of words. 應該 (yīnggāi) is “should”, advice or what is expected. 要 (yào), 該 (gāi) and 得 (děi) are the plain spoken “have to”. 需要 (xūyào) is “need”. 必須 (bìxū) is a firmer, slightly formal “must”. 一定要 (yídìng yào) is “absolutely must”, with the speaker pressing the point. And “don’t have to” is 不用 or 不必, never 不必須.

This guide places each word on the scale, shows what it sounds like in Taiwan, and covers how to negate them. For ability and permission, see 會, 能 and 可以. For wanting and intending, see 想 vs 要.

The obligation scale

Word	Strength	Register	Example
可以	Allowed	Neutral	你可以先走。 You may go first.
最好	Best to	Neutral	你最好先問。 You’d better ask first.
應該	Should	Neutral	你應該多休息。 You should rest more.
需要	Need	Neutral	我需要先問老闆。 I need to ask my boss first.
要 / 該 / 得	Have to	Spoken	我該走了。 I have to go now.
必須	Must	Firm, a little formal	申請人必須年滿十八歲。 Applicants must be 18.
一定要	Absolutely must	Emphatic	你一定要試試。 You really must try it.

應該: should

應該 (yīnggāi) gives advice, or says what is expected or right. The MOE dictionary reads it yīng gāi.

• 你應該多休息。 (Nǐ yīnggāi duō xiūxí.) You should rest more.
• 學生應該準時上課。 (Xuéshēng yīnggāi zhǔnshí shàngkè.) Students should come to class on time.
• 你不應該這樣說話。 (Nǐ bù yīnggāi zhèyàng shuōhuà.) You shouldn’t talk like that.

應該 has a second job. It marks a likely inference about something not yet confirmed.

• 他應該到了。 (Tā yīnggāi dào le.) He should have arrived by now.
• 這家店應該很好吃。 (Zhè jiā diàn yīnggāi hěn hǎo chī.) This place should be good.

要, 該 and 得: the spoken “have to”

In everyday Taiwan speech, 要 and 該 are the common choices for “I have to”, and 得 (děi) is heard too, though it is more characteristic of northern Mandarin.

• 我該走了。 (Wǒ gāi zǒu le.) It’s time I went; I have to go now.

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• 我該睡了。 (Wǒ gāi shuì le.) I should get to bed.

• 我得走了。 (Wǒ děi zǒu le.) I have to go now.

• 明天要早起。 (Míngtiān yào zǎo qǐ.) I have to get up early tomorrow.

• 你得先填表格。 (Nǐ děi xiān tián biǎogé.) You have to fill in the form first.

得 here is read děi (MOE: ㄉㄟˇ). The character 得 has two other readings that matter. 得 as the complement marker is neutral de (跑得很快) and 得 meaning “to get” is dé (得到). This is one of the three characters covered in how to use 的, 地 and 得.

該 (gāi) is the MOE’s 應當, “ought to”. With 了 at the end it says it is now time to do something, which makes it the most natural way to announce you must leave. Plain 應該 is the more deliberate “should”.

得 does not take an ordinary negative. To say “don’t have to”, switch to 不用 (see below). To say “must not”, use 不能 or 不可以.

需要: need

需要 (xūyào) is both a verb and a noun. It fits objects and also takes a verb.

• 你需要一張申請表。 (Nǐ xūyào yì zhāng shēnqǐng biǎo.) You need an application form.
• 我需要先問老闆。 (Wǒ xūyào xiān wèn lǎobǎn.) I need to ask my boss first.
• 這份工作需要耐心。 (Zhè fèn gōngzuò xūyào nàixīn.) This job requires patience.

The negative is 不需要 (bù xūyào), which is neutral and clear: 你不需要帶傘 (Nǐ bù xūyào dài sǎn), “you don’t need to bring an umbrella”.

必須: formal must

必須 (bìxū) states a requirement. It is at home in rules, forms, notices and written instructions, and in serious statements such as 我必須說… (Wǒ bìxū shuō…, I have to say…) or 你必須先預約 (Nǐ bìxū xiān yùyuē, you have to book first). It sounds firm in casual chat about small things.

• 申請人必須年滿十八歲。 (Shēnqǐngrén bìxū nián mǎn shíbā suì.) Applicants must be at least 18.
• 乘客必須繫好安全帶。 (Chéngkè bìxū jì hǎo ānquándài.) Passengers must fasten their seat belts.
• 我們必須在六點以前到。 (Wǒmen bìxū zài liù diǎn yǐqián dào.) We have to arrive before six.

The MOE reading is bì xū. A friend asking you to come early more likely says 你要早點到 or 你得早點到.

一定要: absolutely must

一定要 (yídìng yào) carries insistence. It can be an order, a firm promise or an enthusiastic recommendation.

• 你一定要試試這家的牛肉麵。 (Nǐ yídìng yào shìshi zhè jiā de niúròu miàn.) You really have to try this place’s beef noodle soup.
• 我一定要把這件事做完。 (Wǒ yídìng yào bǎ zhè jiàn shì zuò wán.) I am determined to finish this.
• 明天一定要交。 (Míngtiān yídìng yào jiāo.) It must be handed in tomorrow, no exceptions.

一定 alone also means “certainly”: 他一定在家 (Tā yídìng zài jiā), “he must be at home”. That is an inference, close to 應該 but stronger. The MOE dictionary lists 一定 as yī dìng.

Negating: the traps

This is where most errors happen. The obligation words do not negate the way they appear to.

You want to say	Say	Example
Shouldn’t	不應該	你不應該遲到。 You shouldn’t be late.
Don’t have to	不用, 不必, 不需要	你不用來。 You don’t have to come.
Must not	不能, 不可以, 不准	這裡不能停車。 You can’t park here.

• 你不用來。 (Nǐ bú yòng lái.) You don’t have to come.
• 您不必擔心。 (Nín bú bì dānxīn.) You needn’t worry.
• 這裡不可以抽菸。 (Zhèlǐ bù kěyǐ chōuyān.) Smoking is not allowed here.
• ✗ 你不必須來。 Ungrammatical. 必須 is not negated with 不.
• 我不用去。 (Wǒ bú yòng qù.) I don’t have to go. Use 不用 here, because 得 has no ordinary negative.

不用 (bú yòng) is the common spoken form. 不必 (bú bì) is slightly more formal and often seen in writing. Both mean “no need”. Neither forbids anything.

To forbid, use 不能 or 不可以. You may also see 不得 (bù dé, MOE: 不能、不可以) in written prohibitions such as signs and regulations. 不得不 (bù dé bù, MOE: 必須，必要如此) means “have no choice but to”: 我不得不走 (Wǒ bù dé bù zǒu), “I have no choice but to leave”. 不准 (bù zhǔn) is stricter and sounds like a rule imposed by someone with authority.

Choosing in real conversation

• Advising a friend: 應該 or 最好.
• Saying what you have to do tonight: 得 or 要.
• Reading a form or rule: 必須.
• Stressing a recommendation: 一定要.
• Saying you needn’t: 不用.

A practical approach for adult learners is to take 要 and 該 for talking about your own obligations, 應該 for advice, and 必須 when you want to sound firm or are reading a rule. Listen for which of 該, 要 and 得 the people around you use.

Practice

Fill in the best word: 應該, 必須, 得, 不用, 不能.

1. 對不起，我___先走了。 (Sorry, I have to leave.)
2. 這個問題很簡單，你___擔心。 (This is easy, you don’t have to worry.)
3. 在教室裡___吃東西。 (You can’t eat in the classroom.)
4. 本校規定，學生___準時交作業。 (School rules: students must hand in homework on time.)

Answers: 1. 得 (要 or 該 also work) 2. 不用 3. 不能 4. 必須 (應該 is softer)

Related reading

• 會, 能 and 可以: ability and permission.
• 想 vs 要 vs 想要: wanting, intending and 要 as the future.
• How to Use 的, 地 and 得 in Chinese: the other 得.