The five-modal core

The Foundation-tier inventory: 会, 想, 要, 应该, 可以.

All modals sit BEFORE the main verb. Negate with 不 (except 必须, see below).

会 vs 能 vs 可以: three flavours of 'can'

This is the trickiest distinction in the modal system.

会 (huì): learned ability

Use 会 for skills you've acquired through learning.

• 我会说中文。 (Wǒ huì shuō zhōng wén.) - I can speak Chinese.
• 她会开车。 (Tā huì kāi chē.) - She can drive.
• 你会游泳吗？ (Nǐ huì yóu yǒng ma?) - Can you swim?

Negation: 不会 (can't / don't know how to). 我不会跳舞 (I can't dance).

会 (huì) job 2: likelihood / will

The same 会 also marks 'will' / 'is likely to'.

• 明天会下雨。 (Míng tiān huì xià yǔ.) - It'll rain tomorrow.
• 他会来吗？ (Tā huì lái ma?) - Will he come?
• 这件事不会发生。 (Zhè jiàn shì bú huì fā shēng.) - This won't happen.

Context disambiguates. 我会说中文 is ability (learned skill); 明天会下雨 is likelihood (a forecast).

能 (néng): possibility + permission

能 covers can-because-circumstances-allow-it. Physical possibility, available time, opportunity.

• 我今天不能去。 (Wǒ jīn tiān bù néng qù.) - I can't go today (circumstances).
• 你能等一下吗？ (Nǐ néng děng yí xià ma?) - Can you wait a moment?
• 这里能停车吗？ (Zhè li néng tíng chē ma?) - Can one park here?

能 also covers regained or specific ability: 他病了, 不能工作 (he's ill, can't work).

可以 (kě yǐ): permission + circumstantial 'can'

可以 leans on the 'permission' meaning of 'can'.

• 我可以走了吗？ (Wǒ kě yǐ zǒu le ma?) - May I go now?
• 你可以用我的电话。 (Nǐ kě yǐ yòng wǒ de diàn huà.) - You can use my phone.
• 这里可以吸烟吗？ (Zhè li kě yǐ xī yān ma?) - Can one smoke here?

能 and 可以 overlap considerably. Native speakers often use them interchangeably. The textbook split:

• 会 - learned ability (skills) + future likelihood
• 能 - circumstantial possibility (am I able?)
• 可以 - permission (am I allowed?)

In practice, if you're not sure, 可以 is the safe default for 'can' in everyday speech.

想 vs 要: two flavours of 'want'

想 (xiǎng): want to / would like to

The softer 'want'. Hypothetical, desired, polite.

• 我想去中国。 (Wǒ xiǎng qù zhōng guó.) - I'd like to go to China.
• 你想吃什么？ (Nǐ xiǎng chī shén me?) - What would you like to eat?
• 我想睡觉。 (Wǒ xiǎng shuì jiào.) - I want to sleep.

要 (yào): want / will / be going to

The firmer 'want'. Concrete intent, decided plan.

• 我要去中国。 (Wǒ yào qù zhōng guó.) - I'm going to China.
• 我要一杯咖啡。 (Wǒ yào yì bēi kā fēi.) - I'll have a coffee.
• 他要回家了。 (Tā yào huí jiā le.) - He's about to go home.

Restaurant rule of thumb: 想 if you're still deciding, 要 when you're ordering. 你想吃什么? is 'what do you fancy?'; 我要一碗面 is 'I'll have a bowl of noodles'.

要 also covers 'must' / 'need to' in some contexts: 你要小心 (you must be careful). Sentence-final 要…了 marks imminent action: 要下雨了 (it's about to rain).

应该 (yīng gāi): should

Moral or expected 'should'.

• 你应该睡觉。 (Nǐ yīng gāi shuì jiào.) - You should sleep.
• 我应该走了。 (Wǒ yīng gāi zǒu le.) - I should be going.
• 学生应该努力。 (Xué sheng yīng gāi nǔ lì.) - Students should work hard.

Negate with 不应该: 你不应该这样做 (you shouldn't do that).

必须 / 得: must

A bit stronger than 应该. 必须 (bì xū, must) is formal-ish; 得 (děi, gotta) is colloquial.

• 我必须走了。 (Wǒ bì xū zǒu le.) - I must leave.
• 你必须学习。 (Nǐ bì xū xué xí.) - You must study.
• 我得回家。 (Wǒ děi huí jiā.) - I've got to go home.

The trap: do NOT negate 必须 with 不必须. The negative of 必须 is 不用 (bú yòng, don't need to) or 不必 (bú bì, needn't).

• 你不用来。 (Nǐ bú yòng lái.) - You don't need to come.
• 不必那么客气。 (Bú bì nà me kè qi.) - You don't need to be so polite.

不必须 is ungrammatical. The negative of 'must' in Mandarin isn't 'must not' - it's 'don't need to'. (For 'must not', you use 不能 or 别: 你不能这样做, 别这样做 - 'don't do that'.)

Future intent: 打算 and 准备

For 'planning to do' / 'be about to do', two non-modal verbs pull their weight.

打算 (dǎ suàn): plan to

• 我打算明天去北京。 (Wǒ dǎ suàn míng tiān qù běi jīng.) - I plan to go to Beijing tomorrow.
• 你打算做什么？ (Nǐ dǎ suàn zuò shén me?) - What are you planning to do?
• 他打算下个月结婚。 (Tā dǎ suàn xià ge yuè jié hūn.) - He plans to get married next month.

准备 (zhǔn bèi): preparing to / about to

• 我准备走了。 (Wǒ zhǔn bèi zǒu le.) - I'm getting ready to go.
• 他准备去英国学习。 (Tā zhǔn bèi qù yīng guó xué xí.) - He's preparing to study in the UK.
• 我们准备吃饭。 (Wǒ men zhǔn bèi chī fàn.) - We're about to eat.

准备 is slightly more proximate than 打算. 打算 = plan (could be next year). 准备 = preparing, about to (usually soon).

打算 is Foundation tier; 准备 is technically Higher tier in the AQA inventory but turns up often enough at this level that it's worth knowing.

The full position rule

All modals sit BEFORE the main verb, AFTER the subject, after any time word.

Subject + (time) + modal + main verb + (object).

• 我明天会去。 - I'll go tomorrow.
• 我明天想吃面条。 - I want to eat noodles tomorrow.
• 他应该回家。 - He should go home.

Stack two modals? Rare but possible: 我应该会去 (I probably should go / I should be able to go). Stick to one modal at a time until the patterns are reflex.

What to internalise

1. 会 = learned ability + likelihood. Two jobs.
2. 能 = circumstantial possibility. 可以 = permission. Often interchangeable in practice.
3. 想 = softer 'want'. 要 = firmer 'want' / intent.
4. 应该 = should. 必须 / 得 = must.
5. 不必须 IS WRONG. Negate 必须 with 不用 or 不必.
6. 打算 = plan to (future). 准备 = preparing to (more proximate).

For the wider grammar context, see the Mandarin grammar cheatsheet.