助動詞: 10 Modal Verbs Taiwan Pros Master (2026) | 英文助動詞用法

Ask a Taiwanese employee to email a foreign client and request a deadline extension, and you will usually get one of two things: a curt “I want more time” that lands like a demand, or a flowery apology that buries the actual request. The fix is almost always one word — a 助動詞 (modal verb). Swap “I want” for “Could I have”, and the same sentence stops sounding rude. Modal verbs are how English signals politeness, possibility, obligation, and confidence, and they are the single most overlooked piece of grammar in Taiwan’s English classrooms.

This guide covers the 10 core modal verbs (英文助動詞) Taiwan pros actually need at work and in conversation — what each one means, how to use it without sounding awkward, and the small register shifts that separate beginner English from professional English.

助動詞 (Modal Verbs): What Taiwan Learners Need to Know First

A 助動詞 is a small helper verb that sits in front of a main verb and changes its meaning — usually to add politeness, possibility, ability, permission, or obligation. The 10 modal verbs in standard English are can, could, may, might, will, would, shall, should, must, and ought to. They follow three rules that Mandarin grammar does not, which is why so many learners in Taiwan trip over them.

First, modal verbs never change form. You say “she can swim”, not “she cans swim”. Second, the verb that follows is always the bare infinitive — no à, no -ing, no -ed. So “I must to leave” is wrong, even though every Taiwanese student I have ever taught wants to write it that way. Third, modal verbs form questions by inversion (Could you help me?), not by adding do. Lock these three rules in before you worry about meaning.

The 10 Core Modal Verbs You’ll Use Every Day

You do not need to master all 10 modals at the same speed. Six of them — can, could, will, would, should, must — cover roughly 90% of the modal verbs Taiwanese professionals use at work, according to corpus data published by the British Council. The other four (may, might, shall, ought to) are useful for formal writing, polite English, and TOEIC reading, but they are not survival vocabulary.

Here is the quick map (英文助動詞對照表):

• can / could — ability, requests, possibility (能力、請求、可能性)
• may / might — possibility, formal permission (可能性、允許)
• will / would — future, polite offers, habits (未來、禮貌、習慣)
• shall / should — suggestion, advice (建議)
• must / have to — obligation, strong belief (義務、推測)
• ought to — moral or expected advice (應該)

Each pair has a small but important difference in register. Learn the pair, not the individual word, and you will pick the right one without thinking.

Can / Could — Ability and Polite Requests (能力與請求)

“Can” expresses present ability (I can speak English) or asks for something casually (Can you send me the file?). It is friendly and direct, and Taiwanese learners use it correctly most of the time. The trap is that “can” sounds slightly blunt with strangers, clients, or managers. That is where “could” earns its keep.

“Could” is “can” with one extra layer of politeness baked in. It is also the past tense of “can” when describing past ability — “I could swim before my surgery.” For workplace requests, swap every “Can you…” for “Could you…” when emailing someone above you or outside your team. The verb does the same job; the tone shifts by 20%.

Quick rule: peut = friendly. Could = professional. There is no situation in Taiwan office English where “could” sounds wrong — only situations where “can” sounds too casual.

May / Might — Possibility and Permission (可能性與允許)

“May” and “might” both express possibility, and the difference between them is smaller than most textbooks pretend. “It may rain tomorrow” and “It might rain tomorrow” mean almost the same thing in modern English. If you have to pick one, native speakers slightly prefer “might” for uncertain events and “may” for formal permission (“You may begin the exam”).

Where “may” still matters is in written professional English. Notices, contracts, hotel signs (“Guests may use the pool from 6 AM”), and academic writing still lean on it. For Taiwanese pros taking the IELTS or TOEFL, recognising “may” in reading passages will earn you points the spoken-English crowd misses.

One warning: do not ask “May I close the window?” in casual conversation. It sounds like a Victorian novel. Use “Can I” or “Could I” with friends, and save “May I” for formal situations like job interviews or speaking to elderly relatives in English.

Will / Would — Future, Polite Offers, and Habits (未來與禮貌)

“Will” expresses future actions you have just decided (“I will call him now”) and confident predictions (“It will rain tonight”). It is also the modal you use to make promises and offers (“I will help you with that”). Taiwanese learners overuse “will” to describe planned future events — for those, “going to” or the present continuous is more natural. Save “will” for the moment of decision.

“Would” is more useful than most students realise. It softens requests (“Would you mind sending the report?”), describes hypothetical situations (“I would buy a Tesla if I could afford it”), and expresses past habits (“Every summer in elementary school, my grandmother would take me to the night market”). In business emails, “Would you…” is the workhorse modal — politer than “Will you”, less formal than “May I ask you to”.

If you take one sentence away from this section, take this: “Would” is the most polite modal verb in conversational English. Use it liberally and you will sound 30% more fluent without learning a single new word.

Shall / Should — Advice and Suggestions (建議)

“Shall” is rare in American English and most international English. British speakers still use it to make offers (“Shall I open the window?”) and suggestions (“Shall we begin?”), but Americans almost always say “Should I” or “Let’s” instead. For Taiwanese learners, recognise “shall” in reading but do not stress about producing it.

“Should” is the everyday modal for advice and expectations. “You should drink more water” gives a soft recommendation. “The package should arrive on Tuesday” predicts something expected based on evidence. It is also the modal for moral or ethical statements (“Companies should pay overtime fairly”). Pair “should” with “have” + past participle and you get one of the most useful patterns in conversational English: should have — for regret or hindsight (“I should have studied harder for the TOEIC”).

Must / Have to — Obligation and Strong Necessity (義務)

“Must” expresses strong personal obligation (“I must finish this report tonight”) or strong confidence in a deduction (“She is wearing a coat — it must be cold outside”). The first use is fading in American English in favour of “have to”, but it survives in writing, signs, and formal speech.

“Have to” is “must” with the personal pressure removed and an outside force added. “I have to leave at 5 PM” means somebody or something requires it — your boss, the train schedule, your contract. In casual Taiwan office English, “have to” is more common than “must”. Save “must” for situations where you are genuinely insisting.

The trap: must not et do not have to are not the same. “You must not smoke here” means it is forbidden. “You don’t have to smoke here” means it is optional. Taiwanese learners frequently swap these two and accidentally turn rules into invitations.

Ought To — The Modal Verb Taiwanese Learners Forget (容易忽略)

“Ought to” is the modal Taiwanese cram schools rarely teach, and it shows up on the TOEIC reading section often enough to matter. It means roughly the same as “should” but carries slightly more moral weight. “We ought to call our parents more often” feels heavier than “We should call our parents more often”, even though the literal meaning is identical.

Use “ought to” in writing when you want to sound thoughtful and slightly old-fashioned. Avoid it in fast conversation — native speakers contract it to “oughta”, which sounds odd from an L2 speaker. Recognise it, produce it carefully, and you will already be ahead of most Taiwanese intermediate learners.

Modal Verb Politeness Levels — Critical for Taiwan Office English (職場禮貌等級)

The biggest reason Taiwanese pros sound rude in English is not vocabulary — it is modal verb register. English ranks requests on a politeness scale, and modal verbs are the dial. Memorise this ladder for the same identical request, from blunt to formal:

• Direct (too blunt for work): Send me the file.
• Casual: Can you send me the file?
• Polite (default for colleagues): Could you send me the file?
• Polite + formal (clients, managers): Would you mind sending me the file?
• Very formal (rare, written): Would it be possible for you to send me the file?

The truth is, most Taiwanese learners default to level 1 or 2 and wonder why foreign colleagues seem reserved with them. Levels 3 and 4 are the sweet spot for almost every office situation, including emails to your own teammates. Over-using level 5 makes you sound stiff. The right register builds trust faster than perfect grammar.

If you want a deeper look at how these patterns fit into hypothetical sentences (which is where many modal verbs live), see our companion guide on English conditionals — the 4 types Taiwan pros master. Modal verbs and conditionals are the same toolkit looked at from two angles.

5 Common Mistakes Taiwanese Learners Make with Modal Verbs (常見錯誤)

I have graded thousands of Taiwanese student essays over 20 years of teaching, and the same five modal-verb errors come up again and again. Fix these and your writing will jump a full TOEIC band.

1. “I must to leave now.” — Modal verbs never take à. The correct form is “I must leave now.”
2. “She can sings beautifully.” — The verb after a modal is always bare infinitive. “She can sing beautifully.”
3. “You don’t must come.” — Modal verbs form negatives by adding not, not do not. “You must not come” or “You don’t have to come”.
4. Confusing must not avec don’t have to. The first is a ban; the second is an option. They are opposites in practice.
5. Over-using “can” in formal emails. “Can you reply by Friday?” to a client sounds demanding. “Could you reply by Friday?” or “Would it be possible to reply by Friday?” sounds professional. Same request, different career.

Quick Reference: Modal Verb Past Forms (過去式表達)

Most modal verbs do not have a true past tense, so English fakes it using modal + have + past participle. This is the structure Taiwanese learners reach for last, but it opens up an entire register of regret, deduction, and hindsight. Master it and you sound like an advanced speaker.

• could have done — past ability not used: “I could have gone to the meeting, but I overslept.”
• should have done — past advice in hindsight: “You should have called the customer back immediately.”
• must have done — confident past deduction: “She is not answering — she must have gone home.”
• might have done — possible past event: “He might have missed the train.”
• would have done — past hypothetical: “If I had studied more, I would have passed the exam.”

If past-tense grammar is rusty in general, brush up first with our 7 present perfect rules Taiwan pros master — many modal-have-past-participle structures rely on the same logic.

How to Practice Modal Verbs (Without a Textbook)

Reading rules is the first 10% of learning a modal verb. The other 90% is using it under pressure, which is why drill books rarely produce fluent speakers. Three practice methods actually move the needle for Taiwanese learners.

First, the email rewrite drill. Find five of your old English emails and rewrite every request with a different modal. Change “Can you” to “Could you”, then to “Would you mind”. You will feel which one fits which recipient. Second, the sitcom shadowing drill. Pick a 30-second clip from Famille moderne ou Amis, pause every time a modal verb appears, and try to use it in a sentence about your own day. Third, build a personal modal-verb cheat sheet for your workplace — write down five real situations (asking for time off, declining a meeting, suggesting a coffee chat) and lock in the exact modal phrase you will use.

For a fast video drill that covers all 10 modals with native-speaker examples, this lesson is a good starting point:

FAQ — 助動詞 Quick Answers

Q: How many modal verbs are there in English?
There are 10 core modal verbs: can, could, may, might, will, would, shall, should, must, and ought to. Some grammar references also include besoin, dare, et used to as semi-modals.

Q: Is “have to” a modal verb?
Technically no — it is a phrasal verb. But it functions like the modal “must”, which is why most textbooks teach them together. In American English, “have to” is more common than “must” in everyday speech.

Q: Can I use two modal verbs together?
No. English does not allow stacking modals. “I will can do it” is wrong. Use “I will be able to do it” instead. This is one of the cleanest rules in English grammar.

Q: What is the difference between 助動詞 (auxiliary verbs) and 情態助動詞 (modal verbs)?
Auxiliary verbs include be, do, have and modal verbs. Modal verbs (情態助動詞) are a subset that adds attitude — possibility, obligation, permission. Be, do, have are called primary auxiliaries and mostly help form tenses and questions.

Q: Which modal verbs appear most on the TOEIC?
“Could”, “should”, and “would” appear most often in TOEIC reading, especially in conditional sentences and business emails. “Must” and “have to” come up in the listening section in workplace announcements.

The Single Habit That Locks Modal Verbs In

Pick one modal verb a week and use it on purpose in every English conversation, every email, every Slack message. Week one — “could”. Week two — “would”. Week three — “should”. By week ten you will have rotated through all 10 modals and they will live in your spoken English instead of your textbook. Grammar drills do not build fluency; rotation does. Start tonight by rewriting one Slack message with “could” instead of “can” and watch how the tone shifts.

For more on the broader grammar foundation, read our guide on 25 in / on / at preposition rules Taiwan pros master — prepositions and modals are the two small-word categories that separate intermediate English from advanced.

Sources

1. British Council LearnEnglish — Modal Verbs Reference — official ESL grammar reference with examples and exercises
2. Grammarly — What Are Modal Verbs? Definition and Examples — modern American English usage guide
3. Cambridge Dictionary — Modal Verbs and Modality — authoritative reference for register and modality
4. UNC Writing Center — Modals — academic writing guide for non-native English speakers