助動詞用法完整攻略：10 個必學英文助動詞 | Auxiliary & Modal Verbs

Here is a number that surprises most of my students in Taipei: the single most common verb in written English is not “have” or “go” — it is “be”, and roughly one in four times you see it, it is working as a helper, not a main verb. That helper role is exactly what 助動詞 do. They are the small, unglamorous words that decide whether a sentence is a question, a denial, a fact, or a polite request — and Taiwanese learners lose more points on them than on any flashy vocabulary word.

The rules are short. The practice is what makes them automatic.

什麼是助動詞？(What Are Auxiliary Verbs?)

助動詞 are verbs that “assist” a main verb. On their own they carry very little meaning; their job is to add grammatical information — tense, negation, questions, voice, or attitude. In the sentence “She できる swim,” the real action is “swim”. “Can” is the auxiliary verb, and it tells you she has the ability. Strip the helper away and “She swim” is broken. That is the whole point: the auxiliary is what makes the grammar legal.

English has a fixed, small set of them, and that is good news. Unlike vocabulary, which is effectively infinite, the list of 助動詞 fits on an index card. There are three primary auxiliaries and nine common modal auxiliaries. Learn those twelve words and how they behave, and you have covered the machinery behind nearly every question, negative, and shade of politeness in the language.

One rule ties them all together and it is worth memorising before anything else: an auxiliary verb is always followed by another verb (or clearly implies one). “Do you like coffee?” — “do” helps “like”. “I must leave.” — “must” helps “leave”. If there is no second verb hiding somewhere, the word is probably not acting as an auxiliary at all.

助動詞的兩大分類 (The Two Types of Auxiliary Verbs)

Every 助動詞 falls into one of two families, and confusing the two is the root of most mistakes I see. Primary auxiliaries build the plumbing of a sentence — they form tenses, questions, and negatives. Modal auxiliaries add human judgement — ability, permission, obligation, probability. Here is the split at a glance:

The practical difference: primary auxiliaries change their form (I am, she は, they were; I do, he does). Modal auxiliaries never do — “he can”, not “he cans”. That one habit, adding an “s” to a modal, is the single most common error in Taiwanese student writing, and we will come back to it.

Most Taiwan classrooms teach modal verbs as a vocabulary list. They work better as a system.

be、do、have：三個主要助動詞 (The Three Primary Auxiliaries)

The tricky thing about be, do, and have is that each one lives a double life. Each can be a full main verb そして an auxiliary, and Taiwanese learners often can’t tell which hat it is wearing. The test is simple: if there is a second verb after it, it is an auxiliary.

Be as an auxiliary builds continuous tenses and the passive voice. “She は studying” (continuous). “The report was written by the intern” (passive — 被動語態). Compare that with “She は a teacher”, where “is” is the main verb and there is no second verb to help. Same word, two completely different jobs.

Do is the question-and-negative machine of the present and past simple. English can’t ask “You like it?” in standard writing — it needs “Do you like it?” and “I しないで like it.” This “dummy do” has no meaning of its own; it exists purely so the sentence has an auxiliary to carry the question. Chinese has no equivalent, which is exactly why “You have breakfast already?” slips out so often.

Have as an auxiliary builds the perfect tenses: “I have finished,” “She had left before noon.” Again, contrast the main-verb use in “I have a car,” where nothing follows to be helped. Get comfortable spotting the second verb and be/do/have stop being confusing overnight.

情態助動詞完整列表 (The Complete Modal Verb List)

Now the interesting family. 情態助動詞 don’t change sentence structure — they change meaning and tone. The same event can sound like a certainty, a guess, an order, or a gentle suggestion depending only on which modal you choose. This table is the one I tell students to copy into their notebook:

Two rules govern all of them. First, a modal is always followed by the base form of the verb — no “to”, no “-ing”, no “-s”. It is “She must 行く“, never “She must to go” or “She must goes”. Second, modals have no infinitive and no past participle of their own; when you need a past or future meaning, English swaps in a substitute like “was able to” or “had to”. “Yesterday I できた not sleep” works for ability, but for a single completed action you say “I was able to finish the report.”

Write out your own example sentences — recognition is not the same as production.

Notice the pairs — can/could, will/would, shall/should, may/might. The second word in each pair is not simply the past tense. More often it is the politer, softer, or more tentative version. “Can you help?” is fine among friends; “Could you help?” is what you write to your boss. That politeness shift is worth more in a Taiwan workplace than any single vocabulary word, because it signals respect without changing what you are actually asking.

Ten minutes of focused review beats an hour of passive reading.

台灣學生最常犯的 5 個助動詞錯誤 (5 Common Auxiliary Verb Mistakes)

After two decades of marking English homework in Taipei, the same five errors come up again and again. None of them are about intelligence — they are about the gap between Chinese and English structure. Fix these five and your writing jumps a level.

1. Adding “-s” to a modal. “He cans swim” and “She musts leave” are the classic slips. Modals never take a third-person “-s”. The main verb doesn’t either: “He can swim”, full stop.

2. Adding “to” after a modal. Chinese logic pushes learners toward “I must to study” and “We should to practice”. Every modal except “ought to” is followed by the bare base verb — drop the “to”.

3. Doubling up auxiliaries. “Do you can help me?” stacks two auxiliaries where English allows only one per clause. The modal already forms the question, so it becomes “Can you help me?” No “do” needed.

4. Forgetting “do” in questions and negatives. The mirror-image mistake: “You like coffee?” and “I not like it.” Present and past simple need the “do” auxiliary — “Do you like coffee?” and “I don’t like it.”

5. Confusing “must not” with “don’t have to”. These feel similar but mean opposite things. “You must not park here” is a prohibition (禁止). “You don’t have to park here” means it is optional (不需要). Mixing them up in an email can turn a friendly note into an order.

You already use 助動詞 every time you ask a question in English.

如何快速掌握助動詞 (How to Master Auxiliary Verbs Faster)

Reading a rules table does almost nothing on its own — I have watched students ace a grammar quiz on Monday and produce “He must to goes” on Friday. Recognition and production are different skills, and only one of them wins you IELTS points or gets you understood at work. Three habits close that gap.

Write five original sentences a day, each using a different modal, about your actual life: “I should call my landlord,” “My manager might approve the budget.” Personal sentences stick because your brain has a reason to keep them. Second, read your English out loud — 助動詞 are usually unstressed and swallowed in fast speech (“I’ve finished” not “I have finished”), so hearing them trains your ear for how natives actually string them together. Third, when you catch a mistake, don’t just fix it — say the correct version three times. Repetition is what moves a rule from your notebook into your mouth.

The video below breaks down the be-verb and auxiliary distinction with Taiwan-focused examples, which is a useful second angle if the be/do/have double life still feels slippery.

Writing forces you to choose the right modal — speaking lets you hide.

常見問題 (Frequently Asked Questions)

助動詞和情態動詞一樣嗎？(Are auxiliary verbs and modal verbs the same?) Not quite. 情態動詞 (modal verbs) are a subset of 助動詞 (auxiliary verbs). All modals are auxiliaries, but be, do, and have are auxiliaries that are not modals. Think of “auxiliary verb” as the whole family and “modal verb” as one branch of it.

Can a sentence have two auxiliaries? Yes — in longer tenses. “She has been studying” uses “has” (perfect) and “been” (continuous) together. What you cannot do is stack two modals: “will can” is wrong; English says “will be able to” instead.

Is “ought to” a modal? Yes, and it is the one exception that keeps its “to”. “You ought to rest” means roughly the same as “You should rest,” just a little more formal. Most Taiwan learners can safely default to “should” and save “ought to” for writing.

Grammar references disagree on edge cases. Pick one and move on.

Auxiliary verbs are not the exciting part of English, and that is precisely why they are worth your time — everyone drills vocabulary, so the learners who quietly get their 助動詞 right are the ones who sound fluent. Your next step is narrow and doable: pick one modal you tend to misuse, write ten sentences with it this week, and read them aloud. For more grammar problem-solving built for Taiwan learners, see our guide to confusing English verbs, the difference between make and do, and how to finally sort out “used to” versus “be used to”.

Sources（參考資料）

1. Cambridge Dictionary — Modal verbs and modality — Reference for modal verb usage and meaning.
2. Britannica Dictionary — Auxiliary verbs and main verbs — Explanation of primary auxiliaries be, do, and have.
3. Wikipedia — English modal auxiliary verbs — Complete list of English modal auxiliaries and their grammatical rules.