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English Grammar Guide

Basic Modal Verbs

A2 Basic Modal Verbs 🎛️

Section titled “ Basic Modal Verbs 🎛️”

English has helper verbs that don’t describe actions — they describe possibility, permission, obligation, and advice. Mandarin has them too (能, 可以, 必须, 应该), but the boundaries don’t line up. And English modals have weird rules: no -s on he/she, no to after them, and mustn’t does NOT mean the same as don’t have to.

Welcome to the control panel of English grammar.

Before this, know:
Basic Sentence Structure (SVO)Present SimpleA2 — Expansion overview

What modals actually do

Section titled “What modals actually do”

Regular verbs describe what happens: run, eat, work.

Modals describe how the speaker sees the action: possible? allowed? required? advisable?

She can swim.

Article Noun Verb Adjective Preposition

Can doesn’t mean “swim.” Swim means swim. Can means “it’s possible for her” or “she has the ability.”

Think of modals as volume knobs on a sentence:

Modal vibe Knob setting
can / could 🔓 Permission or ability — “is it possible?”
must / have to 🔒 Obligation — “you gotta”
should / ought to 💡 Advice — “you probably should”

The golden rules of modals

Section titled “The golden rules of modals”

Before anything else — these rules are non-negotiable:

Modal verb rules

Structure: Subject + modal + base verb (no to, no -s)

Correct: He can swim. · She must go.

Wrong: He can to swim · She cans swim · He must goes

Rule 1: Modal + base verb (no “to”)

Section titled “Rule 1: Modal + base verb (no “to”)”
He can to swim.
He can swim.
Modals take the base verb directly. No to. Ever.
She must to finish her homework.
She must finish her homework.
After modals: base verb only. Must finish, not must to finish.

Rule 2: No -s on third person

Section titled “Rule 2: No -s on third person”
He cans speak English.
He can speak English.
Modals never change form. No -s on he/she/it.
She musts leave now.
She must leave now.
Must stays must for all subjects.

Rule 3: Questions — flip the modal

Section titled “Rule 3: Questions — flip the modal”

Can you help me?

Article Noun Verb Adjective Preposition

Must I pay now?

Article Noun Verb Adjective Preposition

No do/does helper for most modals. Just flip: Can you…? Must I…? Should we…?

Exception: have to uses do/does: Do you have to…? Does she have to…?

Section titled “Modal overview table”
Modal Permission Ability Obligation Advice Example
can ✅ ✅ — — You can leave early. / I can cook.
could ✅ (polite) ✅ (past/general) — — Could I ask a question? / I could swim when I was five.
must — — ✅ (strong) — You must wear a seatbelt.
have to — — ✅ (external) — I have to work tomorrow.
should — — — ✅ You should see a doctor.
ought to — — — ✅ (formal) You ought to apologize.

CAN — permission and ability

Section titled “CAN — permission and ability”

Ability (技能)

Section titled “Ability (技能)”

我会游泳。(Wǒ huì yóuyǒng.) — I can swim.

I can speak three languages.

Article Noun Verb Adjective Preposition
She can speaks Chinese.
She can speak Chinese.
Modal + base verb. No -s on speak.

Permission (允许)

Section titled “Permission (允许)”

你可以走了。(Nǐ kěyǐ zǒule.) — You can leave.

Can I use your phone?

Article Noun Verb Adjective Preposition
Can I to sit here?
Can I sit here?
No to after can.

CAN’T — no ability or no permission

Section titled “CAN’T — no ability or no permission”
  • I can’t swim. (ability)
  • You can’t park here. (permission/rule)

Context tells you which meaning. Usually obvious.

COULD — polite permission and past ability

Section titled “COULD — polite permission and past ability”

Polite requests (比 can 更礼貌)

Section titled “Polite requests (比 can 更礼貌)”
Can vs. Could — politeness level
Can — direct, fine

Can I have the menu?

→ Normal, everyday request. Perfectly polite.

Can you help me?

→ Direct. Fine with friends, colleagues, strangers.

Could — extra polite

Could I have the menu?

→ Softer. Restaurant, formal situations.

Could you help me?

→ The “please” is built in. Less demanding.

Both are correct. Could is just the polite upgrade — like adding 请 (qǐng) in Mandarin.

Past ability

Section titled “Past ability”

我小时候会游泳。(Wǒ xiǎo de shíhou huì yóuyǒng.)

I could swim when I was five.

Article Noun Verb Adjective Preposition

Could = past tense of can for ability. “I could swim” = I had the ability then. (Maybe not now — you grew up and chose couch.)

COULDN’T — past inability

Section titled “COULDN’T — past inability”
  • I couldn’t sleep last night.
  • She couldn’t come to the party.

MUST vs. HAVE TO — obligation

Section titled “MUST vs. HAVE TO — obligation”

Both mean “you need to do this.” The vibe is different.

must have to
Source Speaker’s authority / internal rule External rule / circumstances
Vibe “I say so” / strong personal conviction “The rules say so” / life circumstances
Example You must be quiet. (I insist) I have to work tomorrow. (my schedule)
Questions Must I pay now? Do you have to pay now?
Past (no past form of must) I had to leave early.
I must to go now.
I must go now.
No to after must.
She musts study harder.
She must study harder.
No -s on modals.
Must you to wear a uniform?
Must you wear a uniform?
Modal + base verb in questions too.

MUSTN’T vs. DON’T HAVE TO — THE trap

Section titled “MUSTN’T vs. DON’T HAVE TO — THE trap”

This is the modal mistake that causes real-world disasters.

Form Meaning Mandarin vibe
mustn’t ❌ Forbidden — NOT allowed 不许 / 不能
don’t have to ✅ Optional — not necessary 不必
Mustn't vs. Don't have to — opposite meanings
Mustn't = FORBIDDEN 🚫

You mustn’t smoke here.

→ Smoking is not allowed. Illegal. Don’t do it.

You mustn’t tell anyone.

→ Forbidden. Keep it secret.

Don't have to = OPTIONAL ✅

You don’t have to come.

→ Coming is not required. Your choice. Stay home if you want.

You don’t have to pay now.

→ Payment is not necessary right now. You can, but you don’t need to.

You mustn't finish today. (meaning: you don't need to finish)
You don't have to finish today.
If it's optional → don't have to. Mustn't means forbidden.
You don't have to smoke here. (meaning: smoking is banned)
You mustn't smoke here.
If it's forbidden → mustn't. Don't have to means it's optional.

SHOULD / OUGHT TO — advice

Section titled “SHOULD / OUGHT TO — advice”

Both mean “it’s a good idea, but nobody’s forcing you.”

You should get more sleep.

Article Noun Verb Adjective Preposition

You ought to apologize.

Article Noun Verb Adjective Preposition

Should = everyday advice. Ought to = slightly more formal (and yes, to is part of ought to — the one modal that breaks the “no to” rule because to is glued to ought).

should ought to
Formality Everyday Slightly formal
Example You should eat vegetables. You ought to write a thank-you note.
Negative You shouldn’t do that. You ought not to do that. (rare in speech)
You should to rest.
You should rest.
No to after should. (Ought to is the exception — to is built in.)
He shoulds listen more.
He should listen more.
No -s on modals.

SHOULDN’T — advice against

Section titled “SHOULDN’T — advice against”
  • You shouldn’t eat so much sugar.
  • She shouldn’t worry about it.

Soft prohibition — not as strong as mustn’t.

Negative modals — quick reference

Section titled “Negative modals — quick reference”
Affirmative Negative Meaning
can can’t / cannot not able / not allowed
could couldn’t wasn’t able
must mustn’t forbidden
have to don’t/doesn’t have to not necessary
should shouldn’t not advisable
ought to ought not to not advisable (formal)

Modals in questions — real examples

Section titled “Modals in questions — real examples”
Question Typical answer
Can you drive? Yes, I can. / No, I can’t.
Could you help me? Of course! / Sorry, I can’t.
Must I pay now? Yes, you must. / No, you don’t have to.
Do you have to work tomorrow? Yes, I do. / No, I don’t.
Should I call her? Yes, you should. / No, you shouldn’t.
Do you can help me?
Can you help me?
Most modals don't use do/does. Flip the modal: Can you...?
Does she must leave?
Must she leave? (or Does she have to leave?)
Must questions flip the modal. Have to uses do/does.

Modals + other verbs: what NOT to do

Section titled “Modals + other verbs: what NOT to do”
I can to help you.
I can help you.
Modal + base verb. No to.
She should goes home.
She should go home.
Base verb after modal — no -es.
He must finishes today.
He must finish today.
Base form: finish, not finishes.
They can swimming.
They can swim.
No -ing after modals. Base verb only.

Modals in real conversations

Section titled “Modals in real conversations”

Asking permission

Section titled “Asking permission”

A: Could I borrow your charger? B: Sure, go ahead. A: Thanks! Can I also eat your snacks? B: You may not. (formal/no) / No, you can’t. (normal)

Giving advice

Section titled “Giving advice”

You look terrible. You should sleep more. You shouldn’t drink so much coffee. Maybe you ought to see a doctor. (formal friend)

Talking about rules

Section titled “Talking about rules”

You must show your passport at the border. You mustn’t use your phone during the exam. You don’t have to buy a ticket — it’s free.

Talking about ability

Section titled “Talking about ability”

I can cook, but I can’t bake. She could play piano when she was a kid, but she can’t anymore.

Function comparison — side by side

Section titled “Function comparison — side by side”
Situation Best modal Example
Asking permission (casual) can Can I sit here?
Asking permission (polite) could Could I sit here?
Stating ability can I can drive.
Past ability could I could run fast as a kid.
Strong obligation (speaker) must You must stop.
External obligation have to I have to catch the 8am train.
Forbidden mustn’t You mustn’t touch that.
Not necessary don’t have to You don’t have to wait.
Advice should You should try it.
Formal advice ought to You ought to be more careful.
Basic Modals — cheat sheet

Structure: Subject + modal + base verb

Never: ❌ modal + to + verb · ❌ modal + verb-s · ❌ modal + verb-ing

Permission / ability: can · could (polite) Obligation: must · have to Advice: should · ought to

Critical negatives: mustn’t = forbidden 🚫 · don’t have to = optional ✅

Try this right now

Section titled “Try this right now”

Fill in the modal — say it out loud:

  1. I ______ speak English. (ability) → can
  2. ______ I use your bathroom? (polite permission) → Could
  3. You ______ smoke here. (forbidden) → mustn’t
  4. You ______ come if you’re busy. (optional) → don’t have to
  5. You ______ drink more water. (advice) → should

Check: no to, no -s, and #3 ≠ #4. If you got those, you’re ahead of most test-takers.

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