Modals

Level B2–C2 · ability, obligation, advice & deduction

◎What you'll master

Use can / could for ability, possibility and polite requests.
Separate must / have to (obligation) from mustn't (prohibition) and don't have to (no obligation).
Give advice with should / ought to and talk about chance with may / might / could.
Draw logical conclusions with must (sure it's true) and can't (sure it's false).
Keep the form right: modal + base verb, no -s, and no do in questions or negatives.

1The form: modal + base verb (and nothing extra)

A modal is a helping verb — can, could, may, might, must, should, will, would — that adds meaning like ability, obligation or possibility. Every modal follows the same three rules, and TOEFL loves testing them.

Rule	Right	Wrong
modal + base verb (no to)	She can swim.	She can to swim.
no third-person -s	He can drive.	He cans drive.
questions & negatives take no do	Can she come? · He can't swim.	Does she can come?

⚠ Watch out — never stack two modals: not She will can help. → She will be able to help.

2can / could — ability, possibility, requests

Ability

Can is the present; could is the past (or a softer, more distant present).

I can speak Spanish. · When I was five I could already read.

Possibility

Use can for general possibility and could for a specific one.

Winters here can be harsh. · That noise could be the wind.

Requests & permission

Could and can both ask; could sounds more polite.

Could you pass the salt? · Can I borrow your pen?

Ability in the future or perfect

Because you can't stack modals, borrow be able to: I'll be able to join later · She hasn't been able to sleep.

3must / have to — and the trap: mustn't vs don't have to

Both must and have to express obligation. The negatives, however, mean opposite things — this is one of the most-tested points on the exam.

Form	Meaning	Example
must / have to	obligation (you need to)	You must wear a seatbelt.
mustn't	prohibition (you are not allowed to)	You mustn't park here.
don't have to	no obligation (it's optional)	You don't have to come — it's up to you.

⚠ Watch out — You mustn't pay — the entry is free. means it's forbidden to pay. To say it's optional, use You don't have to pay.

Internal vs external

Must often feels like the speaker's own rule (I must call her back), while have topoints to an outside rule (I have to renew my visa). In the past, both become had to.

4should / ought to — advice and expectation

Should (and its close twin ought to) give advice or say what you expect to be true. They're softer than must — a recommendation, not a command.

You should see a doctor. · You ought to apologise. · The bus should arrive soon.

The negative is shouldn't; ought not to exists but is formal and rare.

You shouldn't skip breakfast before a long exam.

⚠ Watch out — ought is the one modal that keeps to: You ought to rest. not You ought rest.

5may / might / could — possibility

When something is possible but not certain, use may, might or could. They're largely interchangeable for present or future chance; might can feel slightly less likely.

It may rain later. · She might be at home. · They could arrive tonight.

May also asks for and grants formal permission.

May I leave early today? · You may begin the test now.

⚠ Watch out — the negative of possibility is may not / might not (perhaps not) — don't confuse it with can't, which means "impossible": She might not come ≠ She can't come.

6must / can't — logical deduction

When you're reasoning from evidence, must means "I'm sure it's true" and can't means "I'm sure it's false." Here can't — not mustn't — is the opposite of deductive must.

Certainty	Modal	Example
sure it's true	must	The lights are on — someone must be home.
sure it's false	can't	He just ate — he can't be hungry.
possible	might / may / could	She's quiet; she might be tired.

That can't be right — the total doesn't add up. · You've been travelling all day; you must be exhausted.

⚠ Watch out — for deduction use can't, not mustn't: That can't be true (impossible), whereas mustn't would wrongly mean "is not allowed to be true."

Practice — 15 questions with instant feedback

0 / 15 correct

Question 1

She ______ swim when she was four.

Question 2

He ______ speak three languages fluently.

Question 3

______ you pass me the salt, please?

Question 4

You (not / park) here — it's a fire lane.

Question 5

It's optional — you ______ stay for the whole talk.

Question 6

You look pale — you ______ see a doctor.

Question 7

You (ought / apologise) to her before it's too late.

Question 8

The sky is grey; it ______ rain later.

Question 9

The lights are on and the car's here — someone ______ be home.

Question 10

He finished a huge lunch an hour ago; he ______ be hungry.

Question 11

When the lift is broken, residents (have to / use) the stairs instead.

Question 12

I'm not free now, but I ______ join you later once the meeting ends.

Question 13

These figures ______ be right — the columns simply don't add up.

Question 14

She's been travelling since dawn, so she (must / be) completely exhausted by now.

Question 15

Visitors ______ take photos inside the gallery, but they

✎Fix the Error

Each sentence has one mistake in the underlined word. Type the correction and check.

1.She can to drive a manual car.

2.He musts finish the essay tonight.

3.You mustn't bring a laptop — pens are provided, but a laptop is fine too.

4.You ought rest before the exam.

5.The account is empty, so that charge mustn't be correct.