Grammar · Verb patterns & moods · B1 · Intermediate

Modal verbs

Last updated 21 July 2026

In short

Modal verbs — can, could, may, might, will, would, shall, should and must — are auxiliaries that add meaning such as ability, permission, advice, obligation or possibility to a main verb. They never change form, take a bare infinitive without 'to', and build questions and negatives without 'do'.

How modal verbs behave

Form	Structure	Example
Positive	subject + modal + base verb	You should book the ferry tickets early.
Negative	subject + modal + not + base verb	You mustn't feed the monkeys at the temple.
Question	Modal + subject + base verb?	Could you turn the music down a little?
Short answer	Yes, subject + modal. / No, subject + modal + not.	“Can I borrow your charger?” “Yes, of course you can.”
Missing forms	be able to / have to replace absent tenses	We'll have to reschedule the workshop.

How do modal verbs behave grammatically?

Modals break most normal verb rules, which is what makes them easy to misuse. They never take -s in the third person, they are followed by a bare infinitive without 'to' (the one exception is ought to), and they form questions by inversion and negatives with 'not' — never with do/does/did.

Modals also lack infinitives, -ing forms and participles, so other expressions fill the gaps: be able to supplies the missing forms of can, and have to supplies those of must.

She cans speak four languages.(modals never take -s → She can speak)
Do you can drive at night?(invert the modal instead → Can you drive at night?)
One day I'd like to be able to code in Python.('can' has no infinitive — use be able to)

Which modals express ability?

Use can for present ability, could for general ability in the past, and will be able to for the future. For one specific past achievement — a single occasion when someone succeeded — English prefers was/were able to (or managed to) rather than could.

My niece can already swim fifty metres.
Before the injury, he could run a marathon in under four hours.(general past ability)
The firefighters were able to reach everyone in time.(one specific success → was/were able to, not could)

Which modals ask for permission and make requests?

Can is the everyday choice for permission and requests; could softens it; may is formal. For requests, the scale runs can → could → would you mind, each politer than the last.

Giving and refusing permission uses can and can't (or may/may not formally): the receptionist decides what visitors can do, the law decides what drivers may do.

May I leave the meeting ten minutes early?(formal permission)
Could you forward me the agenda before lunch?('could' is softer than 'can')
You can use my desk while I'm away.(giving permission)

Which modals give advice and express obligation?

Should and ought to give advice and mild obligation; had better adds a warning of consequences. Must expresses strong obligation, often from the speaker's own authority, and mustn't expresses prohibition.

The negative traps live here: mustn't forbids, while don't have to merely removes the necessity — see the dedicated must vs have to comparison for the full picture.

You should compare a few airlines before you pay.(advice)
Visitors must wear a helmet on the construction site.(strong obligation)
You'd better back up those files tonight.('had better' warns of consequences)
You should to see a physiotherapist about that shoulder.(no 'to' after should → should see)

Which modals express possibility and uncertainty?

May, might and could all present something as possible rather than certain; might is the most tentative. Will states a confident prediction, and would presents imagined or conditional outcomes.

When you reason from evidence — 'he must be at lunch', 'she can't be serious' — you are using modals of deduction, which have their own page.

It might snow in the mountains this weekend.
The 8.15 ferry may be delayed by the strike.
Don't wait for Tomas — he could still be stuck in traffic.

Common mistakes with modal verbs

Real learner errors, corrected and explained — the fastest way to stop repeating them.

He can plays the guitar really well.

He can play the guitar really well.

After a modal, the main verb stays in its bare form — the modal carries the grammar, so 'plays' loses its -s.

We must to submit the form by Monday.

We must submit the form by Monday.

Modals take a bare infinitive: must submit, can go, should ask. Only 'ought' keeps 'to'.

They don't can come to the wedding.

They can't come to the wedding.

Modals form negatives with 'not' directly (cannot/can't) — never with do-support.

I will can finish the translation tomorrow.

I will be able to finish the translation tomorrow.

Two modals can never sit together; for future ability, replace can with be able to.

You don't should eat so late at night.

You shouldn't eat so late at night.

The negative of should is 'should not/shouldn't' — do-support belongs to ordinary verbs only.

When I was a child, I can climb any tree in our garden.

When I was a child, I could climb any tree in our garden.

Past general ability takes 'could' — 'can' has no past meaning of its own inside a past-time frame.

You had better to leave before the storm reaches the coast.

You had better leave before the storm reaches the coast.

'Had better' behaves like a modal and takes a bare infinitive — no 'to' after it.

Modal verbs in IELTS

Grammatical Range and Accuracy is 25% of your Speaking and Writing scores — here is where this structure earns marks.

Speaking

Hedged modals are Part 3 gold: 'It might depend on the family's income' or 'Cities could invest far more in cycling' sound analytical and balanced, while unhedged claims leave answers sounding like Band 6 lists.
Soften opinions with would: 'I would say most teenagers there are under real pressure.' Examiners hear modal softening as natural, flexible range — exactly what the descriptor 'uses a range of structures with some flexibility' describes.

Writing

Task 2 recommendation paragraphs live on modals: 'Governments should subsidise public transport, and employers could stagger working hours.' Vary should, could and might rather than repeating 'should' in every sentence.
Never stack modals in writing ('will can', 'must should'); when you need future ability or obligation, switch to 'will be able to' or 'will have to' — a small substitution that protects the error-free sentence count Band 7 demands.

Practise modal verbs now

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___ I open the window? It's stuffy in here.

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Check this rule in your own writing

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Paste a paragraph into the free IELTS Grammar Checker — it flags every modal verbs mistake, explains the rule, and estimates your Grammatical Range & Accuracy band.

Frequently asked questions

What are the nine modal verbs in English?

The core modals are can, could, may, might, will, would, shall, should and must. Semi-modals such as ought to, need and dare share some of their behaviour, and phrases like have to and be able to supply the forms modals lack. All true modals take a bare infinitive and never change their ending.

Why don't modal verbs take -s in the third person?

Modals are auxiliary verbs, not main verbs, so they stand outside normal subject-verb agreement: 'she can', never 'she cans'. They also have no infinitive, no -ing form and no participles. When you need those missing forms, switch to a substitute — be able to for can, have to for must.

Can you use two modal verbs together?

No — English allows only one modal per verb phrase, so 'will can' and 'must should' are impossible. Combine the meanings with substitutes instead: 'will be able to attend' for future ability, 'might have to move' for possible obligation. This restriction is a frequent source of learner errors in writing.

What is the difference between should and ought to?

They mean essentially the same — advice or mild obligation — but 'should' is far more common, especially in questions and negatives ('Should we wait?', 'You shouldn't worry'). 'Ought to' is the only modal followed by 'to' and sounds slightly more formal; its negative 'oughtn't to' is rare in modern English.

Are 'have to' and 'need to' modal verbs?

Not true modals — they are semi-modal expressions that behave like ordinary verbs: they take -s ('she has to'), use do in questions and negatives ('Do I need to book?'), and have past and future forms. That flexibility is exactly why English borrows them to fill the gaps the true modals leave.

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