What are the nine modal verbs in English?

The core modals are can, could, may, might, will, would, shall, should, and must. They share the same grammar: a single form for every subject, a bare infinitive after them, and negatives and questions made without do (She can't come. Must we leave?). Ought to, have to, need to, used to, and be able to are often taught alongside them as semi-modals because they express similar meanings with ordinary verb grammar.

Why don't modal verbs take -s or to?

Because they are auxiliaries, not main verbs, and they behave like the other auxiliaries be, have, and do rather than like walk or want. Historically they lost their ordinary verb endings and their infinitives, so today they have one frozen form: she can, not she cans; she must go, not she must to go. That is also why they cannot follow another modal and why English borrows be able to and have to for the missing forms.

Is have to a modal verb?

Not a true one: it expresses the same obligation as must, but it behaves like a normal verb, taking -s (he has to), a past tense (had to), and do in questions and negatives (Do you have to go? I don't have to). Must has none of these forms, so English uses have to for the past and future of obligation: I had to work late, and you'll have to book early.

What is the difference between must and should?

Must expresses a strong obligation or a rule the speaker treats as unavoidable: You must have a visa. Should gives advice or describes what is right or expected, leaving the listener free to decide: You should get a visa early. In deductions the gap is similar: She must be home means the evidence makes it certain; She should be home means it is what you expect but you are not sure.

How do modal verbs talk about the past?

Most modals add have plus a past participle: You should have asked, she must have forgotten, they might have left. Could and would work as the past of can and will in some uses: I could read at four; He promised he would help. For obligation and permission, English switches to the semi-modal substitutes: I had to leave (past of must) and We were allowed to stay (past of may).

English grammar · Intermediate

Modal Verbs: The Nine Modals, Their Grammar, and Their Meanings

Written by Eleanor Whitfield, Lead English Curriculum Editor · Reviewed September 2026

Modal verbs are a small set of auxiliary verbs (can, could, may, might, will, would, shall, should, must) that add a speaker's judgement to the main verb: how possible, necessary, permitted, or certain something is. They share one grammar: no -s in the third person, no to before the following verb, and no do in questions and negatives. Each modal carries several meanings, and the context decides which one is meant.

You should see a doctor about that cough.

should + bare infinitive: advice

What it is

A modal verb sits in front of a main verb and colours it with the speaker's attitude: She can swim (ability), She might swim (possibility), She must swim (obligation or certainty), She should swim (advice). The nine core modals are can, could, may, might, will, would, shall, should, and must. Grammatically they are unlike every other verb in English: they have a single form, they are followed by a bare infinitive, and they build negatives and questions on their own. That uniformity is good news, because once you know the grammar of one modal you know the grammar of all nine; what remains is learning which meanings each one carries.

It might rain later. (a possibility, less than certain) You must wear a seatbelt. (an obligation, from the law) That can't be right. (a logical impossibility)

How to spot it

Look for one of the nine words followed directly by a base verb with no to and no -s: can go, might be, should have. Two more tests confirm it: the negative is made with not or n't attached to the modal (mustn't, couldn't), and the question puts the modal in front of the subject (Could you...?).

Can you hear me? (modal in front of the subject makes the question)
He must be at work by now. (must + be: a confident deduction)
We couldn't find the entrance. (not attaches to the modal, no did)
You shouldn't have paid so much. (modal + have + participle looks back at the past)

Have to, need to, ought to, be able to, and used to express modal meanings but are not true modals: they change form (has to, had to), they take to, and most of them need do in questions (Do you have to go?).

Modal Verbs Quick Reference

The nine core modals and their main meanings

Modal	Main meanings	Example
can	ability, permission, possibility, requests	I can drive. Can I open the window?
could	past ability, polite requests, weaker possibility	She could read at four. Could you help me?
may	formal permission, possibility	May I come in? It may snow tonight.
might	weaker possibility, tentative suggestion	He might be late. You might try restarting it.
will	future, predictions, promises, willingness	I'll call you tonight. It will be cold.
would	hypothetical situations, polite requests, past habits	I would go if I could. Would you mind waiting?
shall	offers and suggestions with I and we, formal rules	Shall we start? Shall I carry that?
should	advice, expectation, mild obligation	You should rest. The bus should be here soon.
must	strong obligation, confident deduction	You must sign here. She must be exhausted.

Common Modal Verbs Examples in English

The same nine modals, this time grouped by the meaning they express, since one modal usually belongs to several groups and one meaning is usually shared by several modals:

Ability

My daughter can already ride a bike.: present ability: can
I could swim before I could walk.: past ability: could
Can you speak any other languages?: asking about a skill
I can't come tomorrow, I'm working.: can't for something that circumstances prevent

For a single achievement in the past English prefers was able to or managed to: We were able to get tickets, not We could get tickets.

Permission and Requests

Can I borrow your charger?: informal request for permission
Could you pass the salt, please?: could is more polite than can
May I ask a question?: formal permission
Would you open the window?: would for a polite request

Politeness rises from can to could to would and may; the meaning stays the same.

Possibility and Deduction

It may rain this afternoon.: a real possibility
She might not have seen the message.: might + perfect: a possibility about the past
That must be the new manager.: must: the evidence makes it almost certain
It can't be Tom, he's in Madrid.: can't: the evidence rules it out

Must and can't are a pair for deductions; may, might, and could cover everything less certain. Mustn't is never used for deduction.

Obligation and Advice

You must wear a helmet on site.: must: a rule or strong obligation
You mustn't touch that wire.: mustn't: a prohibition
You should back up your files.: should: advice
Visitors shall sign in at reception.: shall in formal rules and contracts

Must comes from the speaker; have to reports an obligation from outside. Should is softer than both.

How Modal Verbs Work

Every modal follows the same five rules, which is what makes the group worth learning as a set.

One Form for Every Subject

Modals never take -s in the third person and never take -ing or -ed: I can, she can, they can. There is no form cans, musting, or shoulded. This is the first thing that marks a modal out from an ordinary verb, and it also means that a modal has no infinitive and cannot follow another modal.

She can drive. He must leave. It might work.

the same form after every subject

No -s, ever.

A Bare Infinitive Follows

The verb after a modal is the base form with no to: must go, not must to go; can swim, not can swimming. The only apparent exception is ought to, which is not one of the nine core modals. Be, have, and do after a modal are also bare: should be, might have, could do.

You should call her. They may be late.

call and be in the base form

Modal + base verb, no to.

Negatives and Questions Without Do

Because a modal is already an auxiliary, not attaches straight to it (cannot, could not, should not, with the contractions can't, couldn't, shouldn't), and the question is made by inverting the modal and the subject. Do never appears: Can you...? not Do you can...?

Can't you come? Why wouldn't he answer?

the modal inverts and carries the negative

The modal does the work of do.

Have + Participle Looks Back at the Past

Modals have no past tense of their own for most meanings, so English adds have plus a past participle after the modal to talk about the past: must have left, should have called, might have forgotten. Could and would also serve as the past of can and will in some uses (She could read at four; He said he would come), but should have and must have are the standard past for advice and deduction.

You should have told me. They must have missed the train.

advice about the past; a deduction about the past

Modal + have + third form = past.

Context Decides the Meaning

Most modals carry two or more unrelated meanings, and only the situation tells you which one is meant. You must be tired is a deduction; You must be there at nine is an obligation. She can't be serious is a judgement about likelihood; She can't swim is about ability. The listener works it out from what is being discussed, so as a speaker you rarely need to worry about ambiguity.

He may leave early.

permission (he is allowed to) or possibility (he possibly will): the context decides

Same modal, several meanings.

Common Mistakes with Modal Verbs

Incorrect: She cans speak three languages.

Correct: She can speak three languages.

Modals have one form for every subject. The third-person -s that every ordinary verb takes simply does not exist for can, must, should, and the rest.

Incorrect: You must to finish the report today.

Correct: You must finish the report today.

A modal is followed by the bare infinitive. The to appears in have to and ought to, which are not core modals, and learners transfer it across.

Incorrect: Do you can help me with this?

Correct: Can you help me with this?

A modal makes its own question by moving in front of the subject; it never combines with do. The same goes for negatives: I can't, not I don't can.

Incorrect: I will can drive next summer.

Correct: I will be able to drive next summer.

Two modals cannot stand together, and can has no infinitive to follow will. Be able to supplies the missing form, just as have to supplies the future of must: You will have to wait.

Modal Forms and How They Reach the Past

First the form pattern that all nine share, then the substitutes English uses when a modal needs a past tense or a future form.

Affirmative, negative, question

Every modal builds its three forms the same way, shown here with the verb go.

Pronoun	Affirmative	Negative	Question
can	I can go	I cannot (can't) go	Can I go?
could	she could go	she could not (couldn't) go	Could she go?
may	he may go	he may not go	May he go?
might	it might go	it might not (mightn't) go	Might it go?
will	we will (we'll) go	we will not (won't) go	Will we go?
would	they would (they'd) go	they would not (wouldn't) go	Would they go?
shall	I shall go	I shall not (shan't) go	Shall I go?
should	you should go	you should not (shouldn't) go	Should you go?
must	she must go	she must not (mustn't) go	Must she go?

Cannot is written as one word. May not has no common contraction, and shan't survives mainly in British English. Might it go? and Must she go? are grammatical but rare; speakers usually ask Is it likely to go? and Does she have to go?

Talking about the past and the future

Modals have no -ed form and cannot follow will, so English switches to a substitute or adds have + participle.

Pronoun	Present or future	Past
ability	I can swim.	I could swim. / I was able to finish.
permission	You may leave.	We were allowed to leave.
obligation	I must go.	I had to go.
prohibition	You mustn't smoke here.	We weren't allowed to smoke there.
advice	You should call.	You should have called.
deduction	She must be home.	She must have been home.
possibility	It might rain.	It might have rained.

For the future, the substitutes step in again: I will be able to drive next year, You will have to wait, not I will can or You will must.

Semi-Modals and Substitutes

A second group of verbs carries modal meanings but keeps ordinary verb grammar, and English relies on them wherever a true modal cannot go.

Have to and need to

Have to expresses obligation like must, but it behaves as a normal verb: it takes -s, has a past (had to), and forms questions and negatives with do.

She has to work on Saturdays.: has: third-person -s, unlike must
Do you have to leave so early?: do in the question
You don't have to pay; it's free.: don't have to = not necessary (mustn't would mean forbidden)

Must not and do not have to are opposites in meaning: one prohibits, the other removes the obligation.

Be able to and be allowed to

These fill the gaps in can and may: they supply the infinitive, the future, and the perfect forms that the modals lack.

I'd like to be able to speak Japanese.: infinitive: to be able to, since to can does not exist
You'll be able to see the sea from your room.: future ability after will
We haven't been allowed to visit yet.: perfect form of permission

In the present, can is far more common than be able to; the substitute appears where can cannot.

Ought to, had better, and used to

Three more expressions with modal meanings: ought to gives advice like should, had better warns of consequences, and used to describes past habits and states that have stopped.

You ought to apologise.: ought to = should, slightly more formal
We'd better leave now or we'll miss the train.: had better: advice with a warning attached
I used to play the violin.: a past habit that is over

Used to is followed by the infinitive and refers only to the past; would can also describe past habits (We would swim every morning) but not past states.

Quick Check: Modal Verbs

Choose the modal or substitute that fits, and correct the form where necessary.

1. ___ you swim when you were five? (ability, past)

Answer: Could

past ability: could; no did

2. The lights are off. They ___ be out. (confident deduction)

Answer: must

must for a near-certain conclusion

3. You ___ smoke in here; it's against the law. (prohibition)

Answer: mustn't

mustn't forbids; don't have to would mean it isn't necessary

4. She ___ (should / have / call) before she came round.

Answer: should have called

advice about a past action: should + have + participle

5. Next year I ___ (can) work from home two days a week.

Answer: will be able to

can has no future form, so be able to follows will

6. ___ we order pizza tonight? (suggestion)

Answer: Shall

shall with we makes a suggestion

Modal Verbs FAQs

What are the nine modal verbs in English?: The core modals are can, could, may, might, will, would, shall, should, and must. They share the same grammar: a single form for every subject, a bare infinitive after them, and negatives and questions made without do (She can't come. Must we leave?). Ought to, have to, need to, used to, and be able to are often taught alongside them as semi-modals because they express similar meanings with ordinary verb grammar.
Why don't modal verbs take -s or to?: Because they are auxiliaries, not main verbs, and they behave like the other auxiliaries be, have, and do rather than like walk or want. Historically they lost their ordinary verb endings and their infinitives, so today they have one frozen form: she can, not she cans; she must go, not she must to go. That is also why they cannot follow another modal and why English borrows be able to and have to for the missing forms.
Is have to a modal verb?: Not a true one: it expresses the same obligation as must, but it behaves like a normal verb, taking -s (he has to), a past tense (had to), and do in questions and negatives (Do you have to go? I don't have to). Must has none of these forms, so English uses have to for the past and future of obligation: I had to work late, and you'll have to book early.
What is the difference between must and should?: Must expresses a strong obligation or a rule the speaker treats as unavoidable: You must have a visa. Should gives advice or describes what is right or expected, leaving the listener free to decide: You should get a visa early. In deductions the gap is similar: She must be home means the evidence makes it certain; She should be home means it is what you expect but you are not sure.
How do modal verbs talk about the past?: Most modals add have plus a past participle: You should have asked, she must have forgotten, they might have left. Could and would work as the past of can and will in some uses: I could read at four; He promised he would help. For obligation and permission, English switches to the semi-modal substitutes: I had to leave (past of must) and We were allowed to stay (past of may).