Modal Verbs in English: A Complete Guide with Examples and Exercises
A complete guide to modal verbs in English: can, could, may, might, must, shall, should, will and would, with examples, common mistakes and exercises.
Table of contents
Modal verbs look easy until you have to use them. Nine short words, no endings, no conjugation… and still one of the biggest sources of mistakes in the Cambridge exams. I see it every week when I mark writing: «I don’t can», «she must cook dinner yesterday», «I would live in Madrid when I was a child».
This is the complete guide to modal verbs in English: what they are, how each one works, what they mean in context, how deductions are built, what perfect modals are, which mistakes learners really make (documented by Cambridge, not invented by me) and how they are tested at each level. At the end there are forty practice sentences with answers. Get comfortable, there is a lot here. Let’s get started! 🙂
What modal verbs are
A modal verb does not describe an action. It describes your attitude towards that action: whether you see it as possible, obligatory, advisable, likely or impossible. That is why the same sentence changes completely depending on the modal in front of it:
- You must talk to her. (obligation: you have no choice)
- You should talk to her. (advice: it is a good idea)
- You might talk to her. (possibility: perhaps you will)
- You can talk to her. (permission or ability: you are able to)
The main verb has not moved. Only the modal changes, and with it the whole message. That is the entire idea.
Which ones they are
It is worth being precise here, because plenty of lists online mix different things together. Cambridge groups them in three:
| Group | Which ones |
|---|---|
| Core modal verbs | can, could, may, might, will, shall, would, should, must |
| Semi-modals | dare, need, ought to, used to |
| Verbs with modal meanings | have (got) to, be going to, be able to |
The nine in the first group are the ones that behave in a special way, and most of this guide is about them. The other two groups are summarised further down, and each will get its own post.
The rules of form: five things that never change
Get these five rules into your head and you avoid most of the mistakes. They are the same for all nine modals.
- 1. No -s in the third person. She can swim, He must go. Never «she cans», «he musts».
- 2. They are followed by the infinitive without to. I can help, not «I can to help». The exception is ought to, which carries its to in its own name.
- 3. Negatives add not, with no do. We can’t hear you, not «We don’t can hear you».
- 4. Questions invert, with no do. Could you help me?, not «Do you could help me?». The same as in Yes/No and Wh- questions.
- 5. Two modals cannot sit together. She won’t be able to come, not «She won’t can come».
And one consequence of the fifth rule that is worth understanding: modals have no infinitive, no gerund and no participle. There is no «to can», no «canning», no «musted». When the grammar needs one of those forms, you switch to a verb with a modal meaning: be able to for can, have to for must.
| What you want to say | ✘ Impossible | ✔ Solution |
|---|---|---|
| Future of can | «I will can» | I will be able to help. |
| Past of must | «I musted» | I had to leave early. |
| Infinitive | «to can» | I’d love to be able to ski. |
| Gerund | «canning» | I hate not being able to help. |
| After another modal | «might can» | We might be able to come. |
Affirmative, negative, question and short answers
| Form | Example |
|---|---|
| Affirmative | You should call her. |
| Negative | You shouldn’t call her. |
| Question | Should I call her? |
| Short answer | Yes, you should. / No, you shouldn’t. |
| Question tag | You should call her, shouldn’t you? |
Notice that the short answer repeats the modal, not the main verb. A small detail that sounds very natural when you get it right.
Modals by function: the table that solves 80% of it
In practice you do not choose a modal by its name, but by what you want to express. This is the table I would stick on the wall:
| What you want to express | Modal | Example |
|---|---|---|
| Ability (present) | can | I can drive. |
| Ability (past) | could | I could read at four. |
| Permission | can, could, may | May I come in? |
| Request | can, could, would | Could you repeat that? |
| Obligation | must, have to | You must wear a helmet. |
| Prohibition | mustn’t, can’t | You mustn’t park here. |
| No obligation | needn’t, don’t have to | You don’t have to come. |
| Advice | should, ought to | You should rest. |
| Possibility | may, might, could | It might rain later. |
| Deduction (almost certainly yes) | must | She must be tired. |
| Deduction (certainly not) | can’t | That can’t be true. |
| Offer or suggestion | shall, can | Shall I help you? |
| Past habit | would, used to | We would play in the street. |
| Prediction | will | It will be sunny tomorrow. |
The nine modals, one by one
CAN
Present ability, informal permission, general possibility and requests. It is the most frequent modal of all.
- I can speak three languages. (ability)
- Can I borrow your pen? (permission)
- It can get very cold here in winter. (general possibility)
- Can you help me? (request)
The negative is can’t, and in formal contexts cannot, always as one word. The full topic, be able to included, is in my guide to can, could and be able to.
COULD
The past of can for general abilities, a polite request, and possibility in the present or future.
- I could swim before I could walk. (general past ability)
- Could you say that again, please? (polite request)
- We could go to the beach on Sunday. (suggestion)
Two warnings straight from Cambridge. First: for one specific achievement in the past you do not use could but was able to or managed to (I was able to buy the tickets, not «I could buy the tickets»). Second: could does not give permission. If someone asks Could I leave early?, the answer is Yes, you can, never «Yes, you could».
MAY
Possibility and formal permission. It is the modal of signs, announcements and requests in a suit.
- It may rain this afternoon. (possibility)
- May I use your phone? (formal permission)
- Passengers may not smoke on board. (formal prohibition)
Careful with the negative: it is written may not, and the contraction «mayn’t» does not exist.
MIGHT
Possibility, usually a little more remote than may, although in today’s English the difference is very thin.
- I might go to the party, I haven’t decided.
- Take an umbrella. It might rain.
- You might want to check the timetable first. (a very soft suggestion)
Might is not used for ability: that is can or could.
MUST
Two uses that should not be mixed up: obligation (coming from the speaker) and deduction (you are almost certain).
- You must finish this today. (obligation)
- You must be exhausted after that trip. (deduction)
- You mustn’t tell anyone. (prohibition)
And here is one of the most repeated errors Cambridge documents: must has no past. For past obligation you use had to: When she got home, she had to cook dinner, not «she must cook dinner». Nor is must used for predictions about the future: that is what will is for.
SHALL
The most formal and the least frequent, but very much alive in two situations: offers and suggestions with I and we.
- Shall I open the window? (offer)
- Shall we go? (suggestion)
- The tenant shall pay the rent monthly. (legal register)
What shall does not do is give advice. That is should: In my opinion, we should book another hotel, not «we shall book another hotel».
SHOULD
Advice, recommendation and reasonable expectation.
- You should see a doctor. (advice)
- We should arrive at about ten. (expectation)
- You shouldn’t work so much.
Ought to means practically the same and sounds slightly more formal: You ought to apologise. It is far less common, especially in negatives and questions.
WILL
Predictions, spontaneous decisions, offers and promises.
- It will be cold tomorrow. (prediction)
- I ‘ll help you with that. (an offer, decided on the spot)
- I won’t tell anyone, I promise.
Cambridge flags a very typical error here: using the present simple where will belongs. It is I’ll help you with that suitcase, not «I help you with that suitcase». The whole future is explained in my guide to will, going to and the present continuous.
WOULD
Hypothetical situations, very polite requests, preferences and past habits.
- I would travel more if I had the money. (hypothesis; more in conditional sentences)
- Would you mind closing the door? (formal request)
- I ‘d rather stay at home tonight. (preference)
- Every summer we would drive to the coast. (past habit)
Careful with that last use: would works for repeated actions in the past, but not for states. For states you use used to: I used to live in Melbourne, not «I would live in Melbourne».
And there are fixed expressions with would where will does not fit: Would you like…?, Would you mind…?, Would you rather…?.
The certainty scale: how deduction works in English
This is the use that earns most marks from B2 upwards, and the one explained worst almost everywhere. When you do not know something for sure but you have a good idea, English does not say «I think»: it changes the modal. And each modal marks a different degree of certainty.
| Certainty | Modal | Example |
|---|---|---|
| 100% certain, yes | is / are | She is at home. |
| Almost certain, yes | must | She must be at home. Her car is outside. |
| Possible | may / might / could | She may be at home. |
| Unlikely | might not | She might not be at home. |
| Almost certain, no | can’t | She can’t be at home. I’ve just seen her at work. |
Two details make all the difference. First: the opposite of must in deductions is can’t, not mustn’t. Mustn’t is prohibition, not deduction. Second: could works for possibility, but couldn’t does not work the same way; to negate a deduction you need can’t.
Perfect modals: talking about the past
Since modals have no past of their own, English builds the past with modal + have + past participle. This is the structure that separates a B2 from a C1, and the one that earns most credit in writing. If participles are shaky, I have a guide to irregular verbs.
| Structure | Meaning | Example |
|---|---|---|
| must have + participle | An almost certain deduction about the past | She must have left early. |
| can’t have + participle | A negative deduction | He can’t have finished already. |
| may / might / could have + participle | Possibility in the past | They might have missed the train. |
| should have + participle | The right thing was not done (regret or reproach) | I should have studied more. |
| shouldn’t have + participle | Something was done that should not have been | You shouldn’t have said that. |
| could have + participle | It was possible and did not happen | We could have taken the train, but we drove. |
| needn’t have + participle | It was done, but there was no need | You needn’t have brought your laptop. |
And one pair that turns up in every exam: needn’t have done means you did it unnecessarily (You needn’t have cooked, we’ve already eaten), while didn’t need to do means there was no need and, usually, that you did not do it (I didn’t need to cook, so I ordered a pizza). A small nuance, a huge difference.
Semi-modals and verbs with modal meanings
Besides the nine core modals, a group of verbs expresses the same ideas but is conjugated like ordinary verbs. Here they are; each one deserves an article of its own.
| Verb | What it expresses | Example |
|---|---|---|
| have to | Obligation, usually external (a rule, a timetable) | I have to wear a uniform at work. |
| don’t have to | No obligation | You don’t have to come if you’re tired. |
| be able to | Ability, where can cannot go | I’ll be able to help you tomorrow. |
| be allowed to | Permission | We aren’t allowed to use phones in class. |
| used to | Past habits and states that are no longer true | I used to live in Granada. |
| ought to | Advice, slightly more formal than should | You ought to apologise. |
| had better | Urgent advice, with an implied consequence | You’d better leave now or you’ll miss it. |
| would rather | Preference | I’d rather stay in tonight. |
| need | Necessity (as an ordinary verb, with to) | I need to have my hair cut. |
| be going to | Intention and prediction based on evidence | It’s going to rain. |
The difference people ask about most is must versus have to: with must, the obligation comes from the speaker (I must stop smoking); with have to, it comes from outside (I have to wear a uniform). In the negative they are nothing alike: mustn’t is prohibition and don’t have to is freedom.
Common mistakes (documented, not invented)
Every mistake in this table is taken from Cambridge’s own grammar pages, which flag incorrect forms drawn from the Cambridge English Corpus and from real candidate errors in their exams. This is not a list of what I happen to think: it is what actually goes wrong.
| ✘ Wrong | ✔ Right | Which rule it breaks |
|---|---|---|
| I don’t can believe it. | I can’t believe it. | Negatives take not, never do. |
| Do you could help me? | Could you help me? | Questions invert, never with do. |
| He can might hear the music. | He can hear the music. | Two modals cannot sit together. |
| She won’t can concentrate. | She won’t be able to concentrate. | After a modal, be able to. |
| I’d love to can see the Taj Mahal. | I’d love to be able to see the Taj Mahal. | Modals have no infinitive. |
| They musted sell their house. | They had to sell their house. | Modals have no past form. |
| When she got home, she must cook dinner. | When she got home, she had to cook dinner. | Must does not express past obligation. |
| The children can not be left alone. | The children cannot be left alone. | Cannot is written as one word. |
| They can see a light on as they drove past. | They could see a light on as they drove past. | Past ability takes could. |
| I could buy a wonderful bag. | I was able to / managed to buy a wonderful bag. | A specific past achievement, not general ability. |
| A: Could I leave early? B: Yes, you could. | B: Yes, you can. | Could does not grant permission. |
| Although you might visit these places… | Although you can visit these places… | Might does not express ability. |
| We mayn’t know yet. | We may not know yet. | «Mayn’t» does not exist. |
| In my opinion, we shall book another hotel. | In my opinion, we should book another hotel. | Shall does not give advice. |
| The cards shall be ready at the end of the month. | The cards will be ready at the end of the month. | Shall only with I and we. |
| I help you with that suitcase. | I’ll help you with that suitcase. | Offers take will, not the present simple. |
| I would live in Melbourne when I was a kid. | I used to live in Melbourne when I was a kid. | Would does not work for past states. |
| Will you like your steak well cooked? | Would you like your steak well cooked? | Fixed expressions with would. |
| We don’t ought to have ordered so much. | We ought not to have ordered so much. | Ought to does not use do either. |
| We are used to go to the seaside. | We used to go to the seaside. | Used to takes no be in front of it. |
| I need have my hair cut. | I need to have my hair cut. | The ordinary verb need takes to. |
| I think the bill could expensive. | I think the bill could be expensive. | A modal needs a verb after it. |
Look down the list and you will see that almost all of them fall into three boxes: putting do where it does not belong, trying to conjugate a verb that does not conjugate, and picking the modal with the wrong meaning. With that in mind, you start spotting them as you speak.
Modal verbs in the Cambridge exams
They appear at every level, but they are not tested in the same way.
A2 Key and B1 Preliminary
The basics, done well: can for ability and permission, must and have to for obligation, should for advice. In the speaking test they come out by themselves as soon as you are asked what you can do or what the rules are at your school or workplace.
B2 First
This is where deductions come in (must be, can’t be) along with perfect modals, and above all where they appear in Part 4 of the Reading and Use of English paper, the famous key word transformations. Three examples in exactly the style you will get:
- It’s forbidden to use your phone here. MUSTN’T → You mustn’t use your phone here.
- I’m sure she didn’t see us. CAN’T → She can’t have seen us.
- It wasn’t necessary for me to pay. HAVE → I didn’t have to pay.
C1 Advanced and C2 Proficiency
At the higher levels the form is taken for granted and the nuance is tested: needn’t have done against didn’t need to do, should have done for regret, and emphatic structures with inversion such as Not only could they finish on time, but they also…. At that point it is not about getting it right, but about sounding natural.
Summary table
| Modal | Main uses | Past |
|---|---|---|
| can | Ability, permission, general possibility, requests | could / was able to |
| could | Past ability, polite request, possibility, suggestion | could have + participle |
| may | Possibility, formal permission | may have + participle |
| might | More remote possibility, soft suggestion | might have + participle |
| must | Obligation from the speaker, almost certain deduction, prohibition in the negative | had to / must have + participle |
| shall | Offers and suggestions with I and we, legal register | — |
| should | Advice, expectation | should have + participle |
| will | Prediction, spontaneous decision, offer, promise | would |
| would | Hypothesis, formal request, preference, past habit | would have + participle |
Frequently asked questions
How many modal verbs are there in English?
Nine core modals: can, could, may, might, will, shall, would, should and must. Alongside them are the semi-modals (dare, need, ought to, used to) and verbs with modal meanings (have to, be going to, be able to).
Why can’t you say «I will can»?
Because two modals cannot follow one another. You say I will be able to.
What is the difference between must and have to?
With must the obligation comes from the speaker; with have to, from an external rule. And in the negative they part company completely: mustn’t forbids, don’t have to frees you.
What is the difference between mustn’t and can’t in deductions?
Mustn’t is not used in deductions: the opposite of must be is can’t be. Mustn’t only expresses prohibition.
Can modal verbs be used in the past?
They have no past form of their own. You use modal + have + participle (must have gone, should have studied) or an equivalent verb (had to, was able to).
May or might?
Both express possibility and today they are almost interchangeable. Might tends to sound slightly less likely, and may slightly more formal, especially for permission.
Modal verbs exercises
Forty sentences to check that all of the above has sunk in. Below you will find four interactive exercises that mark themselves, so you will know straight away how you did. The third one is special: every incorrect sentence is a real learner error documented by Cambridge.
And if you prefer a version in text that you can copy and paste, you have it down here 👇
Exercise 1: choose the right modal verb
Choose the correct modal verb in each sentence.
- You _______________ (must / might) wear a helmet on a building site. It’s the law.
- I’m not sure, but she _______________ (might / must) be at home now.
- You _______________ (mustn’t / don’t have to) smoke in here. It’s forbidden.
- We _______________ (needn’t / mustn’t) hurry. We have plenty of time.
- That _______________ (can’t / mustn’t) be John. He’s in Japan this week.
- _______________ (Could / Must) you help me with these bags, please?
- You _______________ (should / would) see a doctor about that cough.
- When I was a child, I _______________ (would / will) spend hours reading.
- _______________ (May / Will) I open the window? It’s very hot in here.
- He _______________ (must / can) be tired. He’s been working since six this morning.
Show answers
- must
- might
- mustn’t
- needn’t
- can’t
- Could
- should
- would
- May
- must
Exercise 2: perfect modals
Complete the sentences with the modal verb in brackets + have + past participle.
- The lights are off. They _______________ (must / go) to bed.
- I _______________ (should / study) harder for the exam. I failed it.
- You _______________ (needn’t / bring) your laptop. We have one here.
- She isn’t here yet. She _______________ (might / miss) the bus.
- He _______________ (can’t / finish) already. He only started ten minutes ago.
- We _______________ (could / take) the train, but we drove instead.
- I’m sorry. I _______________ (shouldn’t / say) that.
- They _______________ (must / be) delighted with the news.
- You _______________ (could / tell) me you were coming!
- The keys aren’t here. Someone _______________ (may / take) them.
Show answers
- must have gone
- should have studied
- needn’t have brought / need not have brought
- might have missed
- can’t have finished / cannot have finished
- could have taken
- shouldn’t have said / should not have said
- must have been
- could have told
- may have taken
Exercise 3: right or wrong?
Decide whether each sentence is correct or incorrect, and rewrite the incorrect ones.
- I don’t can believe it.
- Do you could help me?
- When she got home, she must cook dinner.
- We ought not to have ordered so much food.
- They musted sell their house.
- I’d love to can see the Taj Mahal one day.
- He should be able to work in a team.
- I would live in Melbourne when I was a kid.
- In my opinion, we shall book another hotel.
- You may not know the answer yet.
Show answers
- Incorrect → I can’t believe it. / I cannot believe it.
- Incorrect → Could you help me?
- Incorrect → When she got home, she had to cook dinner.
- Correct
- Incorrect → They had to sell their house.
- Incorrect → I’d love to be able to see the Taj Mahal one day.
- Correct
- Incorrect → I used to live in Melbourne when I was a kid.
- Incorrect → In my opinion, we should book another hotel.
- Correct
Exercise 4: key word transformations
Complete the second sentence so that it means the same as the first, using the word in capitals.
- It’s forbidden to use your phone here. (MUSTN’T)
You _______________ your phone here. - It isn’t necessary to book a table. (NEED)
You _______________ a table. - I’m sure he is at work. (MUST)
He _______________ at work. - It’s a good idea to arrive early. (SHOULD)
You _______________ early. - I’m sure she didn’t see us. (CAN’T)
She _______________ us. - It was a mistake to tell him. (SHOULDN’T)
You _______________ him. - Perhaps they forgot about the meeting. (MIGHT)
They _______________ about the meeting. - I managed to finish on time. (ABLE)
I _______________ finish on time. - It’s obligatory to wear a uniform. (HAVE)
You _______________ a uniform. - It wasn’t necessary for me to pay. (HAVE)
I _______________ pay.
Show answers
- mustn’t use / must not use
- needn’t book / need not book / don’t need to book / do not need to book
- must be
- should arrive
- can’t have seen / cannot have seen
- shouldn’t have told / should not have told
- might have forgotten
- was able to
- have to wear
- didn’t have to / did not have to
Conclusion
Modal verbs are not learnt by heart, they are learnt through what they mean. If you keep three ideas: they do not conjugate and they do not take do; for the past you need modal + have + participle or an equivalent such as had to; and in deductions the scale runs from must to can’t, through may, might and could.
This guide is the starting point of a series: every important modal will get its own article, beginning with can, could and be able to, which is already published. Next will come must and have to, then should, then may and might, and the semi-modals in full.
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See you in the next post. Until then, don’t forget to keep smiling! 🙂