Modal verbs in English

Modal verb examples and forms

The core modals are can, could, may, might, must, shall, should, will and would. Use the same form with every subject. Write “she can swim”, with no -s on can or swim. The base verb is the form you find in a dictionary.

Put not straight after the modal for a negative. Write cannot as one word, or use can't. Common short forms include couldn't, shouldn't, wouldn't and mustn't. In questions, move the modal before the subject. Don't add do, does or did.

You can leave out the main verb in a short answer because the question supplies it. But don't use two core modals together in standard English. Say “I will be able to help”, not “I will can help”.

Related expressions follow different rules. Ought to includes to. Have to and need to change with the subject and use do in present simple questions.

Ability with can and could

Use can for a skill or an ability now. Could often describes general ability in the past. It doesn't automatically mean that a particular action happened.

For one successful action in the past, usually use was or were able to, or managed to. Could is still natural with senses, as in “I could hear music”. Couldn't can describe a failed action on one occasion.

• I can read the menu in Japanese.
• When I was younger, I could run for hours.
• The door was stuck, but we were able to open it.
• I couldn't find my keys this morning.

Be able to is useful where can has no form. Use “will be able to” for future ability and “have been able to” for ability up to now. Can also works for a future arrangement, as in “I can meet you tomorrow”.

Permission with can, could and may

Ask “Can I...?” in everyday conversation. “Could I...?” sounds more polite or less direct. “May I...?” is more formal. All three can ask for permission now, so could doesn't mean past time here.

Give permission with can or may. After “Could I sit here?”, say “Yes, you can” or “Of course”. Don't normally answer “Yes, you could” to grant permission now.

• Can I use this chair?
• Could I leave a little early today?
• May I ask a question?
• You may use a dictionary during this task.

Can also describes what a rule permits. “You can't park here” means parking is not allowed. Context tells you whether can't means a rule, an inability or a strong conclusion.

Possibility and deduction

Use may, might or could when something is possible but you aren't sure. These words don't have fixed percentages. Their meanings overlap, and context matters more than a strict ranking.

Use must when evidence makes you very sure something is true. Use can't when evidence makes you very sure it isn't true. These are conclusions, not proof.

• The lights are on. Someone must be at home.
• The shop may be closed today.
• Aya might be on the train, or she could be at work.
• That can't be Ben. He's in Canada this week.

The scale shows the speaker's confidence. Must and can't show strong conclusions, not proven facts. May, might and could share the uncertain area. Their position doesn't mean an exact chance.

Don't normally use can for an uncertain guess about one present event. Say “She may be busy”. Can works for a general possibility, as in “Trains can be crowded”. For uncertain guesses, may not and might not mean “perhaps not”; they don't express the strong negative conclusion can't does. May not can also refuse permission, as in “You may not enter”.

Obligation and necessity

Must, have to and need to say that an action is necessary. Must can express a strong instruction or a duty you feel yourself. Have to often describes a rule or a practical need. Need to puts the focus on what is necessary.

• I must remember to call my sister.
• Staff have to wear their name badges at work.
• You need to charge the tablet before the lesson.
• We had to wait outside yesterday.

Use had to for an ordinary past obligation. Must have followed by a past participle has a different job, explained below. For a future need, use will have to or will need to. Must can refer to the future too, as in “I must call her tomorrow”.

No need and prohibition

Don't have to and don't need to mean that an action isn't necessary. You can still choose to do it. For rules and instructions, mustn't means that an action is forbidden or that you strongly tell someone not to do it.

• You don't have to print the ticket. A phone copy is fine.
• You don't need to bring food, but you can if you like.
• You mustn't share your password.
• Visitors must not enter this room.

Needn't also means “don't need to”. It is more common in British English than American English. To answer “Must I come?”, say “No, you don't have to” if coming is optional. “No, you mustn't” would forbid it. Must not can also express a negative deduction, especially in American English. “She must not know we're here” can mean “I conclude that she doesn't know”.

Advice with should and had better

Use should or ought to when you think an action is a good idea or the right thing to do. Ought to has a similar meaning, but should is more common. Both are usually weaker than must for an instruction.

• You should keep a copy of the receipt.
• You shouldn't leave your bag here.
• We ought to check the opening times.
• You'd better leave now, or you'll miss the bus.

Had better gives advice for a particular situation, often with an unwanted result if you ignore it. The form stays had better even when you mean now or the future. Use the base verb without to. Its negative is had better not, as in “You'd better not be late”.

Should can also express an expectation. “The train should arrive soon” means you expect it to arrive soon. It isn't advice to the train.

Requests and offers

Ask someone to do something with can, could, will or would. Could and would often make requests less direct. They don't make every request polite; tone and the situation also matter.

• Can you hold this for a moment?
• Could you speak a little more slowly, please?
• Would you close the window, please?
• Shall I carry that bag for you?

“Will you help me?” asks for a person's willingness. “I will help you” can be a promise or a decision to help. “I can help you” offers help by saying you are able or available.

Shall I is useful for an offer, and shall we for a suggestion. These uses are more common in British English. American speakers often use “Can I help?” or “Should we leave?” instead. Would you like followed by a noun or to + verb is another offer or invitation, as in “Would you like some tea?”

Past modals with have

Use modal + have + past participle to look back. The participle is the third verb form, such as gone, seen or written. Have stays have, even after he or she.

Must have gives a strong conclusion about the past. Could have can describe something that was possible but didn't happen. It can also give a possible explanation when you don't know what happened. Context separates those meanings.

• The floor is wet. Someone must have cleaned it.
• I could have taken a taxi, but I walked.
• She could have missed the message. I am not sure.
• I should have saved the file before closing it.

Should have often expresses regret or criticism about something that didn't happen. Shouldn't have often criticises something that did happen. “You shouldn't have shared that photo” says sharing it was a mistake.

Should have can also express an expectation, as in “They should have arrived by now”. That doesn't tell us whether they arrived. For an uncertain past guess, may have and might have work too. “She might have left” means perhaps she left.

Must and have to compared

Don't treat the usual difference as a strict rule. Both must and have to can describe the same duty. “You must show your ticket” and “You have to show your ticket” can both state an entry rule.

Must often gives the speaker's instruction. Have to often reports a requirement. Have got to is an informal alternative, especially common in spoken British English. American speakers use it too. “I've got to leave” describes a need now, not a past action.

The negative difference matters more than the positive difference. Check whether you mean “not necessary” or “not allowed”. With have got to, a question is “Have you got to go?” For wider use across both varieties, “Do you have to go?” is a safe choice.

Common mistakes

Notes for Chinese, Japanese and Korean speakers

If you speak Chinese, you may carry a familiar modal word straight into English. Its meanings may not match can, may or must. Practise one situation with two sentences, such as “I can leave” and “I must leave”.

Japanese and Korean often put polite or possibility expressions near the end of a clause. This may make English modal order feel unfamiliar. Keep a small frame in mind, “subject + modal + base verb”. For a question, swap the subject and modal.

For speakers of any of these languages, translating a negative expression word by word can blur “no need” and “not allowed”. Attach a meaning to the whole phrase. Write “optional” beside don't have to and “forbidden” beside mustn't.

Try the quiz

Fill each gap. Where choices are given, use one of them.

1. She can ___ (swim) well.
2. ___ he speak English? Choose can or does.
3. When I was ten, I ___ read music. Choose could or can.
4. After several tries, we ___ open the stuck door. Choose the usual form for one successful past action, were able to or could.
5. ___ I borrow your pen? Use the most formal choice from can, could and may.
6. She ___ be in the office. I am not sure. Choose must, might or can't.
7. That ___ be my bag. Mine is blue, and this one is red. Choose must or can't.
8. You ___ bring a towel. We provide one, but you can use your own. Choose mustn't or don't have to.
9. You ___ open this door. Entry is forbidden. Choose don't have to or mustn't.
10. You ___ better save your work now.
11. Make a request. ___ you close the window, please? Choose would or should.
12. I should ___ (save) the file, but I forgot.

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