Modal verbs are small words with a big job. Put one in front of a main verb and the meaning changes: I go, I can go, I must go, I should go, I might go. They show ability, permission, obligation, advice and possibility.
Their grammar is simple: modals never change (no -s, no -ed, no -ing), the next verb is always in the base form, and questions and negatives don't use do. The hard part is choosing the right modal, especially for obligation, where must and have to are similar but mustn't and don't have to mean very different things.
How to form modal verbs
Modal verbs (can, could, may, might, must, should, would, will, shall) have one form for every person. The verb after them is the base form, without to. Have to works like a normal verb: it changes (has to, had to) and needs do, does or did in questions and negatives.
| Type | Pattern | Example |
|---|---|---|
| Positive | subject + modal + base verb | I can swim. She should rest. It might rain. |
| Negative | subject + modal + not + base verb | He can't drive. You mustn't park here. We shouldn't wait. |
| Question | (Question word +) modal + subject + base verb? | Can you help me? What should I do? |
| Short answers | Yes, subject + modal. / No, subject + modal + not. | Yes, I can. No, you shouldn't. No, it might not. |
| Have to: positive | subject + have/has to + base verb | I have to work on Saturday. She has to wear a uniform. |
| Have to: negative and question | subject + don't/doesn't have to + base verb / Do/Does + subject + have to + base verb? | You don't have to pay. Does he have to work late? Yes, he does. |
- No -s, no to, no do: He can swim (not He cans swim). You must go (not You must to go). Can you come? (not Do you can come?)
- Contractions: can't (cannot), couldn't, shouldn't, mustn't, won't (will not), wouldn't. Cannot is written as one word. In mustn't the first t is silent: /ˈmʌsənt/.
- For past ability, use could (I could ride a bike when I was six). Must has no past form, so use had to for past obligation (We had to wait for an hour).
When to use modal verbs
1. Ability: can, can't, could
Use can for ability now and could for general ability in the past. The negatives are can't (cannot) and couldn't.
- My brother can speak three languages.
- I can't swim very well.
- She could read before she started school.
2. Permission and requests: can, could, may, would
Ask for permission with Can I...?, the more polite Could I...? or the formal May I...? To ask someone to do something, use Can you...?, Could you...? or the very polite Would you...?
- Can I use your charger? Sure, go ahead.
- Could you send me the file, please?
- Would you close the door, please?
3. Obligation: must and have to
Use must or have to when something is necessary. Must often shows what the speaker feels is necessary and is common in written rules; have to often shows a rule or duty that comes from outside. In everyday American English, have to is much more common than must.
- I must call my grandmother. It's her birthday today.
- Nurses often have to work at night.
- All passengers must show their passports.
4. Not necessary or not allowed: don't have to and mustn't
These look similar but mean very different things. Don't have to means it is not necessary, so you can choose. Mustn't means it is not allowed, so don't do it. In American English, mustn't is rare; people usually say can't or aren't allowed to.
- You don't have to bring anything. We have plenty of food.
- You mustn't touch the paintings in the museum.
- You can't park here. It's only for buses.
5. Advice: should and shouldn't
Use should to say that something is a good idea and shouldn't to say that it is a bad idea. Ask for advice with Should I...?
- You should try the soup here. It's delicious.
- You shouldn't drink coffee so late in the evening.
- What should I wear to the interview?
6. Possibility: may, might, could
Use may, might or could when something is possible but you are not sure. Might is very common in conversation, and may is a little more formal. The negatives are might not and may not.
- Take an umbrella. It might rain later.
- I may be late tonight, so start dinner without me.
- Don't eat that mushroom. It could be poisonous.
Useful expressions that work like modals
- be able to
- be allowed to
- need to
- don't need to
- have got to
- would like to
These expressions help when a modal has no form for the tense you need, or when you want an everyday alternative: I'll be able to come tomorrow (not I'll can come). We weren't allowed to take photos. You don't need to pay. I've got to go now.
Examples
Positive
- I can play the guitar.
- You should see a doctor about that cough.
- We have to finish this report by Friday.
- It might snow tonight.
Negative
- She can't come to the meeting today.
- You mustn't use your phone during the exam.
- You don't have to pay. The concert is free.
- He shouldn't eat so much sugar.
Questions
- Can you ride a bike?
- Could you turn the music down, please?
- Do we have to buy tickets in advance?
- Should I call her now or later?
Must or have to? Mustn't or don't have to?
In positive sentences, must and have to are very close: both say that something is necessary. In negative sentences, they are completely different. Mustn't means "it is not allowed", but don't have to means "it is not necessary".
| Must / mustn't | Have to / don't have to |
|---|---|
| I must get more sleep. (I feel it is necessary) | I have to start work at seven. (my job says so) |
| You mustn't tell Mia about the party. It's a surprise! (don't tell her) | You don't have to tell Mia about the party. She already knows. (it isn't necessary) |
| Visitors must wear a badge. (a written rule) | Do I have to wear a badge? (questions usually use have to) |
| I must leave now. (must is only for now or the future) | I had to leave early yesterday. (had to is the past of both) |
Common mistakes
- WrongHe cans swim very well.RightHe can swim very well.
Modal verbs never add -s, even after he, she and it.
- WrongYou must to wear a helmet.RightYou must wear a helmet.
A modal verb is followed by the base verb, without to.
- WrongDo you can help me?RightCan you help me?
Modals make questions by moving before the subject; they never use do.
- WrongI will can drive next year.RightI will be able to drive next year.
Two modals cannot go together, so use will be able to for future ability.
- WrongYou mustn't bring a gift. It's not necessary.RightYou don't have to bring a gift. It's not necessary.
Mustn't means it is not allowed; to say something is not necessary, use don't have to.
- WrongMay you pass me the salt?RightCould you pass me the salt, please?
Use May I...? to ask permission for yourself; to ask someone else to do something, use Can you...? or Could you...?
A note for the house sitter
Examples of modal verbs are highlighted.
Hi Sam! Thanks for looking after our house this week. Here are a few things you should know. You can sleep in the guest room, and you can eat anything in the fridge. You don't have to water the plants, because Mrs. Lee from next door does that. But you have to walk our dog, Bella, twice a day, and you must not give her chocolate. It could make her very sick. The back door is old, so you might need to push it hard. Mrs. Lee may stop by on Thursday. Could you give her the yellow envelope on the table? Oh, and Bella can open the kitchen door with her nose, so you must keep it locked! Call us if you can't find anything.
Modal Verbs quiz
8 questions. Choose an answer to see if it is right and why.
Read texts that use modal verbs
Grammar sticks when you meet it again in real reading. These graded texts use this structure; each one has key words, audio and questions.
Modal Verbs: questions and answers
What are modal verbs in English?
Modal verbs are helping verbs such as can, could, may, might, must, shall, should, will and would. They go before a main verb in the base form and add meanings like ability, permission, obligation, advice or possibility.
What is the difference between must and have to?
In positive sentences they are very similar: both say that something is necessary, and in American English have to is the usual everyday choice. Must often shows the speaker's own feeling or a written rule, while have to often shows a rule from outside. In negatives they are different: mustn't means not allowed, but don't have to means not necessary.
Do you use "to" after modal verbs?
No. After a modal verb, use the base verb without to (You should rest, not You should to rest). In expressions like have to, be able to and ought to, the to is part of the expression.
What is the difference between may and might?
Both show that something is possible, so It may rain and It might rain mean almost the same. Might is more common in everyday conversation, and may sounds a little more formal. Of the two, only may is used to ask for permission (May I come in?).
Is "could" the past of "can"?
Yes, for general ability in the past (I could swim when I was five). But could is also used for polite requests (Could you help me?) and for possibility now or in the future (It could rain later).