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Modal Verbs in English: Rules, Uses and Exercises

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Modal verbs are helping verbs such as can, could, may, might, must, shall, should, will, would and ought to that express ability, permission, obligation, advice or probability. They are followed by the base verb, with no “to” and no “-s”.

Modal verbs are a small group that you use constantly, in general English, business English and exams. This guide shows you the full list, the three rules that make them special, every main use with examples, the mistakes to avoid, and three exercises to practise.

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What modal verbs are

Modal verbs (also called modal auxiliaries) add meaning to another verb: they show how likely, possible, necessary or permitted something is. Instead of describing an action directly, they tell you the speaker’s attitude to it, such as ability, permission, obligation or probability.

The pure modal verbs are: can, could, may, might, must, shall, should, will, would and ought to. Related expressions like have to, be able to and be allowed to are modal substitutes, which fill the tenses that modals cannot.

The three rules of modal verbs

Modal verbs behave differently from ordinary verbs. Three rules make them special:

  1. They never add -s in the third person: She must be hungry, not “She musts”.
  2. They form questions and negatives without do/does/did: Can she go?, not “Does she can go?”.
  3. They are followed by the bare infinitive (the verb with no “to”): I might go, not “I might to go”. (Exceptions: ought to, have to, used to.)

When to use each modal verb

The same modal can have more than one meaning, and different modals can share a meaning. This table shows the main uses with examples.

UseModal verbsExample
Abilitycan, couldI can swim. / She could read at four.
Permissioncan, could, mayCan I sit here? / May I leave?
Obligation / necessitymust, have toYou must wear a seatbelt.
Adviceshould, ought toYou should rest. / You ought to apologise.
Probability (present)must, can’t, may, might, couldShe must be tired. / He can’t be serious.
Probability (past)must have, can’t have, might haveHe must have missed the train.
Requests / offerscan, could, would, willCould you help me? / Will you open the window?
Prediction / futurewillIt will rain tomorrow.

For probability, must means about 90% certain, can’t means impossible, and may, might and could mean about 50%. To use these meanings in tenses modals do not have (past, future, perfect), you need modal substitutes.

Reading the rules is easy; choosing the right modal automatically while you speak is the goal. Practise modal verbs in real conversation with an experienced native teacher in a free trial lesson. No credit card needed.

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Common mistakes with modal verbs

  1. Adding -s in the third person. Wrong: She cans swim. Right: She can swim.
  2. Adding “to” after the modal. Wrong: I must to go. Right: I must go. (Only ought to and have to keep “to”.)
  3. Using do/does in questions. Wrong: Do you can help? Right: Can you help?

Practice exercises on modal verbs

Try this exercise and check your results straight away.

Frequently asked questions

What are modal verbs in English?
Modal verbs are helping verbs such as can, could, may, might, must, shall, should, will, would and ought to. They express ability, permission, obligation, advice or probability, and are followed by the base verb.
What are the rules for modal verbs?
Three rules: they do not add “-s” in the third person, they form questions and negatives without do/does/did, and they are followed by the bare infinitive (the verb with no “to”), with exceptions like ought to and have to.
Do modal verbs take “to”?
No. Most modal verbs are followed by the base verb with no “to”: “I can go,” “She must leave.” The exceptions are ought to, have to and used to, which keep “to”.
What is the difference between must and have to?
In the present, must usually shows an obligation from the speaker, while have to shows one from outside (a rule or law). In the past and future you must use had to and will have to, because must has no past or future.
Which modal do I use for permission?
Can, could and may all ask for or give permission. Could and may are more formal and polite: “Could I leave early?” or “May I come in?” Can is more informal: “Can I sit here?”

Key takeaways

  • Modal verbs express ability, permission, obligation, advice and probability.
  • They take the base verb, with no -s and usually no to.
  • They make questions and negatives without do/does/did.
  • One modal can have several meanings; check the context.
  • For tenses modals lack, use modal substitutes (have to, be able to).

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Written and reviewed by the experienced native English teachers at Live English, online since 2007.