Modal and Non-Modal Verbs

Permission

• We use may or can when we ask for or give permission. We use may not or can’t to refuse permission. May is more formal.
  • A: May / Can we leave?           B: No, you may not / can’t.
• We use be allowed to to talk about rules made by someone else.
  • The teacher says we’re not allowed to use a calculator.
• We use Do you mind if … + present tense to ask for permission. Would you mind if … + past means the same but is more polite.
  • Do you mind if we do that again? Would you mind if we did that again?

Suggestions and expectations

• We use should or shouldn’t to make and ask for suggestions.
  • You shouldn’t be a dictator.
  • They should try to learn from their mistakes.
• Ought to means the same as should, but is less common.
  • You oughtn’t to stay out too late. OR You shouldn’t stay out too late.
• We use be supposed to talk about someone else’s expectations.
  • You’re supposed to be directing, not dictating.

Criticism

• We use should / ought to and should have / ought to have to criticize.
  • You should try a bit harder.
  • I ought to have tried a bit harder.
• We use statements or questions with be supposed to to make mild criticism.
  • You were supposed to be here an hour ago!
  • What’s that supposed to mean?
• We use could have and might have to criticize someone for not doing something.
  • You could / might have told me you were having a party! (= Why didn’t you?)

Obligations

• We use must / mustn’t for strong obligations or prohibitions.
  • A director must understand people.
  • You mustn’t try to make your own versions of their films.
• We use have to or need to to talk about obligation or necessity. We use don’t have to, needn’t or don’t need to when there is no obligations or necessity.
  • You have to find your own style.
  • You needn’t wait if you don’t want to.
• Have got to means the same have to and need to, but is less formal. Gotta is very informal.
  • I have to go. → I’ve got to go. → I’ve gotta go. → Gotta go.
• We usually use must for personal obligations and have to for rules made by someone else.
  • I’m tired. I really must go home soon.
  • You have to use seatbelts, even if you’re only driving a short way.
• Must and mustn’t only refer to present obligations. For past and future obligations, we use have to, need to or not be allowed to.
  • I used to have to practice a lot.
  • I won’t be allowed to go out until I’ve finished.
• We use needn’t have, not didn’t need to, to show that an event or emotion was unnecessary.
  • I really needn’t have worried. (= I worried unnecessarily.)

Ability

• We use can and can’t to talk about present abilities.
  • I can’t hear you. (at the moment)
  • You can spend too much time trying to copy others’ styles. (in general)
• We use be (un)able to in more formal situations.
  • I regret to inform you that we are unable to offer you a job.
• To talk about future abilities, we usually use be able to. We sometimes use can / can’t when we make a decision or plan now about a future action.
  • It’s something I’ll never be able to do anyway.
  • I can’t go out tomorrow night – I’m too busy. OR I won’t be able to go out …
• We normally don’t use could to talk about solving a specific problem in the past. Use a non-modal verb such as managed to.
  • That’s what I managed to do. NOT That’s what I could do.
• We use could and could have when talking about hypothetical situations.
  • If I had more time I could write a book.
  • I could have benefitted from listening to my actors.
• We use be able to after other modals (e.g. might) and in infinitives.
  • I might be able to leave early.
  • I used to be able to swim 50 lengths.

Requests

• We use modals and similar verbs for polite requests. In general, longer structures are more formal and polite.
  • Could you tell me …?
  • Would you mind standing over there?
  • Do you think you might be able to …?

Offers and refusals

• We use Shall I / we …? or I’ll / We’ll to make offers.
  • Shall I bring some sandwiches? We’ll pay for the meal.
• We use will not or won’t to talk about refusal to do something. This does not have a future meaning.
  • I won’t waste time trying to film a perfect scene. (= I refuse to do this.)

Source: Active Grammar, Level 3, Mark Lloyd and Jeremy Day, CUP, 2011 (With Ramrowriter’s adaptation where necessary)