Modal verbs

Modal verbs

1. Obligation and necessity

   • We use must, mustn't, have got to and have to to express a strong obligation. We use don't have to to express a lack of obligation. Generally, when the obligation comes from an external source, we use have to or have got to rather than must, but this is not a strict rule
     • I've got to go to the bank at lunchtime
     • You mustn't wear shoes in the house
   • We use need to and needed to to express necessity
     • I need to finish this report by Friday
   • When we use needn't have we suggest that something which was done was not necessary: when we use didn't need to it means an action wasn't necessary, whether it was actually done or not
     • I'm glad you didn't bring any food, actually, because you didn't need to
     • You needn't have brought any food. We have lots already
   • We sometimes use shouldn't have in this way when someone has done a kind thing
     • Thanks for the flowers, but you shouldn't have brought any
   • When we want to talk about past or future obligations we use the phrasal modal verb have to (not must)
     • We all had to leave work early today because the heating system broke down
     • I can't give you an answer right now. I'll have to speak to my wife about it first

2. Ability, possibility and probability

   • We use the modals could, can't, may, might, must and should to talk about or speculate on what is possible, probable or almost certain
     • I might join you later if I manage to finish my work in time
     • With Vince in their team, they should win easily
   • We use a past modal form (modal+have+ past participle) to speculate on a past action or event
     • He can't have seen me or he would have stopped and said "hello"
     • I didn't feel tired at all. I could have walked another ten miles
     • Why hasn't he replied? He should have read my message by now
   • We can make something seem more probable by adding the word well after could, may or might
     • I may well accept their offer. Luc says I'd be a fool not to
   • We cannot use should if we are expressing a pessimistic idea
     • He may well fail his exam, because he's done no work
   • Sometimes might/ could have+ past participle are used to express criticism, not possibility
     • You might have told me sooner that you weren't going to eat. I've cooked all this food now.
   • When we want to talk about future ability we cannot use can; instead we use the phrasal modal verb be able to
     • Our baby is doing fine. He's still crawling, but he'll be able to walk in another couple of months
   • We use can with certain verbs (appreciate, sympathize, understand) for emphasis
     • I can understand your frustration

3. Advice

   • We use should and ought to to say what is the right and wrong thing to do or to have done, or to express a moral obligation
     • You ought to be more careful about leaving your computer on when you're not at your desk. Anyone could read your emails.
     • He should show his parents more respect
   • The past form is should have or ought to have+ past participle
     • You should have told me that you didn't eat meat. I would have cooked something else

4. Unwillingness

   • We use won't (and wouldn't in the past) to express the idea that someone or something is unwilling to do something
     • This new key won't turn in the lock
     • I'm sick of my car. It wouldn't start again this morning

5. Permission and offers

   • We use can, could, may, and might to ask for permission and to make requests. Could and might are more indirect and so often considered more polite forms
     • May I ask you a personal question?
     • Could you just give me a hand moving this table?
     • Might you be willing to be filmed for a short video we are making?
   • We cannot use may with you in this way
     • Could you just spare me ten minutes of your time later this morning?

6. Would

   • Would is used to add a conditional sense to statements and requests. It is often used to respond to suggestions or offers, when we don't want to commit to a definite answer.
     • Shall we meet for a drink some time? Yes that would be nice
     • Would you be prepared to split the cost with me? That would be difficult for me, I'm afraid