modal verbs

The modal verbs are can, could, may, might, will, would, shall, should, ought. They are known as modal auxiliary verbs because they "help" another verb.

Form:

1. there in No - S in the 3rd person singular : she can swim, he must be tired, it might rain, etc
2. there is no Do/Does in the question: shall we go for a walk?, can I help you?
3. there in not Don't / Doesn't in the negative: I won't be in a minute, he can't dance, you mustn't steal
4. Modal auxiliaries verbs Don't usually have past forms. Other expressions are used instead: I had to work at school;
5. Could is used with a past meaning in some cases. Compare the following sentences: I could swim when I was six (=general ability). The prisioner was able to escape by climbing onto the roof of the prison. (not could escape) (= ability)
6. they have no infinitives and no -ing forms. Other expressions are used instead: I'd love to be able to ski; I hate having to get up on cold, winter mornings
7. they are followed by an infinitive without to. The exeption is ought to: you must go; I'll help you, you ought to see a doctor
8. they can be used with perfect infinitives to talk about past: you should have told me that you can't swim; you might have drowned!