The document summarizes the different uses of modal verbs in English including:
- Ability, request, possibility, inability expressed by can, be able to, can't, could, may/might
- Obligation and necessity expressed by must, have to, need to, needn't, don't have to, mustn't
- Advice, opinion expressed by should/ought to
- Certainty, lack of obligation expressed by modal perfects and other modal constructions like shall, would have