This document discusses different modal verbs used to express rules, obligations, prohibitions, possibilities, and advice. Modal verbs like have to, must, don't have to, mustn't, can't are used to talk about rules and obligations imposed by either the speaker or generally. Verbs like may, might describe future possibilities. Asking for permission is done with may I or may we. Should and ought to give advice about what someone reasonably could or should do in a situation.