Modal verbs: permission, obligation and necessity - 1 Can, must, should, ought to, had better 1. These are the most common verbs for talking about permission and obligation. 2. Should have to or ought to have + past participle are used to talk about events which did not happen and which we regret. 3. Had better is stronger and more urgent than should/ought to and is often used to give strong advice or warning.

Modal verbs: permission, obligation and necessity - 2 Have to/have got to 1. Have to can be used in any tense to express obligations. 2. Have got to, which can also be used, refers to specific occasions rather than repeated or general obligations. (I’ve got to buy a birthday present for my brother.)

Modal verbs: permission, obligation and necessity - 3 Need 1. Need to/don’t need to refers to something necessary/unnecessary and cover habitual, general and specific necessity. 2. We can also use needn’t + bare infinitive when we want to say something is unnecessary on a specific occasion. 3. Use don’t neet to for habitual or general necessity. 4. When something was not necessary, but you did it, we can use either needn’t have + past participle or didn’t need to + infinitive.

Modal verbs: permission, obligation and necessity - 4 Be able to, be allowed to, be permitted to, be supposed to 1. We often use these forms to talk about what is possible or permitted instead of can, particularly when we want to use a form which can does not have (future, present perfect etc.) 2. Be permitted to + infinitive is used in formal situations, eg, notices and announcements to say what can/can’t be done according to the law or to rules and regulations. 3. To be supposed to suggests the idea that rules are not necessarily obeyed, eg, Students are not supposed to have guests after 12.00, but everyone does.