Modals of obligation and advice
must, have to, should, ought to (review).
Modal verbs are special auxiliary verbs that express obligation, prohibition, or advice without changing form for person or number. 'Must' expresses a strong internal obligation or a firm rule that comes from the speaker ('You must finish your homework'). 'Have to' also expresses obligation but usually refers to external rules or requirements ('Students have to wear a uniform'). The negative forms differ critically: 'mustn't' means it is forbidden — you are NOT allowed to do something ('You mustn't smoke here'), while 'don't have to' means there is no obligation — you are free to do it or not ('You don't have to come early'). For advice, 'should' and 'ought to' are near-synonyms expressing a recommendation ('You should drink more water / You ought to see a doctor'). 'Had better' is slightly stronger than 'should' and often implies a warning about a negative consequence ('You had better leave now or you'll miss the bus'). For example: 'You must wear a helmet — it is the law; you don't have to wear gloves, but you should, because it is safer.'
Rules
- 1'Must' expresses strong obligation from the speaker or writer; 'have to' usually expresses an external obligation (rules, laws, duties).
- 2'Mustn't' = prohibition (it is forbidden); 'don't have to' = no obligation (it is not necessary, but allowed).
- 3'Should' and 'ought to' both express advice or recommendation; they are interchangeable in most everyday contexts.
- 4'Had better' expresses urgent advice with an implied warning — use it when there may be a negative consequence if the advice is ignored.
- 5All modals of obligation and advice are followed by the bare infinitive (base form of the verb), never 'to' — except 'ought to' and 'had better' which use 'to' and bare infinitive respectively.
Practice
10 easy · 10 medium · 10 hard