Obligation and necessity
must/have to; shoud/ought to, need
Tammekänd, L. 2009. National Exam in English
must and have to
- must is often personal and expresses someone’s opinion
- have to often refers to laws and regulations
You must get your hair cut. (=I think it’s a good idea)
You have to wear a uniform. (= It’s a regulation)
You mustn’t tell lies. (= It’s necessary that you DO NOT lie; very categorical)
You don’t have to lie. (It’s NOT necessary for you to lie)
- have to exists in all tenses so we can use it whenever must is impossible
She is having to travel by bus instead. (NOT is musting)
need and need to
- we can use need as if it was a modal verb
No one need feel left out.
- we normally use need with a full infinitive (the infinitive with "to"). It means the same as have to
We need to get some soup.
- need is nearly always used in negative. Not need to is also possible.
You needn’t go. (= modal pattern)
You don’t need to go. (= normal negative pattern with don’t)
didn't need and needn't have to
didn't need to = it was not necessary to do so
She didn't need to take a taxi. (= it was not necessary, so she didn't to that)
needn't have to = it was not necessary to do so, but it was done
You needn't have bought any bread. I already did that. (= it was not necessary, but it was done anyway)
- must is often personal and expresses someone’s opinion
- have to often refers to laws and regulations
You must get your hair cut. (=I think it’s a good idea)
You have to wear a uniform. (= It’s a regulation)
You mustn’t tell lies. (= It’s necessary that you DO NOT lie; very categorical)
You don’t have to lie. (It’s NOT necessary for you to lie)
- have to exists in all tenses so we can use it whenever must is impossible
She is having to travel by bus instead. (NOT is musting)
need and need to
- we can use need as if it was a modal verb
No one need feel left out.
- we normally use need with a full infinitive (the infinitive with "to"). It means the same as have to
We need to get some soup.
- need is nearly always used in negative. Not need to is also possible.
You needn’t go. (= modal pattern)
You don’t need to go. (= normal negative pattern with don’t)
didn't need and needn't have to
didn't need to = it was not necessary to do so
She didn't need to take a taxi. (= it was not necessary, so she didn't to that)
needn't have to = it was not necessary to do so, but it was done
You needn't have bought any bread. I already did that. (= it was not necessary, but it was done anyway)
Exercise 1
Obligation and Necessity
Gap-fill exercise
Fill in the gaps with must, mustn't or needn't, don‘t have to, needn't have or didn't need to and the correct form of the verb in brackets. pay attention to the contractions. Fill in all the gaps, then press "Check" to check your answers.
