When we want to express permission, prohibition (not allowing something), obligation or no obligation, we use modal verbs.
When talking about obligations (what you have to do), we use the modal verbs ‘have to’ and ‘must’. There is a slight difference between the way they are used.
- She must stay in bed until her back is better.
- George has to go to New York on business.
| Note: To express a mild obligation or advice, we can use ‘should‘. – You should visit your grandma. To express a recommendation or moral obligation, we can use ‘ought to’: – You ought to drive carefully in bad weather. |
Remember that modal verbs are always followed by a base form of a verb – an infinitive verb without to.
Must
The verb ‘must‘ expresses stronger and shows us that the obligation comes from the speaker. It isn’t a law or a rule.
- I must stop smoking. (I really need to)
- I must call my dad tonight.
- You must come and visit us the next time you come here.
We form positive statements with ‘must’ like this:
subject + must + the verb
| Singular | Plural |
| I must go You must go We/she/it must go | We must go You must go They must go |
- I must call my sister this evening.
- All visitors must go to the reception first.
Have to
The verb ‘have to‘ expresses an obligation due to circumstances or outside factors (e.g. laws, agreements, other people’s orders, etc.). It’s a law or a rule and the speaker can’t change it.
- I have to stop smoking. (doctor’s orders)
We form positive statements with ‘have to’ like this:
subject + have/has to + the verb
| Singular | Plural |
| I have to go You have to go He/she/it has to go | We have to go You have to go They have to go |
- We have to wait here for a taxi.
- Mary has to start work at 8am.
Must vs Have to
Here’s a summary of differences between ‘must’ and ‘have to’:
Watch this video from Oxford Online English to learn how to use ‘must’, ‘have to’ and ‘should’ correctly:
Talking about obligation in the past
There is no past form of ‘must‘, so to talk about obligation in the past we use ‘had to‘.
had to + base form of the verb
- I had to work late last night.
Talking about obligation in the future
There is no future form of ‘must‘ so we use ‘have to‘:
will have to + base form of the verb
- I will have to work late last night.
Read more on this topic:
Modal Verbs for Obligations: Negative and Questions