We use have to and must + infinitive when we talk about something that is necessary to do. Both must and have to are used for obligation.
Example:
I must go to work now.
or
I have to go to work now.
These two words have very similar meanings, but there is a difference in which situations each word is used. While must can generally be replaced by have to, there is a slight difference in their use:
We generally use must when the speaker decides that something needs to be done. Must expresses the speaker’s feelings. Must is used more in formal writing, for example in written notices.
![](https://startyourenglish.com/wp-content/uploads/2021/07/must-english-1024x724.jpeg)
Examples:
- I am having a party on Saturday. You must come. (I want you to come.)
- I must remember to call our client tomorrow. (my opinion)
- I must stop smoking; it is bad for me. (my opinion)
- I must go now, it is late. (my opinion)
- You must be mistaken. (my opinion)
- We must have breakfast first. (my opinion)
- It is a great film. You must see it!
![](https://startyourenglish.com/wp-content/uploads/2021/05/must_en_s_english-1024x788.jpg)
We use have to when somebody else other than the speaker has made the decision. Have to is frequently used in conversation and it is mainly used to express obligations.
Examples:
- You have to go to school tomorrow. (there’s a rule requiring you to go to school)
- You have to take your guinea pig to the vet if it gets sick.
- Do you have to wear uniform at school? (asking about school rules)
- You have to go to work on Monday.
- He has to clean his room.
![](https://startyourenglish.com/wp-content/uploads/2021/05/have-to-1024x597.jpg)
However, in their negative forms, mustn’t and don’t have to have completely different meanings:
We use mustn’t to express prohibition
Examples:
- I mustn’t eat too much bread, I am getting fat.
- Students must not leave their bags here.
- Policemen must not drink on duty.
- You mustn’t be late for class.
- He must not forget his books.
- I mustn’t make a mess on the table.
- You mustn’t drive because you do not have driving licence.
- George must not sleep in class.
![](https://startyourenglish.com/wp-content/uploads/2021/05/must-not-english-1024x724.png)
We use don’t have to to express the absence of obligation or necessity:
- You are tired, you don’t have to drive. I will.
- He doesn´t have to go to work on Sundays.
- Children don’t have to wear a uniform at this school.
- We don’t have to go to shop today. We can go tomorrow.
- We don’t have to watch this movie; we can watch something else.
Forming sentences with must
Affirmative | Negative | Interrogative |
I must work. | I must not (mustn´t) work. | Must I work? |
You must work. | You must not (mustn´t) work. | Must you work? |
He must work. | He must not (mustn´t) work. | Must he work? |
She must work. | She must not (mustn´t) work. | Must we work? |
It must work. | It must not (mustn´t) work. | Must it work? |
We must work. | We must not (mustn´t) work. | Must we work? |
They must work. | They must not (mustn´t) work. | Must they work? |
Forming sentences with have to
Affirmative | Negative | Interrogative |
I have to work. | I do not (don´t) have to work. | Do I have to work? |
You have to work. | You do not (don´t) have to work. | Do you have to work? |
He has to work. | He does not (doesn´t) have to work. | Does he have to work? |
She has to work. | She does not (doesn´t) have to work. | Does she have to work? |
It has to work. | It does not (doesn´t) have to work. | Does it have to work? |
We have to work. | We do not (don´t) have to work. | Do we have to work? |
They have to work. | They do not (don´t) have to work. | Do they have to work? |