Video lesson about modal verbs of obligation: 'must', 'have to', 'don't have to' and 'mustn't'.

Read the explanations and then watch the other videos in this lesson.

To express obligation or strong advice in English we can use HAVE TO or MUST

MUST
This is a modal verb, so it doesn't use DO or adds an -S for the 3rd person singular of the present:

- You must stay here
- Must she come with me?
- No, she mustn't

HAVE TO
This is a normal verb, so it uses DO and has an -S in the 3rd person singular of the present.

- You have to stay here
- She has to go
- Does she have to come with me?
- No, she doesn't

In modern English, "must" and "have to" usually mean the same, so you can use both:

Sorry, I have to go = Sorry, I must go

But the verb MUST sounds stronger than HAVE TO

---- COLLOQUIAL FORMS ----

HAVE GOT TO
This form is more common in Britain. It's a normal verb, so we use DO for negatives and interrogatives
- Sorry, I've got to go
- Do you have to go now?

GOTTA
This form is more common in America.
- Sorry, I gotta go
(gotta = have got to)

NEGATIVE OPTIONS
- You mustn't tell a secret = don't tell a secret!
- You can't park here = you mustn't park here
- You shouldn't park here = it is not a good thing for you, this is my advice

Compare:
- You can go = permission (you can go if you want)
- You can't go = prohibition (stay!)
- You have to go = obligation (go!)
- You don't have to go = no obligation (you can go or you can stay)