Unit 18: must/have to (obligation, prohibition)

Obligation
We use must when we believe something is necessary:

It’s a great book, you must read it
I must call my parents tonight
You must come over for dinner

We use have to when we are obliged to do something, even if we don’t
want to do it.

I have to get up early for work tomorrow
I have to complete my tax return before Friday
Do I have to?

Prohibition

When something is not permitted, we use mustn’t:

You mustn’t smoke here, it’s forbidden
It’s a secret, you mustn’t tell anyone

Don’t have to

Don’t have to is not the same as mustn’t