1) Could you refresh me when to use one and when the other one when expressing obligation?

2) Can Must or Musn't be used in questions and conditional clauses?

3) Is it correct to also say 'I haven't got to get up early tomorrow as I'm not going to work'.

I'm refering to the use of 'have got to' (haven't got to) to express obligation as I've heard that some consider that pattern more appropiate to be used to express possesion.

Thanks in advance.
I hope this can help you with must and have to. I prefer to leave questions 2 and 3 of you rpost to a native speaker.


1 Have to expresses strong obligation. The obligation comes from 'outside' - perhaps a law, a rule at school or work, or someone in authority.

"You have to have a driving licence if you want to drive a car." (That's the law.)
"I have to start work at 8.00." (My company has this rule.)
"The doctor says I have to do more exercise."

2 Don't/doesn't have to expresses absence of obligation (it isn't necessary) .

"You don't have to do the washing-up. I've got a dishwasher."
"She doesn't have to work on Monday. It's her day off."


1. Must expresses strong obligation. Generally, this obligation comes from “inside” the speaker.

"I must get my hair cut." (I think this is necessary)

2. Because must expresses the authority of the speaker, be careful of using “You must ...” It sounds very bossy!

"You must help me." (I am giving you an order)

3. “You must ...” can express a strong suggestion.
"You must see the Monet exhibition. It’s wonderful."
"You must give me a ring when you’re next in town."

4. Mustn’t expresses prohibition.
"You mustn’t smoke here."

'I really must go now.'
'Must you? Well, if you must, please take a piece of this delicious cake with you.'
'Wonderful! If I take this cake though, I must give you something in return.'


That sounds like perfectly acceptable casual spoken English to me, but I would think that 'I don't have to get up early' is both better grammar and in more common use. The affirmative form is less awkward and commonly expresses obligation, often with added emphasis: 'I have got to get up early tomorrow-- I've been late to work twice this week already!'.

'Have got to' expresses obligation; 'have got + noun' expresses possession: 'I have got to study tonight-- I have got a test tomorrow'.

Students: We have free audio pronunciation exercises.
You don't need to hide. You must trust in me. Thanks. They expresses lack of obligation and real possession. Got it?
MajYou don't need to hide. You must trust in me. Thanks. They expresses lack of obligation and real possession. Got it?
What's the difference between trust and trust in?
Why not start a new thread? Nobody would ever dream that a question on the difference between trust and trust in could be found under a thread about must and have to! Emotion: smile

trust in is more intimate and personal and somewhat more vague. trust is more external and specific.

Trust in me. I'll take care of you.
Trust in me. I'll be your true and loyal friend.
Trust me. I'll be on time.
Trust me. I'll sign the papers as you asked.

Students: Are you brave enough to let our tutors analyse your pronunciation?
l'm french and l have the impression l always wrote "musn't" instead of "mustn't"

is MUSN'T a correct form ?

No, it's not correct. You are probably being misled because the first 't' in mustn't is silent, not pronounced.

Best wishes, Clive