Must & have to
Must – I feel strongly about that; speaker’s authority
I must get up early tomorrow. (= I feel that it is necessary for me to get up; I decided)
You must go there. (= I advice you strongly that you go there; I’m telling you to go)
The government must stop wasting taxpayers‘ money! (= I feel very strongly about that but I can’t order the government to stop spending)
They must tell their boss about that costumer complaint. (= It is only my opinion; I can’t make them tell the boss about the problem)
Passengers must travel with the valid ticket only.
Visitors must refrain from smoking inside the museum. (= ‚must‘ in 3rd person is used mainly in written notices and instructions)
Must not – 1) negative obligation imposed by the speaker
2) emphatic advice
You must not smoke here. (= it is banned to smoke here)
also possible: You can’t smoke here.
She mustn’t tell it to anyone. (I feel strongly about that)
We must not go in while the boss is angry. (= it’s a good idea to wait outside; giving the advice)
Have to – external authority, outside influence
I have to work late today because my boss told me to. (I have no control over the situation)
You have to drive carefully because there’s black ice on the roads. (= I’m just saying that, not ordering you)
He has to take an over-night flight to Dubai because there’s no other. (= making a statement about the outside influence)
She has to take her children to school every morning. (= no one else will do it for her; it’s her duty)
We have to stop at Oxford on our way to London. (= statement about the situation)
They have to walk 3 miles to work every day. (= nothing I or them can do about it)
Don’t have to – not obligation; it is not necessary to do it but it is allowed to do it (you have a choice)
I don’t have to write the report tonight. (= I can write it tomorrow; there is no rush)
You don’t have to call me every day. (= It is not an imperative to call me so often)
She doesn’t have to make a coffee for her boss. (= she can do it if she wants BUT it is not in her job description)
We don’t have to drive to work. (= We can but it is not an order)
They don’t have to keep their bedrooms tidy all the time. (= a bit of mess does no harm; their parents are benevolent)
For questions: Do you have to…..?
Do I have to do my homework now? Yes, you do.
Do you have to wear glasses all the time? No, I don’t.
Does he have to work night? Yes, he does.
Does she have to stay at home with their kids? No, she doesn’t.
Do we have to go there tomorrow? Yes, we do.
Do they have to get married? No, they don’t.
Had to – obligation in the past, both speaker’s and outside influence
I had to get up early to catch a bus to school when I was a little boy. (= it was necessary for me to do so; I had no choice)
You had to tell your mother when you will be back tonight. (= her mother wanted to know the time of your arrival)
He had to cancel his holiday because he got a flu. (= outside influence)
She had to go to the dentist last week. (= she had no choice but go)
We had to order a taxi last night. (= there were no buses at night)
They had to go shopping on Sunday. (= they had no food at home)
For future we use ‚ will have to‘
I’ll have to call you tomorrow because I haven’t got that information yet.
You’ll have to book your holiday by Monday. (=Monday is the deadline)
He’ll have to go for a knee operation soon. (=his knee hurts and doctor says he needs an operation)