grammar, English, must, have to, obligation

1. Must vs Have To / Has To
Must and have to express obligation or necessity:
The main differences between must and have to are:
Must means "really should or else it will be bad for you", it expresses an obligation
forced by the speaker.
Have / Has to expresses general obligations. When we are talking about another
person's obligation we use have to, too. We use have to when the obligation comes
from outside.
See Modals Chart / Modals Exercises
See Subject Exercises:
Must vs Have/Has To Exercise 1
Must vs Have To Exercise 2
Mustn't vs Don't Have to
Must/Mustn't vs Needn't vs Have to
Examples Sentences
Teacher : You must listen to me carefully.
Father : You must stop smoking.
You have to put on uniform at school.
She has to buy new dictionary for school.
You have to give your report by 5 p.m. tomorrow.
They have to wake up early in the morning.
MUST
Affirmative Form
Subject + must + verb + complement
You must come home before 8 o'clock.
Negative Form
Subject + mustn't + verb + complement
You mustn't come home before 8
o'clock.
Question Form Must + subject + verb + complement ?

2. Must you come home before 8 o'clock?
Negative Question
Form
Mustn't + subject + verb + complement ?
Mustn't you come home before 8
o'clock?
HAVE TO / HAS TO
Affirmative Form
Subject + has to / have to + verb + complement
He has to take his medicine.
Negative Form
Subject + don't have to / doesn't have to + verb + complement.
He doesn't have to take his medicine.
Question Form
Does / Do + subject + have to + verb + complement ?
Does he have to take his medicine?
Negative Question
Doesn't / Don't + subject + have to + verb + complement ?
Doesn't he have to take his medicine?
Note:
When we say he doesn't have to take his medicine, we mean that he is not
obligated to take his medicine. (Lack of necessity)
We say he mustn't take his medicine to give it a negative obligation meaning.

3. Note:
Must is only used in present and future meanings. Have to can be used in any
tenses.
Note:
Must also has a probability meaning.
He missed the class for the first time, he must be sick.