The usage of "have to "

I will talk about the usage of "have to". I will explain it in three aspects.

The first point: the meaning of have to 

"Have to "means "必须；不得不”

The second point: the basic forms of "have to "

Affirmative  form： have to/ has to / had to...

Negative form: don't  / doesn't /didn't have to...

Question form: Do / Does/ Did sb. have to...

Affirmative  form：

eg: I have to do the housework every day.

She has to do the housework every day.(Here you should change "have" into" has")

I had to do the housework yesterday.(Here you should change "have" into" had")

Negative form:

eg: I don't have to do the housework every day.(Here you should add "don't" to become a negative sentence.)

He doesn't have to do the housework every day.(Here you should add "doesn't" to become a negative sentence.)

We didn't have to the housework every day.(Here you should add "didn't" to become a negative sentence.)

Question form:

eg:  Do you have to do the housework every day?(Here you should add "do" to become a question sentence.)

Does he have to do the housework every day?(Here you should add "does" to become a question sentence.)

Did you have to the housework every day?(Here you should add "did" to become a question sentence.)

The third point：

the same and  differences between “have to "and " must"

the same points are they both mean "必须；不得不"

and you must use the basic form of verb after them.

The differences are :

The First one : "must" focus on subjective.  but "have to " focus on objective.

eg: We must be there on time.

I have to leave school because my family is poor now.

The second one: There are many forms of "have to" . But "must "has only one form.

eg:He had to look after his sister yesterday.

His father has to go to take care of him.

She must go with me.

The third one:

"Must" has the meaning of "一定是；必然”. But "have to "doesn't have this meaning.

eg:Your sister must be a doctor in this hospital.

The forth one:

"Mustn't "means "禁止“

"Don't have to "means "不必”

eg: You mustn't tell him about it.

You don't have to tell him about it.