A.     1) HAVE TO可用在一般的情況:

     We have to go to the doctor right away.

     Students have to turn in their thesis before the graduation.

 2) 也可用在所有的時態(適用於否定句, not have to,見下):

   Jeanette has had to attend the meeting for the whole month. (現在完成式)

   Steve will have to finish his movie production by the end of this year. (未來式)

   They had to apply for the visa to go visit their grandparents. (過去式)

3)也經常用在問句:

   Do we have to be there tomorrow?

   Where will James have to go on Thursday?

B.     1) HAVE GOT TO* 常用在口語或非正式表述的句子中:

     Lucy’s got to eat more; she is so thin that everyone will think she suffers from anorexia.

C.     1) MUST* 常用於標語,警告等表達裡:

     You must stop completely at a stop sign.

 2)用在口語時,通常為一個人有很大的權力,或這件事為非常緊迫的事:

   The gangster said to the informant: “You must disappear from my sight from now on, or you’ll wish you were never born.”

“Susan, you must let your parents know the severity of this matter.”

*注意! Have got to 和Must只能用於現在式與未來式(適用於否定句,must not,見下):

You must hand in the painting by the end of this week.

We’ve got to buy food for the party this afternoon.

D.     否定語:

1) Don’t have to與 Must not的比較:

(沒有必要性) She doesn’t have to go to the meeting.

(有必要性,甚至強制性) She must not be late for the meeting.

                    They must not break the law.

2)Must not通常用於寫作中;若在口語用法上,我們用Can’t:

例如出現在衣物的清洗上:

You must not bleach the blouse.

口語上:

You can’t dry this one in a dryer. It will shrink.