1. have to 比較強調客觀需要，表示因客觀環境或事態促使而不得不做某事；must強調主觀看法，表示主觀上認為有必要做某事。例如：

I must learn another language.

（主觀想法: I want to）

I have to learn another language.

（客觀需要：身為一個外交官）

You must be back before 10 o'clock.

（叮囑或命令）

You have to be back before 10 o'clock because the train is to leave at 10:05.（客觀需要）

2. have to多表示義務或習慣動作；must則用于表示一種重要或急迫的事情。例如：

We have to care for the young.（義務）

She has to be at the office before eight every day. （習慣）

You must go to the manager at once, or you'll be dismissed.

務必馬上去見經理，不然你會被開除的。（急迫的事情）

3. have to可用于不同的時態；而must一般只用于現在時（但也可以表示將來的情況，在間接引語中也可以表示過去時）。例如：

I have to (must) leave now.

We'll have to buy another TV set.

They had to put off the sports meet because of the bad weather.

He said that the work must be finished within two weeks.

4. must還可以表示一種推斷和揣測，而have to則不能。例如：

This must be Jin's pen.

5. "must＋動詞完成式"可以用來表示對過去情況的揣測，而have to則不能。例如：

She must have read the book sometime in the past, or she couldn't have answered the question so well.

她一定在過去某個時候讀過這本書，不然，這個問題她不會回答得這么好的。

Note:

在現代英語中，have to 中不定式和疑問句式既可以按照助動詞的變化規則構成，也可以按照行為動詞的變化規則構成。例如：

Have you to finish the work before supper?

Do you have to finish the work before supper?

have got to 常可同have to換用，但有時表示不同的含義。比較：

He has to report to the headquarters every two days.（例行公事，習慣動作）

He has got to report to the headquarters every two days.（一道指示或命令，必得每天報告一次）

另外，作“有”解時，have got和have通常是可以換用的，have got更口語化，但有時表示不同的含義。比較：

The man has a blind eye.那人有一只眼瞎了。

The man has got a blue eye.那人有一只眼被打青了。

must not表示禁止，是說話人強有力的勸告或命令，意為“一定要，不準”。因此，在回答由must引導的問題時，如果是否定的回答，表示“不必，沒有必要”，不能用mustn't，而要用needn't或don't have to.試比較：

You must not drive fast.你不能開快車。（路險或有速度限制）

You needn't drive fast.（時間充裕）

翻譯下面兩個句子.

1. Though she didn't need to, she must go.

2.You don't have to come again, but you must.

答案：

Though she didn't need to, she must go.

雖然她不用去，她卻偏要去。

You don't have to come again, but you must.

你不必再來，可是你執意要來。