have to/have got to 与 must 两者同义，均表示“必须、有义务做某事”，但略有差别。
(1) 一般说来，表示“客观必须”常用have to/have got to；表示“主观上必须做某事”通常用must。
- I have to go to the office by bike every day.
我每天必须骑自行车上班。 - I must study harder to pass the examination with flying colors.
为了以优异的成绩通过考试，我必须更加努力地学习。 - You must finish it by next Monday. (有“I want you to...”之意)
你下周一前必须完成它。 - I must stop smoking. (是“我”想要戒烟。)
我一定要戒烟。 - You've got to go and see the boss. (有“sb. wants you to...”之意)
你得去见见老板。 - Catholics have to go to church on Sundays. (The religion tells them to do so.)
天主教徒得在星期天去做礼拜。
(2) ①must用在疑问句中表示征询对方的意愿。
- A: Do your homework.
做你的家庭作业。
B: Oh, must I?
哦，我必须做吗？
②must无过去时，表示过去常用had to，但must可用在过去时的间接引语中。
- When I was your age, I had to get up at 5 every morning.
当我在你这么大时，我每天早晨必须5点起床。 - When he comes, I must go.
他来时，我必须走。
＊上句变为过去式，应是：When he came, I had to go.他来时，我必须走。
- I told him he must make a decision.
我告诉他他必须做出决定。
③其否定形式：mustn't, don't have to, haven't got to意思差别较大。
- You mustn't tell George. (Don't tell George.)
你一定不要告诉乔治。 - You don't have to see George. (You can if you like but it isn't necessary.)
你不必去见乔治。
＊在英式英语中，往往用needn't代替don't have to和haven't got to。
- You needn't tell George.
你不必告诉乔治。
(3) 用have to代替must，能灵活地构成各种时态和虚拟语气。
- I had to go there at once.
我必须马上去那里。 - I shall have to go there at once.
我将必须马上去那里。 - I have had to stay here.
我必须留下来。 - Had I to go there, I would go at once.
如果我必须去那里的话，我会马上去的。
＊have to, have got to, must在肯定、否定、疑问句中的形式：
| I have to do this.
Have you to do this? I have not to do this. I had to do this. Had you to do this? I had not to do this. |
I have got to do this.
Have you got to do this? I have not got to do this. I had got to do this. Had you got to do this? I had not got to do this. |
I must do this.
Must you do this? I need not do this.
|
(4) 另外，在英式英语中表示习惯性或重复性的“义务”或“必须”时，用have to形式，疑问句、否定句用do构成。
- I don't usually have to work on Sundays.
星期天我通常不必工作。 - Do you often have to speak French in your job?
你在工作时常常得讲法语吗？ - How often do you have to travel on business?
你多长时间必须出差一次？
(5) ①当说及必须做的一件事时，较常用have got to(特别是在非正式文体中)。
- I haven't got to work tomorrow.
明天我无须工作。 - Have you got to do any interpreting next week?
下周你必须做些口译的工作吗？
②带got的形式用过去时不自然，往往用普通动词形式代替(用did)。
- Did you have to go to church on Sundays when you were a child?
你在孩提时代必须在星期天去做礼拜吗？
(6) 谈及将来，既可用have/got to，也可用will have to。
I've got to get up early tomorrow — we're going to Beijing. (也可用I'll have to ...) 我明天必须早起，我们明天要去北京。
(7) ①在美式英语中，have的普通动词形式(不用got，疑问句、否定句中用do)，可用于各个意思(状况、动作)，这一点，由于受美式英语影响，在英式英语中也已很常见。
- What time do you have to be in Boston tomorrow?
你明天什么时候必须到波士顿？ - You don't usually have to tell her things twice.
你通常不需要把事情告诉她两遍。
②在比较随便的美式英语中，带got形式的也是可以接受的，特别是在肯定句中。比较随便时，have常被省略。
- A: I (have) got to go. 我必须走了。
B: Oh, do you? 哦，必须走吗？ - You (have) just got to help me.
你可要帮助我。
