在公众号输入关键字"英语单词"或是"yydc"可跳转到该文章。
一、have to 与其他情态动词一样也是后接动词原形，表示外界的强制作用，强调被迫性。含有不情愿的色彩，常译为“必须，不得不”。
We have to resolve this matter once and for all.
我们必须彻底解决这一问题。
I have to go and cook the dinner.
我得去做饭了。
You have to demonstrate that you are reliable.
你得证明自己是靠得住的。
二、have to 可用于多种时态，而且不同时态使用不同的形式：一般现在时中，主语为第三人称单数时用has to ; 一般过去时中，用 had to。 have to 还可以用在其他的情态动词之后。例如：
I have to do some washing.
我必须洗洗衣服。
She has to look after her little sister.
她不得不照顾她的小妹妹。
I had to do my homework last night.
昨晚我不得不做作业。
I think he may have to help his Dad in the garden.
我想他可能不得不在花园里帮他爸爸。
三、have to 的否定式和疑问式一般要借用助动词do的适当形式构成。have to 的否定式是don’t have to; has to 的否定式是doesn’t have to; had to 的否定式是didn’t have to。have to的疑问式同样也借用助动词do的相应形式构成。例如：
He doesn’t have to do the homework now.
他没有必要现在做作业。
A: Do I have to go there now?
我现在就得去那儿吗？
B: Yes, you do. （No, you don’t have to.）
是的，你必须去。（不，你不必。）
We didn’t have to answer the question yesterday.
昨天我们没有必要回答这个问题。
注：情态习语是助动词、不定式或副词的组合。
四、have to 与 must 的区别
A、must 与 have to 的强调重点不同
两者都表示“必须”，但 must 侧重于说话者的主观看法，认为有必要或有义务去做某事；have to则重于客观需要，含有“不得不”或 “被迫”之意：
must:
We must go at once.
我们必须马上就走。
I must ask you not to do that again.
我得劝你别再那样做了。
You mustn't say things like that.
你千万别说那样的话。
I must go to the bank and get some money.
我得上银行取点儿钱。
have to:
If I buy that car, I’ll have to borrow some money.
如果我要买那辆汽车, 我得借些钱。
First, you have to think logically about your fears.
首先，你得对你担忧的理由好好地想想。
I have to admit , the idea of marriage scares me.
我不得不承认，一想到结婚我就害怕。
B、must 与 have to 的时态形式不同
must 只有现在时一种形式(在宾语从句中可以表示过去)，而 have to则有多种时态形式：
He said (that) she must go with me.
他说她必须同我一起去。
He has to apply for a permit and we have to find him a job.
他得申请一个许可证，而我们得给他找份工作。
She had to go there on foot yesterday.
昨天她不得不步行去那儿。
They have had to buy a car.
他们不得不买了辆小汽车。
C、must 与 have to 的非谓语形式不同
have to可以有分词、动名词、不定式等形式，而 must 则没有这些形式：
I have had to pay for repairs to the house.
我不得不支付房屋维修费用。
He only saw her in the evening, having to be away all day.
他整天得外出，只能晚上见她。
I regret to have to trouble you again.
我很抱歉不得不再麻烦你一次。
D、must 与 have to 在否定式中意义不同
must 的否定式 mustn’t 意为“一定不要”、“不允许”；而 have to 的否定式 don’t have to 意为“不必”(=needn’t)。
mustn't:
We mustn't be too strict with young people, nor can we let them do whatever they like.
对青年既不能约束过严，又不能一切任其自流。
We mustn't belittle her outstanding achievement.
我们一定不能小瞧了她所取得的杰出成就。
don't have to:
You don't have to be alone with him and I don't think you ought to be
你不必单独跟他呆在一起，而且我认为你也不该这样。
You don't have to shout at me.
你没必要朝我嚷嚷。
比较：
You mustn’t tell him about it.---->这可能是秘密
你一定不要告诉他这件事。
You needn’t tell him about it.---->他可能知道了
你不必告诉他这件事。
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