一些半情态动词的用法

1） 作情态动词的用法：
a. 用于否定结构中，表示“不必”：
You needn’t come to the meeting if you’re too busy. 如果你太忙就不必来了。
We needn’t have packed our thick clothes. The weather was really warm. 我们本来不需要带厚衣服的。天气确实很暖和。
She needn’t have come in person—a letter would have been enough. 她其实不必亲自来的，写封信就够了。
She needn’t have been punished so severely. 她本来不必受这么严厉的惩罚。
△可用在宾语从句中，即使主语动词是过去式，仍可用need：
He said (says) I needn’t pay till the 31st. 他说我到31日才需要付款。
They said he needn’t send a deposit. 他们说他无需寄定金来。
b. 用在带有否定意思的句子中：
I need hardly tell you that the job is dangerous. 我用不着告诉你这工作是危险的。
I scarcely need say how much I enjoyed the holiday. 我简直不用说我假期过得多愉快。
Nobody need be afraid of catching the disease. 谁都不必害怕染上这种疾病。
I don’t believe you need worry. 我认为你不必忧虑。
c. 可构成疑问句：
Need I tell Tom? 我需要告诉汤姆吗？
Need he do it at once? 他有必要马上这样做吗？
Need we come tomorrow? —No, you needn’t (Yes, you must). 我们要来吗？——不必来（你们得来）。
Why need you go today? 你为什么今天就得走？
Need you have paid so much? 你需要支付那么多钱吗？
也可用在表示疑问的从句中：
I asked him whether he need go. 我问他是否必须得去。
I wonder if I need bring my mosquito-net. 不知我是否需要带上蚊帐。
I do not see why we need discuss it further. 我看不出我们还有什么谈下去的必要。
【注】在少数肯定句中，也有用need作情态动词的，例如：
I’ll help you any time, you only need ask. 我随时可以帮你，你只需说一声。
If she wants anything, she need only ask. 如果想要什么，她只需说一声就行了。
Here you need give way to her. 在这一点上你需要向她让步。
2） 作及物动词的用法：
作为及物动词，need表示“需要”，后面可以跟：
a. 名词或代词：
All living things need water. 一切生物都需要水。
Do you need any help? 你需要什么帮助吗？
What we need is some proof. 我们需要的是证明。
Don’t go—I may need you. 别走了，我可能会需要你。
b. 不定式：
I need to ask some advice. 我需要求教。
Do we need to buy tickets in advance? 我们需要预先购票吗？
All you need to do is (to) fill in this form. 你只需要填一下这张表。
The instruments needed to be sterilized. 这些器械需要消毒。
c. 动名词：
His hair needed cutting. 他的头发该理了。
This jumper needs washing (to be washed). 这件套衫需要洗了。
The garden doesn’t need watering—it rained last night. 花园无需浇水，昨晚下雨了。
d. 复合宾语：
He needed his eyes tested. 他需要请人验光。
I need you over to help me with the children. 我需要你来帮我照顾孩子。

1） 作情态动词的用法：
作情态动词时，dare表示“敢…”，这时没有人称形式，但有过去式dared，主要用于：
a. 否定句（有时借助助动词，这时不定式可带to也可不带to）：
I daren’t ask her to marry me. 我不敢求她嫁给我。
The government dared not increase taxes again in this year. 今年政府不敢再加税了。
They dared not move. 他们不敢动。
She dare not say what she thinks. 她不敢说出她的想法。
He doesn’t dare (to) say anything. 他什么都不敢说。
They were so frightened that they didn’t dare go into the room. 他们怕得不敢进屋。
△也可用在带有否定意思的句中：
I daren’t have done it yesterday, but I think I dare now. 昨天我没敢这样做，但我想今天我敢。
No one dared speak of it. 没人敢谈及此事。
He never dared stay long. 他从不敢多待。
We hardly dared (to) breathe as somebody walked past the door. 有人从门口过时，我们几乎都不敢喘气。
I scarcely dare think of it. 这事我简直不敢想。
b. 疑问句及条件从句（有时也可借助助动词）：
Dare you interrupt him? 你敢打断他的电话吗？
How dare you speak to me like that! 你怎么敢对我这样讲话！
I wonder if she dared come home. 不知道她敢不敢回家。
Do you dare tell him? 你敢告诉他吗？
If you dare speak to me like that, you will be sorry. 要是你再敢这样对我说话，你就会后悔的。
Jump if you dare! 你要是敢就跳！
c. 用于I dare say，don’t you dare引导的句子中：
I dare say you’re right. 我认为你是对的。
You’re tired, I dare say. 我想你是累了。
Don’t you dare tell my parents about this! 你敢告诉我父母这件事！
Don’t you dare touch that vase! 不准碰那花瓶！
2） 作及物动词的用法：
作及物动词时可以表示：
a. 敢（做某事）（可用于多类句子）：
He dared to walk the tightrope without a net. 他敢不用安全网来踩钢丝。
He dares to accuse me of dishonesty. 他竟敢说我不老实。
I did not dare to complain. 我不敢抱怨。
I sat at the back, never daring to speak. 我坐在后面，从不敢说话。
Do you dare to suggest that I’m capable of such an act? 你敢说我能做出这样的事情？
b. 敢于面对（尝试）：
He will dare any danger. 他敢于面对任何危险。
He dared the anger of her family. 他敢于面对家人的愤怒。
The actress dared a new way of playing that famous character. 这位女演员敢尝试以新的方式扮演那个名人。
c. 向…挑战，要某人做一件危险的事：
Can you jump off the wall? Go on, I dare you! 你能从墙上跳下来吗？来，我要你跳！
Somebody dared me to jump off the bridge into the river. 有人问我敢不敢从桥上跳到河里去。
I dared them to debate with me about it. 我问他们敢不敢和我辩论这个问题。

1） be able to可以跟一动词，意思和can差不多，有时两者可以换用：
I’m not able to (can’t) answer your question. 我回答不了你的问题。
Are you able to (Can you) type? 你会打字吗？
When he was young he was able to (could) climb any tree. 小时候他什么树都爬得上去。
但be able to可用于更多时态，有时不能用can代替：
I shan’t be able to come to your wedding. 我将不能来参加你的婚礼。
Since his accident he hasn’t been able to leave the house. 他出事以来一直不能出门。
She said she had lost her passport and hadn’t been able to get back that week. 她说她护照丢了，一直无法出境。
She wasn’t sure whether she would be able to get back that week. 她不能肯定那个星期能否赶回来。
2） be able to还可和某些情态动词或系动词连用：
I ought to be able to get in touch with him. 我应当可以和他取得联系。
He might be able to find a good hotel. 他或许能找到一家好旅馆。
She should be able to offer you some good advice. 她应当可以给你出点好主意。
He seemed able to put complicated thought in simple words. 他似乎能把复杂的思想用简单的话语说出来。
3） 还可用于非谓语动词中：
I should like to be able to read the book in the original. 我希望能阅读这本书的原文。
He much regretted not being able to come to your wedding. 他很遗憾没能来参加你的婚礼。
She grasped my hand, not being able to say anything. 她抓住我的手，什么也说不出来。

1） have to的意思接近must，但must强调说话人的意愿：
We must remember this. 我们必须记住这一点。
You must take good care of her. 你要好好照顾她。
而have to表示客观上的必要性，常可译为“（不）得（不）”，否定形式表示“不必”：
You have to have a visa to go to another country. 你到别国去得有签证。
She has to go to the bank this afternoon. 今天下午她得去银行。
We have to be careful in such matters. 处理这类事我们得小心。
△这种结构的疑问式和否定式都借助do构成：
Do you have to leave so soon? 你这么快就得走吗？
Does she have to go with you? 她得和你一起去吗？
What do I have to do to get a license? 我要怎样才能取得驾驶执照？
You don’t have to get up so early. 你不必起这么早。
She doesn’t (didn’t) have to answer all those questions. 她不必回答所有那些问题。
△还可用于多种时态：
I missed the bus and had to walk home. 我没赶上巴士，只好走着回家。
We’ll have to help him as much as we can. 我们将不得不尽力帮助他。
First I’d have to get my father’s consent. 首先我必须取得我爸的同意。
These last few days I’ve had to take a rest. 最近这几天我不得不休息了一下。
If it hadn’t been for your help, I would have had to leave. 要不是你帮忙，我就得离开这里。
2） 这种结构可用于被动语态：
All kinds of difficulties have to be overcome. 有种种困难需要克服。
A lot of letters had to be answered. 有大量信要回。
The whole thing will have to be done all over again. 整件事情不得不重新做一遍。
还可和may，might连用：
We may have to cancel the plan. 我们可能不得不取消这个计划。
They might have to ask her permission to do this. 他们要这样做可能得请求她的许可。
3） have got to和have to意思差不多：
I’ve got to be off now. 我现在得走了。
We’ve got to send her to hospital. 我们不得不送她进医院。
Has she got to get himself involved in this affair? 他有必要卷入此事吗？
She has got to be operated on. 她得动手术。

1） had better也接近一个情态动词，后面总跟动词原形，表示“最好…”（had常可紧缩为’d）
We’d better go before it gets dark. 我们最好趁天没黑就走。
You’d better take a nap after lunch. 午饭后你最好小睡一会儿。
Hadn’t we better take an umbrella? 我们是不是带把雨伞比较好？
What had we better do? 我们最好怎么办？
后面有时可跟不定式的进行式，表示立即做某事：
I think I’d better be going. 我想我最好还是马上走。
We’d better be getting our clothes ready. 我们最好马上把衣服准备好。
had有时可以省略：
You better stop arguing. 你们最好别争论了。
Better not wait for them. 最好别等他们了。
2） had best的用法和had better 差不多：
We had best have his opinion first. 我们最好先听听他的意见。
I had best be going now. 我最好现在就走。