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Infinitive 不定式
不定式在句中充当结构
在句中可作除谓语以外的一切成份：主、表、宾、定、状、(主、宾)补语。
1. 不定式作主语
To say something is one thing, to do it is another.
It is not fair to blame them for the accident. (it 形式主语)
2. 不定式作表语
My suggestion is to carry out the plan immediately.
The question is how to organize the work. (不定式的特殊结构，见后)
3. 不定式作宾语
He offered to go with us.
I don't know where to get the books.
(不定式的特殊结构，见后)
常跟to do(不定式) 作宾语的v:
afford, agree, arrange, ask, attempt, beg, care, choose, claim(声称),dare, decide, decline(谢绝),desire, determine, fail, intend, learn, long, mean, offer, pretend, promise, refuse, seek, tend, undertake(承担), volunteer.
不定式的特殊结构
构成：疑问代词、副词及whether / if + to do
常跟疑问代词、副词及whether / if + to do作宾语的v.有
ask, consider, decide, discover, discuss, explain, find out, inquire, forget, know, learn, remember, show(演示),tell, think, understand, wonder.
Examples:
I still don't know whom to turn to for help.
They are trying to find out how to solve the problem.
Show me where to put the books.
They haven't decided yet (as to) whether to accept our offer of help.
如果不定式作宾语又跟有补语，通常要用“it”作形式宾语，而将不定式放到补语后面去。
eg. 他们发现提前做好一切准备是不可能的。
They found it impossible to get everything ready in advance.
I consider it my duty to point out their shortcomings.
4. 作宾/ 主语补足语
Mr. Smith wants his son to become a lawyer.
The suspected man was seen to enter the building.
跟不带“to”的不定式作宾补的v:
see, hear, look at, listen to, feel, observe, watch, notice 等感官v 及let, make, have, keep.
The teacher makes us write a composition every week.. (被动语态中要加上“to”)
不定式的复合谓语结构
复合谓语结构:(两个或多个部分构成复合谓语，如:He can do it)
(1) be said (reported, known, believed, announced, claimed, stated,…) + to do
=>It is said ... that …
Beijing is known to have rich cultural heritage.
(It is known that Beijing has ...)
(2) seem(happen, appear, prove, tend)+ to do
I happened to be out when she called.
(3) be likely(certain, sure, willing, anxious, ready, bound, eager, reluctant) +to do
They are likely to succeed.
She is always ready to help others.
5. 不定式作定语
通常为后置修饰语:(post-modifier)
He used to have a lot of meetings to attend.
There is nothing to worry about.
6. 不定式作状语
(1)目的状语
He hurried through his work so as to(in order to)catch the train.
They will go to the station to meet the guests.
To survive the severe competition in the future society, one must have all-round abilities.
(2)不定式作状语:结果状语
She was so angry as to be unable to speak.
I hurried to Prof. Wang's house only to find he was out.(常表示令人不快的结果)
(3)不定式作状语:原因状语
We are overjoyed to see you.
I am happy to be here.
I feel honored to give a speech here.
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