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不定式的基本形式与结构
动词不定式指通常由to加上动词原形(如to write)所构成的一种非限定性动词形式，但在有些情况下to可以省略。
动词不定式有进行体和完成体(如上to be writing，to have written)，也有被动态(如to be written)，所有的主动词，不论是及物动词还是不及物动词，也不论是动作动词还是状态动词，都有不定式形式。助动词除be和have外，没有不定式形式。动词不定式在语法功能上可作主语、宾语、表语、定语和状语。
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不定式的用法
1)不定式结构作主语
1.Te get contact with his family in Taiwan made him extremely happy since they separated more than 40 years ago.2.To finish that task in such a short time is really a challenge.
在上述情况下，如果不定式较长，显得头重脚轻，则可由代词让作形式主语(形式主语it不可由that或this等其他代词代替)，而将不定式放到后面。如：
1.It made him extremely happy to get contact with his family in Taiwan since they separated more than 40 years ago.2.John admitted that it is always difficult for him to be on time.
不定式结构所表示的动作是谁做的，即不定式的逻辑主语，通常可以通过for sb.to do sth.结构表达：1.It is quite important for us to read good books during a general review.2.It is not difficult fot those talented students to pass the exam.在某些形容词(如careless，clever，considerate，foolish，good，impolite，kind，naughty，nice，silly，stupid等)作表语时，不定式后可以加of来引导出其逻辑主语：1.It is very kind of you to tell me the truth.2.It is stupid of him to do such a silly thing.
2)不定式作宾语
不定式作宾语有两种：一种是及物动词后直接跟带to的不定式，另一种是“及物动词+疑问词+带to的不定式。
及物动词+带to的不定式结构:只能跟动词不定式的动词，常见的有:afford，agree，aim，appear，ask，believe，care，claim，decide demand，desire，determine，expect，fail，happen，hesitate，hope，intend，learn，long，manage，offer，pretend，promise，prepare，refuse，seek，swear，undertake，want，wish等。
1.He managed to solve the complicated problem.2.The stranger offered to show me the way.3.Mr.Smith undertook to build a new plant in South Africa.
动词+疑问代(副)词+不定式：这类动词常见的有advise，decide，find out，forget，inquire，know，learn，see，regard初中英语语法总结，remember，teach，tell，understand，wonder等。常见的疑问代(副)词有:what，when，where，which，how，whether等。1.He does not know when to start.2.You can decide whether to continue or to stop.3.I will show you how to deal with it.
有时，不定式可由it代替，而把不定式放到后面去。这可以用这一结构表达：动词(如find，think，consider，feel等)+it+形容词+不定式。1.She considers it necessary to make friends with him.2.We find it difficult to finish all the homework before 9 o’clock.
