英语中动词不定式在什么情况下使用

动词不定式是由“不定式符号to+动词原形”构成的一种非谓语动词结构。有些动词不定式不带to，动词不定式可以作句子的主语、表语、宾语、定语、补语、状语或单独使用。不定式保留动词的某些特性，可以有自己的宾语、状语等。动词不定式和它后面的宾语、状语等一起构成短语，叫作不定式短语。现对九年级动词不定式的用法作一次简要梳理。
　　一、用作主语
　　直接把动词不定式置于句首的情况不多，多数情况用it作形式主语，把真正的主语——动词不定式置于句末，特别是不定式短语较长时。动词不定式作主语，谓语动词用第三人称单数形式。带疑问词的不定式短语作主语常置于句首，复合不定式结构作主语常置于句末。如：
　　1.As young adults, it is our duty to try our best to deal with each challenge... (p.8)
　　2.The head teacher said it was necessary to talk with his mother. (p.16)
　　3.How to make requests politely is important.(p.93)
　　二、用作表语
　　动词不定式作表语，常说明主语的内容、性质、特征。如：
　　1.The best way to improve your English is to join an English club. (p.7)
　　2.The first thing is to greet the teacher. (p.96)
　　三、用作宾语
　　1.可以接带to的动词不定式作宾语的动词主要有：要求选择同意(ask, choose, agree)，期望决定学习(expect, hope, decide, learn)，宁可假装知道(prefer, pretend, know)，希望想要愿意(wish, want, would like / love)。如：
　　卜蚂携1)We decided to talk to some students about why they go there. (p.88)
　　2)He prefers to eat white bread and rice.(p.50)
　　3)Id love to visit Mexico.(p.53)
　　2.动词decide, know, learn, show, teach, tell...，介词结构on...可用疑问词带to的不定式短语作宾语，但物笑why后面的不定式不带to。如：
　　1)Could you please tell me where to park my car?(p.92)
　　2)It gives advice on what to do in lots of different situations. (p.32)
　　3.动词feel, find, make, think等后面，可以用it作形式宾语代替真正的宾语——动词不定式，句子结构是...feel / find / make / ... it+adj. / n.+to do...。如：
　　I find it difficult to remember everything. (p.98)
　　4.既可接动词不定式又可接ving形式作宾语，意思差别不太大的动词有begin, start, like, love等。一般说来，动词不定式表一次、数次的具体动作、将来动作或动作的全过程，ving形式表习惯性的连续动作。但是这种区别并不很严型伏格，特别是美国英语，即使是习惯性的动作也可以用动词不定式。如：
　　1)Then I started to watch English-language TV.(p.6)
　　2)I’m beginning to understand my Chinese roots, and who I am. (p.116)
　　begin用了进行时态，后面只接不定式作宾语，表示事情刚开始，还要继续下去。
　　3)I like to eat vegetables. (p.118)
　　感知动词like, love, know等一般不用进行时态。

1.用在一些及物动词后，如 want to do fail to do decide to do manage to do plan to do
2。用在一些疑问词则举后可做主语，宾语，表语等。When to start is not decided.
3 用在介词but后做介词宾语，如 I did nothing but watch TV yesterday./ We had no choice but to wait here.
4。用在动词后也可在句橘盯庆首做状语。如 He came to see me./ To/In order to catch the early bus ,he got up early.
5。用在系动词后做表语。如My dream is to be a scientist.
6. 用在句首做主语, To be a singer is my dream.
7.用在名词或代词后做后置定语圆握， The best time to come to Beijing is autume.
8.用在宾语后补充宾语做了什么，叫宾语补语
Our teacher tells us to read more in the morning .