动词不定式To do that sort of thing is foolish 。I want to see you this evening.All you have to do is to finish it quickly.We found a house to live in.She came here to study English. I warned the patient not to eat cold water after the operation. 主语 宾语表语 定语 状语 宾补 不定式或不定式短语可起名词，形容词和副词的作用，在句中做主语，宾语，表语，定语，状语和宾语补足语。一，不定式在句中的作用：1 、主语：不定式做主语时，可以直接放在谓语动词之前。eg: To make a new dress takes her a lot or time. Not to get there in time is your fault.注：常用 it 做形式主语，将 to do 放在位于之后，使句子保持平衡。句型 1 ： It + 谓语 + to doeg: It takes us an hour to get there by bus.句型 2 ： It’s + n. + to doeg: It’s our duty to help the poor.句型 3 ： It is adj. for/of sb. to do sth.注： for/of sb to do sth 为不定式复合结构。 1) of 引起的复合结构只能做主语。eg: It’s very kind of you to help me.2) for 引起的复合结构在句中可做主语，宾语，表语，定语，状语等。eg: Another method is for them to leave at once. ( 表语 ) We’d better find some work for the children to do. ( 定语 ) He put the paper on desk for you to read. ( 状语 ) What he told her made it impossible for him to go on her work. ( 宾语 ) It’s common for leaves to fall form the trees in autumn. ( 主语 )2 、做表语：主语 + 系动词 + 不定式1). 其主语多为抽象名词 (wish, need)eg: My wish is to be a scientist. The main thing is to keep our room clean.2). 不定式 to let, to blame, to seek 做表语 , 主动表被动 .eg: The house is to let.3). be to do 可构成将来时态 , 表 “准备 / 打算 /计划 / 需要” ; be 是助动词，无词义 , 其主语为具体名词 ( 人 / 事物 ); to be 可用 be going to 或will/shall 代替 , 此时不定式是谓语的一部分 , 而不是表语 .eg: She is to return...
