I saw him cross the road.

　　 He was seen to cross the road.

（5）作定语：

动词不定式作定语，放在所修饰的名词或代词后。与所修饰名词有如下关系：

①动宾关系：

　I have a meeting to attend.

　注意：不定式为不及物动词时，所修饰的名词如果是地点、工具等，应有必要的介词，如：

　He found a good house to live in.

　The child has nothing to worry about.

　What did you open it with?

　如果不定式修饰time, place, way，可以省略介词：

　He has no place to live.

　This is the best way to work out this problem.

　如果不定式所修饰名词是不定式动作承受者，不定式可用主动式也可用被动式：

　Have you got anything to send?

　Have you got anything to be sent?

②说明所修饰名词的内容：

　We have made a plan to finish the work.

③被修饰名词是不定式逻辑主语：

　He is the first to get here.

（6）作状语：

①表目的：

　He worked day and night to get the money.

　She sold her hair to buy the watch chain.

　注意不定式放句首时，逻辑主语与句子主语要一致：

　wrong：To save money, every means has been tried.

　right：To save money, he has tried every means.

　wrong：To learn English well, a dictionary is needed.

　right：To learn English well, he needs a dictionary.

②表结果：

　He arrived late to find the train gone.

　常用only放在不定式前表示强调：

　I visited him only to find him out.

③表原因：

　They were very sad to hear the news.

④表程度：

　It's too dark for us to see anything.

　The question is simple for him to answer.

（7）作独立成分：

　　 To tell you the truth, I don't like the way he talked.

（8）不定式的省略：保留to省略do动词。

　　 If you don't want to do it, you don't need to.

（9）不定式的并列：第二个不定式可省略to。