（1）作主语：To finish the work in ten minutes is very hard.十分钟之内完成这项工作是很难的.To lose your heart means failure.灰心意味着失败.动词不定式短语作主语时,常用it作形式主语,真正的主语不定式置于句后,例如上面两句可用如下形式：It is very hard to finish the work in ten minutes.十分钟之内完成这项工作是很难的.It means failure to lose your heart.灰心意味着失败.常用句式有：1、It+be+名词+to do.2、It takes sb.+some time+to do.3、It+be+形容词+of sb +to do.常用careless,clever,good,foolish,honest,kind,lazy,nice,right,silly,stupid,wise,等表示赞扬或批评的形容词,不定式前的sb.可作其逻辑主语.（2）作表语：Her job is to clean the hall.她的工作是打扫大厅.He appears to have caught a cold.他似乎感冒了.（3）作宾语：常与不定式做宾语连用的动词有：want,hope,wish,offer,fail,plan,learn,pretend,refuse,manage,help,agree,promise,prefer,如果不定式（宾语）后面有宾语补足语,则用it作形式宾语,真正的宾语（不定式）后置,放在宾语补足语后面,例如：Marx found it important to study the situation in Russia.马克思发现研究俄国的情况是很重要的.动词不定式也可充当介词宾语,如：I have no choice but to stay here.我只能留在这里,别无选择.He did nothing last Sunday but repair his bike.他上周日除了修他的自行车什么也没干.动词不定式前有时可与疑问词连用,如：He gave us some advice on how to learn English.他给了我们一些学英语的建议.（4）作宾语补足语：在复合宾语中,动词不定式可充当宾语补足语,如下动词常跟这种复合宾语：want,wish,ask,tell,order,beg,permit,help,advise,persuade,allow,prepare,cause,force,call on,wait for,invite.此外,介词有时也与这种复合宾语连用,如：With a lot of work to do,he didn't go to the cinema． 他有很多工作要做,所以没去电影院.有些动词如make,let,see,watch,hear,feel,have等与不带有to的不定式连用,但改为被动语态时,不定式要加to,如：I saw him cross the road.我看见他横过公路.He was seen to cross the road.他被我看见横过公路.（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.我有一个会议要出席.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.他找到了一个居住的好房子.The child has nothing to worry about.这个孩子无忧无虑.What did you open it with?你用什么打开它?如果不定式修饰time,place,way,可以省略介词：He has no place to live.他无处安身.This is the best way to work out this problem.这是解决这个问题的最好办法.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?你要送什么东西吗?Have you got anything to be sent?你有什么东西需要送吗?②说明所修饰名词的内容：We have made a plan to finish the work.我们制定了一个完成工作的计划.③被修饰名词是不定式逻辑主语：He is the first to get here.他第一个来到这儿.（6）作状语：①表目的：He worked day and night to get the money.他夜以继日地工作来赚钱.She sold her hair to buy the watch chain.她卖掉了自己的头发来买那条表链.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.为了省钱,他使出了浑身解数.wrong：To learn English well,a dictionary is needed.right：To learn English well,he needs a dictionary.为了学好英语,他需要一本词典.②表结果(往往是与预期愿望相反的结果 意料之外)：常放在never only后 He arrived late only to find the train had gone.他来晚了,只见火车已经走了.I visited him only to find him out.我去拜访他,只见他出去了.③表原因：常放在形容词后面 They were very sad to hear the news.他们听到这条新闻非常伤心.④表程度：It's too dark for us to see anything.太暗了,我们什么也看不见.The question is simple for him to answer.这问题由他来回答是很简单的.（7）作目的状语：既可以放在句首,也可以放在句尾 To tell you the truth,I don't like the way he talked.说实话,我不喜欢他讲话的方式.（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.如果你不想做这件事,你就不必做.（9）不定式的并列：第二个不定式可省略to.He wished to study medicine and become a doctor.他希望学医并成为医生.
