不定式的句法功能:(1)作主语:To finish the work in ten minutes is very hard.It is very hard to finish the work in ten minutes.(2)作表语:Her job is to clean the hall.(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,Marx found it important to study English well.(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.(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He found a good house to live in.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.②表结果:He arrived late to find the train gone.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