动词不定式：
动词不定式由“to+ 动词原形”构成,如：to study, to play,动词不定式虽然不能作谓语动词用,但仍留着动词的特征,它可以带有所需要的宾语或状语而构成动词不定式短语,如：to study hard, to play table tennis.
1. 动词不定式的形式变化：动词不定式有下列时态和语态的形式变化.
语态式一般式完成式进行式完成进行式
主动to buildto have builtto be buildingto have been building
被动to be buildto have been build
2. 动词不定式的基本用法：动词不定式能起名词、形容词和副词的作用,可在句中作主语、表语、宾语补足语、定语和状语用,如：
（1）作主语：To help each other is good.（动词不定式作主语时,一般可用it作形式主语,而将作主语的动词不定式置于句末,如：It is good to help each other.
（2）作表语：My job is to drive them to the power station every day. 动词不定式在系动词be之后作表语,与表示将来时的be + 动词不定式结构有所区别,如：Our plan is to set up another middle school for the peasants’ children.我们的计划是给农民子弟再成立一所中学.（句中的谓语动词为is,动词不定式to set up… 为表语,主语为plan,但plan并不是动词不定式的逻辑主语,即动词不定式 to set up所表示的动作不是主语plan产生的.）We are to set up another middle school for the peasants’ children.我们将为农民的子弟再成立一所中学.（句中的are to set up整个结构为句中谓语,主语为we,同时也是动词不定式to set up所表示的动作的逻辑主语,即动词不定式to set up所表示的动作是由we产生的）.
（3）作宾语：① 作及物动词的宾语,如：She wishes to be a musician.；② 作某些形容词的宾语：可以有动词不定式为宾语的形容词一般有glad, sorry, afraid, pleased, determined, willing, eager, anxious, ready, sure等,如：I am determined to give up smoking.；③ 动词不定式一般不作介词的宾语,但动词不定式之前如有疑问词时,就可作介词的宾语,如：Can you give us some advice on what to do next?
（4）作宾语补足语,如：Tell the children not to play on the street. 如果句中的谓语动词为see, hear, watch, notice, have, make, let等,作宾语补足语的动词不定式须将to省去,如：I saw a little girl run across the street.
（5）动词不定式在句中作宾语,如带有宾语补足语时,须先用it作形式宾语,而将该动词不定式后置,如：I don’t think it right to do it that way.
（6）作定语：动词不定式作定语时,须位于被其修饰的名词或代词之后,如：Is this the best way to help him? 和定语用的动词不定式如果是不及物动词,不定式后面就要用必要的介词,如：He is the man to depend on. 如果被不定式修饰的名词为place, time, way,不定式后面的介词,习惯上可以省去,如：The old man is looking for a quiet place to live.
（7）作状语：动词不定式可以作下列的状语：① 目的状语： Every morning he gets up very early to read English. 为了强调不定式表示目的的作用,可在不定式前加in order to或so as to（以便或为了）,但应注意in order to位于句首或句中均可,而so as to不能位于句首,如：She reads China Daily every day in order to （so as to） improve her English. 将表示目的的不定式置于句首,也可强调目的的作用,如：To master a foreign language, one must work hard at it. ② 结果状语：They lived to see the liberation of their home town.他们活到亲眼见到了他们家乡的解放.③ too + 形容词或副词 + 动词不定式,表示“足能…”的结果,如：You are old enough to take care of yourself now.
3. 复合结构不定式：由for + 名词（或代词宾格）+ 动词不定式即构成复合结构的动词不定式.其中for本身无意义.for后面的名词或代词是不定式的逻辑主语,这种不定式在句中可作主语、表语、宾语、定语或状语,如：It is very important for us to get everything ready for the harvest. 当作表语用的形容词表示不定式的逻辑主语的性质或特征时,就用介词of而不用for引出不定式的逻辑主语,这些形容词一般有good, nice, kind, wise, silly, stupid, foolish, right, wrong, careless, impolite等,如：It is very kind of you to help him every day.
4. 疑问词 + 动词不定式：疑问代词和疑问副词后可加动词不定式构成不定式短语,在句中可作主语、表语或宾语,如：How to prevent them from swimming in this river is a problem.
5. 动词不定式的否定式：动词不定式的否定式是由not + 动词不定式构成,如：It’s wrong of you not to attend the meeting.
6. 动词不定式的时态形式所表示的时间关系：（1）一般式：动词不定式一般式所表示的动作是和谓语动词所表示的动作同时发生,但在多数情况下,是在谓语动词所表示的动作之后发生,如：We decided to plant more trees this spring.（其后）,They often watch us play table tennis.（同时）；（2）完成式：动词不定式完成式所表示的动作发生在谓语动词所表示的动作之前,如：I am sorry to have kept you waiting.（3）进行式：动词不定式进行式所表示的动作正在进行中,而且与谓语动词所表示的动作同时发生,如：She happened to be writing a letter in the room when I came in.
7. 动词不定式的被动语态用法：如果动词不定式的逻辑主语为这个不定式所表示的动作的承受者时,不定式一般就用被动语态形式,如：What is to be done next hasn’t been decided yet