动词不定式
1．常用形式：一般主动式to do, 一般被动式to be done
完成主动式to have done, 完成被动式to have been done
进行式to be doing
2．语法功能：可作主语、表语、宾语、宾补、定语和状语（即除谓语之外的各种成分）。例如：
（1）主语：To master a foreign language is very important.
（2）表语：My job is to drive them to the company every day.
（3）宾语：Do you want to visit the Great Wall?
Can you give us some advice on what to do next?
（4） 宾补：The teacher advised us to have a rest first.
I didn’t notice them come in.

注：see, hear, watch, notice, have, make, let等动词后作宾补的动词不定式不带to, 但变为被动语态以后（即不定式作主补时）要带to, 其中let sb. do sth. 变为被动式为sb. is let do sth.
help（帮助）后作宾补的动词不定式可带to，也可不带to. 即help sb.(to)do sth.
（5） 定语：不定式位于所修饰的名词，代词之后，如：Who was the first one to set to the top of the hill yesterday? /He is the man to depend on/to believe in.
（6）状语： in order to
A．目的状语：She reads China Daily every day so as to improve her English.
注：in order to 可以位于句首或句中，so as to 不能位于句首。
B．原因状语： I’m glad to see you . 注：这种be＋形容词＋不定式结构，其不定式有时也可视为宾语，如：He is eager to go to college./ She is sure to come here.
C．结果状语：They lived to see the liberation of their home town.他们一直活到见到家乡解放。
在too…to…结构中表太…结果不能，如：He is too weak to do the work.
注：too之前如果有only, only too 表非常、很意，此时不定式不再表否定意，而表肯定意。如：They are only too lucky to go abroad for a visit. 他们很幸运去国外访问。
另外，too后如果是happy, glad之类形容词时，不定式也表肯定意。
如：She was too happy to meet her old friend in the street.
在形容词/副词＋enough＋不定式结构中表足以能…，如：He is strong enough to do the work .
3．复合结构不定式（for sb. to do sth.），可作主语、表语、宾语、定语和状语。for 本身无意义，sb.可称之为不定式的逻辑主语。例如：I think it necessary for him to go there at once.（复合结构不定式作宾语）。
注：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，不用for, 而用of,
如：It is kind of you to help me .（相当于You are kind to help me .）这类形容词有good,nice,kind,wise, clever, foolish, silly, stupid, careless, impolite（不礼貌）等。right, wrong既可用于for sb. to do sth. 也可用于of sb. to do sth. 例如：It’s right/wrongg for him to do the work alone.
4．疑问词＋不定式：可作主语、表语或宾语。如：How to finish the work in time is a problem.（主语）We don’t know when and where to go .（宾语）
5．动词不定式的否定式（not to do sth.），语法功能同不定式肯定式。