1、不定式的形式
以动词do为例
1.不定式的主动语态与被动语态
一 般式to do (主动，未发生) to be done (被动， 未发生)
完成式to have done (主动，已完成)
to have been done (被动，已完成)
进行式to be doing (主动，正在进行)
完成进行式to have been doing (主动， 完成进行)
2、不定 式的句法功能
(1)不定式作主语
To hear from you is good. 收到你的来信很好
To be a good student is not easy. 做一个好学生不容易
不定式作主语时，为了保持句子的平衡，往往以it作形式主语，不定式作为真正主语置于谓语动词后。如:
It' s good to hear from you.
It’s not easy to be a good student.
(2) 不定式作宾语
通常用于want, hope, wish, like, need, hate, begin, start,remember, agree, learn, refuse, manage, help 等词后。如:
①forgot to close the door.
我忘记关门了
②Please remember to write to me.
请记得给我写信
