动词不动式

动词不定式省略to的情况:
1.在助动词或情态动词后:
May I ask you a question
但在ought, have和be后不能省略.
2.在make, let, see, watch, hear, notice, feel, have, listen to, look at等动词后(作宾补)
Let me hear you play the piano.
3.在why引起的某些问句中:
Why not try again
4.在had better, would rather, would rather…than, cannot but, do nothing but等结构后面:
He could do nothing but wait for the teacher to arrive.
5.在介词except, but之后,如果其前有动词do的某种形式,不定式一般不带to,反之则须带to
There is no choice but ______(wait) till it stops raining.

省to 的动词不定式
1） 情态动词 ( 除ought 外，ought to)：
2） 使役动词 let, have, make：
3） 感官动词 see, watch, look at, notice , observe, hear, listen to, smell, feel, find 等后作宾补，省略to。

注意：在被动语态中则to 不能省掉。
I saw him dance.
=He was seen to dance.
The boss made them work the whole night.
=They were made to work the whole night.
4） would rather，had better：
5） Why… / why not…：
6） help 可带to，也可不带to, help sb (to) do sth：