哪些动词加不带to的不定式

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：
7） but和except：but前是动词do时,后面出现的动词用不带to的动词不定式.
8） 由and, or和than连接的两个不定式,第二个to 可以省去：
9） 通常在discover, imagine, suppose, think, understand等词后,可以省去to be：
He is supposed (to be) nice.　他应该是个好人.