一、当不定式作feel（感觉）的宾补时，若不定式为be动词，不定式带to，若为其他动词则省略to。
He felt them to be right.
All at once she felt herself turn a little dizzy.
二、当rather than在句首或与prefer连用，rather than后的不定式省to。
Rather than wait any more, I decided to go home by taxi.
I prefer to work rather than remain idle.
三、had better/would rather/would rather……than……/can’t but/can’t help but/can’t choose but接不带to的不定式。
They can’t but accept his term.
四、当主语部分是what引导的从句，all+定语从句，the only/first/last/形容词最高级+thing+作定语的不定式结构时，若从句或不定式含实义动词do作表语的，不定式可省可不省to。
All I did was (to) give him a little push.
五、当几个不定式并列时，除第一个不定式外，其余的不定式都可省略to。
She refused to eat, talk or more.
