一、不定式作主语作形式主语
It takes sb some time to do sth
It costs sb some money to do sth.
It’s +adj. +for sb+ to do sth.
作实际主语
To see is to believe。
To play basketball is my favorite sport.
二、不定式作宾语结构：S+V+ to do sth
此用法的动词有：want/ like/ love/ begin/ forget /remember/ start/need/ plan/ hope /try/ learn/ decide + to do sth.
三、不定式作表语
To see is（系动词）to believe。
My task /purpose is to do sth.
四、不定式作宾补结构：S+V+ O +to do sth此用法的动词有：ask/tell / invite/ want/ teach/ allow(允许)/wish….. + sb. + to do sth
注：let, have, make等使役动词以及see，watch，notice，feel，hear等感官动词后常跟不带to的不定式作宾补。结构：S+V+ O + do sth（make sb do sth）
五、不定式作状语
They practiced playing basketball hard to win .他们努力练习练球是为了获胜。
六、不定式作定语t
he best way to do sth. 做某事最好的方式the best place to go/visitI
have some exciting news to tell you .
补：动词不定式还可以和疑问词what，how，when，where，which等连用。
例如：I don’t know what to do.
