动词不定式由“to 动词原形”构成，在句中可作主语、宾语、宾语补足语、表语、定语、状语等。其否定形式是“not to 动词原形”。
动词不定式作主语时，为保持句子平衡，常用it充当形式主语，而将不定式主语放在后面。
动词want, refuse, forget, agree, hope, decide, fail, promise, hope等后可跟动词不定式作宾语。
“疑问词 动词不定式”是动词不定式的复合结构，常用作consider, decide, discuss, forget, know, remember, wonder, find out等动词(短语)的宾语。
当动词不定式作宾语且其后有补语时，常用it作形式宾语，而将真正的宾语放在后面。
动词allow, advise, ask, tell, invite, expect, encourage, order, (would) like等后常跟动词不定式作宾语补足语。
make, let, have等使役动词和feel, see, hear, watch, notice等感官动词后常跟不带to的动词不定式作宾语补足语。
动词不定式作定语时，常置于被修饰词之后。
动词不定式作状语时，可以用来表示目的或结果等。
经典习题
1. — Jessica, when did you come back?
— Just a few minutes ago. I tried ______ you up.
A. to wake
B. not to wake
C. to waking
D. not to waking
2. Mr. Yan used to advise the students ______ the habit of solving problems by themselves.
A. develop
B. develops
C. to develop
D. developing
3. In my opinion, it’s dangerous for people ______ the phone while crossing the street.
A. answer
B. answered
C. answering
D. to answer
4.The study shows that listening to light music is a popular way ______ among middle school students.
A. relax
B. relaxing
C. to relax
D. to relaxing
5. — Don’t worry. We will do what we can ______ your boy.
— Oh, thank you very much.
A. save
B. to save
C. saving
D. saved
KEY：1-5 BCDCB
练一练
1. 要他妹妹学习音乐是恰当的选择。
For his sister ______ music is a proper choice.
2. 红灯时过马路很危险。
It is very dangerous ______ the road when the traffic lights are red.
3. 凯蒂努力学习以便能够通过考试。
Katie worked hard at her lessons ______ the exam.
KEY：
1. to study 2. to cross 3. to pass
