動詞不定式是由“不定式符號to+動詞原形”構成的，它具有名詞、形容詞及副詞的特徵，同時還保留著某些動詞的特徵，在句中可以擔任除謂語以外的其他子句成分，是非謂語動詞的一種。
眾所周知，動詞不定式在助動詞或情態助動詞(ought to除外)之後都省略其符號to。但除此之外，英語中省略動詞不定式符號to的情況還有以下幾種：
1.當兩個或兩個以上的不定式是由and，or，than等連接時，第二個不定式可以省略to。
What We should do now is to open the window and Let fresh air in.我們現在應該做的事情就是打開窗戶讓新鮮空氣進來。
It is easier to praise people than criticize them.表揚人比批評人容易。
2.在“come(go)+不定式”結構中，不定式一般省去to，特別在美國的口語中更為常見。第一個動詞表示“來”“去”這個動作，第二個動詞表示“來”“去”的目的。
Go fetch your notebook.
去把你的日記拿來。
Come sit with me.
來跟我坐在一起。
3.在“try(go，come，etc.)and……”結構中，and之後的不定式常常省去to。
I'll try and remember the matter.
我一定記著那件事。
I hope you will go and see the patient.
我希望你去看看那個病人。
Come and see us.
請來看看我們。
4.用助動詞do，does或did來強調謂語動詞時，動詞不定式不帶to。
Do be careful.
I do believe you.
She does feel that way.
5.用在感官動詞(例如see，watch，observe，feel，look at，hear等)和部分使役動詞(如have，make，Iet等)之後作賓語補足語的動詞不定式常常省略to。
She felt her heart beat fast.
I saw her enter the horse.
6.在動詞help之後作賓語或賓語補足語的不定式，可以省略to，也可保留to。
Will you help me (to) move the table?
Would you like to help (to) peel potatoes?
7.在實義動詞dare之後作賓語的不定式，有時也可省略to。
I don't dare (to) Ask her.
He didn't dare (to) go.
8.在wouId rather，had better(best)等習慣用法之後，動詞不定式不帶to。
I would rather not tell you.
Better get some lunch for yourself.
9.在why(not)引導的省略句中，作謂語的動詞不定式總不帶to。
Why not write a note and put it up on the tree.
Why not think of something you can do.
10.當but，expect，besides之前有一個實義動詞do(助動詞及其變化形式除外)時，這三個介詞之後的動詞不定式總省略to。
There was nothing for me to do except wait till the meeting was over.
What do you like to do besides swim.
11.在口語中，當不定式做表語，且主語中包含有do或其變形，動詞不定式常省略to。
All you need to do now is have a good rest.
All they do is work.
12.當主語是不定式修飾的thing時，作表語的不定式常省略to。
The best way to do is listen to the tape recordings and practise speaking at the first opportunity.
最好的辦法是聽錄音，一有機會就練說。
13.當主語是帶有動詞do的主語從句時，作表語的不定式常常省略to。
What l want to do is take a holiday right away.
14.當主語是以動詞say作謂語的定語從句所修飾的aⅡ時，作表語的不定式常常省略to。
All They said is hurry up, please.
Exercise:
給下列各題選擇一個最佳答案。
1.It's freezing cold outside. You ( ) put on your coat.
A.had better to B. had better
C. would better D. would better to
2. I usually go there by train.
Why not ( ) by boat for a change.
A.to try going B.trying to go
C. to try and go D. try going
3.Mother ( ) us stories when We young.
A. was used to tell B. is used to telling.
C. used to tell D. used to telling.
4. You ( ) after your little sister.
A. should to look B. ought look
C. ought to looking D. ought to look
5. People couldn't help ( ) the foolish emperor.
A.laugh at B. to laugh at
C. laughing at D. laughing on
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