动词不定式通常带有符号to，叫做带to的动词不定式（infinitive withto），动词不定式有时不带符号to，叫做不带to的动词不定式（infinitive withoutto）
不带to的动词不定式通常有下面十八种情况
一、与助动词do连用构成谓语动词的否定、疑问和强调形式。
（1）he does not work in the factory.
（2）Does she work here？
（3）I did not see her yesterday.
（4）Did they take you home?
（5）He does look tired.
（6）They did come yesterday.
二、与情态动词连用构成复合谓语
（1）I can speak English.
（2）May I come in?
（3）Dare he swim across the river?
（4）We must work,and above all we must believe in ourselves.
（5）Could you do something for me?
（6）You shall go at once.
（7）He might be working in the office now.
（8）I dont think you need have come yesterday.
（9）They should be here by now.
（10）If you will go into the fields and turn over a few big stones,you are sure to uncover a city of antpeople.
但与情态动词ought（to）连用时通常带to，和used（to）连用时必须带to
三、在表示感觉的动词如：see,look.at,watch,hear,listen
to,feel,notice,observe,perceive（觉察，看见），behold（书面用语见到）等后用作宾语补足语的动词不定。
（1）I saw her cross the street.
（2）He looked at the children walk up the hill.
（3）I watched the boy cross the road.
（4）I heard her play the piano.
（5）He listend to us talk.
（6）I felt the floor move.
（7）I didnt notice you enter.
（8）He observed someone open the door.
（9）I did not perceive anyone come in.
（10）He beheld her go out.
但除notice,watch不用被动语态外，上述动词变成被动语态时，其后的动词不定式就不省to
（1）She was seen to cross street.
（2）She was heard to play the piano.
四、使役动词make,let,have,bid, leave（=let）后作宾语补足语的动词不定式不带to
（1）You may take a horse to the water,but you cant make him drink.
（2）Ill let him do it.
（3）Dont forget to have them come.
（4）Bid him go home.
（5）Leave him go.
动词have通常不用于被动语态，make和bid可用于被动语态，let偶尔也可用于被动态，用作主语补足语的动词不定式通常带to，但在make和let后有时可以不带to
（1）John was made to wash the truck for a week as a punishment.
（2）He was made（to） laugh.
（3）The child was let（to） do it.
五、never与know连用其后作宾语补足语的动词不定式可省to，其时态多为完成时态。
（1）I never knew him act without thinking.
（2）Ive never known it snow in July before.
（3）I had never known her ask for pity before.
有时ever与known连用也有上述用法。
Have you ever known me tell a lie?
六、在find后作宾语补定语的动词不定式有时可以省to，但如动词为be，那么一般不省to，要省一起省略to be
（1）We found the farm crops（to） do well.
（2）I find the Chinese people to be happy and cheerful.
（3）I found this to be true in all the cities.
（4）We found him （to be） honest/dishonest.
七、在cannot but,cannot help but,can not choose but, had better（best），would（had） rather（sooner）than， would as
soonas后的动词不定一般不带to
（1）When the country calls you for help,you cannot but go.
（2）He cant help but feel sorry for her.
（3）he cannot choose but obey.
（4）I had better leave now,or Ill be late.
（5）He had best buy it now while it is still available.
（6）I would rather go mountain-climbing than just take a walk.
（7）My aunt invited me to the movies,but I said I had rather go on a picnic with the girls.
（8）I had sooner live on a farm than in the city.
（9）He would sooner resign than take part in such dishonest business deeds.
（10）Id rather not tell you.
（11）He said hed sooner die than betray his friend.
八、在but（=except），besides,than后的动词不定式一般要带to，但如果其前有作谓语的实义动词do，则不定式不带to
（1）The soldier has no choice but to obey.
（2）He did not have any choice but to obey.
（3）She did nothing but clean the dishes.
（4）The children found there was nothing they could do with their money,except spend it on sweets.
（5）There seemed nothing else to do but（to）send for a doctor.（but前的实义动词do不作谓语，but后的不定式可带to，也可不带to）
（6）He did nothing else than laugh.
（7）I could hardly do less than wait.
九、不定式作表语时，如主语部分含有实义动词do，且句子的时态为一般现在时或一般过去时（多为is或was），不定式可以带to也可不带to
（1）What we must do now is（to） find anther person to help us.
（2）All he could do was （to） rush into the room.
如句子的动词时态不是一般现在时或一般过去时，作表语的动词不定式一般要带to
（1）She knew that all she would have to do would be to stop crying.
十、rather than位于句首时，其后用不带to的不定式，但rather
than在句中时，其后的动词不定式可以带to，也可以不带to
（1）Rather than ride on a crowded bus,he always prefers to ride a bicyde.
（2）Rather than cause trouble,he left.
（3）He prefers to rent a car rather than（to） have one of his own.
十一、在动词help后作宾语补足语的动词不定式可以带to，也可以不带，在英国英语中，多用不带to的不定式，但在英国英语中，help+宾语+不定式结构中，用不带to的不定式表示主语直接参与不定式的表示的动作，用带to的不定式表示主语没有直接参与不定式的表示的动作。
（1）He helped me repair the bicycle.
（2）He helped me to repair the bicycle.
（3）This kind of soap helps us to wash the clothes more easily.
（4）The book will help you to study English.
但在被动语态中，help后的不定式要带to
She was helped to repair her bicycle.
在help（to） do sth不定式符号to可省略。
He helped（to） repair the machine.
十二、两个或两个以上的动词不定式并列在一起时，第一个不定式带to，后面的不定式一般省去to
（1）Her job is to take care of the children and wash clothes.
（2）The girl doesnt know how to read and write.
但如果是在对照场合，则不省去to
（1）It is better to laugh than to cry.
（2）The purpose of new technologies is to make life easier,not to make it more difficult.
十三、than连接两个动词 不定式没有对比关系时，后一个不定式可以省to
（1）You might do worse than（to） do as he does.
（2）I cannot do better than（to）get away for the few days.
下面句子中than连接的不是两个动词不定式than后的动词不定式通常要带to
（1）I know better than to believe him.
（2）The beaten enemy had no choice than to surrender.
下句中的more than（=only）可以看成复合副词，后面的动词不定式不带to
（1）I did not more than make a beginning.
十四、在why,why not后的不定式不带to
（1）Why spend such a lot of money?
（2）Why not join us?
（3）Why dont you smoke?
十五、实义动词dare在现代英语口语中，其所在的否定句或疑问句中，它后的动词不定式可省to，尤其在一般过去时中
（1）Does he dare go?
（2）We do not dare speak.
（3）He did not dare go.
（4）Did he dare go?
（5）He dared go.
（6）Dared he go?
（7）He knew she dared not open his mouth.
十六、在口语中，特别是在美国，祈使语气谓语动词和构成谓语的不定式go后面的不定式往往不带to
（1）Go ask her.
（2）Ill go see my brother.
这种用法在英国口语中比较少见，一般在动词go后用连词and
（1）GO and ask her.
（2）Ill go and see my brother.
十七、在will you please？和would you please？句型中，要用不带to的不定式。
（1）Will you please give the note to Tom?
（2）Will you please open the window?
（3）Would you please give me a hand?
十八、Better+动原（口语中用）
（1）Better ask them go astray.
（2）Better go at once.
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