什么时候加to?为什么有时候特定动词后面也不加to?

1．感官动词和使役动词在主动语态中不需要带to,即我们常说的“一觉二听三让五看”：
feel, listen to 、hear ,let、make、have, see、watch、notice、observe、look at.
He noticed Tom take a branch of flowers in his hand.
他注意到汤姆手中拿着一束鲜花.
The teacher has us write a composition every week.
老师要我们每周写一篇文章.
注： 除let 外其他在变成被动语态时要加上to.
The person was seen to enter the shop by us .
我们看见那个人进了那家商店.
2．由 all, what 引导的主语从句或者主语被only, first, one, least 或形容词最高级修饰时,而且从句中含有do时,其表语如果是动词不定式,则往往省去to.
All I did was empty the bottle.
我所做的是倒空这个瓶子.
What I wanted to do was drive all night.
我想做的是彻夜开车.
The only thing I could do was do it myself .
我惟一能做的是我自己解决.
3．常用的结构 may well do,may as well do (还是…好了)及but或except后接不定式时,如果它们前面有do便可省略to,其结构为can not do but…,can not help but…等句型,
We might as well put up here for tonight.
我们不妨今晚就在这儿过夜.
She can do nothing but/except sing.
她除了唱歌什么也没做.
There is nothing he could do but play all day long.
他除了整天玩,别无它事可做.
4．不定式做help后的宾语补足语或宾语时,可带to也可不带.
Can I help（to） carry it for you?
我可以帮你搬吗?
I helped him（to） mend the bike.
我帮助他修理自行车.
5．在had better,would rather,rather than之后省略to.
You'd better not tell him the news .
你最好不把这个消息告诉他.
Rather than wait anyone, I decided to go home by taxi.
我决定乘出租车回家而不愿等候任何人.
6. 由并列连词and,except, but, than, or 连接两个以上的具有相同意义或功能的不定式时,第二个动词不定式不带to.
I’d like to stay with you, help you and learn from you.
我想留下和你一起呆着,帮助你并且向你学习.
She told us to stay at home and wait till she came back.
她告诉我们呆在家里一直等到她回来.
注：如果两个不定式表示对照或对比时,则不能省略to.
To try and fail is better than not to try at all.
尝试而失败也比不尝试好.
He hasn′t decided whether to quit or to stay.
他还没有决定是去还是留.
To be or not to be, that is a question.
是生存还是死亡,这是一个问题.
7．以Why或Why not 开头表请求的结构中常跟上动词原形,省略to.
Why not go out for a walk ?
为什么不出去散散步呢?
8．通常在discover, imagine, suppose, think等词后作宾补时,可以省去to be.
含有介词to的常用短语
1．access to 接近,进入(某地的)方法; 通路
The only access to that building is along that muddy track.
到那栋建筑的唯一通路是沿着那条泥泞的路走.
2．according to 按照,依照,视……而定
The work was done according to his instructions.
那工作是依照他的指示做的.
3．be addicted to 沉溺于……,对……上瘾
He became addicted to the drug.
他上了毒瘾.
4．belong to 属于
This dictionary belongs to me.
这本词典是我的.
5．contribute to 为……做贡献,为……撰稿
Everyone should contribute what he or she can afford to society.
人人都应该尽自己的能力为社会做贡献.
6．devote to 献身,致力于……
He has devoted his life to helping disabled people.
他一生献身于帮助残疾人.
7．due to 因为,由于……而起
His lateness was due to the very heavy traffic on the motorway.
他迟到是因高速公路上车辆过多所致.
8. be equal to 与……相当,有能力胜任……的
Bill is quite equal to running the office.
比尔的能力足以管理这个部门.
9. get close to 靠近,接近
Today many people like to go out to get close to nature.
如今许多人喜欢到户外去接近大自然.
10. get down to 开始做某事,认真处理某事
It’s time I got down to some serious work.
我该认真干点正事了.
11. hold to 忠于……,坚持,遵循
Whatever your argument, I shall hold to my decision.
不管你怎样争辩,我将坚持我的决定.
12. help oneself to 自取,自用(食物,饮料等)
Help yourself to a cigarette.
请随便用香烟吧.
13. look forward to 盼望,期待
We are so much looking forward to seeing you again.
我们非常盼望再见到你.
14. lead to 导致
This misprint led to great confusion.
这个印刷错误造成很大的混淆.
15. prefer…to…两者间更喜欢……
I prefer walking to cycling.
我愿意步行,不愿意骑自行车.
16. pay attention to 注意
Pay attention to what the teacher is talking about!
注意老师说的话!
17. refer to 提到,涉及到,关系到,参考,查阅
What I have to say refers to all of you.
我要说的事和你们大家都有关.
18. relate to 与……有关,涉及……
Wealth is seldom related to happiness.
财富鲜于幸福有关.
19. see to 照看或处理某事物
Will you see to the arrangements for the next committee meeting?
你来处理下次委员会会议安排,好吗?
20.stick to 坚持,不改变或不放弃
We don’t want to hear your opinions; stick to the facts!
我们不想听你的想法,只讲事实!
21.turn to 转向,求助于,转而做
The more depressed he got, the more he turned to drink.
他情绪越低落越是借酒浇愁.
22.used to 习惯于……,适应……
She is quite used to working hard.
她很习惯做艰苦的工作.