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.