1． 作介詞的to
to 有兩種用法： 一為不定式+動詞原形； 一為介詞+名詞/動名詞, to 在下面的用法中是第二種，即to+ 名詞/動名詞：
admit to承認， confess to承認，
be accustomed to 習慣于， be used to 習慣于，
stick to 堅持， turn to開始，著手于，
devote oneself to 獻身于， be devoted to 致力于，
look forward to 盼望， pay attention to 注意
2． 省to 的動詞不定式
1） 情態動詞 ( 除ought 外，ought to)：
2） 使役動詞 let, have, make：
3） 感官動詞 see, watch, look at, notice , observe, hear, listen to, smell, feel, find 等后作賓補，省略to。
注意：在被動語態中則to 不能省掉。
I saw him dance.
=He was seen to dance.
The boss made them work the whole night.
=They were made to work the whole night.
4） would rather，had better：
5） Why… / why not…：
6） help 可帶to，也可不帶to, help sb (to) do sth：
7） but和except：but前是動詞do時，后面出現的動詞用不帶to的動詞不定式。
8） 由and, or和than連接的兩個不定式，第二個to 可以省去：
9） 通常在discover, imagine, suppose, think, understand等詞后，可以省去to be：
He is supposed (to be) nice. 他應該是個好人。
舉例：
He wants to move to France and marry the girl.
He wants to do nothing but go out.
比較： He wants to do nothing but go out.
He wants to believe anything but to take the medicine.
典型例題
1) ---- 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
答案：D. why not 后面接不帶to 的不定式，因此選D。
2） Paul doesn't have to be made ___. He always works hard.
A. learn B. to learn C. learned D. learning
答案：B. make后接不帶to 的動詞不定式，當其用于被動時，to 不可省略
3． 動詞不定式的否定式
Tell him not to shut the window…
She pretended not to see me when I passed by. 我走過的時候，她假裝沒看見。
典型例題
1）Tell him ___ the window.
A. to shut not B. not to shut C. to not shut
D. not shut
答案：B。 tell sb to do sth 的否定形式為tell sb not to do sth.
2) She pretended ___ me when I passed by.
A. not to see B. not seeing C. to not see
D. having not seen
答案：A。 pretend 后應接不定式。其否定形式為pretend not to do sth.。
3）Mrs. Smith warned her daughter ___ after drinking.
A. never to drive B. to never driver
C. never driving D. never drive
答案：A。warn sb to do sth. 的否定形式為warn sb not to do sth. 此處用的是否定詞never.
4) The boy wanted to ride his bicycle in the street，but his mother told him ____.
A. not to B. not to do C. not do it
D. do not to
答案：A。not to 為not to do it 的省略形式。可以只用to這個詞，而不必重復整個不定式詞組。及物動詞do后應有名詞、代詞等，否則不對，因此B，D不對。
5) The patient was warned ___ oily food after the operation.
A. to eat no B. eating not C. not to eat
D. not eating
答案：C。warn一詞要求后用不定式，此處為不定式的被動，否定形式為be warned not to do。
4． 不定式的特殊句型too…to…
1）too…to 太…以至于…
He is too excited to speak.
他太激動了，說不出話來。
---- Can I help you ? 需要我幫忙嗎?
---- Well, I'm afraid the box is too heavy for you to carry it, but thank you all the same. 不用了。這箱子太重，恐怕你搬不動。謝謝您。
2) 如在too前有否定詞，則整個句子用否定詞表達肯定， too 后那個詞表達一種委婉含義，意 為"不太"。
It's never too late to mend. (諺語)
改過不嫌晚。
3) 當too 前面有only, all, but時，意思是：非常… 等于very。
I'm only too pleased to be able to help you. 我非常高興能幫助你。
He was but too eager to get home. 他非常想回家。
5． 不定式的特殊句型so as to
1） 表示目的；它的否定式是so as not to do。
Tom kept quiet about the accident so as not to lose his job.
湯姆對事故保持沉默是為了不丟掉他的工作。
Go in quietly so as not to wake the baby.
輕點進去，別驚醒了嬰兒。
2) so kind as to ---勞駕
Would you be so kind as to tell me the time?
勞駕，現在幾點了。
6． 不定式的特殊句型Why not
"Why not +動詞原形"表達向某人提出建議，翻譯為："為什么不……?" "干嗎不……?"
例如：
Why not take a holiday?
干嗎不去度假?
7． 不定式的時態和語態
時態\語態 主動 被動
一般式 to do to be done
進行式 to be doing
完成式 to have done to have been done
完成進行式 to have been doing
1) 現在時：一般現在時表示的動詞，有時與謂語動詞表示的動作同時發生，有時發生在謂語動詞的動作之后。
He seems to know this.
I hope to see you again. = I hope that I'll see you again. 我希望再見到你。
2) 完成時：表示的動作發生在謂語動詞表示的動作之前。
I'm sorry to have given you so much trouble.
He seems to have caught a cold.
3) 進行時： 表示動作正在進行，與謂語動詞表示的動作同時發生。
He seems to be eating something.
4) 完成進行時：
She is known to have been wreaking on the problem for many years.
8． 動名詞與不定式
1） 動名詞與不定式的區別：
動名詞表達的是： 狀態，性質，心境，抽象，經常性，已發生的
不定式表達的是： 目的，結果，原因，具體，一次性，將發生的
2） 接不定式或動名詞，意義相同。
3） 動名詞與不定式語義不同的有11 組：
1 stop to do stop doing
2 forget to do forget doing
3 remember to do remember doing
4 regret to do regret doing
5 cease to do cease doing
6 try to do try doing
7 go on to do go on doing
8 afraid to do afraid doing
9 interested to do interested doing
10 mean to do mean doing
11 begin/ start to do begin/ start doing