我們知道，動詞不定式to do由不定式符號「to」 加動詞原形do構成。
一般情況下to不能省略，但出於語言簡練或習慣表達等需要，有些時候會省略to，
下面為大家做個概括總結，希望對大家有用：
1，情態動詞：
will, would, can, could, shall, should, may, might, must, need, dare, had better, would rather等後面用省略to的動詞不定式一起組成謂語。
You will never win if you never begin.
沒有開始,何談輸贏。
No one can call back yesterday.
光陰一去不復返。
In the silence we could hear the clock ticking.
在寂靜中我們能聽到時鐘滴答作響。
He might get there in time, but I can't be sure.
他可能會及時趕到，但我不能肯定。
You must change in order to survive.
為了生存你必須改變。
2，make, have, let及hear, see等的賓語補足語：
make, have, let, hear, see, watch, notice, help等後面的賓語補足語可以省略to的動詞不定式：
The police had him describe what his robber looked like.
警察讓他描述搶劫犯的樣子。
We know what to do to make it work.
我們不知道如何讓它起作用。
He stepped aside to let me pass.
他走到一邊讓我過去。
I saw him head out Jackson's house.
我看見他從傑克遜家出來。
I often heard the girls sing in the music classroom.
我經常聽到女孩們在音樂教室裡唱歌。
想必大家都知道，see, watch, notice後也可能用現在分詞doing或過去分詞done做賓語補足語。
請參照分詞的用法：
分詞（現在分詞和過去分詞）用法大總結（收藏了）
make, hear, see, watch, notice的賓語做主語，被動句型動詞不定式要加上to：
I was made to wait two hours before I was examined by a doctor.
我等了兩個小時醫生才給我檢查。
She was seen to enter the building about the time the crime was committed.
有人看見她大約在案發時進入大樓。
3，and, or, except, but, than連接兩個並列動詞不定式,後面的要一般省略to：
I』d like to call it a day and go home.
我想現在下班回家。
I would rather do some reading at home than go shopping with them.
我寧願在家看書也不願和他們一起去購物。
I cannot promise anything but think of this week as a trial period.
我不能保證什麼，只能把這周當作試用期。
It's easier to get into debt than (to) get out of it again!
欠債容易還債難。
4，句子中有動詞do，解釋它的具體意思的動詞不定式可以省略to：
The only thing I can do is (to) keep quiet and sit this one out.
我唯一能做的就是保持沉默，等待這件事結束。
If he was prepared to apologize, the least she could do was (to) meet him halfway and accept some of the blame.
如果他準備道歉，她至少可以做個讓步，承認自己的一些不當之處。
5，why (not) 疑問句：
Why study Latin? It's a dead language.
為什麼學拉丁語？這是一種沒人說了的語言。
Why bother asking if you're not really interested?
你如果沒興趣，為什麼還要問？
Why not take a few days off?
為什麼不休息幾天呢？
If you love each other, why not get married?
如果你們相愛，為什麼不結婚呢？
6，and代替to：
英語口語裡，謂語動詞後的動詞不定式，常用and代替to（尤其是come和go後）：
Can Anne come and play?
安妮能來玩嗎？
Come and see us if you're at a loose end.
有空的時候到我們這兒來坐坐。
What time will the taxi come and pick us up tomorrow?
明天計程車什麼時候來接我們？
Go and buy yourself an ice cream.
去給自己買個冰淇淋。
Would you like to go and see a film tonight?
今晚你想去看電影嗎？