(一)不定式：to +動詞原形

　　簡單句中如果已經(jīng)有一個動詞做謂語，那么再有一個動詞就要在這個動詞前加to做不定式。不定式在句子中可以作主語、賓語、表語、賓語補足語、定語、狀語等。

　　To see is to believe.(眼見為實)

　　有時用it做形式主語，真正的主語放在句子最后。

　　It only took us a year to finish the work.

　　Once you get into the habit of smoking， you'll find it extremely difficult to get out of it.(get into the habit 養(yǎng)成……習慣)

　　She likes to play basketball this afternoon.

　　The important thing is to save people.

　　Not to grasp firmly is not to grasp at all.(不定式的否定放在to的前面)

　　She was the first person to think of the idea. (think of 想起)

　　He is always the first to come and last to leave the office.

　　I have nothing to say on the problem.

　　They warned him not to let out the secret.(let out 泄露)

　　We are all happy to hear of the good news.

　　Let's hurry so as not to be late for the meeting. (so as to do sth. 以便為了做某事)

        如果not不是放在to的前面，那么它不是否定不定式而是否定整個句子。

　　They didn't warn him to let out the secret.

　　They warn him not to let out the secret.

　　(一)不定式：to +動詞原形

　　不定式在let， have， make (讓， 使)， see， look at， notice， hear， listen to， feel 等后面作賓語補足語時to 應省略，在被動語態(tài)中to應保留。

　　The coach has the team practice hard every night in the past two years.

　　I saw a man come into the classroom and talk with the teacher.

　　Don't forget to have him come tonight.

　　We felt the house shake.

　　The house was felt to shake.

　　Someone was heard to come up the stairs.

　　在help 后， 不定式可以帶to 也可以不帶to.

　　Help me (to) get him to bed.

　　He help her lift the box.

　　He helped her to mount the bike.

　　She was helped to lift the box.

　　當不定式和其修飾的詞有動賓關(guān)系時，動詞如果是不及物動詞，后面就要有必要加介詞。

　　There is nothing to worry about.

　　Is this something to be ashamed of ?

　　I need a pen to write with.

　　Give me some paper to write on.

　　Let's find a room to put the things in.