<例句>
She didn't know whether to laugh or to cry.
她感觉真是啼笑皆非。
<语法分析>
不定式有时和连接代词或副词一起构成宾语。在这个句子里，不定式就是这种用法。所谓不定式有两种形式，即带to的不定式和不带to的不定式。不定式在多数情况下都带to，不带to的不定式和动词原形相同。不定式在句子里可以充当很多成分，如充当句子的谓语、主语、宾语、定于、状语和表语等。它毕竟还是动词，因此具有动词的某些特征，如它可以有自己的宾语和状语共同构成不定式短语，它也可以有自己的逻辑主语。
<触类旁通>
(1) Will you please call back again in a little while?
请过一会儿再打电话好吗?
语法分析：不带to的不定式和助动词共同构成句子的谓语。
(2) She is said to have been to Canada many times.
据说她曾经多次去过加拿大。
语法分析：不定式和某些被动结构在句子里构成复合谓语。
(3) It is so good to talk to you.
和你谈话真好。
语法分析：it作先行主语后面的不定式是真正的主语，这样可以使主语避免显得过长，常见的这类句子结构有it+be+形容词+不定式， it+名词或动词+不定式以及it+be+介词短语+不定式等。
(4) I asked her to convey my best wishes to her mother.
我请她向她的母亲问好。
语法分析：“名词或代词+不定式”的形式跟在动词后面可以在句子中做复合宾语，这样的动词有很多。
(5) Did you see anyone enter the office?
你看见什么人进办公室了吗?
语法分析：在诸如see, hear, let, watch, notice, have, fell等某些动词后面可以跟不带to的不定式，构成句子的复合宾语。
(6) She's a nice person, to be sure.
可以肯定，她是个好人。
语法分析：不定式修饰整个句子，因而称之为句子状语。
<巩固练习>
1. She likes to half _____[close] his eyes.
2. I told him to stay at home and _____[wait] till I came back.
3. She was sent abroad _____[educate].
4. The baby seemed _____[dream].
5. She was known _____[work] for the International Olympic Committee.
6. Would you like something _____[drink]?
7. It isn't right _____[waste] so much money on it.
<参考答案>
1. close 2. wait 3. to be educated 4. to be dreaming 5. to have worked 6. to drink 7. to waste
