有时为了避免重复，可以用to 来代替前面的不定式，这种情况出现在下列动词之后：expect, hope, wish, mean, prefer, care, forget, want, try；或出现在be glad / happy, would like / love 等的后面。

如果在省略的不定式结构中含有：be, have, have been，这些词要保留。如：

I haven’t been to Hong Kong, but I wish to.

- Are you on holiday ?

- No, but I’d like to be.

- I didn’t tell him the news. 我没有告诉他那个消息。

- Oh, you ought to have. 噢，你本应该告诉他的。

4．在there be 结构中，当说话人考虑的是必须有人去完成某件事时，不定式用主动形式；如果说话人强调的事情本身必须被完成，则用被动形式。如：

There is a lot of work to do. (Someone has to do the work. )

There is a lot of work to be done. (The work has to be done. )

There is nothing to do. (无事可做，感到十分乏味。)

There is nothing to be done. (某东西坏了，无法使之恢复正常。)

3．不定式作表语形容词的关语，和句中主语构成逻辑上的动宾关系时，不定式多用主动形式，这是因为人们往往认为形容词后省去了for sb. 。如：

This book is difficult to understand.

This kind of fish is nice to eat.

2．不定式和它前面被修饰的名词或代词构成逻辑上的动宾关系，又和该句主语构成逻辑上的主谓关系时，不定式常用主动形式。如：

She has a sister to look after. (She looks after her sister.)

I know what to do. (I do what.)

1．不定式修饰的名词或代词和不定式逻辑上构成主谓关系时，不定式往往用主动形式。如：

Do you have a knife to cut the watermelon ?

(A knife cuts the watermelon.)

疑问词(who, which, when, where, how, what等)+ 不定式，这个结构在句中起名词作用，可充当主语、表语、宾语。如：

I didn’t know what to do. (宾语)

When to hold the meeting is not known yet. (主语)

My question was how to get so many books. (表语)

注意句型：Why not do sth. ? Why do sth. ?

4．独立成分作状语

有些分词短语，其形式的选择不受上下文的影响，称作独立成分。常见的有：

Generally speaking … 一般说来

Frankly speaking … 坦白地说

Judging from … 根据……来判断

Considering … 考虑到……

To tell you the truth … 说实话

清单六　 非谓语动词其它用法

3．分词作状语的句法功能

分词或分词短语作状语时，可以表时间、原因、结果、条件、让步、行为方式、伴随状况等。表示时间关系的分词短语有时可由连词while 或when 引出。如：

Hearing the news, they got excited. (时间)

Be careful while / when crossing the street. (时间)

Having been bitten by a snake, she was frightened at it. (原因)

Given a chance, I can surprise the world. (条件)

The cup dropped to the ground, breaking into pieces. (结果)

Having been told many times, he still repeated the same mistake. (让步)

The teacher came into the lab, followed by some students. (伴随状况)

2．分词作状语的基本原则

分词作状语时，分词的逻辑主语必须与句子的主语保持一致。

分词作状语必须和句中主语含有逻辑上的主谓或动宾关系，否则不能使用分词作状语。

1．分词作状语形式的选择