放榜前的日子:介词不定式的使用

带介词的不定式短语作后置修饰语

(1) It is not a tent in which to spend the night before we rise in the morning to go on to some other place. (Passage A, Unit 2)
(2) The reason is that there are too many things to pick from .… (Passage A, Unit 5, Preband 1)
(3) …the bad people had fewer and fewer empty buildings to hang out in. (Passage A, Unit 8, Preband 1)
(4) Suppose you want to find someone to play bridge with. (Passage A, Unit 10, Preband 1)

上列各句中的斜体部分是一个带介词的不定式短语，作后置修饰语，修饰它前面的名词短语。就其意义而言，这四句中的后置修饰语都可用关系分句(relative clauses, 即定语从句)来改写：

(1) It is not a tent in which we can spend the night before we rise in the morning to go on to some other place.
(2) The reason is that you have too many things from which you can pick...
(3) …the bad people had fewer and fewer empty buildings in which they could hang out.
(4) Suppose you want to find someone with whom you can play bridge.

不定式短语作名词短语的修饰语（modifiers, 即定语），通常放在它所修饰的名词短语之后，也就是说，它通常充当名词短语的后置修饰语(post-modifiers)。当不定式短语和它所修饰的名词短语之间的关系需要通过介词来起中介作用时，不定式短语的末尾就必须有一个合适的介词，如上例(2)、(3)、(4)。又如：
Let’s find some chairs to sit in. 我们找几把椅子坐下吧。
What they need most now is a house to live in. 他们目前最需要的是有房子可住。
In the library we have many books to choose from. 图书馆里有许多书可供选择。
You need first to find some tools to clean the toilet with. 首先你必须找几样工具来打扫厕所。
The nurse has eight patients to look after. 这个护士要照顾八个病人。

有时，为了避免句子以介词收尾，可把介词前移，使之紧跟被修饰的名词短语。这时，介词后必须用一个关系代词(relative pronoun)，如which, whom等，如上例(1)。又如：
Let’s find some chairs in which to sit.
What they need most now is a house in which to live.
In the library we have many books from which to choose.
You need first to find some tools with which to clean the toilet.

请注意，把介词前移再加关系代词的用法只适用于动词与介词的关系较松散的情况。如果动词与介词的关系较紧密，从而形成了固定的短语动词，则用以介词收尾的结构比较合适。例如：
There is nothing to worry about. 没什么可担心的。
[误] There is nothing about which to worry.
The nurse has eight patients to look after. 这个护士要照顾八个病人。
[误] The nurse has eight patients after whom to look.

很复杂啊