我们常常听人家说：不要把介词（prepositions）放在句尾，以免削弱句子的气势。
实际上，英语的介词是可以在句尾出现的；有时还是非在句尾不可。请看这句：
“I may give you financial aid. But it all depends on what the money is for .”
这句话的介词“for”在句尾出现。如果把“for”移到宾语之前，就不合句法了：
*“...But it all depends on for what the money is.”
这么看来，英语介词是可以放在句尾的。既然如此，在什么情况下，英语介词才可以放在句尾呢？
常见的情况有下面 4 种：
㈠当疑问代词或疑问副词作为介词的宾语时，理论上要在介词后面出现，但在实际用法上，它被转移到疑问句前头，介词则留在句尾。例如：
① What are you dreaming of?
② Where are you from?
①不能改为“Are you dreaming of what?”也不能是“Of what are you dreaming?”②不是“Are you from where?”，更不是“ From where are you?”
㈡介词不能移到限定性形容词分句中的关系代词（the relative pronoun in the restricted adjective clause）之前；因此，我们可以③表示心意，但不能用④这样的句子：
③ Is this the book that you asked me for?
*④ Is this the book for that you asked me?
同样的，⑤是对的，⑥是错的：
⑤ This is the goal that we are striving towards.
*⑥ This is the goal towards that we are striving.
㈢在不可分开的片语动词（the inseparable phrasal verb）里，如果介词在句尾，也只好随遇而安，不便移动。例如：
⑦ This is something which I refuse to put up with.
⑧ Such a matter should be immediately dealt with.
⑨ An 8% increase in salary is not to be sniffed at.
⑩ The rising cost is really a thing to be reckoned with.
㈣当带介词的不定式动词修饰名词而又出现在句尾时，这介词只好保留在原位。例如：
11. David is a nice person to work with.
12. I like to have someone to talk to.
13. This is not a comfortable place to live in.
14. Give me a good pen to write with.
15. Is this a box to put coins in?
16. There is some useful information for you to refer to.
综上所述，英语介词不但可以在句尾出现，有时还非在句尾不可！
除了所举的情况之外，尽量避免把介词放在句尾。例如17－19虽没有什么问题，但不如20－22好和自然：
17. Can you tell me whom do you share your office with?
18. This is the last way which the idea can be pushed through.
19. What reason have you chosen this scheme for?
20. Can you tell me with whom do you share your office?
21. This is the best way through which the idea can be pushed.
22. For what reason have you chosen this scheme?
