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.
