定语从句中介词一定提前吗？

Question

he is the student with whom my teacher talked我可以写成he is the student whom my teacher talked with吗

Answer 1

看情况，如果是which/ whom/ whose，介词前提后置均可；如果是that，则介词必须后置，不能提前。

Answer 2

不一定。
你改写的句子也是对的。
一般地，与定语从句谓语动词构成动词词组的介词既可以提前到引导定语从句的关系代词前面，也可以保持原有动词短语的次序，但下列情形除外：
1.当定语从句由that引导时；
2.在口语会话里---将介词提前至关系代词之前的做法一般只发生在正式的语言表达里，口语里罕有这么做的。
口语里这种介词一般都不提前，而正式文体里又总是提前的。

Answer 3

两个句子都行。
He is the student with whom my teacher talked.
He is the student whom my teacher talked with.
但如果是一个动词短语，习惯上不提前。如look at; laugh at之类的。

Answer 4

定语从句中的句首或者句尾的介词位置，除了关系代词that比较特殊，that前面不能放介词，如果前面有介词就得用which或者whom，其他引导词的介词前置后置都无所谓。
We found a bed that/which/(空) the boy was lying on.
We found a bed on which the boy was lying.