关系代词who只能指人。可在定语从句中作主语或宾语，但who之前不可用介词，比如不能说with who，可以说with whom。请看以下例句：

（1）The woman who lives next door is a famous dancer.

---关系代词who既指代先行词the woman, 又在who lives next door 这个定语从句中作主语。

（2）He who is not handsome at twenty, nor strong at thirty, nor rich at forty, nor wise at fifty, will never be handsome , strong , rich, or wise. (一个人若在20岁不俊美、30岁不健康、40岁不富有、50岁不明智，那么他将永远不会拥有这些。）

---关系代词who即指代先行词he，又在who is not handsome at twenty, nor strong at thirty, nor rich at forty, nor wise at fifty这个定语从句中作主语。

（3）There is the difference between happiness and wisdom: the person who thinks himself the happiest man really is so; but the person who thinks himself the wisest is generally the greatest fool.(幸福与智慧的区别于此：认为自己是最为幸福的，他真的就最幸福；而认为自己最具智慧的，却往往是最大的傻瓜。）

---关系代词who即指代先行词the person，又分别在who thinks himself the happiest man 和who thinks himself the wisest 这两个定语从句中作主语。

（4）The world is a book, and those who do not travel read only one page.(世界犹如一本书，而那些从不出门旅行的人仅仅读了这本书的一页。）

---关系代词who即指代先行词those,又在who do not travel 这个定语从句中作主语。

（5）Only the people who have the patience to do simple things perfectly will require the skill to do difficult things easily. (只有有耐心圆满完成简单工作的人，才能够轻而易举地完成困难的事。）

---关系代词who即指代先行词the people,又在who have the patience to do simple things perfectly这个定语从句中作主语。

(6)I want to talk to somebody who I can trust.

---关系代词who即指代先行词somebody,又在who I can trust这个定语从句中作宾语。（本句中的who可以省略）

（7）I am talking about friends who you can share almost everything with.(我说的是那些可以分享一切的朋友）

---关系代词who即指代先行词friends，又在who you can share almost everything with这个定语从句中作介词with的宾语。本句不可以改为I am talking about friends with who you can share almost everything. 但可以改为I am talking about friends with whom you can share almost everything.

关系代词whom只能指人，在定语从句中不能作主语，但可以作宾语。请看以下例句：

（8）I think you should stay faithful to the person to whom you are married.(我认为你应该对你的配偶忠诚。）

---关系代词whom即指代先行词the person，又在to whom you are married这个定语从句中作介词to的宾语。本句还可以改为I think you should stay faithful to the person whom you are married to.

（9）I like the people with whom I work.

---关系代词whom即指代先行词the people，又在with whom I wokr这个定语从句中作介词with的宾语。本句还可以改为I like the people whom I work with.