代词，就是代替其他名词。
Mary is one of the heads of the ToJi Corporation. Mary works with Mr. James and Mr. James' son Tom. Mr. James and Mr. James' son Tom are experts in biochemistry. Mary, Mr. James, and Tom researched and invented a drug for cancer treatment.
使用代词改写上述文字：
Mary is one of the heads of the ToJi Corporation. She works with Mr. James and his son Tom. He and his son Tom are experts in biochemistry. They researched and invented a drug for cancer treatment.
人称代词，代表一个或多个人
I go to school.
You are a student.
They are Koreans.
He works here.
We gave her food.
it 代表一件东西
I drank it.
It is big.
They cut it into halves.
返身代词
返身代词，表示受一个动作影响的人，恰恰是发起这个动作的人。
I give myself a book.
代词助记表格
| 第一人称 | 第二人称 | 第三人称 | |||
|---|---|---|---|---|---|
| 男 | 女 | 中性 | |||
| 单数主语 | I | you | he | she | it |
| 单数宾语 | me | you | him | her | it |
| 单数返身 | myself | yourself | himself | herself | itself |
| 复数主语 | we | you | they | ||
| 复数宾语 | us | you | them | ||
| 复数返身 | ourselves | yourselves | themselves |
参考
http://www.talkenglish.com/grammar/pronouns.aspx