A ；分号
1.与中文一样，分号用于分隔地位平等的独立子句。在某些情况下，使用分号比使用句点更显出子句之间的紧密联系，另外分号也经常与连接副词 thus, however, therefore一起使用(放在这些词语之前)。如   I realize I need exercise; however, I’ll lie down first to think about it.

2.在句子中如果已经使用过逗点，为了避免歧义的产生，就用分号来分隔相似的内容。如 The employees were Tom Hanks, the manager; Jim White, the engineer; and Dr. Jack Lee.

需要注意的是：一个完整的句子以大写字母开始，以句点结束。写英文时用逗点代替句点、分号、冒号或破折号叫“逗号错”，这正是中国学生所要避免的。请比较下列例句：
误：It was raining hard, they could not work in the fields.
（注意：上面句子中划横线的部分是两个不同的主语，而且逗点前后的句子是完整的-----单独拿出来都能代表一个完整的意思。因此，用逗号违反了英文规定，即一个句子只能有一套主干。）
正：It was raining hard; they could not work in the fields.
It was raining hard. They could not work in the fields.
It was raining so hard that they could not work in the fields.
They could not work in the fields because it was raining hard.
It was raining hard, so they could not work in the fields.
As it was raining hard, they could not work in the fields.
误：The essay is poorly organized, there is no central idea.
正：The essay is poorly organized; there is no central idea.
The essay is poorly organized: there is no central idea.

B ，逗点
1.逗点用于分隔一系列的简单内容，如 I will go to Shanghai, Beijing, and Shenzhen.

2.逗点用于修饰名词的多个形容词之间，如 a small, fancy bike

（今天遇到的问题终于得以解决了）
3.逗点用于连接两个较长的独立子句，而且每个句子的主语不同，如 The Grizzlies were out of timeouts, and Miller missed a desperation 3-pointer as time expired.

4.逗点用于关联的子句之间，如 Since he’s your younger brother, please take care of him.

5.逗点用于一个较长的修饰短语之后，如 In the middle of the coldest winter on record, the pipes froze.

6.逗点用于直接引用的句子之前，如 Mary said, “Let’s go fishing.”（注意：这里说的和上面提及的冒号在直接引语中的使用不一样。如果是引用比较正式的发言讲话就要用冒号，一般情况下就用逗点。）

如果句中含有间接引用就不需要逗点，如 Mary said we should go fishing.
在反问句之前要使用逗点，如 :
He worked very hard, didn’t he？