Speak比较庄重，表示某人(即讲者)在一段对话中所说的话较其它人多。

举例：

The Principal speaks to us every morning at the assembly.

Tom, your boss wants to speak to you.

Talk不及speak庄重，而且多用于说话，少用于书写。 Talk表示两个或更多的人在对话。

举例：

The students were talking loudly in the classroom, in the very presence of the teacher.

当宾语是一种语言时，要用 speak 不用 talk 或 say：

正确： Victor speaks fluent Putonghua.

错误： Victor talks fluent Putonghua.

错误： Victor says fluent Putonghua.

在书面英语， talk 极少用作及物动词，除非在 talk 后接用以下的宾语：

Stop talking nonsense.

They are talking business again.

若不是接用上列的宾语，talk 后必需接用前置词 about。

举例：

正确： Betty and Susan are talking about the trip to London.

错误： Betty and Susan are talking their trip to London.

Say通常跟讲者所说的话一起使用，不论是直述句或陈述句：

Please say hello / thank you to your mum.

What did your father say when you told him about your plan to get married? 'I cant believe it,' he said.

He said that he could not believe it.

可是， say 有时也可用于一些非直述句或陈述句中。

看看以下的例子：

I want you to say something about how we met at our wedding party.

注意 something about how we met并不是用于引述别人所说的真实语句。

另一方面， tell 并不是用于引述别人所说的话语，而是表达别人的说话中所述的事实或资料：

He told me about the accident.

He told his parents the truth.

He told us a funny story.

在陈述命令句中，应用 tell 而不用 say：

'Keep quiet,' the teacher said to the students.

The teacher told the students to keep quiet.

'Dont stay up late,' my mother said to me.

My mother told me not to stay up late.