So作为替代词，词典的释义为：used to refer to something that has just been stated or suggested。

1 它可以替代前面提及的一个分句：

“Has she left?” “I believe so.” [so替代she has left]

“Is it true?” “I think/hope so.” [so替代it is true]

I didn't like the dress and told her so. [so替代 I didn't like it]

I might be late. If so [so替代I am late], please start the meeting without me.

2  so也可以与系词be合用，so替代前面提及的表语：

“You were late this morning.” “So I was—what's it to you?” [so替代 late]

“Today is the first day of winter.” “Why, so it is.” [so替代the first day of winter]

3  so还可以与实意动词do合用，替代前面提及的动词+宾语或/和状语：

If you have not yet returned the form, please do so immediately. [do so替代 return it]

He said he would sell his car, and he did so three days later. [did so替代 sold his car]

4 so也可以用作指示代词，意为this，为非正式用法。例如：

You can fold the paper like so. [so= this]