它是指与主语之间无任何语法关系的名词或代词加上一个分词的结构。它不修饰单个的词，而修饰整个句子。独立主格结构可位于句子的任何部位。它构成一个单独实体，并具有如下两种功能： 解释原因或情景 提供主句中重点部分的相关细节。
例 Freud distinguished three kinds of anxiety, each arising from a different source of perceived danger.
each 是独立主格结构，arising from是动词短语。注意这个独立主格结构是一个干巴巴的句子。通过改变动词形式，它的面貌可焕然一新：Each arises from a different source of perceived danger.
Before: His nose was running and his hands were shaking. He left the theater like that.
Interesting: His nose running and his hands shaking, he left the theater.
Before: He is known for his bad temper, so I fear the encounter.
Interesting: I fear the encounter, his temper being what it is.
Plain: If the weather is favorable tomorrow, we will spend the entire day climbing Huang Shan.
Good: Weather permitting, we will spend the entire day tomorrow climbing Huang Shan.