用逗号隔开的那个字一般是插入语或呼语，它与全句完全没有语法联系，去掉后，句子依然成立。例如：
The peasant woman receives nothing, since whatever she earns is the property—as she herself if —of the husband who has bought her as his wife.
The writer tells us that the war lasted from 939(sic) to 1945!
Business, he reflected, appeared as brisk as ever.
希望我能帮助你解疑释惑。