1.当一个句子中，加入了两个或两个以上的概念（从句），而这些概念又互为平等时：

例子：The universe has always called to human beings; there could be no more final frontier than space.

 

2.当一个句子加入了两个用连接副词或转折片语连接的独立从句时：

例子：Sam thought David was inviting him to the picnic to enjoy a nice day out; as it turned out, David was planning a surprise birthday party.

 

3.当一个句子中陈列出许多或一系列不同的项目，其中这些陈列的项目中包含逗号时，或者项目相对长且性质较复杂时：

例子：Our family members came all the way from Denver, Colorado; Rochester, Minnesota; and even Paris, France.

 

4.在句子中使用对等连接词连接两个独立从句(若两个从句已使用逗号分隔)，或者当两个从句较长时：

例子：My main research objective is to isolate the cause of the disease, as well as to contribute to the existing literature; for this will bring an end to starvation across the continent, create new study designs related to epidemiology, and change the very paradigm of my research field.