通常而言，主题句就是一段话的第一句。后面的句子一般为支持性的细节，以解释、发展或是支持主题句所表现的主要论点。
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The recent string of corporate scandals provided a rude awakening to the importance of these internal checks. In the case of WorldCom, it was internal auditor Cynthia Cooper who blew the whistle on the company for inflating profits by $3.8 billion. She didn’t intend to be a hero, she said to Time magazine when it named her one of its Persons of the Year. She was just doing her job.
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Chief constables had disapproved of the use of league tables. They complained that they provoked unfair criticism because they did not compare like with like. Mr. Denham said the graphs were easier to comprehend than tables. “As people get familiar” with this type of graphical presentation they will realize it contains a lot of data that can be understood after an initial glance. “ The spidergrams are based on five indicators: reducing crime, investigation crime, public safety, deployment of resources and the view of a focus group of local citizens.
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有时候主题句也会出现在整段话的最后。这样的结构安排，通常出现在一个讨论困难的、不为大众所接受的话题或者文章的主要目的是为了说服读者接受某种结论的段落中。因为先把道理说清楚，那么读者就会比较容易接受新的观点和看法。