文章的正文應以文章的開頭為線索，具體地敘述、的說明或論證文章的主題。文章不論長短，每個段落都必須為主題服務。像說明文和議論文這一類的文章，一個主題還常分成幾個小主題，每個小主題要用一個段落處理，另起一段時，應是一層新的意思。每一段的開頭，要放一個表示段落小主題的主題句，這樣可使文章條理化，易于閱讀，便于讀者抓住主題。段內的所有句子應圍繞主題句的意義加以闡述或論證，為中心思想服務。句子之間應銜結自然，有條不紊，而且還要合乎邏輯，段落中不能出現任何與主題無關的句子；英語寫作比較重視主題句的作用，缺少它段落意義就會含糊不清。主題句也可放在段落的中間和末尾等部位，但對初學者來說，以放在段首為好。見下列這篇題為“How to Be a Good Student”(怎樣做個好學生)的文章：

    We students are the builders and masters of the country. It is important for us to know how to be a good student.

    A good student, I think, should be diligent in his studies. The more he studies, the more he will increase his knowledge. Without enough knowledge, we cannot make great contributions to the modernization of our country.

    To take care of one's own body is another important thing for good student to do. Anyone, who hasn't got a strong body, can do nothing for his country, even if he has much knowledge. There was a man, who, when he was student, studied hard but neglected his health. No sooner did he come to serve the country than he died of poor health. From this we may see that to have a strong body is really very important for a student.

   Lastly, to cultivate one's own virtue is most important. Virtue is the essence of a noble and good character. It will greatly help one to be useful and his country heart and soul. When learned people go astray, they do more harm than good to society. We should draw lessons from this.

   這篇文章的第一段引出了文章的主題，第二、第三和第四段則是文章的正文，每—段的第一句即是段落的主題句，它們既支持了文章中心的觀點和思想，同時又概括了全段的意思。在同一段落中，其余的句子都圍繞主題句所表示的中心展開，同時句子間的銜結也很自然；各層的意思都很連貫。
 
   分段是文章組織上重要的一步，但如果寫的題目范圍很小，那就無須再將題目分成小的主題，并分入各個段落去闡述了。像一篇簡短的評論；某一事情的簡短記載，某一個想法的說明，對一個人物或一件事情的簡要敘述或說明等，就可以只用一個段落來表現主題。

   在記敘文中，段的結構有時可以很簡單，不需要有主題句，敘事一氣呵成，中途沒有停頓。段與段之所以分開，只是為了起修辭作用，以便把某一細節置于顯著的地位。某些測試用的表達題，在題目中就已經說明只需要根據。所給的提示寫一個段落，而不是一篇文章。對于這一類的寫作試題，就可以予以簡潔的處理，并不是非要擴充成一篇有頭有尾的完整文章。

  下面這篇題為“Weekend Homework”(談周末作業)的短文，就是用一個段落來論述問題和表達觀點的。

  Usually Saturday night is the time for students to get back to their desks and do their weekend homework. Six school days are enough for the students who have many other interests. I think weekend homework should not be given. With homework arranged for Saturday night and the whole of Sunday, when can he find time to help around the house, play a game of football or see a good film, or just relax? In fact weekend homework is usually put off until Sunday night. As a result our homework is done very poorly and we achive no results. If there were no homework on weekends, students would go to school on Monday well rested, willing to work. Teachers, don't you agree?