在應(yīng)試型(雅思或新托福等)議論文寫作中，通常遵循introduction- body-conclusion(引言段-主體段-結(jié)論段)的“三步曲”。Body(主體)段落提供了論證觀點的理由，是整個文章的主體，在評分中占有很大的比重。例如一篇滿分的雅思作文(9分)必須“presents a fully developed position in answer to the question with relevant, fully extended and well supported ideas”。這里的“fully extended / well supported”，必須通過主體段來體現(xiàn)。

　　1.Write a topic sentence for each paragraph you plan to write. Each topic sentence should relate to your thesis statement and introduce what the paragraph will be about. If you find that the topics you want to discuss do not support the thesis statement you have written, revise your thesis statement or reconsider your topic sentences.

　　(每個主體段都必須有一個明確的主題句)

　　2.Write ideas that support your topic sentences. The topic sentence for each paragraph tells the reader what the paragraph will be about. The ideas stated in the rest of the paragraph should all relate to the topic sentence.

　　(支持句必須圍繞主題句展開)

　　新托福滿分作文(5分)也要求“is well organized and well developed, using clearly appropriate explanations, exemplifications, and/or details”，同樣必須通過主體段落發(fā)展來實現(xiàn)。一般來說，一篇議論文必須包含至少兩個主體段。每個主體段都必須有明確的主題句“topic sentence”和若干支持句“supporting sentences”。他們共同組成文章的理由段，對全文的論點提供理由支持。專家建議初學(xué)者在練習(xí)議論文寫作時，必須遵循理由段發(fā)展的幾個簡單原則，這對迅速完成理由段、構(gòu)建連貫和理由充分的議論文大有幫助。