规则：每个段落以一句主题句 (topic sentence)开头，结尾须与开头呼应。

本原则的目的同样是帮助读者阅读，这种写作方式能让读者在开始阅读每个段落时，就掌握该段落的目的，且直到段落结束时都铭记在心。因此，在阐释或议论时最常使用的段落结构为：
(a) 主题句在首句或前几句出现；
(b) 接下来的句子解释、建立或发展主题句的叙述；
(c) 末句强调主题句的想法，或陈述一些重要结论。
请避免以离题的叙述，或无关紧要的细节作为段落的结尾。

若文章的篇幅较长，写作时可能必须说明某个段落与前述内容的关联，或该段落在通篇文章中的功能。有时只须在主题句中加入一个词语，如 again（同样地）、therefore（因此）、for the same reason（由于同样的原因），有时则须在主题句前加上一或数句有引导或连接功能的句子。若需要多个句子才能与主题句顺利衔接，则建议将这几个句子独立为一个段落。

如上所述，同学在写作时可以运用数种方式连结段落中的本文与主题句。你／你也可以用不同的句式重述主题句、定义句中的词汇、反驳与主题句相反的事实、提供通例或特例、说明句子的隐含意义或其可能导致的结果，来让主题句要表达的意义更加明确。在写作较长的段落时，同学可能会用到以上数种方法。

范例1 苏格兰小说家史蒂文森的经典散文〈徒步旅行〉
❶主题句。
Now, to be properly enjoyed, a walking tour should be gone upon alone.
若要好好享受徒步旅行，你应该自己一个人去。

❷否定相反的做法以阐明主旨。
If you go in a company, or even in pairs, it is no longer a walking tour in anything but name; it is something else and more in the nature of a picnic.
如果是一群人去，或就算只有两个人，也只会是趟有名无实的徒步旅行；比起徒步旅行，这更像是去野餐。

❸以简短的方式重述主题句，并提出三个原因支持；其中，第三个原因（“你必须拥有自己的步调”）是用反驳与主题句相反的事实的方式，来阐明意见。
A walking tour should be gone upon alone, because freedom is of the essence; because you should be able to stop and go on, and follow this way or that, as the freak takes you; and because you must have your own pace, and neither trot
alongside a champion walker, nor mince in time with a girl.
徒步旅行应该自己一个人去，因为自由是其中的精髓；因为如此一来，你便能随时走走停停，或随兴改变路径；因为你必须拥有自己的步调，而不是在一位快走冠军旁小跑步，或因为一位女孩而停驻许久。

❹用两种方式叙述第四个原因。
And you must be open to all impressions and let your thoughts take colour from what you see.
你也应该敞开心胸接受任何映入眼帘的印象，并让所见之物为你的想法增色。

❺用另一种方式叙述同一个原因。
You should be as a pipe for any wind to play upon.
你该像把笛子，不管什么风吹来，都能奏出美妙乐音。

❻引述英国散文家Hazlitt 的话说明同一个原因。
“I cannot see the wit,” says Hazlitt, “of walking and talking at the same time. When I am in the country, I wish to vegetate like the country,” which is the gist of all that can be said upon the matter.
海兹利特说道：“我看不出边散步边讲话的好处。当我走在乡间时，我只想像植物般悠然生长。”这段话说得实在中肯。

❼将Hazlitt 的话换句话说。
There should be no cackle of voices at your elbow,
to jar on the meditative silence of the morning.
你身边不该有呶呶不休的人声，破坏早晨冥想般的宁静。

❽以丰富、生动的用词再次重述第四个原因，形成强而有力的结论。
And so long as a man is reasoning he cannot surrender himself to that fine intoxication that comes of much motion in the open air, that begins in a sort of dazzle and sluggishness of the brain, and ends in a peace that passes comprehension.
而且当一个人用理性思考时，他便无法美好地沉醉在自然之中，这种沉醉来自空气中的律动，源于大脑的微醺与慵懒，并在一种难以名状的平静之中落幕。

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英文原文：

RULE9

As a rule, begin each paragraph with a topic sentence, end it in conformity with the beginning.

Again, the object is to aid the reader. The practice here recommended enables him to discover the purpose of each paragraph as he begins to read it, and to retain this purpose in mind as he ends it. For this reason, the most generally useful kind of paragraph, particularly in exposition and argument, is that in which

(a) the topic sentence comes at or near the beginning;
(b) the succeeding sentences explain or establish or develop the statement made in the topic sentence; and
(c) the final sentence either emphasizes the thought of the topic sentence or states some important consequence.

Ending with a digression, or with an unimportant detail, is particularly to be avoided.

If the paragraph forms part of a larger composition, its relation to what precedes, or its function as a part of the whole, may need to be expressed. This can sometimes be done by a mere word or phrase (again; therefore; for the same reason) in the topic sentence. Sometimes, however, it is expedient to precede the topic sentence by one or more sentences of introduction or transition. If more than one such sentence is required, it is generally better to set apart the transitional sentences as a separate paragraph.

According to the writer’s purpose, he may, as indicated above, relate the body of the paragraph to the topic sentence in one or more of several different ways. He may make the meaning of the topic sentence clearer by restating it in other forms, by defining its terms, by denying the contrary, by giving illustrations or specific instances; he may establish it by proofs; or he may develop it by showing its implications and consequences. In a long paragraph, he may carry out several of these processes.
Example 1 Robert Louis Stevenson, Walking Tour

❶ Topic sentence.
Now, to be properly enjoyed, a walking tour should be gone upon alone.

❷ The meaning made clearer by denial of the contrary.
If you go in a company, or even in pairs, it is no longer a walking tour in anything but name; it is something else and more in the nature of a picnic.

❸ The topic sentence repeated, in abridged form, and supported by three reasons; the meaning of the third (“you must have your own pace”) made clearer by denying the contrary.
A walking tour should be gone upon alone, because freedom is of the essence; because you should be able to stop and go on, and follow this way or that, as the freak takes you; and because you must have your own pace, and neither trot alongside a champion walker, nor mince in time with a girl.

❹ A fourth reason, stated in two forms.
And you must be open to all impressions and let your thoughts take colour from what you see.

❺ The same reason, stated in still another form.
You should be as a pipe for any wind to play upon.

❻ The same reason as stated by Hazlitt.
“I cannot see the wit,” says Hazlitt, “of walking and talking at the same time. When I am in the country, I wish to vegetate like the country,” which is the gist of all that can be said upon the matter.

❼ Repetition, in paraphrase, of the quotation from Hazlitt.
There should be no cackle of voices at your elbow, to jar on the meditative silence of the morning.

❽ Final statement of the fourth reason, in language amplified and heightened to form a strong conclusion.
And so long as a man is reasoning he cannot surrender himself to that fine intoxication that comes of much motion in the open air, that begins in a sort of dazzle and sluggishness of the brain, and ends in a peace that passes comprehension.

─ ─摘自:《英文写作圣经《The Elements of Style》》野人出版提供@

责任编辑：黎薇