一般來說,一個(gè)好的段落應(yīng)該具有這樣的特點(diǎn):意思完整，主題一致,前后連貫,過渡自然。換句話說，一個(gè)好的段落必須能夠充分地表達(dá)思想，內(nèi)容上沒有任何殘缺;一個(gè)段落只有一個(gè)主題，所有的擴(kuò)展句都為主題句服務(wù),主題句與擴(kuò)展句在意義上始終保持統(tǒng)一;段落結(jié)構(gòu)安排合理、條理清楚，句與句之間的轉(zhuǎn)換自然、順理成章，所有這些都要求段落在組織時(shí)要堅(jiān)持以下三個(gè)原則： 

(一）統(tǒng)一性 

一個(gè)段落應(yīng)該只說明一個(gè)問題，或一個(gè)問題的某一方面;應(yīng)該只敘述一件事情，或一件事情的某一個(gè)階段。也就是說，一個(gè)段落內(nèi)的各個(gè)句子必須服從于一個(gè)中心，任何游離于中心思想以外的句子都是不可取的。 一個(gè)好的段落應(yīng)該具有統(tǒng)一性。統(tǒng)一性就是一個(gè)中心思想統(tǒng)領(lǐng)整個(gè)段落。每個(gè)細(xì)節(jié)都應(yīng)支持主題句，不應(yīng)有無關(guān)的細(xì)節(jié)。為了支持主題，要盡可能多地提供細(xì)節(jié)，但又要避免濫用細(xì)節(jié)。請看下面的例子：

 

Millions of years ago，Australia was linked to Asia by a land bridge. Then an earthquake caused the land bridge to sink. The sea rushed in, and Australia became an island. Later, this island became a British colony. Many animals that once wandered back and forth across the land bridge were left in Australia. And kangaroos were among them. Though they were killed off by large animals in other places，they were about to survive in Australia.

 

這一段講的是遠(yuǎn)古時(shí)期的澳大利亞，當(dāng)時(shí)連人類都沒有，但其中畫線的句子偏離主題，應(yīng)當(dāng)被刪掉。又如：

 

Learning a foreign language has changed. Not long ago, students would sit with pen in hand, writing the basic forms of a language, learning structures they would never be able to speak. In that same classroom today, pens and notebooks have been put away. The spoken sounds of foreign tongue fill the room. Today the last skill learned writing a foreign language comes as a natural and possible part of the total language learning process. Yet, just a few years ago, the last skill learned was the first skill mastered today—speaking a foreign tongue. To visit some foreign countries, travelers have to apply for visas.

此段落每句均圍繞主題句“Learning a foreign language has changed. ”展開，但其中畫線的一句“To visit some foreign countries，travelers have to apply for visas. ”則是說申請護(hù)照的，明顯地不符合此段主題， 所以應(yīng)該刪除。

 

(二）完整性 

 

一個(gè)段落的主題思想要靠擴(kuò)展句來實(shí)現(xiàn)，如果只有主題句而沒有擴(kuò)展句來進(jìn)一步交代和充實(shí)，就不能構(gòu)成一個(gè)完整的段落。同樣，如果只有擴(kuò)展句，但主題思想沒有得到相對圓滿的交代，給讀者一種意猶未盡的感覺，這樣的段落也不能完成其交際功能。請看下面段落：

Physical work can be a useful form of therapy for a mind in turmoil. Work concentrates your thoughts on a concrete task. Besides, it is more useful to work—you produce something rather than more anxiety or depression.

本段的主題句是段首句，其后兩個(gè)擴(kuò)展句均不能回答主題句所提出的問題，什么是a mind in turmoil? physical work又如何能改變這種情況？為什么它能起therapy的作用？讀者得不到正確答案。 又如下面一例：

In my English study, I have many difficulties. My first difficulty is that my vocabulary is not large. The second difficulty I have is that I cannot write well. The third difficulty is that my listening comprehension is not good enough. Now I have a plan to study English well.

此段落看似完整，第一句是主題句，后文提到的“my first difficulty, the second difficulty, the third diffuuilty”分別為擴(kuò)展句，最后一句為結(jié)尾句。此段落雖然有頭有尾，但缺少實(shí)質(zhì)內(nèi)容——沒有分析學(xué)英語困難的原因，使得文章空洞無物。此外，結(jié)尾句提到了英語學(xué)習(xí)計(jì)劃，具體內(nèi)容卻沒有交代，給人留下話好像沒說完的感覺。我們比較一下修改補(bǔ)充之后的效果：

 

In my English study, I have many difficulties. The following are some of them. My first difficulty is that my vocabulary is not large. As a result, I can not read fast or understand well. As I am coming to middle age, it is not so easy to keep many new words in mind quickly. The second difficulty I have is that I cannot write well. As I have been very busy with my work which really doesn’t need any foreign language, I seldom have a chance to write something in English. The third difficulty is that my listening comprehension is not good enough. This is because I had little training in listening while I was at college.