首先，一個段落必須有一個中心即主題思想，該中心由主題句特別是其中的題旨來表達(dá)。整個段落必須緊扣這個主題，這就是段落的統(tǒng)一性。其次，一個段落必須有若干推展句，使主題思想得到充分展開，從而給讀者一個完整的感覺，這就是完整性。再者，一個段落不是雜亂無章的，而是有機(jī)的組合，句子的排列順序必須合乎邏輯，從一個句子到另一個句子的過渡必須流暢，這就是連貫性。下面我們就對這三個標(biāo)準(zhǔn)分別加以說明。

1.統(tǒng)一性

一個段落內(nèi)的各個句子必須從屬于一個中心，任何游離于中心思想之外的句子都是不可取的。請看下例：

Joe and I decided to take the long trip we'd always wanted across the country. We were like young kids buying our camper and stocking it with all the necessities of life. Bella bakes the best rhubarb pie. We started out in early spring from Minneapolis and headed west across the northern part of the country. We both enjoyed those people we met at the trailer park. Joe received a watch at his retirement dinner. To our surprise, we found that we liked the warm southern regions very much, and so we decided to stay here in New Mexico.

本段的主題句是段首句，controlling idea是take the long trip across the country。文中出現(xiàn)兩個irrelevant sentences，一個是Bella bakes the best rhubarb pie，這一段是講的是Joe and I，中間出現(xiàn)一個Bella是不合適的。還有，Joe received a watch at his retirement dinner這一句更是與主題句不相關(guān)?？忌谧魑木砩铣３Ｒ?yàn)樵斐鰅rrelevant sentences而丟分，值得引起注意。再看一個例子：

My name is Roseanna, and I like to keep physically fit. I used to weigh two hundred pounds, but I joined the YMCA for an exercise class and diet program. In one year I lost eighty pounds. I feel much better and never want to have that much weight on my five-feet frame again. I bought two new suitcases last week. Everyday I practice jogging three miles, swimming fifteen laps, lifting twenty-pound weights and playing tennis for one hour. My mother was a premature baby.

本段的controlling idea是like to deep physically fit，但段中有兩個irrelevant sentences，一個是I bought two new suitcases last week，另一個是My mother was a premature baby。

從上面兩個例子可以看出，native speakers同樣會造出來irrelevant sentences。卷面上如果這種句子多了，造成偏題或離題，那問題就更嚴(yán)重了。

2.完整性

正象我們前面說得那樣，一個段落的主題思想靠推展句來實(shí)現(xiàn)，如果只有主題句而沒有推展句來進(jìn)一步交待和充實(shí)，就不能構(gòu)成一個完整的段落。同樣，雖然有推展句，但主題思想沒有得到相對圓滿的交待，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。例如：

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。本段的兩個推展句均不能回答主題句中提出的問題。什么是“a mind in turmoil”Physical work又怎樣能改變這種情況?為什么它能起therapy的作用?讀者得不到明確的答案。

若要達(dá)到完整就必須盡可能地簡明。例如：

It is not always true that a good picture is worth a thousand words. Often writing is much clearer than a picture. It is sometimes difficult to figure out what a picture means, but a careful writer can almost always explain it.

段首句所表達(dá)的主題思想是一種看法，必須有具體事例加以驗(yàn)證。上述兩個推展句只是在文字上對主題作些解釋，整個段落內(nèi)容空洞，簡而不明。如果用一兩個具體的例子的話，就可以把主題解釋清楚了。比如下段：

It is not always true that a picture is worth a thousand words. Sometimes, pictures are pretty useless things. If you can't swim and fall in the river and start gulping water, will you be better off to hold up a picture of yourself drowning, or start screaming Help?

3.連貫性

連貫性包括意連和形連兩個方面，前者指的是內(nèi)在的邏輯性，后者指的是使用轉(zhuǎn)換詞語。當(dāng)然這兩者常常是不可分割的。只有形連而沒有意連，句子之間就沒有內(nèi)在的有機(jī)的聯(lián)系;反之，只有意連而沒有形連，有時行文就不夠流暢。

1)意連

段落中句子的排列應(yīng)遵循一定的次序，不能想到什么就寫什么。如果在下筆之前沒有構(gòu)思，邊寫邊想，寫寫停停，那就寫不出一氣呵成的好文章來。下面介紹幾種常見的排列方式。

A.按時間先后排列

We had a number of close calls that day. When we rose, it was obviously late and we had to hurry so as not to miss breakfast; we knew the dining room staff was strict about closing at nine o'clock. Then, when we had been driving in the desert for nearly two hours ----- it must have been close to noon ---- the heat nearly hid us in; the radiator boiled over and we had to use most of our drinking water to cool it down. By the time we reached the mountain, it was four o'clock and we were exhausted. Here, judgement ran out of us and we started the tough climb to the summit, not realizing that darkness came suddenly in the desert. Sure enough, by six we were struggling and Andrew very nearly went down a steep cliff, dragging Mohammed and me along with him. By nine, when the wind howled across the flat ledge of the summit, we knew as we shivered together for warmth that it had not been our lucky day.

本段從rose寫起，然后是吃早餐，然后是close to noon，一直寫到這一天結(jié)束。

B.按位置遠(yuǎn)近排列。例如：From a distance, it looked like a skinny tube, but as we got closer, we could see it flesh out before our eyes. It was tubular, all right, but fatter than we could see from far away. Furthermore, we were also astonished to notice that the building was really in two parts: a pagoda sitting on top of a tubular one-story structure. Standing ten feet away, we could marvel at how much of the pagoda was made up of glass windows. Almost everything under the wonderful Chinese roof was made of glass, unlike the tube that it was sitting on, which only had four. Inside, the tube was gloomy, because of the lack of light. Then a steep, narrow staircase took us up inside the pagoda and the light changed dramatically. All those windows let in a flood of sunshine and we could see out for miles across the flat land.

本段的寫法是由遠(yuǎn)及近，從遠(yuǎn)處寫起，然后get closer，再到，最后是inside the pagoda……當(dāng)然，按位置遠(yuǎn)近來寫不等于都是由遠(yuǎn)及近。根據(jù)需要，也可以由近及遠(yuǎn)，由表及里等等。

C.按邏輯關(guān)系排列

a.按重要性順序排列

If you work as a soda jerker, you will, of course, not need much skill in expressing yourself to be effective. If you work on a machine, your ability to express yourself will be of little importance. But as soon as you move one step up from the bottom, your effectiveness depends on your ability to reach others through the spoken or the written word. And the further away your job is from manual work, the larger the organization of which you are an employee, the more important it will be that you know how to convey your thoughts in writing or speaking. In the very large business organization, whether it is the government, the large corporation, or the Army, this ability to express oneself is perhaps the most important of all the skills a man can possess.

這一段談的是表達(dá)能力，它的重要性與職業(yè)，身份有關(guān)，從not need much skill或of little importance到more important，最后是most important。

b.由一般到特殊排列

If a reader is lost, it is generally because the writer has not been careful enough to keep him on the path. This carelessness can take any number of forms. Perhaps a sentence is so excessively cluttered that the reader, hacking his way through the verbiage, simply doesn't know what it means. Perhaps a sentence has been so shoddily constructed that the reader could read it in any of several ways. Perhaps the writer has switched tenses, or has switched pronouns in mid-sentence, so the reader loses track of when the action took place or who is talking. Perhaps sentence B is not logical sequel to sentence A ---- the writer, in whose head the connection is clear, has not bothered to provide the missing link. Perhaps the writer has used an important word incorrectly by not taking the trouble to look it up. He may think that sanguine and sanguinary mean the same thing, but the difference is a bloody big one. The reader can only infer what the writer is trying to imply.

這一段談的是a writer's carelessness，先給出一個general statement作為主題句，然后通過5個perhaps加以例證。
c.由特殊到一般排列

I do not understand why people confuse my Siamese cat, Prissy, with the one I had several years ago, Henry. The two cats are only alike in breed. Prissy, a quiet, feminine feline, loves me dearly but not possessively. She likes to keep her distance from people, exert her independence and is never so rude as to beg, lick, or sniff unceremoniously. Her usual posture is sitting upright, eyes closed, perfectly still. Prissy is a very proper cat. Henry, on the other hand, loved me dearly but possessively. He was my shadow from morning till night. He expected me to constantly entertain him. Henry never cared who saw him do anything, whether it was decorous or not, and he usually offended my friends in some way. The cat made himself quite comfortable, on the top of the television, across stranger's feet or laps, in beds, drawers, sacks, closets, or nooks. The difference between them is imperceptible to strangers.

本段的主題句是段首句，它僅提出一個問題：為什么兩只貓會被搞混。然后對兩者進(jìn)行比較，末句才下結(jié)論。

2)形連

行文的邏輯性常常要靠適當(dāng)?shù)霓D(zhuǎn)換詞語及其他手段來實(shí)現(xiàn)。請讀下面這一段文字并找出文中用以承上啟下的詞語：

Walter's goal in life was to become a successful surgeon. First, though, he had to get through high school, so he concentrated all his efforts on his studies --- in particular, biology, chemistry, and math. Because he worked constantly on these subjects, Walter became proficient in them; however, Walter forgot that he needed to master other subjects besides those he had chosen. As a result, during his junior year of high school, Walter failed both English and Latin. Consequently, he had to repeat these subjects and he was almost unable to graduate on schedule. Finally, on June 6, Walter achieved the first step toward realizing his goal.

本文中起承上啟下的詞語有兩種，一種是轉(zhuǎn)換詞語，另一種是起轉(zhuǎn)換作用的其他連接手段。前者依次有：first, though, so, in particular, and, because, however, besides, as a result, both…and, consequently, and, finally.后者依次是：he, he, his, his, he, these, them, he, those, his, he, these, his.本段中共有詞匯105個，所使用的轉(zhuǎn)換詞語及其他連接用語共26個詞，約占該段總詞匯量的四分之一。由此可見，掌握好transitions不僅對行文的流暢有益，而且對于學(xué)生在規(guī)定時間內(nèi)寫足所要求的字?jǐn)?shù)也是不無好處的。

一個段落里如果沒有transitions也就很難有coherence了.我們看下面一個例子：

Speaking and writing are different in many ways. Speech depends on sounds. Writing uses written symbols. Speech developed about 500 000 years ago. Written language is a recent development. It was invented only about six thousand years ago. Speech is usually informal. The word choice of writing is often relatively formal. Pronunciation and accent often tell where the speaker is from. Pronunciation and accent are ignored in writing. A standard diction and spelling system prevails in the written language of most countries. Speech relies on gesture, loudness, and rise and fall of the voice. Writing lacks gesture, loudness and the rise and fall of the voice. Careful speakers and writers are aware of the differences.

本段中除了第6句開頭出現(xiàn)一個起過渡作用的it之外，沒有使用其他的過渡詞語.這樣，文中出現(xiàn)許多重復(fù)的詞語，全段讀起來也顯得生硬而不自然。如果加上必要的過渡詞語來修飾的話，這一段就成了下面一個流暢連貫的段落：

Speaking and writing are different in many ways. Speech depends on sounds; writing, on the other hand, uses written symbols. Speech was developed about 500 000 years ago, but written language is a recent development, invented only about six thousand years ago. Speech is usually informal, while the word choice of writing, by contrast, is often relatively formal. Although pronunciation and accent often tell where the speaker is from, they are ignored in wiring because a standard diction and spelling system prevails in most countries. Speech relies on gesture, loudness, and the rise and fall of the voice, but writing lacks these features. Careful speakers and writers are aware of the differences.

4.有損連貫性的幾種情況：

考生在寫作中經(jīng)常出現(xiàn)下面幾種錯誤：

1)不必要的改變時態(tài)，比如：

In the movie, Robert Redford was a spy. He goes to his office where he found everybody dead. Other spies wanted to kill him, so he takes refuge with Julie Christie. At her house, he had waited for the heat to die down, but they come after him anyway.

2)不必要的改變單復(fù)數(shù)，比如：

Everybody looks for satisfaction in his life. They want to be happy. But if he seeks only pleasure in the short run, the person will soon run out of pleasure and life will catch up to him. They need to pursue the deeper pleasure of satisfaction in work and in relationships.

3)不必要的改變?nèi)朔Q，比如：

Now more than ever, parents need to be in touch with their children's activities because modern life has the tendency to cause cleavages in the family. You need to arrange family like it so that family members will do things together and know one another. You need to give up isolated pleasures of your own and realize that parents have a set of obligations to sponsor togetherness and therefore sponsor knowledge.

因此寫作中，一定要注意時態(tài)，人稱以及數(shù)的變化是否正確，要注意保持一致。

更多信息請查看留學(xué)英語寫作