首先，一个段落必须有一个中心即主题思想。主题思想在雅思考试中主要是通过段落的首句来表达的。这个句子在雅思写作中，我们把它称为主题句。整个段落必须紧扣这个主题，这就是段落的统一性(unity)。其次，一个段落必须有若干扩展句，使主题思想得到充分展开，句子与句子之间环环相扣，这就是完整性。再者，一个段落不是杂乱无章的，而是有机的组合，句子的排列顺序必须合乎逻辑，从一个句子到另一个句子的过渡必须流畅，这就是连贯性。雅思写作四项评分标准中的coherence and cohesion在这里占了较大的比重。

　　1. 统一性

　　一个段落内的各个句子必须从属于一个中心，任何游离于中心思想之外的句子都是不可取的。

　　请看下例：

　　Amittedly, 这个地方需要一个与开头衔接的词。There are a lot of evidences showing that the rich-poor gap is increasing with the updating of technology. One of the reasons is that the usage of household appliances is gradually taking the place of labour force, for it is convenient and economical to use the man-made devices #pared with employing someone. In this situation, many of the labours who are not skilful and well-educated in other sectors would be paid at lower level for the same work or even lose their jobs. Moreover, the lack of education expenditure in such families leads to the lack of skill and knowledge of their children, so such gap can be hardly eliminated of generations. 本段落里面论据和主题句里提到的evidences不一致，或者说人们的工作技能和其受教育的程度与科技会加大贫富之间的差距有什么关系？

　　However, parents should not take these as excuses and escape their responsibility. 主题句这样写，就要在段中以解释父母的职责为主线来论述父母对孩子的影响。但是段落的第二句话与主题句或与后续的句意都衔接不连贯。Children may feel more convenient #municating with parents, and accept what they told better. Besides, parents have their own way influencing children. For example, they can encourage children by giving special gift which teachers cannot offer. 卷面上如果这种句子多了，造成偏题或离题，那问题就更严重了。

　　2. 完整性

　　正像我们前面说的那样，一个段落的主题思想靠推展句来实现，如果只有主题句而没有推展句来进一步交待和充实，就不能构成一个完整的段落。同样，虽然有推展句，但主题思想没有得到相对圆满的交待，给读者一种意犹未尽的感觉，这样的段落也不能完成其交际功能。

　　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.

　　本段的主题句是段首句。本段的两个推展句均不能回答主题句中提出的问题。什么是“a mind in turmoil”（心境不平静），Physical work又如何能改变这种情况？为什么它能起therapy的作用？读者得不到明确的答案。

　　又如：

　　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.

　　段首句所表达的主题思想是一种看法，必须有具体事例加以验证。上述两个推展句只是在文字上对主题作些解释，整个段落内容空洞，简而不明。如果用一两个具体的例子的话，就可以把主题解释清楚了。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. 连贯性(coherence)

　　连贯性包括意连和形连两个方面，前者指的是内在的逻辑性，后者指的是使用转换词语。当然这两者常常是不可分割的。只有形连而没有意连，句子之间就没有内在有机的联系；反之，只有意连而没有形连，有时行文就不够流畅。

　　1) 意连

　　段落中句子的排列应遵循一定的次序，不能想到什么就写什么。如果在下笔之前没有构思，边写边想，写写停停，那就写不出一气呵成的好文章来。下面介绍几种常见的排列方式。

　　a. 按重要性顺序排列(arrangement in-groups importance)

　　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.

　　这一段谈的是表达能力，它的重要性与职业，身份有关，从"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(general-to-specific arrangement)

　　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.

　　这一段谈的是a writer’s carelessness, 先给出一个general statement作为主题句，然后通过5个"perhaps"加以例证。

　　c. 由特殊到一般排列(specific-to-general arrangement)

　　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 #fortable, 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.

　　本段的主题句是段首句，它仅提出一个问题：为什么两只猫会被搞混。然后对两者进行比较，末句才下结论。

　　2) 形连

　　行文的逻辑性常常要靠适当的转换词语及其他手段来实现。请读下面这一段文字并找出文中用以承上启下的词语：

　　Walter’s goal in life was to be#e 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.

　　本文中承上启下的词语有两种，一种是转换词语(transitional words or phrases)，另一种是起转换作用的其他连接手段(linking devices)。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。本段共有105个词汇，所使用的转换词语及其他连接用语共26个，约占该段总词汇量的四分之一。由此可见，掌握好transitions不仅对行文的流畅(smoothness)有益，而且对于学生在规定时间内写足所要求的字数也是不无好处的。

　　一个段落里如果没有transitions也就很难有coherence了，下面我们看一个例子：

　　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句开头出现一个起过渡作用的"It"之外，没有使用其他的过渡词语。这样，文中出现许多重复的词语，全段读起来也显得生硬而不自然。如果加上必要的过渡词语来修饰的话，这一段就成了下面一个流畅连贯的段落：

　　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. 有损连贯性的几种情况

　　考生在写作中经常出现下面几种错误：

　　1) 不必要的改变时态，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 #e after him anyway.

　　2) 不必要的改变单复数，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) 不必要的改变人称，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.

　　因此写作中，一定要注意时态，人称以及数的变化是否正确，要注意保持一致。