一个段落可以通过分析事物的因果关系(cause-effect)来展开。分析事情发生的原因和结果，力求推理客观严谨，正确严密，逻辑性强。一种原因会导致多种结果，一种结果的背后也可能有多种原因，一个事物又可能引发因果的连锁反应，即一种原因产生某种结果，而这种结果又是另一种结果的原因，以此发展下去形成链条。一般说来，因果展开法有三种模式。

　　一、一果多因展开法

　　I enjoy living in big cities. The main reason is that it is very convenient to live in big cities. There is fast public transport, a wide variety of goods to choose from, all the latest modern conveniences and plenty of public places for enjoyment. Above all, the better health care system helps you live in greater comfort.

　　作者喜欢住在大城市为事情的结果，结果背后的原因有二：生活方便和完善的医疗服务。

　　Now people are able to pay more attention to the food they eat. Firstly, with the development of China's economy, people earn more and more money, so they can afford to choose the food they like to eat. Secondly, more and more people have realized that what they eat greatly concerns their health. So people tend to choose those healthy and nutritious food to eat.

　　人们现在能关注他们的饮食为事情的结果，结果背后的原因有二：收入的提高和人们认识到了饮食对健康的影响。

　　以上两段都是先阐述结果，再扩展原因，而且是用多种原因支持一个结论。结果放于句首，引起读者关注，重点突出。然后分别用举例和列举的方式层次分明地阐述人们喜欢住在大城市和关注饮食的几个原因。

　　二、一因多果展开法

　　Cigarette smoking contains nicotine, several cancer producing or irritating substances and carbon monoxide gas. As a result, damage to the lining of the bronchial tubes is much more common among cigarette smokers than nonsmokers, even when there is no obvious disease. Some of these changes are considered to be pre-cancerous. Moreover, lung function is generally reduced among cigarette smokers. Worst of all, cigarette smoking is a greater hazard than other factors-such as community air pollution-in the causation of lung cancer and chronic bronchitis.

　　该段首先说明了烟内所含的有害成分，然后分析了因这些有害成分，吸烟后所产生的三个不良后果：对气管的损害；对肺功能的损害和致癌。这些后果按危害的严重性递增顺序排列。

　　Up to now, the practical benefits resulting from space research have included the deve-lopment of new methods and skills, new services, new products, and even new companies created to make use of what has been learned through space travel. Also among the benefits are better education, more efficient management, higher quality of industrial products, and rapid economic growth. People all over the world are now served by improved weather predictions, better communication systems, and better understanding of the earth and its environment. Everyone will benefit from space research which makes it possible to measure the earth's resources and to observe whether or not they are being used properly. Increasingly, the space program will help our world deal with the problems of the environment. It has brought a new appreciation of the complex systems of which man is only a part.

　　该段开门见山点明主题，说明了宇航事业为各行各业所带来的诸多好处。原因是宇航事业的发展，其结果用排比结构一一列举，新方法、新技术、新服务、新产品……。条理清晰，连贯自然。

　　以上两段均属于一因多果的段落模式。原因在先，结果在后，且一因多果。为了行文连贯，段中还恰当地应用了连接词语。如：第一段中应用了As a result, some, moreover, worst of all。第二段中应用了also, increasingly 等词使各句之间自然衔接，自然过渡，自然照应，使读者一目了然。

　　三、因果连锁展开法

　　Take facial tissues as an example of how mass production works. When facial tissues were first put on the market in 1924, they were made in limited quantities and sold at 65 cents per box of 200. People liked these facial tissues immediately and began asking for them when they went into different stores. Because there was such a demand for the product, manufacturers began making tissues in larger and larger quantities. Because the manufacturers were making tissues in greater quantities, their production costs were lowered, so that the cost of tissues went down. In the meanwhile, the quality of facial tissues was constantly improving, because more and more manufacturers went into the business of making tissues, and each manufacturers strove to make his product better than his competitors'. Today, instead of costing 65 cents, a box of 200 facial tissues costs around one-third of that price, and they are both softer and stronger.

　　本段以1924年面巾纸上市后由于人们对它的喜爱所出现的市场大量需求现象为初始原因，该原因导致的结果是制造商的批量生产，批量生产又导致生产成本的下降，经过一系列的因果连锁反应，最后的结果是面巾纸既便宜质量又好。

　　As the price of everything from toothpaste to tuition increases, workers demand higher wages to keep up with rising costs. This can produce further increases in prices or a decreased demand for manufactured goods, or both. Since production tries to keep pace with demand, a decreased demand is followed by decreased production. This, in turn, can lead to layoffs and unemployment, which further decrease the demand for goods.

　　在本段，需求、物价、生产互为因果，形成连锁反应。

　　以上两段均属于表示因果链的类型，即一种原因产生某种结果，而这种结果又是另一结果的原因，如此发展下去形成连锁反应。文中恰当使用连词、代词作为转换词，把因变成果，果变成因，形成因果关系的互相转化。

　　因果段落常用于议论文中。"因"是指证明论点的理由；"果"是指要证明的论点。但是，写好一篇议论文，通常要用不同的方法论证，仅用一种方法写成的文章是很少见的。优秀的文章或段落需要不同方法的互相结合，互相补充。本文通过以上三种因果展开法的模拟来指导读者，再加上平时的刻苦练习，日积月累，相信你的写作水平会大大提高。

　　Exercise:

　　Develop a paragraph based on the topic sentence given below by cause-effect.

　　Television is having vast effects on other sources of entertainment.

　　A possible version:

　　Television is having vast effects on other sources of entertainment. It has caused a serious decline in the cinema, and many cinemas have had to be closed down. Indeed, many other sources of entertainment outside the home have been affected by television; for why go out, many people feel, when you can be entertained at your own fireside. Sometimes the very football match or horse race which you might otherwise have gone out to watch is brought into your own living-room by television.

　　(文/武英杰；英语通大学英语六级考试版 03～04学年第4期； 版权归英语辅导报社所有，独家网络合作伙伴新浪教育，未经许可，不得以任何形式进行转载。)