Ⅰ.段落的构成
段落既是全文的组成部分，又自成一体，有相对独立的主题思想。为了阐明主题思想，段落往往用一个句子概括主题，并置于段首，这就是主题句。段落中的其他句子都围绕主题句展开，对其进行叙述、说明或论证，这些就是发展句。在段落结尾处，常需要对段落的主题作进一步说明、强调或总结的句子，这就是结论句。主题句是整个段落的核心，支撑句是整个段落的主体。段落的基本结构是“主题句+发展句+结论句”。段落写作首先是主题句、发展句和结论句的写作，这是英语段落写作中的最基本要素。下面我们分别介绍如何写主题句、发展句和结论句。
1.主题句
主题句（Topic Sentence）是表达段落主题的句子。它用以概括段落大意，要求全段其他文字都围绕它展开。如：
My mother has passed along to me certain rules for getting along with others. Don't argue with parents； they will think you don't love them. Don't argue with children ； they will think themselves victimized. Don't argue with spouses； they will think you are a tiresome mate. Don't argue with strangers； they will think you are not friendly. My mother's rules， in fact， can be summed up in two words : Don't argue.
主题句中提出的“certain rules”指的是什么？展开句中通过四个“Don't argue...”逐一加以交代。从结构来看，这是一个比较典型的段落，它包括了主题句、推展句和结论句（即本段中的末句）。一个段落之内的句子都是围绕主题句的中心思想所展开的，并非杂乱无章地堆砌在一起。这些句子一定要与该段所表达的要点密切相关，并且按照一定的逻辑关系排列。句子之间可以使用恰当的关联词语衔接起来，以保持段落的完整性。主题句是表达段落主题的句子。它用以概括段落大意，要求全段其他文字都围绕它展开。一个好的主题句就是一个好段落的开始。要写好主题句需要做到三点：一是主题句放在合适的位置；二是主题句的关键词明确；三是主题句语言简洁明了。
主题句通常放在段落的开端，其特点是开门见山地摆出问题，然后加以详细说明。其作用是使文章的结构更清晰，更具说服力，便于读者迅速地把握主题和想象全段的内容。主题句可以放在段中起到承上启下的作用，或放在段尾起概括全段的作用。但初学者比较难于掌握，因而在考试中，应尽量采用将主题句放在段落开头的写作手法。如：
Our life today depends very much on energy. In towns and in villages， on farms and in factories， machines have made life easier than it used to be. The machines use energy， and energy is needed for heating， lighting， communications， carrying goods—everything. Factories and industrial plants use a great deal of energy to make the things that we use and buy and sell.
这段文字所讲的主要是能源问题。第一句就概括性地提出“我们目前的生活很大程度上依赖于能源”。而随后出现的三句都是具体事例，对第一句进行说明和论述。我们可以断定第一句为该段的主题句。再如：
No one canavoid being influenced by advertisements. Much as we may pride ourselves on our good taste， we are no longer free to choose the things wewant， for advertising exerts a subtle influence on us. In their efforts to persuade us to buy this or that product， advertisers have made a close study of human nature and have classified all our little weakness.
以上这段由三句话组成。第一句是主题句，直截了当指出无人不受广告影响这个主题，接着两个推展句对其进行补充和支持，指出我们已无法自由选择所需的商品，理由是广告商已极细研究了我们的心理，并完全掌握了我们的弱点。句子衔接自然，步步紧扣主题。
段落的主题句对主题的限定主要是通过句中的关键词来表现的，关键词要尽量写得具体些。对“具体”的要求包括两个方面：一是要具体到能控制和限制段落的发展；二是要具体到能说明段落发展的方法。准确地把握关键词是清楚地表达段落主题、写好段落主题句的重要前提之一。在上面的两例中，主题句的关键词分别为：depends very much on energy； no one can avoid being influenced.我们再看下列主题句：
（1） He can fixa bicycle himself.
斜体部分应为该主题句中的关键词，但它只是限制了段落发展的部分内容，并没有告诉读者该用哪种方法展开，是用因果关系法还是用分类法？因此，这个主题句的关键词就不能够给我们指出段落发展的方向，因此，我们有必要进行一些修改，请看：
（1） He can fix a bicycle himself in several simple steps.
（2） There are several reasons why he can fix a bicycle himself.
这样，这个主题句的关键词才能发挥他的限定和导向作用，从第一个句子我们可以得知，这段文字主要围绕修自行车的步骤展开，而第二个句子给我们的信息则是该段落围绕他自己修自行车的原因展开。再如：
（2） She tries to improve her looks.
斜体部分应为该主题句中的关键词，而至于她试着改变她面容的理由是什么？或者她采取什么方法来改善呢？我们则无法从关键词中清楚得知。因此，我们同样可进行如下修改：
（1） She tries many ways to improve her looks.
（2） There are some reasons why she tries to improve her looks。
通过修改，该主题句的关键词就有了它应有的作用，第一种改法限制了该段的内容，即要围绕她为了改善容貌所采取的方法展开，而第二种改法则给了该段另外一种导向，即要围绕她为何努力改善容貌的原因展开。
主题句由两部分组成，即主题（Topic）和中心思想（Controlling Idea）。中心思想的作用是导向（Control）和制约（Limit）。我们前面谈到的关键词就反映了中心思想。所谓导向就是规定段落的发展脉络，所谓制约就是限制主题的覆盖范围，两者不可分割。没有导向，内容就会离题或偏题；没有制约，内容就可能超出一个段落所能容纳的范围。
对于初学写作的人来说，“导向”的重要性容易理解，但如果由他们自己来构思一个主题句，就可能忽视“制约”这一面。如：
There are two ways in which one can own a book. The first is the property right you establish by paying for it， just as you have made it a part of yourself and the bestway to make yourself a part of it is by writing in it.
本段的主题句如果没有in which引出的定语从句，那么two ways不仅不能起制约作用，而且也不能起导向作用，句子本身读起来也就使人觉得欠缺点什么。再如：
Exercise is beneficial to your heart. A 22-year studywas conducted by doctors in California. They found that people who work at physical jobs experience fewer heart attacks than other people. These active peoplework all the time at moderate speeds ；their daily routine gives them an adequate amount of exercise and helps them stay in shape.
本段的主题句“Exercise is beneficial”，这是毫无疑义的。但主题句中如不加上“to your heart”来加以制约，那就流于空泛。因此，紧紧把握主题句中中心思想的导向和制约作用，是写作成功关键之一。
2.发展句
英语段落的推展句包括主要推展句和次要推展句，主要推展句（Major Supporting Statement）的主要特点是：围绕段落主题句展开的每一个推展句本身都不要求作进一步的说明或证明，句与句之间的关系是相互独立又是互相连接的。如：
（主题句）There are several factors affecting climate. （推展句1）One factor is the amount of sunlight received.（推展句2）Altitude， or the height above sea level ， also determines climate.（推展句3） The oceans have an effect on the climate of adjacent land.（推展句4） In addition， climate is influenced by the general circulation of the atmosphere.
主题句指出影响气候的几个因素。然后用四个扩展句说明四种因素。第一种是太阳光的接收量，第二种是海拔高度，第三种和第四种分别是海洋和大气环流因素。
次要推展句（Minor Supporting Statement）是指对主要推展句作进一步的事实分析和举例说明。它从属于某一个或某几个推展句。如：
（主题句）I don't teach because teaching is easy for me. （主要推展句1） Teaching is the most difficult of the various ways I have attempted to earn my living: mechanic， carpenter， writer. （主要推展句2） For me， teaching is a red-eye，sweaty-palm， sinking-stomach profession.（次要推展句1） Red-eye ， because I never feel ready to teach no matter how late I stay up preparing.（次要推展句2） Sweatypalm， because I'm always nervous before I enter the classroom， sure that Iwill be found out for the fool that I am.（次要推展句3）Sinking-stomach， because I leave the classroom an hour later convinced that I was even more boring than usual.
从属于主要推展句2的三个次要推展句起着解释说明的作用，分别解释red-eye， sweaty-palm， sinking-stomach的含义，这就更加形象生动地证明了“teaching is not easy”这个主题。
主要推展句与次要推展句的关系（relation）基本可以遵循“三部分”（three-part）规则，即：第一部分，每个主要推展句都应该是对主题句中表示主要思想的关键词的直接、明确的说明。第二部分，每个次要推展句都应该说明它的主要推展句。第三部分，含有讨论说明或分析的问题通常既要有主要推展素材，又要有次要推展素材。
段落主题句给出段落的主题思想，发展句则用来发展、证明或支持这一主题思想。发展句必须切题、明确、层次分明，如：
（1） Women are generally believed to be less intelligent than men. （2） For thousands of years they have been thought to be inferior to men. （3） Those who believe in this idea argue that few women have made remarkable achievements in the history. （4）Even now， there are still far fewerwomen professors， women scientists and women doctors. （5） All these factors show that women can't compete with men.
上面一段共有五个句子，其中句（1）是该段的主题句，句（2）、（3）、（4）为发展句，它们从各自不同的角度对段落主题句的主题思想进行说明。
发展句是对主题句进一步的引申与发展，然而引申与发展的方法是多种多样的，下面我们讲一种最为实用的方法，即设问→解答法（Why→Because），按照这种方法就是要在句子展开之前先加以设问，也就是提出一个问题，然后再针对这一问题进行解答，如：
主题句：To most visitors， New York is both a fascinating and a frightening city.
设 问：Why do we say New York is both a fascinating and a frightening city？
解 答：Because: It is a city of great wealth and of great poverty. There are many rich people， but there are many poor people too. There are many luxury apartment buildings and there are slum tenements.
Because: There is a great deal of beauty and a great deal of ugliness. The parks and the shops are beautiful， but the dirty streets and subways are ugly.
Because: Most things are expensive， but some things are free.The cost of entertainment is generally high， but there are usually many free lectures， concerts， and art exhibits.
Because: There are people who work all day and people who work all night.
上述设问→解答法为我们提供一种考虑问题的方法，我们把上面的思考的结果加以整理，就得到了下面一个段落：
To most visitors， New York is both a fascinating and a frightening city. It is a city of great wealth and of great poverty. There are many rich people， but there are many poor people too. There are many luxury apartment buildings and there are slum tenements. There is a great deal of beauty and a great deal of ugliness. The parks and the shops are beautiful， but the dirty streets and subways are ugly. There is a great deal of beauty and a great deal of ugliness. The parks and the shops are beautiful， but the dirty streets and subways are ugly. There are people who work all day and people who work all night.
3.结论句
结论句位于全段的末尾，是对全段的内容进行总结、归纳或提出结论性观点的句子。结论句不仅仅是重复主题句提出的段落主题，更为重要的是，它可以进一步强调段落的中心思想，以引起读者的重视和注意。在撰写结论句时我们应该注意，结论句的结构形式没有必要与主题句保持一致，但结论句所表达的内容必须要和主题句的内容保持一致，不能相互矛盾。如：
The students in the class come from many different parts of theworld.（主题句）Some are from European countries such as France， Spain and Italy. Others are from Middle Eastern countries like Saudi Arabia and Israel. Still other students were born in Asian countries including Japan and Korea. The largest number of students are from Latin American countries like Mexico，Venezuela， and Peru.（支撑句）The class is an interesting mixture of people from many different countries.（结论句）
这段的主题句是：The students in the class come from many different parts of the world.结论句是：The class is an interesting mixture of people from many different countries.主题句和结论句在关键措辞和表达方式上进行了转换，但表达的实质意思是一样的。
在写结论句时，首先要把握主题句的关键词。例如，在这段中，中心思想是the students come from different parts of the world，关键词是students， different parts， world。其次要总结细节，回答主题句中隐含的问题。在有些段落中，主题句隐含某些问题，隐含的问题通过支撑句论述或说明，结论句就是总结细节，回答隐含问题。最后要用与主题句不同的措辞表达同一中心思想。
在上一段落中，主题句的关键词是students， different parts和world；而在结论句中，关键词是people， mixture， different countries，将students用people替代，different parts of the world用different countries替代，但表达的中心思想一致。再如：
My hometown has changed greatly. When I last visited here，about half the houses had been torn down to make way for a highway. The remaining buildings were plastered with billboards and surrounded by traffic signs and litter. Now it has become dirty， noisy and full of cars.
本段的主题句是My hometown has changed greatly.主题句关键词是“changed”，主题句隐含的问题是How has the hometown changed？本段的细节是a highway built—noisy and full of cars； full of billboards， traffic signs and litter—dirty；结论句则是Now it has become dirty， noisy and full of cars.结论句的关键词是dirty， noisy， full of cars，结论句总结了细节，并回答了主题句中隐含的问题。
当然，并非每个段落都需要结论句，对于一些描述性段落也可以不使用结论句。例如，在下面这一段中，由于该段的内容具有很强的描述性，作者就没有使用结论句。
In fact， there are lots of better things to do in our leisure time. Going to concerts or theater is a pleasant experience.Visiting parks or art exhibition brings us great joy. And there is more entertainment in interesting books or pleasant music than in everyday TV programs.
下面我们再通过三个段落从整体上说明段落的构成：
例1. Wherever one lives， in the city or the country， there are some good reasons for owing a car. （主题句）First， cars provide the most convenient form of transportation. （发展句）Second， a car is a comfortable way to travel ， especially in winter time. （发展句）Finally， a driver is usually safe in his carwhen he is out at night. （发展句）Therefore， many people favour owing a car.（结论句）
例2. Computer is a wonder of this era.（主题句）Because of it， our work and life have changed dramatically.（发展句）At the moment it plays an extremely important role in our life. （发展句）Computers are able to do a great variety of jobs. （发展句）They are widely used in offices， laboratories， banks， airports，etc. （发展句）Businessmen use them to make more money ；policemen use them to find criminals； scientists use them to make new discoveries. （发展句）Many modern families are equipped with it. （发展句）It has become so important in our life that we can't imagine what life would be like without it. （结论句）
例3. In the future， the computer will be more powerful. （主题句）Students may receive their education through it. （发展句）There will be more intelligent robots to relieve us from arduous work and even to look after children or nurse the sick. （发展句）In a word， we can expect to see the development of the computer for more purposes in the future. （结论句）