英语主题句面面观

英语主题句面面观

一、主题句的定义及重要性

主题句(topic sentence)是对一个自然段中心思想或主要内容的高度概括，它阐述了作者的观点、看法或态度，并为该自然段的发展提供了依据。主题句写得贴切与否，会直接影响到作者是否能围绕着主题展开进一步的论证、解释、说明等，同时也是段落内容能否切题和有无连贯性的基本保证。

二、主题句的位置

在大多数情况下，主题句都位于段落之首，但有时也会出现在段落的其它位置，有些段落甚至没有主题句。作者往往根据文章结构的需要，突出重点或表达语气的不同，而采取不同的方式安排主题句，或根本不安排主题句。请看例文:

1.主题句位于段首

Eating in the Student Center Cafeteria is a quite pleasant experience. First，the food is excellent. The food served there is well-prepared and tastes delicious. The students also have a variety of food to choose from. Moreover，each person has quick access to the food he wants. Second，the environment in the Student Center Cafeteria is nice. Many happy young people are talking and laughing，yet the atmosphere is still calm. So it is possible for the students to study and do homework there. Finally，there are many friendly people at the Cafeteria. Even the strangers say“Hi!”and offer to share their tables. When that happens，practice in speaking English and friendship often follow. For these reasons，it is nice for the students to go to the Student Center Cafeteria once in a while to enjoy eating，studying，and talking with new people.

2.主题句靠近段首

Throughout history people have joked about the turtle because of its shell，its walk，and its stupidity. In fact a turtle's shell is a great work of engineering and design. The two parts of the shell are jointed at the sides to provide the animal with armor. This armor protects the turtle from enemies. While a turtle may not walk fast on land，it can move with amazing speed in the water. Its shape and slow walk make us think that the turtle is stupid，but that is not the case. A box turtle taken far from its home can find it sway back. It seems to follow the sun or stars.

3.主题句位于段中

For many years about 50，000 people have been killed annually in automobile accidents on the nation's roads. Seat-belt laws，reduced speed limits，and increased police patrols have had almost no effect on changing the number of fatalities. The most promising way to bring the figure down，however，is to make cars safer. New cars have airbags on both the passenger and the driver's side. They also come equipped with antilock brakes. The steel frames of many automobiles have also been strengthened by 50 percent，enabling people to survive crashes that would certainly have killed them before.

4.主题句位于段尾

One of Benjamin Franklin's rules was“Never ask another to do what you can do for yourself.”It is a good rule. Students who depend on others to do their math problems or French translations not only run the risk of getting the wrong answers but also are not acquiring self-reliance. There is no substitute for self-reliance. We cannot expect to go through life depending on others to do our thinking or to solve our personal problems.

5.主题句隐含在段落里面

Television is an invention that has greatly changed our lives. The automobile and the airplane altered the way we travel and made the world a“smaller”place. Rockets and satellites have made it possible to explore outer space. The computer has helped gather and store millions of bits of information. The telephone is a quick and easy way for us to communicate. Even our eating habits have been changed by refrigerators and microwave ovens.

虽然本自然段没有一个明确的主题句，可是读者并不难找出其隐含的主题句是:“Inventions have changed our lives.”

尽管主题句在一个自然段中的位置比较灵活，甚至含而不露，但对初学者或尚未充分掌握自然段写作规律及技巧者而言，最好还是要有一个明确的主题句，并将其置于段落之首，目的在于:(1)主题句既为该段落确定了主题，又限定了该主题在本段落详细论述的范围，作者在限定范围内铺陈展开下文，不易跑题;(2)主题句如同路标，有助于读者预先对该段落的主要内容有一个大致了解。

三、主题句的写作规则

写好主题句是写好一个自然段的先决条件。一个好的主题句通常具备以下四个特点:

1.主题句必须是一个完整的句子，要有主语和动词。请看例句:

(1) Good study habits are useful to a college student in three ways.(句中: study habits是主语，are是动词。)

(2) Important research has shown some of the reasons for shyness.(句中: research是主语，has是动词)

(3) Giving a good first impression depends on many things.(句中: giving a good first impression是主语，depends on是动词。)

(4) There are three characteristics of a good paragraph.(句中: three characteristics是主语，are是动词。)

(5) Deliver your messages clearly and directly.(句中:因是祈使句，所以主语是隐含的you，deliver是动词。)

(6) It's important to become independent at a young age.(句中: to become independent为真正的主语，is为动词。)

我国学生有时会写出缺主语、少动词的所谓“主题句”。请看一个反面例子:

how to achieve my dream?

这是一个典型的非完整句(sentence fragment)。如果说achieve是动词的话，那么how to显然不是主语;如果说how to achieve my dream可当主语，那么动词在哪里呢?经修改，下面的句子都是合格的主题句了:

(1) how can I achieve my dream?(句中: I是主语，can achieve是动词。)

(2) It's not easy to achieve my dream.(句中: to achieve my dream是真正的主语，is是动词。)

(3) There are a variety of methods to achieve my dream.(句中: a variety of methods是主语，are是动词。)

(4) To achieve my dream，I need to make the following preparations.(句中: I是主语，need是动词。)

(5) I can't achieve my dream without others' help.(句中: I是主语，can't achieve是动词。)

2.主题句通常是陈述句，而不是问句。请看例句:

(1) Why are sports and games very useful for character training?

(2) Sports and games are very useful for character training.

虽然以上两个句子都可以用做主题句，但主题句更多是以陈述句，即以第(2)句的形式出现。

3.主题句所限定的范围要宽窄适中。请看例句:

(1) There are many good teachers in China.

(2) A good teacher should have a sense of humor.

(3) Good teachers usually have the following characteristics.

在以上三个例句中，例(1)所包含的内容过于宽泛，无从下笔;例(2)所要讨论的内容又过于具体，不易写够字数;而例(3)所包含的内容则宽窄适中，习作者可从多方面讨论一个称职的教师所具备的特点，因此更适合做主题句。

4.主题句由主题(topic)和中心思想(the controlling idea)两部分组成。“主题”是指这一自然段主要谈及的内容，如:人物、事件、问题等;“中心思想”是指作者对该主题所持有的观点、看法或态度，它的作用是限定自然段中其它的句子，使它们紧紧地围绕这个主题展开。在下列三个主题句中，下划线部分为主题，括号中的部分为中心思想:

(1)Wolves are one of(the most mysterious wild animals) living in North America.

从这一主题句可以看出，该自然段主要谈及的内容与wolves有关，中心思想把扩展句限定在以下范围内:“Why are wolves one of the most mysterious wild animals living in North America?”

(2) It is(difficult) to estimate the number of those who use English as a foreign language.

从这一主题句可以看出，该自然段主要谈及的内容是“to estimate the number of those who use English as a foreign language”，中心思想把扩展句限定在以下范围内:“What are the difficulties?”或“Why is it so difficult to estimate?”

(3)Boys and girls have(different)dreams.

从这一主题句可以看出，该自然段主要谈及的内容是有关“boys and girls have dreams”，中心思想把扩展句限定在以下范围内:“What are boys' dreams and what are girls' dreams?”或“how different are their dreams?”

总之，只有写出规范的主题句，才有可能写出紧扣主题的扩展句(developing sentences)。