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Paragraphs are essential building blocks of writing.Most simply a paragraph is a group of related sentences that present and develop one main idea.There is no ideal length that can apply to all paragraphs since length depends largely on the content.However，as a general guide，it is helpful to the reader to keep most of your paragraphs to between three and six or seven sentences.Occasionally paragraphs can be shorter where a point needs to be made briefly or with special emphasis or longer where more detailed elaboration of a point is needed.

Most paragraphs can be classified into four types，depending on the writer’ s main purpose.For example:

Whatever the purpose may be，an effective paragraph follows the structure and characteristics introduced in this chapter.

The Structure of a Paragraph

In most cases，a well written paragraph has three parts，a topic sentence，supporting sentences，and a concluding sentence.A good paragraph will contain a main idea that is often expressed in one key sentence，sometimes called a topic sentence，which usually appears at the beginning or end of the paragraph (Narrative paragraphs and descriptive paragraphs often have no topic sentences.).This main idea will be supported by other ideas，which will include examples，clarifying details，reasons，personal references，and so on.These supporting sentences should flow logically and easily from one to the other，being linked by some of the means described in Chapter 3.You should avoid writing in too many short paragraphs.Paragraphs should also be logically linked together and follow on from each other.In some paragraphs，especially long ones，a concluding，or clincher sentence restates the main idea or summarizes the information given.A concluding sentence may also emphasize an important point or suggest a course of action.These three parts are illustrated in Example 1 in the below chart.

Characteristics of an Effective Paragraph

An effective paragraph is well structured，displaying at least two characteristics:unity and coherence.

A paragraph in which all of the sentences are directly related to the main idea has unity.Any sentence that is not related to the main idea as it is expressed in the topic sentence should be omitted.The best way to achieve a unified paragraph is to check each sentence against the topic sentence，both as you write and as you evaluate what you have written.

As you read the following Example 2，you will find out that the sentence that destroys the paragraph’s unity begins with “It doesn’t mean...” .This sentence has nothing to do with the main idea“demand for perfection meant long and hard work” ，as stated in the topic sentence.Therefore，it should be removed.

2.Beethoven's demand for perfection meant long and hard work.Unlike Mozart，he couldn't dash off three great symphonies in six weeks.It doesn't mean he was not as talented as Mozart.Sometimes he worked years on a single symphony，writing other works at the same time.He carried music sketchbooks everywhere，jotting down new ideas，revising and refining old ones.These early notes often seem crude and uninspired when compared with their final versions，which were hammered out through great labor.

A paragraph in which the ideas are easy to follow has coherence.In a coherent paragraph， information is presented in an orderly way， and the relationship between the ideas is clear.Three types of logical order may be used to help the reader easily follow the ideas from one sentence to the next:chronological order，spatial order and order of importance.

It is natural to arrange the events in a story or incident in chronological order.Such an order is also used to explain a process， with the steps in the process arranged in the order in which they must be carried out，as shown in Example 3.

3.Cooking up a spicy Italian sauce for spaghetti is not difficult.The first step is to brown four strips of bacon in a large frying pan.When the bacon begins to turn brown，add one pound of ground beef and salt and pepper to taste.Stir the meat to brown it on all sides.As soon as the hamburger loses its bright red color，add one chopped onion and one chopped green pepper.After the meat is thoroughly browned，pour off the grease and add three cans of tomato paste and three cans of tomato sauce.Finally，allow the sauce to simmer for at least an hour before serving.

If your purpose is to describe，you may want to use spatial order to show where objects are in relation to one another.The order you choose depends partly on what you are describing and partly on the impression you want to create.You have to avoid “transitions for transitions”sake，as exemplified in 4a and 4b.

4a.ARTIFICIAL:We enjoyed our visit to Dr.Chilton’ s house.The house was perched high up on a hill.First，we walked up the long driveway.Then we approached the huge bronze door.A butler was standing there.Then he ushered us and the other guests into the house.The first thing we passed was the oak-paneled library.Next we went by the formal dining room.Finally we arrived at the ballroom where the reception was being held.There were three sparkling chandeliers.More than a hundred people were enjoying champagne.

4b.MORE NATURAL:We enjoyed our visit to Dr.Chilton’ s house，perched high up on a hill.Walking up the long driveway，we approached the huge bronze door.A butler was standing in the open doorway，ushering guests into the house.Going in，we passed the oak-paneled library and formal dining room before we arrived at the ballroom，where the reception was being held.Under three sparkling chandeliers， more than a hundred people were enjoying champagne，and good conversation.

In paragraphs that give information or persuade，details are often arranged according to the order of importance.An expository paragraph may begin with the least important or striking details and build up to the most important ones.A persuasive paragraph may save the most convincing reason until last.

In addition to the three types of logical order，coherence can be achieved by using direct references as they link sentences by referring the reader to a noun or an idea mentioned earlier.For example，you may use a word or phrase that means the same thing as a word or phrase in a preceding sentence，as in Example 5; you may also repeat a key word from a preceding sentence，as in Example 6.

5.The runaway engine sped down the inclined track.On and on the mighty monster raced as we watched in horror，overcome by the unharnessed power of the giant machine.

6.We do not choose to be born.We do not choose our parents.We do not choose our historical epoch，or the country of our birth，or the immediate circumstances of our upbringing.We do not，most of us，choose to die; nor do we choose the time or conditions of our death.But within all this realm of choicelessness，we do choose how we shall live，courageously or in cowardice，honorably or dishonorably，with purpose or in drift.

Coherence in a paragraph may also be achieved by using transitional expressions， as done in Examples 3 and 4a (the italicized words).Such expressions must be chosen carefully，for each one indicates a particular kind of relationship.Transitional expressions are not required in every sentence.A paragraph in which all the sentences are linked by means of such expressions sounds artificial，as shown in 4a.Direct references are needed more frequently and should be used whenever possible.

Development of a Paragraph

You have known how a paragraph is structured and what characteristics an effective paragraph must have.Now you will learn how the stages of the writing process introduced in Chapter 1 apply to the paragraph form.

Before you write，you will first choose and limit a subject.Usually the broader，or more general，a subject is，the more space is required to cover it adequately.A general subject must be limited to a topic that can be covered clearly and precisely in the space available in a paragraph.One way to limit a general subject is to divide it into its smaller，more specific parts.

7a.TOO BROAD:Solar energy in the People’ s Republic of China

7b.LIMITED:The solar water heater installed at our dorm

Then you have to determine your purpose for writing:to explain or inform，to persuade，to narrate，or to describe.Your purpose for writing affects both your manner of expression and the details you include in your paragraph.Next，consider how your audience will affect your writing.Bear in mind that your audience affects your writing in the topic you choose，the details you include， and the language you use (see Chapter 2 for more suggestions).

With a limited subject，a clear purpose and audience in your mind，develop for your paragraph a working plan，which consists of a topic sentence and a list of supporting details arranged in logical order.

When writing a topic sentence，pay attention to the following points.

A Topic Sentence Should Be Neither Too Broad No r too Limited

It serves as an umbrella that must“cover”all of the other sentences in the paragraph.A topic sentence is too broad if it states an idea that cannot be fully developed in one paragraph.It is too limited if it states a fact that needs no further development or if it covers only some of the information in the other sentences.Wording your topic sentences clearly and directly helps you focus your main idea.It tells the reader precisely what the paragraph is about.Compare the following topic sentences.

8a.TOO BROAD:Water is an important natural resource.

8b.TOO LIMITED:Water is made up of two atoms of hydrogen and one atom of oxygen.

8c.EFFECTIVE:Water is a chemical compound that can occur in three different states:liquid，gas and solid.

9a.WEAK:Bicycling can lead to problems.

9b.WEAK:Some people wish they’ d never seen a bicycle.

9c.IMPROVED:Whenever you get on your bicycle， keep these three basic rules in mind if you want to reach your destination safely.

A Topic Sentence Should Suggest the Writer’ s Purpose

You should not give direct explanations of purpose，see Example 10.If your purpose is to inform，you can begin your paragraph with a question and then provide specific information that answers the question，as shown in Example 11.Note that a good topic sentence usually does not begin with an interrogative word.If your purpose is to persuade，the topic sentence must clearly state your opinion by containing a word (or words)which makes a comment on the subject and shows your attitude towards the subject.

10a.WEAK:I am going to tell you about people from my country.

10b.IMPROVED:Most people from my country share two characteristics:friendly personalities and fierce national pride.

11a.WEAK:Should college students be required to take four years of English?

11b.IMPROVED:All college students should be required to take four years of English for three important reasons.

Whenever possible，you should introduce the topic in a forceful and lively way.A topic sentence can be made more interesting by using unusual comparison，unexpected statement，or by using strong verbs and vivid modifiers，for example:

12a.WEAK:Costumes are important in planning a play.

12b.IMPROVED :“Clothes make the man”and nowhere more than on stage in a new play.

When you have worked out an effective topic sentence，you must decide which details support your main idea.To make the decision，you examine each detail to see how it relates to the main idea in your topic sentence and to the other details in the paragraph.Your goal is to produce a unified，coherent paragraph，one in which all of the sentences are directly related to the main idea and to each other.Read the following example:

13.Different people spend their weekends in different ways.Some enjoy playing ball games，such as basketball，soccer，tennis，and so on.However，playing soccer sometimes can be very tiring.Some people prefer to go to the countryside to spend a quiet weekend.They can no longer endure the noise in the city.There are still others who like to stay at home to watch TV or read an interesting book.

这段话的主题是“Different people spend their weekends in different ways.” ，接下来列举了三种度周末的方式:做球类运动，去宁静的乡村，呆在家里看电视或看书。这三句话都紧紧地围绕主题句，为中心思想服务。可其中两句话“However，playing soccer sometimes can be very tiring.”和“They can no longer endure the noise in the city.”和主题句无关，属于跑题，应将其删掉。

Reinforcement　知识复习

1.The following paragraph lacks coherence.Change the order of sentences to make it coherent.

Why not start now? Use it correctly in conversation three times before tomorrow’ s class.A good vocabulary，then can give you a real sense of power and a feeling of pleasure.The word will then be yours to keep.You’ ll be on your way toward making yourself a master of words.If you learn a new word every day，in a year’ s time you will have 365 new sources of power and pleasure.Look up the word Genial in a dictionary before you leave school this afternoon.

2.Which one does not develop the controlling idea in the topic sentence?

(1)Topic sentence:I enjoy weekends.

A.I can sleep late on Saturday morning.

B.My friends and I can visit and run around.

C.I can do all kinds of shopping.

D.School assignments are due on Monday.

E.We usually go for a ride on Sunday afternoons.

(2)Topic sentence:The weather has been changeable.

A.On Sunday we had a high wind that blew down some trees.

B.Monday was so cold that we had to turn on the heat and wear our winter coats.

C.On Tuesday we formed a group to go roller skating.

D.By Wednesday the weather cleared and the sun came out.

E.Thursday was as hot and humid as an August day.

F.Friday morning it began to rain，and it looked as if we’ d have a cold，steady wind for a few days.

(3)Topic sentence:I easily give up doing my homework.

A.I always start to feel hungry and go into the kitchen for a snack.

B.I’ ll leave my studying to investigate any noise I hear.

C.While I study，I try to listen to the radio with one ear.

D.For me，physics is the hardest subject.

E.I often leave my desk to go to the mirror to comb my hair.

F.Often，in the middle of an assignment，I decide that my shoes need polishing and do that instead of the assignment in front of me.

(4)Topic sentence:Carlos is very interested in cars.

A.He knows all the details about all the manufacturer’ s models.

B.His parents allow him $ 5. 50 a week for gas.

C.He spends a lot of time each week making improvements on his old Ford.

D.If there is a new-car exhibit in town，you will find him there.

(5)Topic sentence:All the people on our block give us trouble.

A.Mrs.Brown calls the police whenever we want to play ball on the street.

B.Mrs.Gonxales invites us in for lemonade every day.

C.If we happen to stray into Mr.Hardy’ s yard，he yells at us.

D.Mrs.Johnson complains that skateboarding makes too much noise.

E.Yesterday Mr.Chan kept the Frisbee when it landed on his front porch.

3.Identify the topic sentence for each of the following paragraphs.

(1)①A woman with a master’ s degree in English finds a job as a salesclerk in a large department store after a six-month search in trying to find position in her field.②She earns $ 500 a month.③A man with a double B.A.in philosophy and history accepts a $ 600-a-month position as a beginning file clerk for an insurance company.④Thousands of others，college graduates，register for unemployment; in their desperate quest for work，they are repeatedly turned away because their education is counted as a strike against them.⑤College no longer brings the rewards，financial or professional，which it once promised.⑥“Overqualified and underpaid”describes the average college graduate in the United States.

The topic sentence is______.

(2)①Diamonds have lured many people into trouble.②The famous Nikolas Verden stole the Khybar stone from a shop in Amsterdam，Holland，fled to Naples，and died trying to escape from the police.③Thomas Bright，a jewelry salesman，swallowed the Van Noos diamond in order to smuggle it out of South Africa and was arrested after it was found during an operation for appendicitis.④Five members of the Burton family died trying to hide the Courtney stone from the authorities.

The topic sentence is______.

(3)①Harry Swickert turned the Schuyler Shoe Company，a dying business，into a profitable company.②First he moved from his outmoded factory in Philadelphia to a modern facility in Stroudsburg.At Philadelphia，expenses were high; work space was cramped; the workers were unreliable.③He also changed the company’ s product line.④In addition to work boots，the company manufactured a new product called the wildness boot.⑤In order to advertise the new boot，he then hired Prescott，who successfully created several eye-catching ads.⑥And these ads，which appeared in quality magazines，helped to increase sales by 50 percent in the last five years.⑦With a new factory，a new product line，and a good advertising campaign，Swickert has saved the company from bankruptcy and has turned it into a solid money maker.

The topic sentence is______.

(4)①American might be embarrassed because their Japanese friends are so formal with them.②Japanese might feel insulted because American acquaintances greet them casually.③Still，the forms of greeting in both countries only show respect for others.④It just happens that Americans and Japanese have a different way of looking at human relationships and thus have a different way of showing respect.

The topic sentence is______.

(5)①Every educated person has at least 2 ways of speaking his mother tongue.②The first is that which he employs in his family，among his familiar friends，and on ordinary occasions.③The second is that which he uses in discoursing on more complicated subjects，and in addressing persons with whom he is less intimately acquainted.④It is，in short，the language which he employs when he is on his dignity，as he puts on evening dress when he is going to dine.

The topic sentence is______.

4.Use one of the following sentences as a beginning topic sentence to write a 100-word coherent paragraph.

(1)Students have different ways of providing themselves with transportation.

(2)It is not a good idea to go to bed after 12.

(3)I considered several factors before I decidedto major in______.

(4)A school library plays an important role in students’life.

Extension　知识拓展

A generalization is a general conclusion about a group of people，events，objects，places，or ideas.To be valid，or well-grounded on evidence，a generalization must be based on a fairly large number of facts or unbiased observations.A valid generalization suggests that additional facts or observations about the group will also probably support the conclusion.For example:

More traffic accidents are caused by men between the ages of 18 and 25 than caused by women of the same age.

Often，the topic sentence of a paragraph states a generalization.The other sentences provide evidence—facts，examples，or reasons—to support the generalization.