就“說明對象”而言，英語說明文可分為對“客觀具體事物”的說明和對“主觀抽象觀念”的說明兩大類，比如：對“LASER(激光)”、“Computer Problem of Year 2000(計算機2000年問題)”等等的說明都是對客觀或者具體事物的說明，而“The Successful Interview(談成功的面試)”、“How to Write Good English Composition(如何才能寫好英語作文)” 等是對主觀抽象觀念的說明。對我們中學(xué)生朋友來說，在漢語說明文的教學(xué)中似乎比較側(cè)重前者，即解釋客觀具體事物的說明文。但在英語說明文中，闡述和說明 “主觀抽象觀念”的說明文占了很大的比重，其中有些類似漢語中的議論文。但是無論是對“客觀具體事物”的說明還是對“主觀抽象觀念”的闡述，英語說明文從結(jié)構(gòu)上看大致可分為三個部分：第一部分一般是文章的第一段，提出文章的主題，也就是說，文章想要闡述、說明的主要內(nèi)容;第二部分是文章的主體，可由若干個段落組成，對文章的主題進行展開說明;第三部分是結(jié)尾段，對文章的主題作歸納總結(jié)。從英語說明文的結(jié)構(gòu)可以看出，要寫好英語說明文的關(guān)鍵在于第二部分如何對文章主題進行展開說明。在英語中，常見的用來展開文章主題的方法有下列幾種：

　　1.羅列法(listing)

　　在文章開始時提出需要說明的東西和觀點，然后常用first，second，…and finally加以羅列說明。羅列法廣泛地使用于各類指導(dǎo)性的說明文之中，下面這篇學(xué)生作文就是用羅列法寫成的：

　　Early Rising

　　Early rising (早起) is helpful in more than one way. First， it helps to keep us fit (健康)。 We all need fresh air. But air is never so fresh as early in the morning. Besides， we can do good to our health from doing morning exercise (做早操)。

　　Secondly， early rising helps us in our studies. We learn more quickly in the morning， and find it easier to remember what we learn in the morning.

　　Thirdly， early rising enables (使能夠) us to plan the work of the day. We cannot work well without a good plan. Just as the plan for the year should be made in the spring， so the plan for the day should be made in the morning.

　　Fourthly， early rising gives us enough time to get ready for our work， such as to wash our faces and hands and eat our breakfast properly.

　　Late risers may find it very difficult to form the habit of early rising. They ought to make special efforts to do so. As the English proverb says，“Early to bed and early to rise， makes a man healthy， wealthy and wise.”

　　羅列法經(jīng)常用下列句式展開段落，我們可以注意模仿學(xué)習(xí)：

　　There are several good reasons why we should learn a foreign language. First of all， …Secondly， …And finally， …

　　We should try our best to plant more trees for several good reasons First of all， …Secondly， …And finally，

　　必須指出的是，有時羅列法并不一定有明確的first， second…等詞，但文章還是以羅列論據(jù)展開的。

　　2.舉例法(examples)

　　舉例法是用具體的例子來說明我們要表達(dá)的意思，常用for example， for instance， still another example is…等詞語引出。下面這篇學(xué)生作文就是用舉例法寫成的：

　　Recreation

　　It is impossible to keep in good health unless we take enough recreation (娛樂)。 The mind， too， needs change to make it fresh and vigorous (有活力的) There is much truth in the old saying， All work and no play makes Jack a dull boy.“

　　There are many games which boys and girls can play after their school work is done， for instance， football， tennis， and kite-flying. Other examples of recreation are boating， fishing， gardening， cycling， walking， chess-playing， and reading. Persons who sit much at their business should take a kind of recreation that will supply their muscles (肌肉) with exercise. Those who spend most of their time in the open air and do manual work (體力活) should adopt (采納) reading or some other quiet form of recreation.

　　Cycling is said to be an important means of recreation， but many persons foolishly tire out themselves by cycling too much. The same may be said in regard to football. Tennis is a pleasant form of recreation. Many persons take great delight in boating. Fishing requires much patience， and there is much danger of taking cold by sitting still on a cold day too long. A good brisk (輕松) walk is one of the finest forms of exercise. For persons engaged in outdoor labor， chess-playing is another excellent form of recreation.

　　可以看出，舉例法和羅列法有時可以結(jié)合使用：即用羅列法來列出例子，用例子充實羅列的說明。

　　3.比較法(comparison and contrast)

　　比較法是對兩個對象進行比較，從而進行說明的寫作手法。比較法又可細(xì)分為比較相同點(comparison)和比較不同點(contrast)兩種方法，比如：

　　From Paragraph to Essay

　　Although they are different in length (長度)， the paragraph and the essay are quite similar in structure (結(jié)構(gòu))。 For example， the paragraph starts with either a topic sentence (主題句) or a topic introducer followed by a topic sentence. In the essay， the first paragraph sets up the topic focus (主題所在) Next， the sentences in the body of a paragraph develop the topic sentence. Similarly， the body of an essay consists of a number of paragraphs that discuss and support the ideas given in the introductory (引導(dǎo)的) paragraph. Finally， a concluding sentence (結(jié)束句) ——whether a restatement， conclusion， or observation——ends the paragraph. The essay， too， has a concluding paragraph which ends the essay logically and satisfactorily. Although there are some exceptions (例外)， most well written expository (說明文的) paragraphs and essays are similar in structure.

　　可以看出，在比較相同點的時候，常用到similarly，also，too，in the same case，in spite of the difference等這樣的詞語。

　　European Football and American Football

　　Although European football is the parent of American football， the two games show several major differences. European football， sometimes called association football or soccer， is played in 80 countries， making it the most widely played sport in the world. American football， on the other hand， is popular only in North America (the United States and Canada)。 Soccer is played by eleven players with a round ball. Football， also played by eleven players in somewhat different positions (位置) on the field， is played with an elongated (拉長的) round ball. Soccer has little body contact (接觸) between players and therefore needs no special protective equipment. Football， in which players make the greatest use of body contact to stop a running ball-carrier and his teammates， needs special protective equipment. In soccer， the ball is advanced toward the goal by kicking it or by butting (頂) it with the head. In American football， on the other hand， the ball is passed from hand to hand or carried in the hands across the opponent's (對手) goal. These are just a few of the features which distinguish (區(qū)別) association and American football.

　　這是一篇用比較不同點的手法寫的說明文。從文章中可以看出：however，on the other hand，in contrast，but，nevertheless等表示轉(zhuǎn)折的詞語常用來引導(dǎo)對不同點的比較。

　　4.定義法(definition)

　　定義法也是英語說明文中常用的寫作手法，特別是在對具體事物概念進行說明時經(jīng)常使用。定義法的基本要素是定義句。英語中常見定義句的模式是：

　　被定義對象is所屬類別+限制性定語

　　可以看出，定義句中限制性定語越詳細(xì)，定義就越精確，比如：

　　A bat is a small mouse-like animal that flies at night and feeds on(以……為食品)fruit and insects but is not a bird.

　　其實，在英—英詞典中，對英語單詞的英文解釋就是定義法的典型例子。比如，看看Longman詞典對student和teacher的定義是很有意思的：A student is a person who is studying at a place of education or training. A teacher is a person who gives knowledge or skill to sb. as a profession (專業(yè))。

　　5.順序法(sequence of time， space and process)

　　順序法是指按時間、空間或過程的順序進行說明的一種寫作手法。比如按照時間順序介紹一個科學(xué)家的生平，用空間順序闡述逐漸開發(fā)西部的重要意義，用過程順序法解釋葡萄酒的生產(chǎn)過程等等。

　　下面這篇學(xué)生作文就是用順序法寫成的：

　　Coal

　　Coal underwent (經(jīng)受) many changes before it became the bright， brittle (脆的)， black substance which we now use. During ancient times (在上古時代)， when the earth enjoyed a very warm and wet climate， the land was covered with large forests and big plants. As time went on， the ground changed and began to sink (下沉) a little. These very large numbers of trees and vegetables received a deposit (沉淀) of sand and clay. This layer of sand and clay pressed upon the layer beneath and prevented it from contact with air. These trees and plants received the pres sure and changed its appearance.

　　Generations after generations (幾世紀(jì)后)， as the ground kept gradually sinking， another layer of sand and clay was again deposited (積聚) above the layers already formed. A great pressure was thus exerted (作用) and the peat (泥煤) was changed into the black and brittle substance which is known as coal.

　　Coal is a kind of mineral which is formed by nature as above stated. It is an important industrial material and is chiefly used as fuel. It is very valuable in the industrial world. The place where coal deposit is called a coal mine (煤礦)。 In China， coal mines are largely found in the north-west part of the country. Shanxi is a famous province for producing coal. It has the most coal of China.

　　6.分類法(classification)

　　分類法是將寫作對象進行分類說明的一種寫作手法。比如：著名的英國哲學(xué)家弗朗西斯·培根(Francis Bacon)在其膾炙人口的《談讀書》(Of Studies)一文中就用到了分類法：

　　Some books are to be tasted， others to be swallowed， and some few to be chewed and digested， that is， some books are to be read only in parts， others to be read， but not curiously， and some few to be read wholly， and with diligence and attention. Some books also may be read by deputy， and extracts made of them by others; but that would be only in the less important arguments， and the meaner sort of books…

　　參考譯文：書有可淺嘗者，有可吞食者，少數(shù)則須咀嚼消化。換言之，有只須讀其部分者，有只須大體涉獵者，少數(shù)則須全讀，讀時須全神貫注，孜孜不倦。書亦可請人代讀，取其所需摘要，但只限題材較次或價值不高者……

　　——轉(zhuǎn)摘自《英漢翻譯教程》(張培基等)

　　可見，如果能夠根據(jù)具體情況，選用合適的寫作手法，就可為文章增添無窮的魅力。

　　除了上述提到的6種展開英語說明文主題的寫作方法之外，還有因果法、歸納法等其他方法。但相比之下，對于中學(xué)生來說，上述6種方法是首先值得掌握的。另外必須指出的是：在一篇文章中往往是以一種寫作手法為主，同時輔以其他寫作手法。有時，甚至?xí)追N寫作手法混用而不分主次。因此，必須根據(jù)具體情況，選用合適的展開主題的寫作手法，才能寫出優(yōu)秀的英語說明文。