说明文是对事情的发生、发展、结果、特征、性质、状态、功能等进行解释、介绍、阐述的一种文体。这类文章的目的和性质是客观地介绍、解释事物，使读者获得知识和信息，并不需要发表主张、做出证明。一般说来，知识简介，商品介绍，旅游指南，科技读物，工作总结，实验报告，教材辅导等均属说明文之列。
写说明文，可以按时间、空间、结构、逻辑顺序来写，也可以采取举例、比较、对比、分类、分析、说明、叙述等方法。
1.比较对照
比较对照有两种，一是逐点比较，二是整块比较，即AB交错或先A后B：
1)逐点比较：多数人认为这种AB交错的方式可以避免行文的单调沉闷，对比的效果更鲜明突出。如：
There are basic differences between large and small enterprises. In a small enterprise, you operated mainly through personal contacts. In a large enterprise, you have established “policies” , “channels” of organization, and fairly strict procedure. In the small enterprise you have immediate effectiveness in a very small area. You can see the effect of your work and of your decisions ground. In the large organization you are normally taught one thing thoroughly. In the small one the danger is of becoming a Jack-of-all-trades-but-master-of-none. In the large it is of becoming the man who knows more and more about less and less.
2) 整块比较
It is easy to be a winner. A winner can show his joy publicly. He can laugh and sing and dance and celebrate his victory. People love to be with winners. Winners are never lonely. Unlike winners, losers are the lonely ones of the world. It is difficult to face defeat with dignity. Losers can not show their disappointment publicly. They can not cry or grieve about their defeat. They may suffer privately, but they must be composed in public. They have nothing to celebrate and no one to share their sadness.
2.分类
分类是人类认识客观世界的.重要手段之一，也是描写事物、解释观点最有效的方式之一。通过将一事物分类，可使复杂事物变得清晰明了，便于作者阐述自己的观点。
分类段落的各类排列要条理，可采用从主要到次要，从次要到主要，从多到少或从少到多等方式排列，亦可平行排列。如：
1) As far as political views are concerned, people fall into three categories. First are the conservative people. Conservatives are opposed to sudden or great changes. Second are the liberal people.These people are in favor of progress and reform. But their opinions often seem to idealistic. The third type is the moderate people. The moderates keep everything within reasonable limits. They are more practical in this hard world. In my opinion, most people seem to belong to this group.
本段采用平行排列的方式，按人的政治观点分为三类：保守、自由和温和。
2) These are several reasons why I decided tom attend Bingston University . First of all, the tuition is reasonable. Secondly, the university has a deferred payment plan, which lessons the load of peasant families like mine. Another reason is that Bingston has the finest teachers in its graduate program. My chief reason, however, is Bingston’s program in agriculture, my chosen field, which is recognized as the leader in this area.
该段采用主次排列的方式，分析了作者决定上Bingston大学的原因。
3) According to Mr. Li, the fifteen students of his class fall into three groups. Seven of them work hard and study well. They always get good marks in examinations and are often praised by the teachers. Li calls them “good students”. The monitor, the secretary of the Youth League, and the captain of the class volleyball team, are quick in finding out what their fellow students are interested in or what they should do as a collective. They always organize proper activities at the proper time. So Li calls them “good organizers”. Four other students are very kind to their classmates, always ready to lend them a helping hand. They help to clean the classroom and the corridor even when they are not on duty. Li says that they are “good comrades”. “What about yourself?” someone asks him. “I’m a group by myself ——a good observer”.
该段不同于以上两段，不是先分类再解释，而是先说明其特点，然后定义分类。虽分类并不科学，却达到了其幽默之目的。
3.特征
例证指具体说明人或事物特点、本质及其规律的方法。所用例子需有代表性、典型性。例证型段落的写作方式多为先提出主题再列举事例。在事例之前一般有For example或For instance。例证后面，根据情况还可以加上结论句。如：
In order to prevent non-smokers from being affected, measures must be taken to reduce the chances of smoking. A lot of work can be done concerning this. For example, in some public places, such as in the theatres and cinemas, smoking should be forbidden. Even on the train or plane people should not be allowed to smoke. Doctors, teachers and government leaders should take the lead not to smoke. Above all, the harmfulness and dangers caused by smoking should be made known to all through newspapers, broadcast, or TV programs. Also the growing of tobacco and the production of cigarettes should not be encouraged. If these measures can be taken, we can effectively reduce the chances of smoking.
4 因果
因果是两个事物之间的关系。一些说明文，议论文通过分析因果关系说明一个中心思想。如不能把因果关系解释清楚，文章将无法说明任何主题。
因果型段落的扩展模式有两种，一是分类编法，另一个是连环编排法。如果只讨论成因或只讨论结果，细节比较简单，只需按其重要性或其逻辑顺序进行编排。分类编排法指先讨论原因，然后讨论结果;或先讨论结果，后讨论原因。
1)分类编排法：
Music is my chief hobby. When I listen to music, good things happen to me. If I am lonely or homesick, I listen to pop music. The quick rhythm, the strong beats of drums lift my sprits. If I am familiar with a song, I will sing alone with it and my depression disappears. When I am bored or very tired, I listen to Mozart. His music makes me feel alive. Music also reminds me of home. Before I came to college, my sisters and I would listen to music and sing songs together and cheer us. Now I enjoy listening to music and singing with my roommates because their smiles make me remember the happy times with my family. For me, music is an excellent escape, and without it, I wouldn’t be so happy.
2) 连环编排法是先讨论一组因果，再一组因果，再一组因果，形成一个锁链。当因果紧密相连，前一果为后一果之因时，经常使用这种方式。
Students shouldn’t stay up so late. Because of the pressure of examinations, many students burn night candles. The next day, they have to get enough sleep. As a result, many of them get sleepy in class. They couldn’t catch what the teacher says. Not having studied their lessons well, they find it difficult to make good performance in examinations. So, it is not worthwhile to stay up late if you want to study well.
5.人物描写
人物描写包括外部特征、性格特征、思想状态、行为语言等，用于表现人物精神面貌、披露人物内心活动、揭示人物性格变化，借以突出作品主题思想。如：
My sister is a boyish girl. She has short and straight hair like a boy’s. She likes white, black and grey colors, as most boys do. She never cares for shirts, stockings but loves jackets and jeans. Sometimes she wears a men’s suit and leather shores as if she were a gentleman. Basketball and football are her favorite sports. She also enjoys watching boxing. She always shouts and cheers excitedly when she is watching a football match. When she is with her friends, she always says Ladies first” to other girls. The most interesting thing is that she has been mistaken for a boy many times. And she is pleased with that. She always says that she should be a boy.
第一句作者明确表示他眼中的妹妹是个男孩子气十足的小姑娘。这样读者大都会在心中勾画出一种从长相、穿着到言谈举止都特男孩化的女孩。下文作者正是通过穿着、外貌和性格等方面向读者展现一个活生生的人物形象。
6.地点描写
地点描写指用生动形象的语言对某一地点、某一环境进行具体逼真的描绘，使读者如临其境、如睹其物。地点描写的对象可大可小，在可以为城市、国家，小可是一间教室，一个房间。
地点描写自然按空间顺序排列，作者应立足于一个出发点，由远及近，由近到远，从里到外，从外到里，由左到右，或由右到左进行描写，顺序不可混乱，否则读者会迷失方向。如下面一段作者从大门开始，由外向里逐步介绍学校的布置，读者如同跟着作者参观了一所校园。
Now I will show you around our school. It is one of the largest middle schools in the city. When you step into the gate, you will see a beautiful flower bed before you. In the middle of the flower bed there is a fountain with many colored flowers around it. If you walk along the school road, you will come to the playground, on each side of which are rows of trees. We often read books under the trees. On the right of the playground are two classroom buildings. On the left is the newly-built four-storied building. I’m lucky to study here. I love my school very much.
7.物体描写
描写物体时应侧重物的形状、规格大小、颜色和功能。任何一段文字都应有叙述的中心，对物的描写也不例外。同样，主题句也应反映出作者对所要描写物体的看法、态度。如：
The first thing I notice in the bride’s room is the beautiful curtain. This curtain is patchwork in design, and is sewn out of squares of materials of different colors like white, light green, brown and orange. It is made of silk, trimmed with delicate braids. It is about six feet long and hangs from a wooden rail. The curtain matches perfectly with the dark wooden rail and furniture in the room.
通过主题句可以看出作者想向读者描写的是一幅漂亮的窗帘。
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