通過范文學習寫作－原因模式

　　范文：

　　In recent decades, cities have grown so large that now about 50% of the Earth's population lives in urban areas. There are several reasons for this occurrence. First, the increasing industrialization of the nineteenth century resulted in the creation of many factory jobs, which tended to be located in cities. These jobs, with their promise of a better material life, attracted many people from rural areas. Second, there were many schools established to educate the children of the new factory laborers. The promise of a better education persuaded many families to leave farming communities and move to the cities. Finally, as the cities grew, people established places of leisure, entertainment, and culture, such as sports stadiums, theaters, and museums. For many people, these facilities made city life appear more interesting than life on the farm, and therefore drew them away from rural communities.

　　分析：

　　Notice how each supporting sentence is a cause that explains the effect mentioned in the topic sentence. In the chart below are the main ideas of the above paragraph, to help you understand the relationships better:

　　EFFECT

　　(Topic Sentence) CAUSES

　　(Supporting Sentences)

　　Cities have grown very large.

　　[There are several reasons for this.] Factory jobs attracted people.

　　(Cities have grown very large.) Better schools attracted families to move

　　to the city.

　　(Cities have grown very large.) Places of leisure, entertainment, and culture

　　made city life appear more interesting.

　　Notice also how the topic sentence is followed by the "focusing" or "prediction" sentence, There are several reasons for this. Such sentences help the reader anticipate the organization of the paragraph or essay.

　　Cause and Effect Conjunctions

　　Here are some common conjunctions that can be used to express cause and effect:

　　since as a result because of + noun phrase

　　because therefore due to + noun phrase

　　consequently for this reason so

　　There are two things you must be careful of when using these conjunctions. First, you must order the cause and the effect corerctly. For example, in the sentence

　　Sally closed the window because the weather outside was cold.

　　the CAUSE is the fact that the room was cold, and the EFFECT is Sally's closing the window. The conjunction because is placed in the correct position here, which is right before the cause. Similarly, in the sentence

　　Because the weather outside was cold, Sally closed the window.

　　the conjunction because is correctly placed before the part of the sentence that expresses the cause, even though the subordinate clause because the room was cold is now at the beginning of the sentence. (Note that the first letter of the conjunction is now capitalized.) However, in this sentence:

　　??The weather outside was cold because Sally closed the window.

　　even though it is grammatical, it does not make sense because a person's opening or closing a window does not influence the weather.

　　Second, you should be careful when using commas. Conjunctions such as therefore, consequently, as a result, and for this reason are usually followed by a comma, as in these examples:

　　The weather was cold; therefore, Sally closed the window.

　　The weather was cold. Therefore, Sally put on her coat.

　　The weather was cold. Consequently, Sally put on her scarf.

　　A blizzard hit the town. As a result, the schools were closed.

　　The adverbial clause conjunctions since and because are exceptions. These are attached directly at the beginning of CAUSE-sentence without a comma, as in the example above, Because the weather outside was cold, Sally closed the window. The comma here is placed at the end of the subordinate clause.

　　The coordinating conjunction so is also different from the ones above. This conjunction has a comma before it, as in this sentence:

　　The weather was warm, so Jim turned on the air conditioner.

　　However, in formal academic writing, so may not be used at the beginning of a sentence (although you will often see it in informal writing):

　　The weather was warm. So Jim turned on the air conditioner.

　　(too informal -- avoid this usage)