Topic, Topic Sentence, Main Idea

要快速理解文章的重點，首先要分辨topic, topic sentence, 以及main idea三者的不同。

TOPIC是文章討論的主題(subject)，它可能是一個單字，也可以是個片語，例如：War, abortion, civil rights, water safety, pain等。

TOPIC SENTENCE是每一個段落的主要概念，如同thesis主旨句是貫串整篇文章思想的句子一般，主旨句和主題句的格式不外乎是subject + treatment，或者是subject + specific opinion (+ blueprint)，如果主題是汽車，作者的treatment有可能是"汽車雖然帶來交通的便捷，但對空氣汙染的嚴重影響不容小覷"，這樣的一個thesis，就可以知道作者後面的文章要論說什麼了，這個從寫作的角度來閱讀文章，對閱讀GRE的長篇閱讀非常有幫助，讀完主旨句之後，我們就可以猜測後面文章要說的內容。

 MAIN IDEA在The Reading Edge裡給的說明是：The main idea is always expressed as a complete thought in a complete sentence. This primary idea of the passage, the main idea, may also be stated in different words and in many locations. The main idea is the important one, no matter how it is expressed.要找出main idea必須從文章的許多地方找蛛絲馬跡，但這並不表示必須把玩張全部讀過，只要找出一些關鍵句就可以讀出main idea了。

分辨上述概念之後，在閱讀文章之前先問三個問題：
1. What is the topic?
2. What is the purpose in discussing the topic (or subject)?
3. What is the main idea that the author wants you to know about this specific subject?

找出topic非常簡單，通常文章第一句話就會出現topic，為了保險起見，可以從各段隨便瀏覽，看哪個字或片語是每段都出現的，那就是topic，這個字或片語對作答非常有幫助，可以刪去很多答案。

找出topic之後要問，作者討論這麼topic的目的是什麼？一般來說，目的有以下幾種：

to inform	to defend an idea or action
to describe some idea or thing	to entertain
to tell a story	to discuss some idea or thing
to convince, persuade	to define something
to state a problem	to compare
to analyze something	to evaluate
to classify	to present new information
to offer a solution	to criticize
to suggest an alternative

(表格摘自The Reading Edge)

找出topic，再從thesis以及topic sentence試著讀出作者的目的，基本上，文章就算讀得差不多可以做題了。基本上，讀到這裡也差不多知道作者的main idea了。以下舉一篇Big Book的長閱為例。

文章第一段第一句：The molecules of carbon dioxide in the Earth's atmosphere affect the heat balance of the Earth by acting as a one-way screen.

第二段第一句：Today, however, the potential problem is too much carbon dioxide.

第三段第一句：Under present conditions a temperature of -18℃ can be observed at an altitude of 5 to 6 kilometers above the Earth. (顯然這句不是主題句，純粹陳述事實)

第四段第一句：One mathematical model predicts that doubling the atmospheric carbon dioxide would raise the global mean surface temperature by 2.5℃. (從這句可以判斷第四段是有關一個數學模型)

由於每句話都有carbon dioxide，可以推知是文章主題。再多加第一段的最後兩句：If there were no carbon dioxide in the atmosphere, heat would escape from the Earth much more easily. The surface temperature would be so much lower that the oceans might be a solid mass of ice.可以推知(儘管不用看也知道)二氧化碳跟溫度有關，第二段第一句點出作者要討論的要旨，因此從這幾句就可以描繪出整篇文章的輪廓，並找出作者的purpose，讀完這幾句，心裡對文章應該要有清楚的map，因此就可以開始看問題了找答案了。