加拿大留学考试托福阅读关于“不干净”的段落
加拿大留学考试托福阅读关于“不干净”的段落
加拿大留学考试很多人对托福阅读文章有一个根深蒂固的误区，那就是每个段落有一个段落主旨，而这个段落主旨多数情况下是通过一个所谓的主旨句（topic sentence）来体现的。
为什么我们说这是一个误区呢？我们来看一个典型的段落吧。
TPO 36-1 Soil Formation
Paragraph 1
Living organisms play an essential role in soil formation.The numerous plants and animals living in the soil release minerals from the parent material from which soil is formed,supply organic matter,aid in the translocation(movement)and aeration of the soil,and help protect the soil from erosion.The types of organisms growing or living in the soil greatly influence the soil’s physical and chemical characteristics.In fact,for mature soils in many parts of the world,the predominant type of natural vegetation is considered the most important direct influence on soil characteristics.For this reason,a soil scientist can tell a great deal about the attributes of the soil in any given area simply form knowing what kind of flora the soil supports.Thus prairies and tundra regions,which have characteristic vegetations,also have characteristic soils.加拿大托福
认真读一下这个段落，我们觉得大多数人都会认为第一句话就是这段的主旨句，因为这个段落的内容都是在围绕着第一句话展开的，也就是典型的“总--分”结构。如下：
TPO 36-1 Soil Formation
Paragraph 1
Living organisms play an essential role in soil formation.The numerous plants and animals living in the soil release minerals from the parent material from which soil is formed,supply organic matter,aid in the translocation(movement)and aeration of the soil,and help protect the soil from erosion.The types of organisms growing or living in the soil greatly influence the soil’s physical and chemical characteristics.In fact,for mature soils in many parts of the world,the predominant type of natural vegetation is considered the most important direct influence on soil characteristics.For this reason,a soil scientist can tell a great deal about the attributes of the soil in any given area simply form knowing what kind of flora the soil supports.Thus prairies and tundra regions,which have characteristic vegetations,also have characteristic soils.
不过，上面的这个想法是很危险的。你可以说这个段落是“总--分”结构，第一句话是总，剩下的是分。但是你不太能说第一句话就是这段的主旨句。
为什么呢？我们来思考一下：
第一句的意思是“活的生物在土壤的形成中起到了重要的作用。”
如果第一句话是这段的主旨句的话，那就是说这个段落就是在说“活的生物在土壤形成中起到了重要的作用”。
可是，如果你去看这篇文章的后文（可以去TPO 36找到全文），你会发现，后面的段落分别还主要讲了细菌，树，动物等对土壤形成的影响。也就是说，这个第一句话实际上已经囊括了后面的段落的核心意思。所以，与其说它是第一段的段落主旨，不如说它是全文的文章主旨。
加拿大留学考试托福阅读关于“不干净”的段落
可见，说这个第一句话是第一段的主旨句是偏颇的，是不利于抓住第一段真正的主旨的。实际上第一段真正的主旨应该是原文中In fact那句话，即：
In fact,for mature soils in many parts of the world,the predominant type of natural vegetation is considered the most important direct influence on soil characteristics.
也就是说，第一段主要是聊植被对土壤形成起到了最关键的作用。然后第二段，第三段和第四段又主要分别展开细菌，树，动物对土壤形成所起到的作用。这里作者暗含了它们都没植被对土壤形成起到的作用大，植被是最大的影响因素。
按我们说的意思，这个段落的层次划分如下：
TPO 36-1 Soil Formation
Paragraph 1
Living organisms play an essential role in soil formation.The numerous plants and animals living in the soil release minerals from the parent material from which soil is formed,supply organic matter,aid in the translocation(movement)and aeration of the soil,and help protect the soil from erosion.The types of organisms growing or living in the soil greatly influence the soil’s physical and chemical characteristics.In fact,for mature soils in many parts of the world,the predominant type of natural vegetation is considered the most important direct influence on soil characteristics.For this reason,a soil scientist can tell a great deal about the attributes of the soil in any given area simply form knowing what kind of flora the soil supports.Thus prairies and tundra regions,which have characteristic vegetations,also have characteristic soils.
这就是我们说的“不干净”的段落了，你无论以哪句话为主旨句都没法把段落“干净”地单独拎出来。如果你说第一句话是段落主旨，那这句话还包括了第二段，第三段和第四段。你没法把第一段单独地，“干净地”拎出来。如果按我们说的In fact那句话是段落主旨，你又发现In fact之前的三句话不是只讲植被，是一种总括。所以我们也没法用In fact这句话就把第一段的所有内容都“干干净净地”包括了。
这样的段落在托福阅读中比比皆是。你会发现，你好像几乎永远都无法找到一个“干干净净“的段落。
再举一个例子：
The Chaco Phenomenon
Paragraph 2
For more than a century archaeologists have struggled to understand the circumstances surrounding the rise and collapse of Chacoan society—dubbed the Chaco Phenomenon.In particular,research has focused on determining why such an apparently inhospitable place as Chaco,which today is extremely arid and has very short growing seasons,should have favored the concentration of labor that must have been required for such massive construction projects over brief periods of time.Until the 1970s,it was widely assumed that Chaco had been a forested oasis that attracted farmers who initially flourished but eventually fell victim to their own success and exuberance,as they denuded the canyon of trees and vegetation to build large great houses.In the 1980s this reconstruction was largely dismissed in response to evidence that there had never been a forest in Chaco,and that canyon soils had poor agricultural potential.As scientific interpretations about Chaco changed,the focus of explanatory models changed from the attractiveness of the canyon for farmers to the position of the canyon within a regional network of dispersed agricultural communities.
分析一下这个段落，你很可能会觉得第一句话是总，后面是分。也就是如下分层：
The Chaco Phenomenon
Paragraph 2
For more than a century archaeologists have struggled to understand the circumstances surrounding the rise and collapse of Chacoan society—dubbed the Chaco Phenomenon.In particular,research has focused on determining why such an apparently inhospitable place as Chaco,which today is extremely arid and has very short growing seasons,should have favored the concentration of labor that must have been required for such massive construction projects over brief periods of time.Until the 1970s,it was widely assumed that Chaco had been a forested oasis that attracted farmers who initially flourished but eventually fell victim to their own success and exuberance,as they denuded the canyon of trees and vegetation to build large great houses.In the 1980s this reconstruction was largely dismissed in response to evidence that there had never been a forest in Chaco,and that canyon soils had poor agricultural potential.As scientific interpretations about Chaco changed,the focus of explanatory models changed from the attractiveness of the canyon for farmers to the position of the canyon within a regional network of dispersed agricultural communities.
其实这么分层的话，就非常粗糙，根本抓不住这段真正的主旨。这个段落的第一句话实际上同样也是囊括了后面的第3段，第4段和第5段，根本不能算是第2段的段落主旨。
认真研究之后，细致的分层应该如下：
The Chaco Phenomenon
Paragraph 2
For more than a century archaeologists have struggled to understand the circumstances surrounding the rise and collapse of Chacoan society—dubbed the Chaco Phenomenon.In particular,research has focused on determining why such an apparently inhospitable place as Chaco,which today is extremely arid and has very short growing seasons,should have favored the concentration of labor that must have been required for such massive construction projects over brief periods of time.Until the 1970s,it was widely assumed that Chaco had been a forested oasis that attracted farmers who initially flourished but eventually fell victim to their own success and exuberance,as they denuded the canyon of trees and vegetation to build large great houses.In the 1980s this reconstruction was largely dismissed in response to evidence that there had never been a forest in Chaco,and that canyon soils had poor agricultural potential.As scientific interpretations about Chaco changed,the focus of explanatory models changed from the attractiveness of the canyon for farmers to the position of the canyon within a regional network of dispersed agricultural communities.
第一层是一个大的总：科学家们关于围绕着Chaco社会的兴衰的来龙去脉不太能理解，尤其他们不太明白为什么Chaco这么一个鸟不拉屎的地方会聚集这么多人去建大房子。
第二层是对第一层的疑问的第一个假说：这个地方之所以聚集这么多人建大房子是因为这个地方曾经是森林绿洲，后来森林被砍光建房子了，导致社会衰落。
第三层是对第一个假说的批判：80年代的证据表明了这个地方根本就没有森林，所以科学家们开始从别的角度去寻找解释，他们开始思考这个地方在整个区域交通网络中的位置问题，这算是要引出第二个假说了。
而接下来的第3段就是紧接着聊第二个假说的，如下：
Paragraph 3
The adoption of a regional perspective in explaining the Chaco Phenomenon was based in part on the discovery of formal trails connecting many of the great houses in Chaco,as well as linking the canyon to smaller great houses located throughout the San Juan basin,the latter are referred to as Chaco“outliers.”These trails are densest around the concentration of great houses in the center,and the canyon itself is roughly at the center of the basin.Consequently,the canyon occupies the geographical and social center of the network formed by the connecting trails.The current consensus view is that religion provides the fundamental explanation for this centrifugal pattern.
所以，你发现没，对于文章的第2段，你是无法用段落中的任何一句话去作为主旨句去概括整个段落的意思的。你能做的就只是把这个段落层次分出来，并理解层次和层次之间的关系，如下：
The Chaco Phenomenon
Paragraph 2
For more than a century archaeologists have struggled to understand the circumstances surrounding the rise and collapse of Chacoan society—dubbed the Chaco Phenomenon.In particular,research has focused on determining why such an apparently inhospitable place as Chaco,which today is extremely arid and has very short growing seasons,should have favored the concentration of labor that must have been required for such massive construction projects over brief periods of time.Until the 1970s,it was widely assumed that Chaco had been a forested oasis that attracted farmers who initially flourished but eventually fell victim to their own success and exuberance,as they denuded the canyon of trees and vegetation to build large great houses.In the 1980s this reconstruction was largely dismissed in response to evidence that there had never been a forest in Chaco,and that canyon soils had poor agricultural potential.As scientific interpretations about Chaco changed,the focus of explanatory models changed from the attractiveness of the canyon for farmers to the position of the canyon within a regional network of dispersed agricultural communities.
而为什么要把这三个层次放在这同一个段落中呢？这好像还真是随机的，没有一点道理。
我们完全可以把第一层单拎出来作为一个段落，也完全可以把第三层拎出来跟后面第3段的内容放在一起作为一个段落。
所以，你如果还是天真地去托福阅读的段落中去找所谓的“主旨句（Topic sentence）”，那你真的是要掉大坑了！你要么找不到所谓主旨句，要么就算找到了，它也无法提供给你关于段落主旨的有效信息。
