托福阅读中常出现的隐形逻辑。西方思维在论证和推演中认识事物的本质和规律，重视分析和实证必然会借助逻辑。托福阅读文章中所占比较多的科普性说明文，便是典型的以事物或事件发生演变的条理性来布局文章，以较强的语言逻辑性来说明各事物间和事件中的内在联系，传达信息。
我们在阅读托福文章段落，统筹文章结构时，经常强调语言逻辑的重要性，从考察基本功的词汇题开始，便会引入句内逻辑，句间逻辑的知识点，当阅读中遇到常见的表示并列，转折，因果，对比等显形逻辑词时，大部分考生都能抓住论述对象的各个论述内容以及各论述内容之间的关系，但有些隐形逻辑词却使得大家在解题时裹足不前，错误频出。
TPO 24-3 Moving into Pueblos中：
Some scholars expand on this idea by emphasizing a corresponding need for arable land to feed growing numbers of people: construction of small dams, reservoirs, terraces, and field houses indicates that farmers were intensifying their efforts during the 1200s.
A. Some scholars even claim that the intensification of farmers’ various efforts during the 1200s led to further population growth and the consequent need for more arable land.
B. Evidence of intensifying agriculture in the 1200s indicates a need to feed a larger population and so extends the argument that a growing population was the cause of the move to pueblos.
C. During the 1200s, farmers met the demand for more arable land, but they also succeeded in cultivating existing land more intensively with the help of agricultural construction projects.
D. Some scholars feel strongly that the construction of small dams, reservoirs, terraces, and field houses in the thirteenth century is independent evidence for growth in the number of people.
这道题可谓是难度五颗星的一道句子简化题，很多考生看到这个长难句后，并不能非常快速地将这个句子分层次抓主干，甚至会纠结于冒号前后句子的关系。
首先句子1为“Some scholars expand on this idea by emphasizing a corresponding need for arable land to feed growing numbers of people”句子2为“construction of small dams, reservoirs, terraces, and field houses indicates that farmers were intensifying their efforts during the 1200s”，两句之间由一个标点“：”连接，表示解释说明，实则句子2可以同意转换成“（To feed growing numbers of people） accounts for the intensifying agricultural efforts in the 1200s”, 对等B选项中的“Evidence of intensifying agriculture in the 1200s indicates a need to feed a larger population”，句子1中expand on这个词意为“进一步阐述”，实则是一个隐形因果逻辑，“指示代词+名词this idea” 指的是前文的“domestic architecture became larger, culminating in crowded pueblos”，也就是“people moved into the pueblos”, 因此整合句子1就可以得到“the growing number of people expands on the fact that people moved into the pueblos.” 对等B选项中的“a growing population was the cause of the move to pueblos”, 本题题干中出现的expand on和冒号，以及选项中出现的evidence，我们都将其视为“隐形”的因果逻辑关系词。
因果关系是阅读中一项非常重要的逻辑关系，显形的因果关系无需赘述，隐形的因果逻辑关系词我们稍加整理，有诸如表示导致，产生（因→果）：cause, lead to, result in, produce, give rise to, support, render, account for等词语，还有诸如表示由……产生，反映（果←因）：result from, derive from, attribute to, ascribe to, reflect, suggest等词语。
至于evidence这个词，我们很容易想到一道经典句子简化题TPO1-3 Timberline Vegetation on Mountains中:
Wind velocity also increases with altitude and may cause serious stress for trees, as is made evident by the deformed shapes at high altitudes.
A. Because of their deformed shapes at high altitudes, trees are not likely to be seriously harmed by the strong winds typical of those altitudes.
B. As altitude increases, the velocity of winds increase, leading to a serious decrease in the number of trees found at high altitudes.
C. The deformed shapes of trees at high altitudes show that wind velocity, which increase with altitude, can cause serious hardship for trees.
D. Increased wind velocity at high altitudes deforms the shapes of trees, and this may cause serious stress for trees.
此题题干中 “as is made evident by” 也体现了隐形的因果关系，后面的“the deformed shapes at high altitudes”为结果reflect the wind velocity increasing with altitude, 对应C选项中的“the deformed shapes of trees at high altitudes show that wind velocity, which increase with altitude”。
除了上文举出的TPO中句子简化题中的实例，托福阅读其他题型如句子插入题、修辞目的题、推理题等题型中都可能运用到语言逻辑，其中推理题本身就有一个逻辑推理的过程，而应用其中最为广泛的，便是利用“比较”这类逻辑进行反推。例如TPO20-1 Westward Migration中有这样一道推理题：
Two other developments presaged the end of the era of turnpikes and started a transportation revolution that resulted in increased regional specialization and the growth of a national market economy. First came the steamboat; although flatboats and keelboats continued to be important until the 1850’s steamboats eventually superseded all other craft in the carrying of passengers and freight. Steamboats were not only faster but also transported upriver freight for about one tenth of what it had previously cost on hand-propelled keelboats. Next came the Erie Canal, an enormous project in its day, spanning about 350 miles. After the canal went into operation, the cost per mile of transporting a ton of freight from Buffalo to New York City declined from nearly 20 cents to less than 1 cent. Eventually, the western states diverted much of their produce from the rivers to the Erie Canal, a shorter route to eastern markets.
Which of the following can be inferred from the paragraph about flatboats and keelboats?
A. They ceased to be used as soon as the first turnpikes were built.
B. They were slower and more expensive to operate than steamboats.
C. They were used for long-distance but not for regional transportation.
D. They were used primarily on the Erie Canal.
根据题干信息flatboats and keelboats，我们很容易首先定位至原文中句子“although flatboats and keelboats continued to be important until the 1850s, steamboats eventually superseded all other craft in the carrying of passengers and freight”，这句话中continue…until, 和supersede均为隐含的比较关系词，这句话的大意为steamboats蒸汽船最终取代了flatboats平底船和keelboats龙骨船，至于取代的原因，则是紧邻的下一个句子“Steamboats were not only faster but also transported upriver freight for about one tenth of what it had previously cost on hand-propelled keelboats.”中由比较级形式faster, 分数one tenth of…, 和表示时间点的词previously体现出比较关系，steamboats蒸汽船速度更快且运费更便宜，因此这道题目选B，是原文信息的取反。
在托福阅读比较的逻辑关系中，我们能够比较轻易地识别出compare, compare to这类显性的比较关系词，同时也应该注意表示比较级-er，表示变化的词，例如change, increase, enhance, continue, supersede, surpass等，以及表示分数和倍数诸如此类的表示隐含的比较关系词。
对于参加托福阅读的考生来说，除了具备考试所需的学术类词汇和分析长难句所必备的语法知识，在阅读过程中还应该注意联系短语之间，句子之间乃至段落之间重要的逻辑线索。“知人者谓之智”，托福阅读的乐趣就在于找出文章中的暗语，知悉考官对于我们的一些隐性考点的考察。对于字里行间的弦外之音，我们需要的不只是在考场上遇到这类问题时发挥的“急智”，而是平时在练习刷题过程中对于自己错处的重视和反思，以及对于这些隐形知识点的总结和积累。当我们将这些知识点融会贯通，运用自如时，就是阅读能力根本性的提高，外在表现便是高效解题，获得高分。