托福閱讀推斷題：逆向推理

托福閱讀中的推斷題其實是事實信息題的加強(qiáng)版，其所有的推斷都是基于原文事實信息的邏輯推斷，也就是說我們所作出的推斷要建立在讀懂文章意思的基礎(chǔ)上的。既然如此，事實信息題的做法可以遷移到推斷題上——找詞定位，邏輯推斷，匹配答案。

找詞定位這一步我們在事實信息題中已經(jīng)闡述得很清楚了在這里不再贅述。這里重點要闡述的是推斷題中最常考的逆向推斷。
　　逆向邏輯類似于“非”的關(guān)系。比如，2014年寒假之后，小明開始準(zhǔn)備托福考試了。這里蘊含的逆向邏輯推理是：2014年寒假之前，小明還沒開始準(zhǔn)備托�？荚嚒�TPO 20 Westward Migration中第1題考得就是上述逆向邏輯推理：

What can be inferred from paragraph 1 about western farmers prior to 1815?
　　O They had limited their crop production to wheat, corn, tobacco, and cotton.
　　O They were able to sell their produce at high prices.
　　O They had not been successful in raising cattle.
　　O They did not operate in a national market economy.

根據(jù)題干中的數(shù)字1815，我們定位至原文中After 1815 improved transportation enabled more and more western farmers to escape a self-sufficient way of life and enter a national market economy.這句話——“1815年之后，改善后的交通使得更多的西部農(nóng)民擺脫自給自足的生活方式并參與到國有市場經(jīng)濟(jì)中來”。那么也就是說，1815年之前，西部農(nóng)民是沒有擺脫自給自足的生活方式并沒有參與到國有市場經(jīng)濟(jì)中。所以答案選第三個選項。

當(dāng)然不是每個逆向推理都只是簡單的時間上的逆向推斷，還有意義上的逆向推斷，如TPO 12 Water in the Desert 中第1題：

2. Which of the following statements about annual rainfall can be inferred from paragraph 1?
　　○ Flat desert areas receive more annual rainfall than desert areas with mountains.
　　○ Areas that receive more than four inches of rain per year are not considered deserts.
　　○ Many areas receive less than four inches of annual rainfall, but only a few are deserts.
　　○ Annual rainfall has no impact on the groundwater resources of desert areas.

Paragraph 1:
　　Rainfall is not completely absent in desert areas, but it is highly variable. An annual rainfall of four inches is often used to define the limits of a desert. The impact of rainfall upon the surface water and groundwater resources of the desert is greatly influenced by landforms. Flats and depressions where water can collect are common features, but they make up only a small part of the landscape.

利用題干中主題詞annual rainfall回原文定位第二句“An annual rainfall of four inches is often used to define the limits of a desert.”意思是：年降水量為四英寸定義了沙漠的界限。很明顯，利用反義推斷，年降水量低于四英寸是沙漠，那么高于四英寸的肯定就是非沙漠。故選項3為正確答案。

類似的逆向邏輯在托福閱讀中比比皆是，比如TPO 12 Transition on Sound in Films 第5題、TPO-17 Europe’s Early Sea Trade with Asia 中第6題等等，大家可以利用此法實際演練一下。

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