GMAT邏輯推理中的假設(shè)題型作為一類�？碱}型有著非常重要的意義，往往在考試時，考生卻不知道應(yīng)該如何有效找到可以使得整個推理成立的必要條件，或者考生往往出于使推理一定正確的心理，在各個選項中游走不定，最終導(dǎo)致考生無法清楚到底哪個選項才是“真正”的符合題干要求的推理條件。其實我們在解題的過程中把握一個宗旨，也許我們就會發(fā)現(xiàn)其實假設(shè)題型并非我們想象的那樣難，這個宗旨就是：只需要找到一個能使得推理成立的條件或者說是必要條件，我們不需要去保證通過這個條件推理一定做到正確。下面就讓我們通過實例對考生在假設(shè)推理的過程中容易出現(xiàn)的錯誤進(jìn)行解析。

一、無法找出題干中討論對象之間的本質(zhì)關(guān)系

例：A thorough search of Edgar Allan Poe’s correspondence has turned up not a single letter in which he mentions his reputed morphine addiction. On the basis of this evidence it is safe to say that Poe’s reputation for having been a morphine addict is undeserved and that reports of his supposed addiction are untrue.

Which of the following is assumed by the argument above?

(A) Reports claiming that Poe was addicted to morphine did not begin to circulate until after his death.

(B) None of the reports of Poe’s supposed morphine addiction can be traced to individuals who actually knew Poe.

(C) Poe’s income from writing would not have been sufficient to support a morphine addiction

(D) Poe would have been unable to carry on an extensive correspondence while under the influence of morphine

(E) Fear of the consequences would not have prevented Poe from indicating in his correspondence that he was addicted to morphine.

上述題干中提到：一、研究發(fā)現(xiàn)Poe的信件中未提及他患有嗎啡癮；二、Poe沒有嗎啡癮

本題極力在讓考生從“對Poe的信件調(diào)查[證據(jù)]→Poe未患有嗎啡癮[結(jié)論]”找出兩者的內(nèi)在聯(lián)系，5個選項中也給出了不同的假設(shè)，那么我們只需通過反推，來找出一種能夠使得推理成立的假設(shè)條件即可，但考生往往會拋開“信件調(diào)查”去思考其他使得上述結(jié)論正確的條件（假設(shè)），換句話說考生往往會認(rèn)為除了對信件的調(diào)查這樣一個證據(jù)以外，還可以有其他證據(jù)能夠推出Poe未患有嗎啡癮。通常來講，當(dāng)一個推理是從一個我們已知的，已經(jīng)發(fā)生的事實推斷出一個結(jié)論的時候，我們需要記住的就是，其中的隱含假設(shè)多為這個結(jié)論的唯一原因，換句話說，在本題中要想對Poe的信件做出說明，那么我們只能假定Poe不會因害怕后果而不在其信件中提及對嗎啡的嗜好，本題的正確假設(shè)選項為E.

二、無因就無果

在假設(shè)題型里，如果想要找出段落推理的一個必要條件，那么我們首先就應(yīng)明確，這個必要條件就是使得推理必然成立的一個假設(shè)，假設(shè)必為支持性假設(shè)。

例：

The population of peregrine falcons declined rapidly during the 1950’s and 1960’s and reached an all-time low in the early 1970’s. The decline was attributed by scientists to the widespread use of the pesticide DDT in rural areas

Which of the following, if true, gives the strongest support to the scientists’ claim?

(A) DDT was not generally in use in areas devoted to heavy industry

(B) In the time since the use of DDT was banned in 1972, the population of peregrine falcons has been steadily increasing

(C) Peregrine falcons, like other birds of prey, abandon eggs that have fallen out of the nest, even if the eggs remain intact

(D) Starlings, house sparrows, and blue jays-birds the peregrine falcon preys on were not adversely affected by DDT in their habitats

(E) Other birds of prey, such as the osprey, the bald eagle, and the brown pelican, are found in the same areas as is the peregrine falcon.

題干是由果推因，游隼數(shù)量下降由使用殺蟲劑（DDT）所致，我們不妨將“游隼數(shù)量下降”視為B, 而將“使用DDT”視為A, 如果由B→A正確,那么我們就可以得出沒有A就不會存在現(xiàn)在的B,因此我們就可以推斷兩種情況，DDT禁用前與DDT禁用后游隼在數(shù)量上的比較，如果在DDT禁用后，游隼數(shù)量開始增加的話，那么我們就會非�？隙ǖ氖谴_實是殺蟲劑的使用導(dǎo)致了游隼數(shù)量的減少。這種類型的題目出錯的主要原因有兩點(diǎn)：一：考生無法把握題干要求，在段落內(nèi)容之外進(jìn)行推理；二：無法將題干給出的原因視做唯一原因。

建議：

考生應(yīng)能在平時的不斷練習(xí)的過程中，學(xué)習(xí)找出論點(diǎn)和結(jié)論的能力，并依據(jù)兩者的關(guān)系進(jìn)行判斷，只要弄清論點(diǎn)和結(jié)論也就相當(dāng)于找出了答案。在實踐練習(xí)中，考生也應(yīng)善于從題干所描述的對象中找出核心關(guān)鍵詞語，一般來講，我們可以通過在選項中加入Not 來判斷推理成立的有效性并排除那些誤選項。