GMAT逻辑assumption解题思路：构建桥梁

GMAT逻辑中的assumption要求考生找出一个选项来当做题面上的推理或计划的前提，只有当该前提存在时该推理才成立或者该计划才能达到目的。换句话说，在做出该推理或计划时已经默认了某个前提的存在，否则该推理或计划是不行的、没道理的，只是题面上没有明说而已。

如： 我多想把你留在身边啊，但城市里不能养狗。所以，我只能放弃你了。

这句话中的前提可以认为是“城市里不能养狗”，结论是“我只能放弃你了”。乍看我们不觉得有什么问题，因为平时生活中我们都在这么说。但从推理的角度去理解，凭什么“城市里不能养狗”就能得出“我只能放弃你了”？除非——除非这个“你”就是一条狗，而且“我”养这条狗就养在城市里；如果“你”不是条狗，或者“我”养狗不是养在城市，那么这个推理就不成立了。

因此这里我们就找到了这个推理的两个assumption——“你”是一条狗，且“我”养这条狗养在城市。这里我们就得出了assumption的第一个解题方向：构建桥梁。

什么时候需要“构建桥梁”？如果你发现结论里比较突兀地出现了一个前提中并没有提到过的概念，那你可能就需要构建桥梁来把这个结论中的概念与前提中的东西联系起来。否则凭什么结论中可以如此任性地提到不想关的东西？

例1：
　　Even though most universities retain the royalties from faculty members’ inventions, the faculty members retain the royalties from books and articles they write. Therefore, faculty members should retain the royalties from the educational computer software they develop.
　　The conclusion above would be more reasonably drawn if which of the following were inserted into the argument as an additional premise?

A. Royalties from inventions are higher than royalties from educational software programs.
　　B. Faculty members are more likely to produce educational software programs than inventions.
　　C. Inventions bring more prestige to universities than do books and articles.
　　D. In the experience of most universities, educational software programs are more marketable that are books and articles.
　　E. In terms of the criteria used to award royalties, educational software programs are more nearly comparable to books and articles than to inventions.

这个题目还比较短，不过很多学生会对royalty一词产生疑虑，明显不是我们平时讲的“皇室”的意思。但这对我们做题并不产生多大的影响，把它当做一个东西即可。阅读完题面，我们大致能知道在讲什么：尽管学校能retain 来自invention的royalty，但教职员工能retain来自books and articles的royalty。

因此，教职员工能retain来自educational computer software的royalty。
　　这里，结论中提到了的educational computer software在前提中一点都未提及，属于空降兵，因此我们必须得构建桥梁，把它和前面讲的东西联系起来。对语义稍作分析，我们明显发现，在“royalty由谁来retain”这件事情上，educational computer software更接近于books and articles，而不像是inventions。最终答案选E。

例2：

The technological conservatism of bicycle manufacturers is a reflection of the kinds of demand they are trying to meet. The only cyclists seriously interested in innovation and willing to pay for it are bicycle racers. Therefore, innovation in bicycle technology is limited by what authorities will accept as standard for purposes of competition in bicycle races.

Which of the following is an assumption made in drawing the conclusion above?

A. The market for cheap, traditional bicycles cannot expand unless the market for high-performance competition bicycles expands.
　　B. High-performance bicycles are likely to be improved more as a result of technological innovations developed in small workshops than as a result of technological innovations developed in major manufacturing concerns.
　　C. Bicycle racers do not generate a strong demand for innovations that fall outside what is officially recognized as standard for purposes of competition.
　　D. The technological conservatism of bicycle manufacturers results primarily from their desire to manufacture a product that can be sold without being altered to suit different national markets.
　　E. The authorities who set standards for high-performance bicycle racing do not keep informed about innovative bicycle design.

题面推理如下：对innovation感兴趣同时也愿意买单的只有bicycle racers，因此，innovation受到authorities建立的competition standard的限制。

这里，结论中的authorities和competition standard就是前提中没有提到的东西。前提说innovation受bicycle racers的影响，结论却说innovation受authorities和他们的competition standard的影响，这当然非常突兀。

相当于在说，“我听爸爸的，所以我听妈妈的”。这个推理的成立必须基于一个前提——“爸爸听妈妈的”。整体是，“我听爸爸的，而爸爸听妈妈的，所以我听妈妈的”。因此这个题目最终的答案应该是说bicycle racers听authorities和他们的competition standard，选C。

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