Example：

　　Whether the world is Euclidean or non-Euclidean is still an open question.

　　However， if a star's position is predicted based on non-Euclidean geometry，

　　then when a telescope is pointed¹ toswheresthe star should be it will be ther

　　e. Whereas， if the star's position is predicted based on Euclidean geometry，

　　then when a telescope is pointed toswheresthe star should be it won't be th

　　ere. This strongly indicates that the world is non-Euclidean.

　　Which one of the following best expresses the main idea of the passage？

　　（A） The world may or may not be Euclidean.

　　（B） The world is probably non-Euclidean.

　　（C） The world is non-Euclidean.

　　（D） The world is Euclidean.

　　（E） The world is neither Euclidean nor non-Euclidean.

　　Choice （A） understates the main idea. Although the opening to the passage st

　　ates that we don't know whether the world is non-Euclidean， the author goes

　　on to give evidence that it is non-Euclidean. Choice （C） overstates the main

　　idea. The author doesn't say that the world is non-Euclidean， just that evi

　　dence strongly indicates that it is. In choice （B）， the word “probably” prop²

　　erly limits the scope of the main idea， namely， that the world is probably n

　　on-Euclidean， but we can't yet state so definitively³. The answer is （B）。

　　Premises⁵

　　Once you've found the conclusion， most often everything else in the argument

　　will be either premises or “noise.” The premises provide evidence for the c

　　onclusion； they form the foundation or infrastructure⁶ upon which the conclus

　　ion depends. To determine whether a statement is a premise⁴， ask yourself whe

　　ther it supports the conclusion. If so， it's a premise. Earlier we saw that

　　writers use certain words to flag conclusions； likewise writers use certain

　　words to flag premises. Following is a partial list of the most common premi

　　se indicators⁷

Premise Indicators

　　because for

　　since is evidence that

　　if in that

　　as owing to

　　suppose inasmuch as

　　assume may be derived⁸ from

　　Example：

　　Since the incumbent's views are out of step with public opinion， he probably

　　will not be reelected.

　　Here “since” is used to flag the premise that the incumbent's positions are

　　unpopular.

　　Suppressed Premises

　　Most arguments depend on one or more unstated premises. Sometimes this indic

　　ates a weakness in the argument， an oversight⁹ by the writer. More often， how

　　ever， certain premises are left tacit because they are too numerous， or the

　　writer assumes that his audience is aware of the assumptions， or he wants th

　　e audience to fill in the premise themselves and therefore be more likely to

　　believe the conclusion.

　　Example：

　　Conclusion： I knew he did it.

　　Premise： Only a guilty person would accept immunity¹⁰ from prosecution¹¹.

　　The suppressed premise is that he did， in fact， accept immunity. The speaker

　　assumes that his audience is aware of this fact or at least is willing to b

　　elieve it， so to state it would be redundant¹² and ponderous¹³. If the unstated

　　premise were false （that is， he did not accept immunity）， the argument would

　　not technically¹⁴ be a lie； but it would be very deceptive¹⁵. The unscrupulous

　　writer may use this ploy¹⁶ if he thinks that he can get away with it. That is，

　　his argument has the intended effect and the false premise， though implicit¹⁷

　　， is hard to find or is ambiguous. Politicians are not at all above using th

　　is tactic

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