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