GMAT考试-Testprep数学精解(11)

Of the three types of inductive reasoning we will discuss， causal reasoning

is both the weakest and the most prone to fallacy. Nevertheless， it is a us

eful and common method of thought.

To argue by causation is to claim that one thing causes another. A causal ar

gument can be either weak or strong depending on the context. For example， t

o claim that you won the lottery because you saw a shooting star the night b

efore is clearly fallacious. However， most people believe that smoking cause

s cancer because cancer often strikes those with a history of cigarette use.

Although the connection between smoking and cancer is virtually certain， as

with all inductive arguments it can never be 100 percent certain. Cigarette

companies have claimed that there may be a genetic predisposition in some p

eople to both develop cancer and crave nicotine. Although this claim is high

ly improbable， it is conceivable.

There are two common fallacies associated with causal reasoning：

1. Confusing Correlation with Causation.

To claim that A caused B merely because A occurred immediately before B is c

learly questionable. It may be only coincidental that they occurred together

， or something else may have caused them to occur together. For example， the

fact that insomnia and lack of appetite often occur together does not mean

that one necessarily causes the other. They may both be symptoms of an under

lying condition.

2. Confusing Necessary Conditions with Sufficient Conditions.

A is necessary for B means “B cannot occur without A.” A is sufficient for B

means “A causes B to occur， but B can still occur without A.” For example，

a small tax base is sufficient to cause a budget deficit， but excessive spen

ding can cause a deficit even with a large tax base. A common fallacy is to

assume that a necessary condition is sufficient to cause a situation. For ex

ample， to win a modern war it is necessary to have modern， high-tech equipme

nt， but it is not sufficient， as Iraq discovered in the Persian Gulf War.

SEVEN COMMON FALLACIES

Contradiction

A Contradiction is committed when two opposing statements are simultaneously

asserted. For example， saying “it is raining and it is not raining” is a co

ntradiction. Typically， however， the arguer obscures the contradiction to th

e point that the argument can be quite compelling. Take， for instance， the f

ollowing argument：

“We cannot know anything， because we intuitively realize that our thoughts a

re unreliable.“

This argument has an air of reasonableness to it. But “intuitively realize”

means “to know.” Thus the arguer is in essence saying that we know that we d

on't know anything. This is self-contradictory.

Equivocation

Equivocation is the use of a word in more than one sense during an argument.

This technique is often used by politicians to leave themselves an “out.” I

f someone objects to a particular statement， the politician can simply claim

the other meaning.

Example：

Individual rights must be championed by the government. It is right for one

to believe in God. So government should promote the belief in God.

In this argument， right is used ambiguously. In the phrase “individual right

s“ it is used in the sense of a privilege， whereas in the second sentence ri

ght is used to mean proper or moral. The questionable conclusion is possible

only if the arguer is allowed to play with the meaning of the critical word

right.

Circular Reasoning

Circular reasoning involves assuming as a premise that which you are trying

to prove. Intuitively， it may seem that no one would fall for such an argume

nt. However， the conclusion may appear to state something additional， or the

argument may be so long that the reader may forget that the conclusion was

stated as a premise