Now that you can break a stimulus
into premises and conclusions and put the argument into your
own words, how do you find errors in the arguments?
The Usual
Suspects: Common Logical Fallacies
We've identified several logical
errors that commonly appear in the Critical Reasoning questions.
1. Circular Reasoning
Here,
an unsubstantiated assertion is used to justify another unsubstantiated
assertion, which is, or at least could be, used to justify the
first statement. For instance, Joe and Fred show up at an exclusive
club. When asked if they are members, Joe says "I'll vouch
for Fred." When Joe is asked for evidence that he's a member,
Fred says, "I'll vouch for him."
2. The Biased Sample Fallacy
The
Fallacy of the Biased Sample is committed whenever the
data for a statistical inference is drawn from a sample that
is not representative of the population under consideration.
The data drawn and used to make a generalization is drawn from
a group that does not represent the whole.
Here is an argument that commits
the fallacy of the biased sample:
ln a recent survey conducted
by Wall Street Weekly of its readers, 80% of the respondents
indicated their strong disapproval of increased capital gains
taxes. This survey clearly shows that increased capital gains
taxes will meet with strong opposition from the electorate.
The
data for the inference in this argument is drawn from a sample
that is not representative of the entire electorate. Since the
survey was conducted of people who invest, not all members of
the electorate have an equal chance of being included in the
sample. Moreover, persons who read about investing are more likely
to have an opinion on the topic of taxes on investment different
from the population at large.
3. The Insufficient Sample Fallacy
The
Fallacy of the Insufficient Sample is committed whenever
an inadequate sample is used to justify the conclusion drawn.
Here's an argument that commits the fallacy of the insufficient
sample:
I have worked with three people
from New York City and found them to be obnoxious, pushy and
rude. It is obvious that people from New York City have a bad
attitude.
The data for the inference in
this argument is insufficient to support the conclusion. Three
observations of people are not sufficient to support a conclusion
about 10 million.
4. Ad hominen
One
of the most often employed fallacies, ad hominen means "to
the man" and indicates an attack that is made upon a person
rather than upon the statements that person has made. An example
is "Don't listen to my opponent; he's a homosexual."
5. The Fallacy of Faulty Analogy
Reasoning
by analogy functions by comparing two similar things. Because
they are alike in various ways, the fallacy is that it is likely
they will share another trait as well. Faulty Analogy
arguments draw similarities between the things compared that
are not relevant to the characteristic being inferred in the
conclusion.
Here's an example of a Faulty
Analogy fallacy:
Ted and Jim excel at both
football and basketball. Since Ted is also a track star, it is
likely that Jim also excels at track.
In this example, numerous similarities
between Ted and Jim are taken as the basis for the inference
that they share additional traits.
6. Straw Man
Here
the speaker attributes an argument to an opponent that does not
represent the opponent's true position. For instance, a political
candidate might charge that his opponent "wants to let all
prisoners go free," when in fact his opponent simply favors
a highly limited furlough system. The person is portrayed as
someone that he is not.
7. The "After This, Therefore,
Because of This" Fallacy (Post
hoc ergo propter hoc)
This
is a "false cause" fallacy in which something is associated
with something else because of mere proximity of time. One often
encounters people assuming that because one thing happened after
another, the first caused it, as with "I touched a toad;
I have a wart. The toad caused the wart." The error in arguments
that commit this fallacy is that their conclusions are causal
claims that are not sufficiently substantiated by the evidence.
Here are two examples of the
After This, Therefore Because of This Fallacy:
Ten minutes after walking
into the auditorium, I began to feel sick to my stomach. There
must have been something in the air in that building that caused
my nausea.
The stock market declined
shortly after the election of the president,thus indicating the
lack of confidence the business community has in the new administration.
In
the first example, a causal connection is posited between two
events simply on the basis of one occurring before the other.
Without further evidence to support it, the causal claim based
on the correlation is premature.
The
second example is typical of modern news reporting. The only
evidence offered in this argument to support the claim that the
decline in the stock market was caused by the election of the
president is the fact that election preceded the decline. While
it has been a causal factor, to argue that it is the cause without
additional information is to commit the After This, Therefore,
Because of This Fallacy.
8. The Either or Thinking
This
is the so-called black or white fallacy. Essentially, it says
"Either you believe what I'm saying, or you must believe
exactly the opposite." Here is an example of the black or
white fallacy:
Since you don't believe that
the earth is teetering on the edge of destruction, you must believe
that pollution and other adverse effects that man has on the
environment are of no concern whatsoever.
The argument above assumes that
there are only two possible alternatives open to us. There is
no room for a middle ground.
9. The "All Things are Equal" Fallacy
This
fallacy is committed when it is assumed, without justification,
that background conditions have remained the same at different
times/locations. In most instances, this is an unwarranted assumption
for the simple reason that things rarely remain the same over
extended periods of time, and things rarely remain the same from
place to place.
The last Democrat winner of
the New Hampshire primary won the general election. This year,
the winner of the New Hampshire primary will win the general
election.
The
assumption operative in this argument is that nothing has changed
since the last primary. No evidence or justification is offered
for this assumption.
10. The Fallacy of Equivocation
The Fallacy
of Equivocation occurs when a word or phrase that has more
than one meaning is employed in different meanings throughout
the argument.
"Every society is, of course, repressive to some
extent - as Sigmund Freud pointed out, repression is the
price we pay for civilization." (John P. Roche- political
columnist)
In this example, the word repression
is used in two completely different contexts. "Repression"
in Freud's mind meant restricting sexual and psychological desires.
"Repression" in the second context does not mean repression
of individual desires, but government restriction of individual
liberties, such as that in a totalitarian state.
11. Non Sequitor
This
means "does not follow," which is short for the
conclusion does not follow from the premise. To say, "The
house is white; therefore, it must be big" is an example
of the Non Sequitor fallacy. It may be a big house, but there
is no intrinsic connection with its being white.
12. Argument ad populum
A
group of kindergartners are studying a frog, trying to determine
its sex. "I wonder if it's a boy frog or a girl frog,"
says one student. "I know how we can tell!" pipes up
another. "All right, how?" asks the teacher, resigned
to the worst. Beams the child: "We can vote."
This is argumentum ad populum,
the belief that truth can be determined by more or less putting
it to a vote. Democracy is a very nice thing, but it doesn't
determine truth. Polls are good for telling you what people think,
not whether those thoughts are correct.
w E. Evaluate an argument's strength
and validity
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