QUESTION OF THE DAY: TAKE A LOOK AT THE ALGEBRA
PROOF BELOW, AND COPY IT DOWN IN YOUR NOTES.
CHALLENGE: THE FINAL LINE CAN’T BE CORRECT! CAN YOU
TELL WHAT WENT WRONG??
If we advance to the next slide too soon, use
a copy of the presentation to make notes.
PLEASE RETURN all copies of the slides.
Prologue
Recognizing Fallacies
ARGUMENT
An argument is a set of facts or assumptions,
called premises, that support a conclusion.
Argument Examples
In the below arguments, identify the premise(s) and conclusion.
• Everyone in San Francisco is a liberal.
• Michael Savage lives in San Francisco.
• Michael Savage is a liberal.
• All US Presidents have been men.
• JFK was a man.
• JFK was a US President.
People generally quarrel because
they cannot argue.
G.K. Chesterton (1874-1936)
LOGIC
Logic is a branch of mathematics that
studies the methods and principles of
reasoning.
Studying Logic enables one to learn how to create
valid arguments, reason clearly, and develop
excellent critical thinking skills. These skills will
allow you to interpret and analyze events in every
area of life.
FALLACIES
Some arguments are invalid. There is an error
in reasoning. Such an argument is called a
fallacy.
A fallacy is a deceptive, misleading, or unsound
argument—an argument in which the conclusion
is not well supported by the premises.
FALLACY STRUCTURES
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Appeal to Popularity
False Cause
Appeal to Ignorance
Hasty Generalization
Limited Choice
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Appeal to Emotion
Personal Attack
Circular Reasoning
Diversion
Straw Man
Remember, all fallacies contain faulty
reasoning. That is, the conclusion does not
follow logically from the premises.
APPEAL TO POPULARITY
The fallacy of appeal to popularity (or appeal to
majority) uses the fact that large numbers of people
believe or act some way as evidence that the belief is
correct.
*Many people believe p is true; therefore ……p is true.
EXAMPLE 1: Microsoft makes the best computer
operating system. After all, more people use Windows
than any other operating system.
APPEAL TO POPULARITY
EXAMPLE 2: Ford makes the best automobile in
America; after all, more people drive Fords than any
other American car.
FALSE CAUSE
The fallacy of false cause uses the fact that one event
came before another as evidence that the first event
caused the second event.
*A came before B; therefore . . . A caused B.
EXAMPLE 1: Timmy took some cold medication
before his math test. He made a 100 on the test. The
cold medication made Timmy ace his math test.
FALSE CAUSE
EXAMPLE 1: “I placed a quartz crystal on my
forehead, and in five minutes my headache was gone.
The crystal made my headache go away.”
APPEAL TO IGNORANCE
The fallacy of appeal to ignorance uses ignorance (lack
of knowledge) about the truth of a proposition to
conclude the opposite.
*There is no proof that p is true; therefore . . . p is false.
EXAMPLE 1: Scientists have not found any evidence of
Bigfoot. Therefore, anyone who claims to have seen
Bigfoot must be hallucinating.
*An absence of evidence is not evidence of absence.*
APPEAL TO IGNORANCE
EXAMPLE 2: Scientists have not proved that global
warming will have any bad consequences for the human
race. Therefore, the global warming catastrophes that
people are talking about will never happen.
HASTY GENERALIZATION
The fallacy of hasty generalization draws a conclusion
from an inadequate number of cases or cases that have
not been sufficiently analyzed.
*A and B are linked one or a few times; therefore . . . …
A causes B (or vice versa).
EXAMPLE 2: Three cases of brain cancer have
occurred in people who use cell phones. Therefore, cell
phones must cause brain cancer.
LIMITED CHOICE
The fallacy of limited choice artificially precludes
choices that ought to be considered.
*p is false; therefore . . . only q can be true.
EXAMPLE 1: “You don’t support the President, so you are not a
patriotic American.”
EXAMPLE 2: “Have you stopped smoking?”
In court, this is called ‘Leading
the Witness’.
EXAMPLE 3: “You’re wrong, so I must be right.”
APPEAL TO EMOTION
The fallacy of appeal to emotion uses an emotional
reaction (instead of logic) as a tool of persuasion.
*p is associated with an emotional response;
therefore . . . p is true.
EXAMPLE 1: In a commercial for Michelin tires, a picture of a
baby is shown with the words “because so much is riding on your
tires.”
EXAMPLE 2: If my opponent is elected, your tax burden will rise.
PERSONAL ATTACK
The fallacy of personal attack (ad hominem) uses a
dislike of a person or group making an argument to
conclude the argument is not valid.
*I have a problem with the person or group claiming p;
therefore . . . p is not true.
EXAMPLE 1: There is no way Senator Smith’s bill can help the
cause of gun control because he is one of the biggest recipients of
campaign contributions from the National Rifle Association.
The provisions of the Senator’s bill were not challenged.
PERSONAL ATTACK
EXAMPLE 2:
Mike: “Tom, you should stop drinking because it is hurting your
grades, endangering people if you drive, and hurting your
relationship with your family.”
Tom: “I’ve seen you drink a few on occasion yourself.”
CIRCULAR REASONING
The fallacy of circular reasoning just restates the
premise in different words.
*p is true; p is restated in different words.
EXAMPLE: Schools must implement a zero tolerance
policy toward drug use, because any tolerance of drugs is
unacceptable.
DIVERSION
The fallacy of diversion (or red herring) diverts the
attention from one issue, p, to another (related) issue, q.
*p is related to q and I have an argument concerning q;
therefore . . . p is true.
EXAMPLE: We should not drill for oil in the Alaskan
National Wildlife Refuge (ANWR), because we have too
many gas-guzzling automobiles as it is.
DIVERSION
The term “red herring” is traced back to the 19th
century, when British fugitives discovered they could
divert bloodhounds from their pursuit by rubbing a red
herring across their trail.
STRAW MAN
The fallacy of straw man makes an argument based on a
distortion of someone’s words or beliefs.
*I have an argument concerning a distorted version of p;
therefore . . . I hope you are fooled into concluding that I
have an argument concerning the real version of p.
EXAMPLE: The mayor of a large city has proposed
decriminalizing drug possession in order to reduce overcrowding in
jails. His challenger in the upcoming election says, “The mayor
doesn’t think there’s anything wrong with drug use, but I do.”
DUE NEXT CLASS:
Write two paragraphs about the following:
Describe an instance in which you were persuaded of
something that you later decided was untrue. Explain
how you were persuaded and why you later changed your
mind.
Did you fall victim to any fallacies? If so, how might you
prevent the same thing from happening in the future?
PLEASE TYPE OR WRITE NEATLY. IDENTIFY THE
FALLACY YOU ARE DESCRIBING. I WILL NOT GRADE
SPELLING, GRAMMAR, ETC.