Fallacies of Reason

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International Debate Education Association

• Fallacies of Reason
• David Douglass

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Acceptability, Relevance, and Sufficiency

• These are three criteria for evaluating argument.
  All arguments should be considered in light of
  whether they meet these standards. Failure to do
  so results in fallacies of reasoning. Debates
  can be won or lost on such issues.

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Acceptability

• Primarily related to evidence or premise,
  acceptability is the question of whether the
  evidence used for a claim is appropriate for the
  claim itself. Three ways to achieve
• Debater provides solid argument
• Common knowledge
• Relevant authority

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Fallacies of Acceptability

• Begging the Question The evidence for a claim
  simply repeats the claim in a slightly different
  way, or it takes the claim for granted. E.g.,
  Active euthanasia is morally acceptable because
  it is a decent, ethical thing to help another
  human being escape suffering through death."
• Incompatibility An argument is incompatible
  with other arguments already made. E.g., I
  believe that no one should ever take another
  persons life. Thats why murderers should be
  put to death.

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More Fallacies of Acceptability

• Appeal to Authority Asserting that something is
  true or right because some authority says so.
  This is a fallacy when (1) not in area of
  expertise (2) high level of disagreement among
  experts (3) authority is known to be biased (4)
  authority is not identified. E.g., Jackie Chan
  is against factory farms.

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Relevancy

• This involves the reasoning or logic of the
  connection between the claim and the evidence
  used to support it. The standard of relevance
  asks whether the evidence is, in fact, connected
  to the claim.

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Relevancy Fallacies

• Ad hominem (against the person) Attack on the
  source of the argument not relevant to the
  content. E.g., Of course my opponent argues
  that tobacco poses no threat to healthhes a
  smoker!
• Straw Person A weak version of an argument,
  usually the opponents argument, created for the
  sole purpose of knocking it down.

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More Relevancy Fallacies

• Red Herring An intentional distraction from the
  primary focus, often used in POIs. This serves
  to delay progress or to sidestep issues.
• Poisoning the Well Discrediting a source in
  advance of an argument. E.g., Dr. Wong is
  notoriously conservative, so how can we trust
  anything that he says?

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Still More Relevancy Fallacies

• Guilt by Association A person or argument is
  attacked on the basis of some association. E.g.,
  How can he advise us on drinking when he is a
  member of a fraternity?
• Appeal to fear Evoking fear as the primary
  reason in an argument. E.g., Our adjudicators
  should be aware that we are prepared to file a
  grievance if we lose this case.

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The End of Relevancy Fallacies (finally!)

• Appeal to popularity Asserting that because
  everyone does or thinks something, it is
  acceptable. E.g., This is the best style in the
  world. Everyone is wearing it!
• Appeal to tradition Asserting that because
  something has always been done a particular way,
  it should continue to be done that way in the
  future. E.g., My family has always farmed the
  land. It is a noble tradition.

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Sufficiency

• The question of sufficiency involves how certain
  we must be that an argument is valid and true to
  agree with a claim. The level of certainty
  required varies depending on the nature of the
  claim and the consequences of being wrong.

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Sufficiency Fallacies

• Hasty Generalization The examples used to
  establish a claim are not representative or are
  too few in number. E.g., My grandmother smoked
  2 packs of cigarettes every day and lived to be
  102 years old.
• Slippery Slope Connecting a series of events in
  an unlikely causal chain usually culminating in
  disaster. E.g., If the US withdraws from Iraq
  it will signal weakness. Other countries will
  attack and America will be forced to draft young
  people into the armed forces. This draft will
  reduce the number of men available to marry.
  Fewer marriages will mean fewer children, and so
  and the population will suffer.

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More Sufficiency Fallacies

• Two Wrongs This is a misplaced appeal to
  consistency in which because one bad thing
  happened another should be allowed to happen.
  E.g., But officer, every other driver is also
  speeding.

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More Sufficiency Fallacies

• Composition fallacy A part of the whole is
  assumed to be identical with the whole. E.g.,
  The Ford Mustang is a great car, so Ford Motors
  is a great company.
• Division fallacy A characteristic of the whole
  is applied erroneously to every single part.
  E.g., This is the most prestigious English
  language debate tournament in China. Thus, each
  of you is an excellent debater.

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Still More Sufficiency Fallacies

• Post Hoc, Ergo Propter Hoc (after this,
  therefore because of this) This fallacy
  assumes that because something happened after
  something else, the first thing cause the second
  thing. E.g., When I became a vegetarian, the
  economy improved.
• Faulty Analogy Two things are treated as
  similar in a comparison when, in fact, they are
  dissimilar or the similarities are inadequate to
  support the point argued. E.g., Guns and
  hammers can both kill people. Both should be
  banned.

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Fallacy QuizQuestion 1

• PM China should send a human to Mars because
  it would create patriotic goodwill.
• LO Why should we listen to your opinions about
  this? Youre only a student
• Ad hominem (against the person)

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Question 2

• LO How can you consider Bush to be a great
  leader? He crippled the US economy, violated
  human rights, and involved his country in an
  unjust war?"
• PM "I have a book that says he is acting in the
  best interest of the people.
• Appeal to authority

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Question 3

• PM Prostitution is clearly immoral and spreads
  disease. Therefore, it should be outlawed.
• LO But it is present in every country in the
  world, and is even legal in many of them.
• Appeal to popularity

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Question 4

• POI Are you questioning the reality of God?
  Because if you are, you will face the horrors of
  hell.
• Appeal to fear

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Question 5

• Old man Brown claims that he saw a flying saucer
  in his farm, but he never got beyond the fourth
  grade in school and can hardly read or write. He
  is completely ignorant of what scientists have
  written on the subject, so his report cannot
  possibly be true
• Ad hominem

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Question 6

• Those who say that extra-sensory perception is
  not reliable are mistaken. The police, movie
  stars, and politicians have all relied on it.
• Ad populum (Appeal to popularity)

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Question 7

• Tiger Woods believes that the United Nations
  deserves our support, and I think that a person
  of his importance should be listened to.
• Appeal to authority

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Question 8

• Everyone knows that factory farm-raised food is
  less healthful and nutritious than food raised on
  family farms in the countryside.
• Appeal to popular opinion

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Question 9

• After George W. Bush took office, the economy
  went into a recession. Therefore, his policies
  were responsible for the downturn in the US
  economy.
• Post Hoc

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Question 10

• Eating fast food is like putting water in your
  cars gas tank. It wont give you energy and may
  ruin your engine.
• Faulty analogy

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Question 11

• Peking University is an excellent college.
  Therefore, Professor Zhang, who teaches there,
  must be an outstanding faculty member.
• Fallacy of division.

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Question 12

• Yao Ming is the best center in the National
  Basketball Association, so his team must have the
  best record.
• Fallacy of composition

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Question 13

• My opponent has argued that a space mission to
  Mars will be cheap and easy. I will refute these
  statements in my speech.
• Straw Person

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Question 14

• Rural farmers have used the same trustworthy
  techniques for thousands of years, and so there
  should be no reason to change now.
• Appeal to tradition

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Question 15

• I saw three birds flying south today. Winter
  must be coming.
• Hasty generalization

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Question 16

• Tom Cruise is a Scientologist, so we really
  shouldnt listen to anything that he has to say.
• Poisoning the Well/Ad Hominem

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Question 17

• Hannah Arendt had an affair with a Nazi, so it is
  very difficult to take her philosophical writings
  seriously.
• Guilt by Association

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Question 18

• "We have pure food and drug laws why can't we
  have laws to keep movie-makers from giving us
  filth?"
• Faulty Analogy

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Question 19

• Every time the street lights come on, the sun
  goes down. We should avoid turning on the street
  lights so that we might have sunshine 24 hours a
  day.
• Post Hoc

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Question 20

• I believe in the Bible because it is the written
  word of God through his prophets. Obviously, God
  would not lie to his prophets. After all, the
  Bible says so.
• Begging the question.