Logical Fallacies Adopted from Steve Richardson, George Mason University

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Logical Fallacies(Adopted from Steve Richardson,
George Mason University)

• Zainal A. Hasibuan/Siti Aminah
• Fakultas Ilmu Komputer
• Universitas Indonesia

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Definitions

• Logic is the set of rules by which one can
  formulate convincing arguments
• It is "the science of argument."
• When presenting an argument, one takes a set of
  premises that are proven to be true, and uses
  logic to show how they prove a certain "foregone
  conclusion."
• Logical errors in scientific writings are known
  as fallacies

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Logical errors in scientific writings

• If an argument contains a fallacy, then the
  conclusion will not necessarily be proven
• Some fallacies are just accidental, but they can
  also be used to trap an unwary listener or reader
  into believing faulty conclusions

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Three general categories of logical fallacies

• Material fallacies
• Deal principally with a premise and its evidence.
• When the premises of an argument, or its
  evidence, contain material fallacies, the
  conclusion is not sufficiently proven.
• "Material fallacies arise out of the fabric (or
  'material') used to express an argument."
• Fallacies of relevance
• Deal principally with the relationship between
  the premise/evidence, and the conclusion of the
  argument.
• For example, someone who tries to prove a point
  using emotion, or who proves the wrong point,
  commits a fallacy of relevance.
• The point that is proved is usually "an issue
  about which people have strong opinions, so that
  no one notices how their attention is being
  diverted" from the real issue.
• Verbal fallacies.
• Deal principally with the misusage of words.
• An argument which contains "improper or ambiguous
  use of words" is invalid.

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 Material Fallacies

• False Cause
• Assuming that one event is caused by another,
  just because one happens after the other, is the
  fallacy of false cause. The two events could have
  both been caused by another event, or they could
  be totally unrelated.
• For example "More people die in hospitals than
  anywhere else. Therefore, going to a hospital
  causes death
• Hasty Generalization
• A hasty generalization is a general rule that is
  formed from only a few examples, or examples that
  are really exceptions.
• For example "A bear lives at the zoo, therefore,
  all bears live at zoos.
• Misapplied Generalization
• Generalizations applied to cases that are
  exceptions to the rule are said to be misapplied.
  
• For example "Tools are useful, therefore this
  hammer will be useful." One may not need a
  hammer, or the hammer may be broken.

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Material Fallacies

• False Dilemma
• When an argument overlooks alternative
  possibilities, it creates a false dilemma.
• For example "America Love it or Leave it."
• Compound Question
• A compound question is one which is phrased in
  such a way so as to unfairly limit the
  possibilities of one's answer.
• For example "Are you still as selfish as you
  used to be?" Even if one answers "no," one would
  still be admitting that one had been selfish in
  the past.
• One subset of the compound question fallacy is
  the persuasive definition.
• Redefining the terms of an argument to make them
  support the conclusion is the persuasive
  definition fallacy.
• False Analogy
• When an analogy is drawn between dissimilar
  objects or ideas, it is called a false analogy.
• Comparing "apples and oranges" is a well known
  example of a false analogy.

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Material Fallacies

• Contradictory Premises
• A conclusion which is drawn from premises which
  cannot both be true at the same time is the
  fallacy of contradictory premises.
• For example "'What would happen if an
  irresistible force met an immovable object?' (One
  student's answer 'An inconceivable smash!')"
• Circular Reasoning
• An argument which contains the fallacy of
  circular reasoning uses its conclusion as support
  of its premises.
• It uses "the original thesis as proof of itself."
  
• For example "C. S. Lewis was a good author,
  because he wrote good books. I know he wrote good
  books because he was a good author."

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Material Fallacies

• Insufficient or Suppressed Evidence
• Someone who uses the fallacy of insufficient
  evidence draws a conclusion from only a few
  unrepresentative examples.
• For example "That type of car is poorly made a
  friend of mine has one, and it continually gives
  him trouble."
• An argument that uses the fallacy of suppressed
  evidence uses as evidence only the facts that
  support the conclusion, disregarding the rest of
  the pertinent facts.
• This fallacy illustrates how the conclusion was
  formed before all the evidence for it was
  gathered, or even in spite of it.
• In scientific writing, this fallacy is seen in "a
  failure to look for evidence that will confirm or
  deny a proposed hypothesis," and it is also seen
  "when one believes an alternate explanation
  refutes another explanation without a comparison
  of the merits between the two explanations."

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Fallacies of Relevance

• Fallacies of relevance deal principally with the
  relationship between the premise/evidence, and
  the conclusion of the argument.
• For example, someone who tries to prove a point
  using emotion, or who proves the wrong point,
  commits a fallacy of relevance.
• The point that is proved is usually "an issue
  about which people have strong opinions, so that
  no one notices how their attention is being
  diverted" from the real issue.

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Fallacies of Relevance

• Irrelevance
• An argument is irrelevant if it proves or
  disproves the wrong point.
• This fallacy is really a broad category that
  includes almost all of the fallacies of
  relevance.
• "In a discussion of the relative safety of
  different makes of car, for instance, the issue
  of which cars are made domestically and which are
  imported is a red herring.
• Personal Ridicule
• Someone who ridicules his opponent instead of
  addressing the premises of the argument commits
  this fallacy.
• "You wouldn't believe someone with his political
  views would you?"
• One type of the personal ridicule fallacy is the
  'straw man.' When someone uses this fallacy, he
  applies a characterization or stereotype to his
  opponents to make them easy to refute.
• For example, saying that "a person who advocates
  reduced military spending is . . . in favor of
  giving in to the Russians," is a straw man
  fallacy.

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Fallacies of Relevance

• Appeal to the People
• Using the feelings, actions, and/or prejudices of
  the general populous as a support of an argument
  may invalidate it.
• "Everyone's doing it!"
• Appeal to Authority
• Using the opinion of an expert in a field other
  than the one being discussed may invalidate the
  argument.
• "Coke is the favorite soda of 9 out of 10 actors,
  therefore we should have Coke at our picnic."
• Appeal to Ignorance
• Assuming that a premise is correct because it
  can't be disproved displays the fallacy of
  ignorance. This is the "guilty until proven
  innocent" fallacy.
• "A classic example is this statement by Senator
  Joseph McCarthy, when asked to back up his
  accusation that a certain person was a communist
  'I do not have much information on this except
  the general statement of the agency that there is
  nothing in the files to disprove his Communist
  connections."

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Fallacies of Relevance

• Appeal to Pity
• An argument that uses this fallacy may be invalid
  because it depends on the idea that one will be
  more likely to accept the conclusion if one feels
  sorry for someone or something associated with
  it. This is the "victim" mentality.
• "I know I flunked every exam, but if I don't pass
  this course, I'll have to retake it in summer
  school. You have to let me pass!
• Appeal to Force
• Threats and intimidations used to force someone
  to accept an argument constitute an appeal to
  force.
• "If you don't do what I tell you, you'll lose
  your job!"
• Appeal to Money
• Advertisers frequently appeal to the desire to
  save money or get more money to induce people to
  make purchases. Despite their success, their
  appeals are fallacious.
• "Buy our products and save up to 50 every year!"

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Fallacies of Relevance

• Emotive Language
• Using a word, phrase, or argument only to
  stimulate emotions invalidates ones argument.
• "President Clinton's best allies are the Clinton
  Haters." The author of this quote used the term
  "Clinton Haters" to stimulate emotions. He
  described the "Clinton Haters" as willing to "say
  anything and charge him Clinton with anything
  that comes out of their heads when they get out
  of bed in the morning." He gives no evidence that
  anyone that impulsive actually exists. In this
  case, this fallacy is similar to the personal
  ridicule fallacy.
• Tu Quoque
• This fallacy is used as a defense, where the
  person being criticized accuses his critic of
  doing the same thing himself. ("Tu quoque" means
  "you too.")
• "Son, it is your bedtime. Go to bed." "But dad,
  you are staying up!"
• Genetic Error
• When someone disregards a premise or an argument
  only because of where it came from, they commit a
  genetic error. "The source of an argument is
  irrelevant so far as logical proof is concerned.
• "Clinton's lieutenants . . . dismiss even
  legitimate questions as products of 'the attack
  machine.'"

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Fallacies of Relevance

• Anthropomorphism
• When someone projects human feelings and
  qualities to animals and inanimate objects, he
  commits a fallacy of anthropomorphism.
• "After millions of years of work, Nature had
  created many diverse species of plants and
  animals."
• Non Sequitur
• When the premises of an argument are not
  logically connected to the conclusions, the
  argument contains a non sequitur.
• "Trees are green therefore human beings enjoy
  spinach."

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Verbal Fallacies

• Verbal fallacies deal principally with the
  misusage of words. An argument which contains
  "improper or ambiguous use of words" is invalid.
  Here are some descriptions and examples of verbal
  fallacies.
• Ambiguity
• Using undefined words or words whose meaning is
  vague constitutes an ambiguity. For example, in
  1997 the Commonwealth of Virginia proposed buying
  "probe kits" for every student to help in math.
  Regarding this ambiguity, C. R. Taft said,
• "To be sure, there is the matter of 6,000 'probe
  kits,' or data-collection devices. What data
  these devices collect and how they do so was
  never defined clearly."
• Equivocation
• Someone who uses a word in more than one sense,
  but gives the impression that only one meaning
  was meant, is using an equivocation. Anyone who
  presents an argument needs to use only one
  definition for each of his terms. When more than
  one definition is used for a certain word, it can
  cause confusion and be misleading.
• "Death is a subject of utmost gravity. Gravity is
  what keeps us from falling off the Earth. Thus,
  death is primarily what keeps us from falling off
  the Earth."

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Verbal Fallacies

• Composition
• Assuming that a group will have the same
  qualities as the individuals in it is the fallacy
  of composition. This fallacy and the next one are
  types of equivocation. "In the fallacy of
  composition, the individual terms that comprise a
  group . . . are equivocally confused with the
  collective term."
• "A spider is a beneficial member of an ecosystem.
  Therefore, introducing millions of spiders into
  an ecosystem would be advantageous."
• Division
• When one assumes that the individuals in a group
  will have the same qualities as the group they
  are in, one commits the fallacy of division.
• "That orchestra is the best in the world,
  therefore it is made up of the best musicians in
  the world." However, the best orchestra in the
  world may not have the world's best solo
  violinist.
• Amphibology
• A sentence that is structured in such a way as to
  make more than one interpretation possible is an
  amphibology.
• "Wanted to sell A highchair for a baby with a
  broken leg."

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Verbal Fallacies

• Abstraction
• Taking a quote out of context is known as
  abstraction. Using this fallacy can totally
  change what was originally meant. Francis Bacon
  purportedly said,
• "Philosophy inclineth a man's mind to atheism."
  But what he actually said was, "A little
  philosophy inclineth man's mind to atheism, but
  depth in philosophy bringeth men's minds about to
  religion."
• Identifying logical fallacies is an important
  skill for everyone to have.
• It not only helps one to avoid accepting false
  conclusions, but it also helps one to learn
  better reasoning and debating skills.
• The process of looking for logical fallacies can
  help one to better understand the subject one is
  reading about or discussing.
• Knowing how to identify fallacies and how to
  avoid using them, can make one better prepared to
  refute false ideas and present the truth.