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Logical Fallacies


Title: Logical Fallacies Author: Rutherford County Schools Last modified by: Rutherford County Schools Created Date: 11/13/2011 12:13:30 AM Document presentation format – PowerPoint PPT presentation

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Title: Logical Fallacies

Logical Fallacies
Get Notebooks!
What is a fallacy?
  • A fallacy is an error in reason
  • May be accidental or intentional
  • In arguments or propaganda, they are often used
    to persuade

There are various types of fallacies
  • Appeal to fear
  • Personal attack (Ad hominem)
  • False dilemma
  • False analogy
  • Slippery Slope
  • Non sequitur (should sound familiar)
  • False authority
  • Red Herring

Appeal to fear (Scare tactics)
  • Creates fear in people as evidence to support a
  • Examples
  • "If you continue to drink, you will die early as
    your father did."
  • "If you cannot graduate from high school, you
    will live in poverty for the rest of your life."

Personal attack (Ad hominem)
  • Involves insulting or belittling one's opponent
    in order to attack his claim or invalidate his
  • attacks the person and not the issue

Personal attack (Ad hominem)
  • Examples
  • "You can't believe John when he says the proposed
    policy would help the economy. He doesn't even
    have a job."
  • "Candidate Jane's proposal about zoning is
    ridiculous. She was caught cheating on her taxes
    in 2003."

False dilemma
  • A reasoner who unfairly presents too few choices
    and then implies that a choice must be made among
    this short menu of choices commits the false
    dilemma fallacy, as does the person who accepts
    this faulty reasoning.
  • In other words. limits the possible choices to
    avoid consideration of another choice

False dilemma
  • Example
  • Either the eyewitness saw an alien spacecraft or
    he's a liar. Perhaps he's simply mistaken.
  • "It wasn't medicine that cured Ms. X, so it must
    have been a miracle."

False analogy
  • When reasoning by analogy, the fallacy occurs
    when the analogy is irrelevant or very weak or
    when there is a more relevant disanalogy
  • Examples
  • A school is not so different from a business. It
    needs a clear competitive strategy that will lead
    to profitable growth.
  • People are like dogs. They respond best to clear

Slippery Slope
  • Someone claims that a first step (in a chain of
    causes and effects, or a chain of reasoning) will
    probably lead to a second step that in turn will
    probably lead to another step and so on until a
    final step ends in trouble
  • If the likelihood of the trouble occurring is
    exaggerated, the slippery slope fallacy is

Slippery Slope
  • Examples
  • If we pass laws against fully-automatic weapons,
    then it won't be long before we pass laws on all
    weapons, and then we will begin to restrict other
    rights, and finally we will end up living in a
    communist state. Thus, we should not ban
    fully-automatic weapons.
  • You should never gamble. Once you start gambling
    you find it hard to stop. Soon you are spending
    all your money on gambling, and eventually you
    will turn to crime to support your earnings.

Non sequitur (should sound familiar)
  • When a conclusion is supported only by extremely
    weak reasons or by irrelevant reasons
  • Example Nuclear disarmament is a risk, but
    everything in life involves a risk. Every time
    you drive in a car you are taking a risk. If
    youre willing to drive in a car, you should be
    willing to have disarmament.

False authority
  • Fallacious whenever the authority appealed to is
    not really an authority on subject
  • Name dropping
  • Example "We should abolish the death penalty.
    Many respected people, such as Snooki, have
    publicly stated their opposition to it."

Red Herring
  • A red herring is a smelly fish that would
    distract even a bloodhound.
  • It is also a digression that leads the reasoner
    off the track of considering only relevant
  • Basically a distracter

Red Herring Examples
  • I know your car isn't working right.  But, if you
    had gone to the store one day earlier, you'd not
    be having problems.
  •   I know I forgot to deposit the check into the
    bank yesterday.  But, nothing I do pleases you.
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