CS 100 - Week 8 Lecture 1 - 10-9-12

Now -- starting Chapter 6 
Fallacies of INSUFFICIENT EVIDENCE

*   These are mistakes in reasoning in which the
    premises, though RELEVANT to the conclusion
    (provided potentially-positive support to the
    conclusion), FAIL to provide SUFFICIENT evidence
    for the conclusion;

*   ^^^ that's our unifying theme for these 9
    fallacies in this chapter;

1.  Inappropriate Appeal to Authority

*   we already know that argument from authority
    is a common pattern of inductive reasoning;
    ...this fallacy is committed when the arguer
    cites a witness or authority who, there is good
    reason to believe, is unreliable for some reason;

*   some EXAMPLES of circumstances where this
    fallacy might occur:
    *   when the source is not an genuine authority
        on the subject at hand
    
        authority: a person who possesses special 
                   knowledge, competence, or expertise
                   in a particular field

        IS the source really an authority on the
	conclusion? If not, you might have an
	inapproriate appeal to authority

   *   when the source is biased or has some other
       reason to lie or mislead

       ...and this potential motivation along with
       other information suggests that the appeal
       authority may be fallacious; (may not
       really provide sufficient support for the
       conclusion);

   *   when the accuracy of the source's observations
       is questionable

   *   when the source cite is known to be generally
       unreliable

       ...consider a supermarket tabloid...
       ...if an argument's main support is that it
          was cited by an rather-known-to-be unreliable
	  source,
	  that's insufficient evidence;

   *   when the source has not been cited correctly
       OR the cited claim has been taken out of context

   *   when the source's claim conflicts with
       expert opinion
   
   *   when the issue is one that cannot be
       settled by expert opinion

   *   when the claim is highly improbable on its
       face

2. Appeal to Ignorance

   *   the fallacy of appeal to ignorance occurs
       when an arguer asserts that a claim MUST
       be true because NO ONE has proven it false,
       OR conversely that a claim MUST be false
       because NO ONE has proven it true.

   e.g.,

   There must be intelligent life on other planets.
   No on has proven that there isn't.

   There cannot be intelligent life on other planets.
   No one has proven that there is.

   *   it CAN be legitimate to treat a lack of
       evidence AS evidence that a claim is false --

       for example, an extensive search for something
       not finding it MIGHT be reasonable evidence
       toward something not being there

       e.g., A team of 20 experts searched the car
       from top to bottom, including x-ray and
       tearing up the upholstery and taking apart
       the engine. The jewels were not found. Therefore,
       the jewels probably aren't hidden in the car.

       so, a search not finding something can be
       reasonable evidence for it not being there
       when:
       1) a careful search has been conducted
       2) it is likely a search of that carefulness
          WOULD have found something if there had been
          anything to be found

3. False Alternatives

*   the fallacy of false alternatives if committed
    when the arguer poses a false either-or choice