Assessing Adequacy by fjzhangxiaoquan

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									Assessing Adequacy
      Chapter 8
    The Criterion of Adequacy
 There are three criteria of a sound
  argument:
1. the premises must be acceptable
2. the premises must be relevant
3. the premises must be adequate
      The Criterion of Adequacy
   Even if the premises are acceptable and
    relevant, the argument may still not be
    sound if the premises are not adequate to
    support the conclusion.
   If the premises do not provide adequate
    support, we say that we have jumped to
    conclusions.
      The Criterion of Adequacy
   Adequacy is a matter of degree.
   It is important to determine whether the
    argument attempts to prove a conclusion,
    or presents it tentatively.
      The Criterion of Adequacy
   Compare:

   Look at those dark clouds on the horizon. We
    might be in for some rain, so maybe we should
    head back to the car.

   Look at those dark clouds on the horizon. It’s
    going to rain, and if we don’t head back to the
    car right away, we are going to get soaked.
        The Criterion of Adequacy
   There are two generic criteria of
    adequacy:
       Deductive validity (ch. 9)
       Inductive strength (ch. 10)

   In this chapter, however, we are going to
    be looking at several familiar arguments
    that pose problems for determining
    adequacy.
          Appeals to Authority
   We saw in the previous chapter that an
    appeal to an irrelevant authority is a
    fallacy.
   But if the authority is relevant, we need to
    determine whether appealing to that
    authority is adequate to establish our
    conclusion.
           Appeals to Authority
    5 criteria we should use in determining the adequacy
     of an appeal to an authority.
1.   The authority must be identified.
2.   The authority must be generally recognized by the
     experts in the field.
3.   The particular matter in support of which an authority
     is cited must lie within his or her field of expertise.
4.   The field must be one in which there is genuine
     knowledge.
5.   There should be a consensus among the experts in the
     field regarding the particular matter in support of
     which the authority is cited.
         Appeals to Ignorance
   This is a fallacy of reasoning.
   It is committed when you attempt to
    establish that a claim is true by suggesting
    that there is no evidence to the contrary.

   It usually comes in two forms
         Appeals to Ignorance
1.   There is no evidence that p
     Therefore, not p

2.   You can’t prove that p is false
     Therefore, p.
           Appeals to Ignorance
   E.g.

   You can’t prove that the planets don’t
    affect our personality and relationships
    with others. Therefore, I will continue to
    believe in astrology.
      The Slippery Slope Fallacy
   The premises of a slippery slope argument
    introduce a chain of predictions, each of which is
    strong, but taken together form a weak chain.
   E.g.,
    A will   probably lead   to   B
    B will   probably lead   to   C
    C will   probably lead   to   D
    A will   probably lead   to   D
      The Slippery Slope Fallacy
   Why is this wrong?
   Probabilities can be quantified
    A will   probably (70%) lead to B
    B will   probably (70%) lead to C
    C will   probably (70%) lead to D
    A will   probably (??%) lead to D
Conclusion would be true if it were probable (e.g.,
  maybe greater than 50%?)
Probability that A will lead to D = 34%
     The Slippery Slope Fallacy
If abortion on demand were to become legal, there would
   be a great increase in abortions. And once abortion
   became commonplace, there would be a weakening of
   respect for human life in general. Once respect for
   human life was weakened, we would see an increase in
   euthanasia of all kinds: the elderly, the mentally
   handicapped, and the physically disabled. Before long
   we would be getting rid of anyone who is unproductive.
   In short, it would threaten our civilization. Therefore we
   should oppose any move to broaden the grounds for
   legal abortion.
      The Slippery Slope Fallacy
   NB: In many slippery slope arguments
    then premises that constitute the chain of
    reasoning are absent (they are missing
    premises).
   Even though the author does not explicitly
    have a “chain-like” argument, it is still a
    slippery slope argument once the
    premises have been provided.
      The Slippery Slope Fallacy
   E.g.,

You should never drink during the day.
 Once you start doing that you will end up
 as a skid-row bum.
      The Slippery Slope Fallacy
    2 sorts of arguments which look like, but are not, slippery slopes.

1.   If   A then B
     If   B then C
     If   C then D
     If   C then D

Here, if the premises are true (100% probability), then the conclusion
      is also true (100% probability).
This is a deductive argument (we look at these in the next chapter).
     The Slippery Slope Fallacy
2.   A will probably lead to B
     A will probably lead to C
     A will probably lead to D

If B, C and D are bad or unwanted, then this
    will be an argument not to do A.
Not a slippery slope as B, C and D are
    independent of each other.
             Causal Fallacies
   What is causation? This is a perennial
    philosophical problem!
   For the purposes of the causal fallacies we
    will simply this picture and say that each
    event (the effect) has a single cause.
    1. Post Hoc Ergo Propter Hoc
   (trans) After this, therefore because of
    this

   It is the nature of causation that the
    causes precede their effects. If A is the
    cause of B, then A occurs before B.
   But (and this is the fallacy), not everything
    that occurs before B is the cause of B.
  1. Post Hoc Ergo Propter Hoc
e.g.

The stove in your apartment was working perfectly until
  you moved in, but the next day the oven stopped
  working. It must be something that you’re doing that is
  causing the problem.

In Aesop’s fable, the rooster reasoned as follows: Every
   morning without fail, the sun rises just a few minutes
   after I start crowing. I must be the greatest creature in
   the world since I cause the sun to rise every day.
    2. Confusing Cause and Effect
   If A is the cause of B, then they will
    always occur together. The fallacy here is
    to think that B is the cause of A.
   This sort of reasoning happens often in
    statistical interpretation.
 2. Confusing Cause and Effect
E.g.

According to a recent Statscan report,
  married couples with no children have
  approximately 20 per cent more
  disposable income than married couples
  with children. This shows that it is
  affluence which causes declining birth
  rates.
           3. Common Cause
   If A causes B, then they will always occur
    together.
   But just because two events always occur
    together it does not follow that one is the
    cause of the other.
   They may have a common cause.
        3. Common Cause
E.g.

Recent studies have shown that people who
 are commonly regarded as being
 successful have much larger vocabularies
 than average. This is no accident. Having
 an extensive vocabulary is an important
 factor in producing success.
Self Test No. 14
      p. 173

								
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