Assessing the Acceptability of the Premises

1
Assessing the Acceptability of the Premises

• In determining whether an argument is sound we
  need to determine whether the premises are
  acceptable.
• Up to this point we have looked at many standards
  of acceptability for the individual premises
  (taken one by one), based on whether the
  statement is an empirical claim, non-empirical,
  general, statistical, or common knowledge.

2
Some Particular Fallacies

• Premises can also be deemed unacceptable (as a
  group) if they commit either of these 4
  fallacies
• Begging the question
• Inconsistency
• Equivocation
• False dichotomy

3
Begging the Question

• Aka circular argument
• Aka petitio principii
• This fallacy is committed when the premises
  presuppose (directly or indirectly) the truth of
  the conclusion.

4
Begging the Question

• P1
• P2
• P3
• .
• .
• .
• ___________
• P1

5
Begging the Question

• Examples
• The Bible frequently says that it is the word of
  God and the word of God must obviously be true.
  Therefore, whatever the Bible says is true.

6
Begging the Question

• Example from Rene Descartes (the Cartesian
  Circle)
• P1 I have a clear and distinct idea that God
  exists
• P2 God is no deceiver
• P3 Therefore my clear and distinct ideas are true

7
Inconsistency

• A set of premises are inconsistent when it is
  impossible for all of them to be true.
• That is, if we affirm all of the premises we will
  commit ourselves to a contradiction.

8
Inconsistency

• Example
• P1 Mary is older than Gord.
• P2 Gord is older that Mary.

9
Inconsistency

• Example
• Albert is brighter than all her sisters
• Albert and Sally are brother and sister
• Sally is brighter than all her brothers
• Albert is brighter than Sally

10
Equivocation

• This is a fallacy that concerns the ambiguity of
  language.
• The fallacy occurs when there exist more than one
  interpretation of a premise one which is
  acceptable, and one which is not.

11
Equivocation

• Example
• Noisy children are a real headache.
• An aspirin makes a headache go away.
• An aspirin will make the children go away.

12
Equivocation

• Example
• P1 It is well known that the average family has
  2.5 children.
• P2 Well, Jane's family is very average.
• C Therefore, they must have 2.5 children.

13
Equivocation

• Example
• Professor Jones says that no one will get an A in
  his course unless they attend every seminar.
  Well, Ive attended every seminar so I am
  expecting an A.

14
False Dichotomy

• A dichotomy is a choice between two alternatives.
• Alternatives can be said to be
• Exhaustive the list of alternatives covers all
  the possibilities
• Deciding which university to go to in Halifax
  Dal, SMU, Kings, MSVU
• Exclusive when one alternative rules out the
  other.
• am, pm pregnant, not pregnant, etc.

15
False Dichotomy

• A false dichotomy presents a choice between
  alternatives that purports to be exhaustive or
  exclusive, when it is not.

16
False Dichotomy

• Example
• These days students have to choose whether they
  want to get good grades or whether they want to
  have fun. Well, Tamsin has decided that she
  wants to have fun at college, so I guess shes
  not going to get good grades.

17
False Dichotomy

• Example
• Evolutionary theories arent able to account for
  instances of irreducible complexity, therefore,
  creation science must be correct.

18
Self Test No.12

• p. 140