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, Tamsen 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

19
Chapter 7

• Assessing Relevance

20
The Criterion of Relevance

• 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

21
The Criterion of Relevance

• Compare
• You should vote for Johnson because she is honest
  and is well informed about the issues.
• You should vote for Johnson because her mother
  used to be my kindergarten teacher.
• You should vote for Johnson because she is the
  only female candidate.

22
The Criterion of Relevance

• So we can say that a premise is relevant if
• a. it is more likely that the conclusion would be
  true if we accepted it
• b. helps make it reasonable to accept the
  conclusion.
• Otherwise, it is a non sequitur.

23
The Criterion of Relevance

• Example
• I am opposed to the proposed anti-smoking by-law
  and will vote against it at the Council meeting.
  Such a by-law is inappropriate in a city in which
  the Imperial Tobacco Company is one of the
  largest employers.

24
Some Particular Fallacies

• 1. Appeal to Pity (ad misericordium)
• 2. Appeal to Force (ad baculum)
• 3. Appeal to Popularity (ad populum)
• 4. Appeal to Authority (ad verecundium)
• 5. Ad Hominem
• i. Tu Quoque
• 6. Straw Man

25
Appeal to Pity (ad misericordium)

• P1 A argues for p
• P2 A deserves pity
• C Therefore, p is true

26
Appeal to Pity (ad misericordium)

• Example
• Student "I didn't deserve a C on this paper! I
  am trying to get into law school and I need an A-
  average and if I dont get into law school I am
  going to be very depressed."

27
Appeal to Pity (ad misericordium)

• Example
• The judge was very unfair. He shouldnt have
  found Evelyn guilty. She is a single parent with
  three small children and an ex-husband who
  refuses to make his support payments, and Im
  sure she would not have started shoplifting if
  she werent really hard pressed for money.

28
Appeal to Force (ad baculum)

• P1 A says that you should accept p, or else x
  will happen
• P2 x is threatening or bad
• C Therefore p is true

29
Appeal to Force (ad baculum)

• Example
• Employer "Sure, you can unionize the shop, but I
  won't be responsible if you are permanently
  unemployed afterwards."

30
Appeal to Force (ad baculum)

• Example
• Listen, Im telling you that my son did not cheat
  on his exam if you dont agree, well step
  outside and settle this matter man to man.

31
Appeal to Popularity (ad populum)

• Many people believe p
• Therefore p is true
• Nobody believes p
• Therefore p is false

32
Appeal to Popularity (ad populum)

• Example
• Marijuana can't be all that bad for you.
  According to a recent poll 70 of university
  students smoke it.

33
Appeal to Popularity (ad populum)

• Example
• Phrenology is unscientific nonsense. Nobody
  believes it any longer.

34
Appeal to Authority (ad verecundium)

• A says p
• A is not an authority/expert on p
• Therefore p is true

35
Appeal to Authority (ad verecundium)

• Example
• Mats Sundin, forward and captain of the Toronto
  Maple Leafs, says that the Ford Explorer is the
  safest car on the market. Therefore it is the
  safest car!

36
Appeal to Authority (ad verecundium)

• Example
• Albert Einstein, even after all his research into
  the nature of the universe, still believed in
  God. He once wrote, I do not believe the
  universe was the result of blind chance. If
  belief in God made sense to Einstein, then it
  makes sense to me.

37
Appeal to Authority (ad verecundium)

• However
• Sometimes we can appeal to authorities, when
• a. we lack the ability to attain information
  ourselves, and
• b. the authority appealed to is authoritative

38
(Attacking the Person) Ad Hominem

• A says or believes p
• A is insert insults here
• Therefore p is false

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(Attacking the Person) Ad Hominem

• Three forms
• Abusive a direct personal attack
• E.g.
• "Jones argues for vegetarianism. He says it is
  wrong to kill animals unless you really need to
  for food, and that, as a matter of fact, nearly
  everyone can get enough food without eating meat.
  But Jones is just a nerdy intellectual. So we
  can safely conclude that vegetarianism is
  nonsense."

40
(Attacking the Person) Ad Hominem

• 2. Circumstantial not necessarily abusive, but
  draws attention to the circumstantial situation
  of the person who is putting forward the claim
• E.g.,
• The Ontario Medical Association claims that the
  governments ban on extra-billing will produce a
  second-class system of medical care. It is
  difficult to accept their claim, however, since
  it is so obviously self-serving. Let us not
  forget that the OMA is essentially nothing more
  than a trade union and that it is trying to
  negotiate a contract that gets the best deal for
  its members.

41
(Attacking the Person) Ad Hominem

• Of course, sometimes it is important (e.g., in
  the legal system) to determine whether someone is
  trustworthy (can they be a reliable witness or
  expert) or to determine what someone's personal
  qualities are (for the role of babysitter, e.g.)

42
(Attacking the Person) Ad Hominem

• 3. Tu quoque (you too)
• A argues that those who endorse p are wrong
• B replies that A is one of those people
• Therefore p is true

43
Tu Quoque

• E.g.
• "During the 1980's many American journalists
  passed harsh judgments on South African
  apartheid. They wrote that it was unjust, cruel
  and immoral. But given the disgraceful history
  of race relations in America, these American
  journalists were in no position to pass judgment
  on South Africa. So their judgments were without
  value."

44
Tu Quoque

• E.g.
• Wilma You cheated on your income tax. Dont you
  realize thats wrong?
• Walter Hey, wait a minute. You cheated on you
  income tax last year. Or have you forgotten
  about that?

45
Straw Man

• Theory X is a weaker version of theory Y
• A refutes theory X
• Therefore theory Y is refuted

46
Straw Man

• E.g.
• "Susan advocates the legalization of cocaine.
  But I cannot agree with any position based on the
  assumption that cocaine is good for you and that
  a society of drug addicts can flourish. So I
  disagree with Susan"

47
Straw Man

• E.g.
• Those who want the death penalty restored have
  not really thought their position through. They
  hold that every murderer would have been deterred
  from committing murder had the death penalty been
  in force, and this is absurd. Otherwise,
  countries with the death penalty would have no
  murders which is obviously false.

48
Self-Test No. 13

• p. 157

49
Chapter 8

• Assessing Adequacy

50
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

51
The Criterion of Adequacy

• Even if the premises are acceptable and relevant
  to the conclusion, it can still be the case that
  we have an argument which is not sound.
• Arguments that violate this criterion are usually
  said to be jumping to conclusions, or making a
  hasty conclusion.

52
The Criterion of Adequacy