Fallacies: Weak Induction

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Fallacies - Weak Induction
Homework
• Review:
• Fallacies
» pp. 103-105, §4.1 “Fallacies in General”
» pp. 121-131, §4.3 “Fallacies of Weak Induction”
• Inductive Argumentation
» Analogical Reasoning, e.g., ex. 8.4
» Causal Argumentation, e.g., 8.3b
» Inductive Generalization, e.g., 8.2b
• Read for Next Class
– pp. 106-116, §4.2 “Fallacies of Relevance”
Induction – Final Unit
ANALOGICAL REASONING
Arguments from Analogy?
Both my dog and my
neighbor's dog are wellloved members of the
– Identify Subject and Analogue family. Each one is well
fed, house broken,
walked on a regular
basis. My dog has a very
calm temperament. So I
infer that my neighbor's
1. Are common features relevantly
similar to
dog also has a calm
inferred feature?
temperament.
• Analysis
• Criticism
2. Is there a disanalogy?
Transition
Fallacies
WEAK INDUCTION
Kinds of Fallacies
Formal Fallacies
Form
a defect or error
traceable to the
very structure (or
form) of the
argument
vs
Informal Fallacies
Content
a defect which can
be detected only by
reference to the
content of an
argument
Kinds of Informal Fallacies
Fallacies of:
1.
2.
3.
4.
See pages 153f
for a complete list
Relevance
Weak Induction
Presumption
Ambiguity
a. Amphiboly/Equivocation
b. Whole/Part
Only required to
classify each
fallacy according
to these four
types
Fallacies on Exam
Your Task on the Exam
Explain how the argument is fallacious.
fallacy of relevance
fallacy of weak induction
fallacy of presumption
fallacy of ambiguity
none of the above
Fallacies
WEAK INDUCTION
Weak Induction
• Inferential connection
– evidence not strong enough to support conclusion
• Premises are relevant to conclusion
• Premises do not warrant conclusion
The Five Fallacies of Weak Induction
1.
2.
3.
4.
5.
Appeal to Ignorance
Appeal to Unqualified Authority
Hasty Generalization
False Cause
Weak Analogy
In each case,
1. The premises are relevant to conclusion
2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
1.
2.
3.
4.
5.
Appeal to Ignorance
Appeal to Unqualified Authority
Hasty Generalization
See earlier presentations
False Cause
for assessment criteria
Weak Analogy
In each case,
1. The premises are relevant to conclusion
2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
1. Appeal to Ignorance
See in-class example:
Mill’s Method of Residue
– Smoking has not been proven to cause cancer,
therefore tobacco products are not carcinogenic
•Exceptions
Premises offer only a lack of evidence
If search
for evidence
has been
(seemingly)
• A 1.
definite
assertion
is made
on this
basis exhaustive by
2.
qualified personnel
American Legal Standard: “reasonable doubt”
In each case,
1. The premises are relevant to conclusion
2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
2. Appeal to Unqualified Authority
– I was speaking to my brother at his auto shop, and
he believes the Democrats will lose Maryland in
the next election. So I think it’s likely.
•Question
Premisesrests
offerontestimony/opinion
from an
authority
the relevant expertise
of the
authority
consulted
• Conclusion about subject matter is made on this basis
In each case,
1. The premises are relevant to conclusion
2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
3. Hasty Generalization
See Presentation “Induction: Generalizations”
Two Issues Affecting Strength
• Representativeness of Sample
• Interviewer Bias
In each case,
1. The premises are relevant to conclusion
2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
4. False Cause
– Four variants (complex fallacy)
a. Post hoc ergo propter hoc (“after this, there because
of this”)
b. Non causa pro causa (“non-cause for the cause”)
c. Oversimplified cause
d. Slippery Slope
The Five Fallacies of Weak Induction
4. False Cause: “after this”
– After we arrived, the baby got sick. So I think we
were the cause of the baby’s illness.
• No causal relation apparent or explained
• Causal conclusion based on mere temporal succession
In each case,
1. The premises are relevant to conclusion
2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
4. False Cause: “non-cause”
– Computer scientists do better at logic. So to do
better in this course, you should study computer
science
• Typically, no assertion of temporal succession
• Mistaken assertion of causal agency
In each case,
1. The premises are relevant to conclusion
2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
4. False Cause: oversimplification
– Your car is causing global warming.
• Phenomenon in question caused by complex number of
factors
• A single one of these factors is asserted as sole cause
In each case,
1. The premises are relevant to conclusion
2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
4. False Cause: slippery slope
• If you fail this class, then your GPA will go down. If you GPA falls,
you’ll lose your scholarship. If you lose your scholarship, you’ll
spend all your money on school. If you do this, you’ll have no
money for food and shelter. So if you fail this class, you will
become a starving, homeless beggar.
– A chain of causal events is asserted
– The causal connection between some or all events is highly
unlikely
» At least the ultimate conclusion is highly unlikely
In each case,
1. The premises are relevant to conclusion
2. Premises provide insufficient evidence to warrant
conclusion
The Five Fallacies of Weak Induction
5. Weak Analogy
See earlier slides of this presentation!
Two Issues Affecting Strength
• Common features relevantly
similar to inferred feature
• No relevant dissimilarities
(no disanalogy)
In each case,
1. The premises are relevant to conclusion
2. Premises provide insufficient evidence to warrant
conclusion
Arguments from Analogy?
Both my dog and my
neighbor's dog are wellloved members of the
family. Each one is well
fed, house broken,
walked on a regular
basis. My dog has a very
calm temperament. So I
infer that my neighbor's
dog also has a calm
temperament.
Fallacies on Exam
Fallacies of weak induction
In each
case:
– Five
identifiable kinds
1. The premises are relevant to conclusion
–2.Not
expected
to provide
theevidence
names to
ofwarrant
these on
Premises
provide
insufficient
exam
conclusion
Homework
• Review:
• Fallacies
» pp. 103-105, §4.1 “Fallacies in General”
» pp. 121-131, §4.3 “Fallacies of Weak Induction”
• Inductive Argumentation
» Analogical Reasoning, e.g., ex. 8.4
» Causal Argumentation, e.g., 8.3b
» Inductive Generalization, e.g., 8.2b
• Read for Next Class
– pp. 106-116, §4.2 “Fallacies of Relevance”

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