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Page 1: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

Fallacies - Weak Induction

Page 2: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

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”

Page 3: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

ANALOGICAL REASONINGInduction – Final Unit

Page 4: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

• Analysis– Identify Subject and Analogue

• Criticism1. Are common features relevantly similar to

inferred feature?

2. Is there a disanalogy?

Arguments from Analogy?

Both my dog and my neighbor's dog are well-loved 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.

Page 5: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

WEAK INDUCTIONFallacies

Transition

Page 6: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

Kinds of Fallacies

a defect or error traceable to the very structure (or form) of the argument

a defect which can be detected only by reference to the content of an argument

vsForm ContentFormal Fallacies Informal Fallacies

Page 7: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

Kinds of Informal Fallacies

Fallacies of:1. Relevance2. Weak Induction3. Presumption4. Ambiguity

a. Amphiboly/Equivocationb. Whole/Part

See pages 153f for a complete list

Only required to classify each

fallacy according to these four

types

Page 8: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

Your Task on the ExamExplain how the argument is fallacious.

Fallacies on Exam

fallacy of relevancefallacy of weak inductionfallacy of presumptionfallacy of ambiguitynone of the above

Page 9: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

WEAK INDUCTIONFallacies

Page 10: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

Weak Induction

• Inferential connection – evidence not strong enough to support conclusion• Premises are relevant to conclusion• Premises do not warrant conclusion

Page 11: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

The Five Fallacies of Weak Induction

1. Appeal to Ignorance2. Appeal to Unqualified Authority3. Hasty Generalization4. False Cause5. Weak Analogy

In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant

conclusion

Page 12: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

The Five Fallacies of Weak Induction

1. Appeal to Ignorance2. Appeal to Unqualified Authority3. Hasty Generalization4. False Cause5. Weak Analogy

In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant

conclusion

See earlier presentations for assessment criteria

Page 13: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

The Five Fallacies of Weak Induction

1. Appeal to Ignorance– Smoking has not been proven to cause cancer,

therefore tobacco products are not carcinogenic • Premises offer only a lack of evidence• A definite assertion is made on this basis

In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant

conclusion

Exceptions1. If search for evidence has been (seemingly) exhaustive by

qualified personnel2. American Legal Standard: “reasonable doubt”

See in-class example: Mill’s Method of Residue

Page 14: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

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.• Premises offer testimony/opinion from an authority• Conclusion about subject matter is made on this basis

In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant

conclusion

Question rests on the relevant expertise of the authority consulted

Page 15: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

The Five Fallacies of Weak Induction

3. Hasty Generalization

See Presentation “Induction: Generalizations”

In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant

conclusion

Two Issues Affecting Strength• Representativeness of Sample• Interviewer Bias

Page 16: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

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 caused. Slippery Slope

Page 17: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

The Five Fallacies of Weak Induction

4. False Cause:– 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

“after this”

In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant

conclusion

Page 18: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

The Five Fallacies of Weak Induction

4. False 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

“non-cause”

In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant

conclusion

Page 19: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

The Five Fallacies of Weak Induction

4. False Cause:– 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

oversimplification

In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant

conclusion

Page 20: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

The Five Fallacies of Weak Induction

4. False Cause:• 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

slippery slope

In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant

conclusion

Page 21: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

The Five Fallacies of Weak Induction

5. Weak Analogy

In each case,1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant

conclusion

See earlier slides of this presentation!

Two Issues Affecting Strength• Common features relevantly

similar to inferred feature• No relevant dissimilarities

(no disanalogy)

Page 22: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

Both my dog and my neighbor's dog are well-loved 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.

Arguments from Analogy?

Page 23: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

Fallacies of weak induction– Five identifiable kinds– Not expected to provide the names of these on

exam

Fallacies on Exam

In each case:1. The premises are relevant to conclusion2. Premises provide insufficient evidence to warrant

conclusion

Page 24: Fallacies - Weak Induction. Homework Review: Fallacies » pp. 103-105, §4.1 “Fallacies in General” » pp. 121-131, §4.3 “Fallacies of Weak Induction” Inductive.

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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